All-metal hotend, cooling fan failures, and cold-side PTFE

First of all, we need to discuss the failure mode and what can be done. LEt's do a
Failure mode 1: coolend-fan stops working.
Let's assume the coolend-fan for whatever reason (cut cable, defect fan, burnt board...) stops working. As a result, the coolend starts to rise in temperature, as it doesn't drain as much heat into the room air as before. This directly leads to an increase of the hotend temperature, which results in a case differentiation:

The hotend does not cope well with the loss of the heatsink and it triggers Thermal Runaway protection as for a given voltage bump the heating gets too high - the print gets aborted before the hotend reaches a temperature above 275 °C.
The hotend does not trigger Thermal Runaway Protection but the controller alters its heating behavior and works the heater on a lower duty cycle. As long as the hotend temperature is ordered to stay low enough, we will get a lot of extrusion problems from heat-creep, but the PTFE seated into the heatbreak stays below the heater break's temperature, as the thermal mass of the coolend alone draws away thermal energy into the room, even without the fan that keeps it at room temperature. As long as you don't print at above 300 °C and the thermosensor is intact, the failure mode does not release any fumes that could result in Polytetrafluoroethylene Toxicosis.

Failure Mode 2: coolend fan stops Working, no TRP, Thermosensor OK
But what if TRP is off? Let's look at this Double Failure: The hotend does not trigger Thermal Runaway Protection (or it was turned off to begin with) and the temperature increases due to the lack of cooling from the coolend.
As the hotend reaches 275 °C (few printers print that hot, and they use specialized setups), it should trigger the next safety line: a MaxTemp error and cut power. Heating stops before the coolend gets to the dangerous zone of 300 °C, as the coolend always is less hot than the heater block.
Failure Mode 3: no TRP, Thermosensor broken
We are getting desperate and turn off TRP, then break or disconnect the thermosensor to get a static low temperature. NOW we are getting serious, as only with such a failure we can trick our controller to continuously heat the heater cartridge and not trigger any of the error conditions. Only now there is the mere possibility to heat the coolend over 300 °C.
Marlin Firmware is designed to carefully work with checks and balances to keep the heater block in the wanted margin, and it would need a deliberate manipulation of the software to disable all safety features in conjunction with the failure of the thermosensor for the printer to go into Thermal runaway in such a degree that the coolend goes over 300 °C. And then you have different problems: your printer surely is turning into a molten pile in that failure mode. The presence or absence of the coolend fan would just delay the inevitable, should you run such a fire hazard-machine
Conclusion
Configure and install a recent firmware distribution (Marlin 1.1.9 and Marlin 2.x come with TRP enabled by default) and be sure to have MaxTemp enabled at 275 °C and Thermal Runaway Protection on, and you have a 3-layer safety against PTFE-fumes.
Adding more layers surely is possible, but the cost-effect calculation gets worse starting there.


How to extract 3D information from a 3D model for calibration?

Extracting various measurements from 3D models is easily done using the following free online tool:

https://0x00019913.github.io/meshy/

I scanned a person using the Sense 2 scanner and I compared the values from meshy for the hip and waist with those measured in real life one day after the scan: the difference was about 1 cm, which can easily be explained by the uncertainties in the choice of the measurement point and moment of the day.

This shows that both the 3D scanner and meshy are quite accurate. The tool is also very easy to use.


PLA bubbling in the first layer of a print

Oh wow. You are way over cooking your PLA. It is bubbling because it is BOILING. I can tell you have it too hot because the lines are all blurred as if they are liquid and pooled together.

That said I can't give you details because you didn't post settings. I would start by turning the temps to 170 °C for hotend and 60 °C for plate. Also the gluestick it self should never bubble. It is unclear if that is an issue..


There is very little information about safety available, as home 3D printers are relatively new. However, plastics such as ABS have a long history in making plastic products, and a study found that at traditional manufacturing methods (such as injection molding and hot wire cutting) do not release dangerous levels of carcinogens and/or respiratory sensitizers in to the air.

Of course, 3D printers are not among the processes covered in the study. In home 3D printing circles, this study that looks at ultrafine particle (UFP) emissions, is often cited. It finds that printing ABS releases relatively high levels of UFP's and PLA releases significantly fewer (but still quite a large amount). However, it is unclear whether/how dangerous these UFP's are in the amounts emitted.

It is often suggested that PLA, partly because of the reduced UFP emissions is safer to print than ABS, partly because of its "natural" origins as it can be derived from materials such as cornstarch. I would caution against this line of reasoning since "natural" materials can still be poisonous (snake venom is natural, after all) and the cornstarch is heavily processed so it hardly resembles its original form. The lower UFP emissions may suggest it is safer, but the study is only quantitative, not qualitative.

That said, PLA does probably pose less of a risk (despite my earlier argumentation against "natural" materials, PLA does play quite nicely with the human body), but I contend the risk with ABS is not too large anyways, given that it has been safely used in factories for decades.

Another study is often miscited, supposedly saying that 3D printing ABS releases hydrogen cyanide. The study only looks at the thermal decomposition of ABS, which happens at significantly higher temperatures than are reached during printing (but a significantly malfunctioning printer might cause toxic gasses to be released, but I contend that at that point you should worry about your printer being on fire, rather than temporary exposure to some toxins).

There are no printers out there that are fundamentally safer than others. However, some printers have an enclosure (containing the fumes) and some even have a carbon filter and a fan for fume extraction. If you would like to err on the side of caution, this might be a good choice (but again, it is not clear if a carbon filter is totally effective).

Finally, as printers are generally quite noisy it tends to be preferrable to keep your printer in a separate room from where you usually work. In this case, fume exposure (during the few minutes that you go to check on your print) is minimal, and the potential advantages of a "safer" printers or using "safer" materials diminish.

Incidental exposure as a hobbyist is probably not a big deal; workers in factories are exposed to the fumes of melted plastic their entire lives and they don't seem to be dropping dead. On the other hand, if you are going to be printing structurally then it is probably preferable to move your printer to a separate room, if not because of health and safety because of the noise.


What materials would be appropriate for pool parts (chlorine & UV exposure) using SLA or FDM?

Have you thought about using ASA filament? ASA filament is very strong. ASA filament is similar to ABS filament (if you have ever worked with that). When contrasting it to ABS filament, ASA has a higher resistance against UV and chemical exposure. It will also have no problem with the water. Both ASA and ABS filament print at about the same temperatures.

Here are some links that might be helpful :

UV-Resistant ASA Filament: Properties, How to Use, and Best Brands
Want to Use ABS in Hot Sun? We Compare ABS vs ASA Filaments

Hope this is helpful.


Top layers failing/underextruding on Creality CR-10

If you decrease layer thickness, you should increase bottom and top layer amount, or set it to a fixed shell thickness. The thinner the layers the more difficult to span over the infill (there is much less filament extruded).

You could try extra part cooling, higher percentage infill, reduced hotend temperature and slower top layer printing. But, best results are reached with more top layers and higher infill percentage.

See e.g. this answer by user "dnewman":

  That said, with very low layer heights (e.g., 0.1 mm), there's a tendency to use very sparse infill to speed up printing time.  However, very low layer heights bridge over voids very, very poorly.  So poorly that you can have the print nearly finished only to find that the top won't close up.  Thus, don't make the infill too sparse when doing low layer heights.  MOREVER, you definitely need more top layers to get the final finished top to look acceptable.  The thin layer heights will take many more layers (many more in physical height, not just layer count) to give a nice top.  At issue (again) is how poorly low layer heights will bridge voids.  With 0.2 mm on up, you generally get a nice, thin strand extruded which can stretch across voids. But at 0.1 mm layer heights the printer is just doing tiny, discrete squirts of plastic which it spreads like cake icing across the lower layer.  There's not a single, fine strand extruded and instead tiny little beads.  When there's a solid layer below, these squirts have something to be spread against by the extruder nozzle.  But when there's a void, the squirts just build up on the nozzle and then come off in a big blob when the nozzle next brushes over a non-void space.


PLA Issue printing first 3 mm with Ender 3 Pro

This answer hints to the correct diagnosis but doesn't explain how to fix this in Cura or any other solution other than babysteps. You don't want to adjust babysteps at every print...

Basically, your nozzle is too close to the bed (from comment 0.1 mm to be exact). To increase the distance between the nozzle and the bed you can:

level with a little thicker paper,
move the bed down on all corners,
move the Z endstop up,
redefine the Z=0 in your start code,
G1 Z0.1 ; Move to 0.1 mm height
G92 Z0  ; Redefine zero height
install Cura plugin "Z Offset Setting" from fieldOfView (through the Cura Marketplace) and define a Z Offset of 0.1 mm, and/or
increase the first layer height a little.


Why am I getting Z banding/shifted layer on a single layer?

I started this as a comment but it couldn't fit.  If it isn't a true answer and should be removed, I understand.

You suggest in your question that perhaps the defect could be caused by a problem in the Z-axis lead screw.  Indeed, that is possible.  If so, it would probably introduce a defect at that position across the entire print bed.  If you print a test object and the defect is on all faces at the same height, check your Z-axis.  With the power removed, try slowly moving the bed up and down through the region where the defect occurs, feeling for any hangup, hesitation, looseness, or any other non-uniformity.

If the defect is along a particular line, check the complementary axis.  If the glitch is a X-axis line, check the Y-axis.  If a Y-axis line, check the X-axis.  Slid the axis back a forth slowly, feeling for any non-uniformity in the motion.  It could be a scratch on the linear bearing, or a ding from dropping something.  Any discontinuity  can cause a linear Z-axis defect, up or down.

It could even be cause by the printer not being firmly sitting on the table at an angle, so that after a particular point the balance point changes and the printer rocks, introducing a glitch.

3D printers, and many other motion control systems, relay on flat, smooth, uniform bearing surfaces connected to smooth, continuous drive systems.

If you attach photos of all four surfaces, we might have a better idea of how to look for the problem.

It wouldn't hurt at this point to wipe and clean all sliding surfaces, and then re-lubricate them.


Monoprice maker select v2 doesn't extrude but is not clogged

Try advancing the extruder manually using the control interface. Extrude about 10 cm of filament to verify that everything is OK with the machine.
Is the filament curling on the way out of the nozzle? If so then there may really be a clog and you should clean it. Invest in some cleaning filament as well.
The idler bearing may not be pushing down on the filament tightly enough. Check that the spring which holds it in place has not become soft or broken.
The drive gear could be dirty. Plastic particle build up on the gear will cause it to slip. Clean the drive gear to remove all plastic build up.

Outside of this you could have a mechanical problem with extruder. Advance the motor using the control system (without filament installed) to verify that it is working properly.


Monoprice Maker Ultimate Extrudes Too Much Filament At Start

Changing the Simplify3D start script to this will change the nozzle purge to the same length as what was on your SD card.

    G28 ; home all axes
    G92 E0 ; zero the extruded length
    G1 Z10 ; lower
    G1 E20 F200 ; purge nozzle quickly<---------Change E20 to E3, E is the extrusion length
    G1 E10 F60 ; purge nozzle slowly <----------Remove this line
    G92 E0 ; zero the extruded length again
    G1 E-1.5 F400 ; retract
    G1 X170 Z0 F9000 ; pull away filament
    G1 X180 F9000 ; wipe
    G1 Y20 F9000 ; wipe
    G1 E0 ; feed filament back

The rest of it is just moves to try to clean the nozzle.


As long as you provide enough energy to heat the nozzle and keep its temperature, that is possible, as steppers power usually is limited by driver to reduce noise.

see the attached video: A fully mobile printer example here


Slow down first layer above infill in Ultimaker Cura

Cura can do this. It's a bit convoluted though. Here's what you need to do:

Load your model / scene in the build plate.
Load an additional cube and make it as big as the entire build plate so that it overlaps with everything (in the preferences you may need to disable "Ensure that models are kept apart).
Select the cube and go to the per-object settings tool.
Change the cube's mesh type to "modify settings for infill".
For the cube, set Wall Line Count to 0, Top/Bottom Thickness to 0 and Top Layers to 1. This effectively makes the cube add one additional layer on the top side of all infill volumes.
For the cube, set the Top/Bottom Speed to your desired speed for the one slower layer.
(Optional) In the normal settings panel on the right, set the number of top layers to be one less, so that you get the same number of top layers again.


What are some cheaper versions of Multi Jet 3D printing?

Objet by Stratasys is a comparable technology (they call it PolyJet). SolidScape is also somewhat comparable (they also use jetting).

The FormLabs printers are not comparable. They use a completely different process, which can only print in one material. With jetting, you can mix different materials in the same part.


How to slice this wing so it has a smooth infill like perimeters

I found a great solution!

In Cura, there is a setting under Shell called Horizontal Expansion. What this does is it controls the distance between the two perimeters. A negative value in this field will make them come closer together, thus removing the gap between them.

I found that -0.1 is the perfect value for 1 mm thick walls like the ones in my design. So I set it to -0.1, then set the infill to 100% because in some spots the thickness is a little bit more than 1 mm, so the infill closes the gaps in those places. Here is the result:

You can see the perimeters are now sticking to each other and there is no gap between them. The result estimated weight is 71 g, which is a quite good reduction from the estimated 92 g when not using horizontal expansion.


Printer with two extruders but one as a backup

You could use a "filament runout sensor" and combine it with a "filament running sensor". If either fails the controller needs to be notified by a signal. If you configure the Configuration.h filament runout setup such that it doesn't call M600 but instead a series of codes to park tool 0, activate tool 1, home tool 1, prime tool 1, and commence printing, you are near a solution.


Is 3D printing suitable for repairing a refrigerator shelf glide rail?

Can 3D printing be used for this task to make the repair any easier or more successful to complete than simply cutting a piece of plastic and (again, somehow) affixing it to the shelf?

Yes. 3D printed parts can be plenty strong enough to handle the kind of load you're considering. You'll need to create a 3D model of the part you want it a CAD program, which is something that takes some practice if you don't already know how to do it, so it may or may not be easier for you than milling the from a plastic blank.
One advantage that 3D printing brings with it is the ability to iterate rapidly on your design: you can model and print the part that you think will work, try it out, adjust your model to incorporate what you learn from the first try, and print new versions until you get it just right. If the existing shelf is broken in some irregular way, for example, you can design a new part that mates tightly with the broken edge of the part you have.

The rail was part of a large plastic shelf, which is no longer available for purchase.

Perhaps you've already looked, but there are a great many parts suppliers online. If you have the part number, be sure to look beyond just what the manufacturer can supply -- it's very likely that someone out there has the part you need.


It seems that Marlin adjusts acceleration just for print speed, without adjusting it too for the extruder, so the extruder extrudes a constant amount of filament, which on slow speeds (corners) results in an overextrusion and on high speeds (lines) results in an underextrusion, causing bad corners and inaccurate prints.

This is not the case. Marlin accelerates the extruder perfectly in sync with the printhead, and the speed of the extruder is perfectly proportional to the movement speed. However, the extruder itself has a certain amount of "lag": as you feed in filament, pressure builds up. As you stop feeding filament (or slow down), the built up pressure causes the extrusion to continue for a while. Thus, even with "correct" control of the extruder, you don't necessarily get the desired amount of extrusion.

Marlin has a feature, that you can enable in the advanced configuration file, called "extruder advance". It looks at the acceleration/deceleration of the extruder, and advances the extruder a few extra steps when the speed increases, and backs it off again as the speed decreases. You will need to tune this feature to get rid of the overextrusion at the corners.


Tevo Tarantula incorrectly auto leveling of bed

From your configuration.h file you see that (in line 643):

#define MANUAL_HOME_POSITIONS

is not commented out, there is no // in front, so this means that manual homing with accompanying coordinates is enabled.

This should not be enabled, as this setting is used by Delta printers only. This may cause the problems you experience as there may be some sort of a conflict between manual and auto positioning.


Lead screw holder - shall I buy metal or just use a printed one?

Update:
To answer your question, you could use either metal ones or printed ones. Metal housings are way more heavy that printed parts. The housing you refer to is not attached to the platform, but a static part connected to the frame. Weight is not an issue, stiffnes, strength and temperature stability should be of higher importance.

For metal housings attached to the Z platform weight may be an issue (if have many microsteps where the incremental torque may not be enough to raise the Z platform). Printed parts can be made stiff enough to house the linear bearings. In my experience printed bearing housings can be just as effective, I use those on my platform for my CoreXY printer as well as using leadscrew and linear guide rails brackets made of printed parts.

Old answer, before question update:
With platform movement (or printer head Z movement for Prusa designs) you face a few challenges related to the quality of the parts you buy. Note you want smooth operation of the platform (or head) without wobbling. It is customary to add linear rods or rails to guide the platform up and down, this is their sole purpose, therefore these rods need to be very straight and bought from a local trustworthy vendor (the Eastern oversea specimens are usually of less quality as I know from experience). Securing these linear guide rods could be done with printed parts, the plastic is stiff enough to hold the rods in place, and temperatures are usually not that high to play a large role (if so like in boxed up printers, print in high temperature resistance material), personally I use black PETG.

Secondly, the drive of the platform. Note that leadscrews are not perfectly round, nor is the coupling 100% in the center of the screw. From a mechanics point of view you should never constrain the leadscrews at both ends. This results in an over-constrained (indeterminate) system (of forces) that can induce even more problems. Optimally you fix one end close to the stepper, or the drive of the belt), it is arbitrary whether you use a metal or a plastic part for that unless there are constrains on size and thickness for a requested rigidity and leave the opposite side free. For Prusa clones I use lifting parts that house the lead screw nut rather than embedding the nut in the x-y idler coupler (this separates eccentric x-y movement from z movement and a handy advantage is that if something goes wrong in z min direction, the head will not destroy the glass or bed as it is not fixed to the lead screws). Something similar can be done for your platform. For my CoreXY however, I have not done so, it uses 4 linear rails of 12 mm and 2 leadscrews. PETG stepper mounts at the bottom drive the leadscrews using plum, not spring, couplers (the springy types should be avoided or a ("fixate-able") bearing or KFL08 mount should be placed at the other side of the driven side of the coupler and correctly mounted to the frame). Furthermore, I use Delrin or POM anti backlash nuts on a mount connected to the platform. All tall prints I make are perfectly straight, no wavy or wobbly vertical walls.


It seems my filament is burnt when I use PETG

It looks like you have a clogged nozzle/hot end. I use 225°C @ 40mm/s for PETG with 235°C @ 30mm/s for the first layer.

If you print at 245°C, you risk burning the PTFE liner in your hot end. You really need an all-metal hot end to print at such temperatures.

It is possible that you have already damaged the PTFE liner, and this may be the cause of your problem. However, I would check for a clogged nozzle first.


Are there any simple solutions I can implement out there?

A gasket made of rubber or other elastic or deformable material is probably the best option. Printing one or both of the parts using a deformable material like TPU might also work. Finally, if you don't need to open the unit during the experiment, you could use a sealant like silicone caulk might make sense.


What UART port to use for RPi GPIO pins on an SKR v1.3 board

If you followed the video verbatim then the pins file will be wrong, because he's changing the pins based on an MKS Gen 1.4 and not the SKR 1.3. All pins on the SKR will look similar to P2_04, which is the pin for the 2nd hotend terminal.


How to fix wall separation in 3D prints (gaps in between wall perimeters)?

Now that print settings are shared we can see that this problem is not related to too fast printing (only 20 mm/s) or too low print temperature (210 °C should get PLA fluid enough). To explain this, a low temperature and too fast printing cause under-extruded lines.

There are 2 other causes that might be worth investigating:

Under-extrusion. From the top layers one can see that there may be insufficient material printed. Calibration of the extruder helps in this respect.
Inaccurate positioning. This may for instance be caused by loose belts or a mechanical defect.


As is typical with many CAD type programs, a feature in Onshape known as revolve may be your solution. As you have a clear formula for the cross-section, half of the work is complete.

You would generate a sketch representing the curve, then use the Revolve feature with the axis oriented to vertical. According to the Onshape video, you can generate a solid or a surface from the options that appear when selecting that feature.

As you can see in the images above, the axis selected in the tutorial video is horizontal. Other features of revolve are covered in the video. Your post suggests it will also be necessary to perform a subtraction action on the assembly in order to get the scoop/concave result.


Why does MakerBot software shows holes in the wall of a 3d model?

I guess you are referring to the corner of the part facing you in the first figure, and the sliced corner on the left in the second figure and not the white lines on the wall facing you. This latter effect is called Moiré or moiré pattern which is an optical illusion created by interference.

This appears to be a slicer error or a rendering error, the walls are not finished. Furthermore from your sparse question it is noteworthy to say that you have sliced the model on a raft.

Why not print the model, it will start a raft and when you come to the part it will clearly show whether it is a slicing or a rendering problem!

If it is a rendering problem, keep continuing printing, if not, stop the print and download a most recent version of any other free available slicer tool. The most commonly used free slicer tools are Ultimaker Cura and Slic3r. Setup a printer profile and select and modify material and slicing properties to create a new G-code file for you to print. You can now compare the rendering of used new tool to your current rendering and print the model to see if the part now prints well.


For making V6 or Mk8 nozzle what tolerance specification we've to follow?

The short answer is it really doesn't matter. None of these surfaces are interfacing with other rigid parts. They're conducting filament that's being melted. The specifications are likely optimized for favorable flow properties, and following them as closely as your tooling allows is probably a good idea, but there's no hard tolerance cutoff.
CNC Kitchen has a video producing a working nozzle with a mini lathe and had good luck without any rigorous process for tolerances.
It should be noted that the exactness of the nozzle orifice size and other dimensions are for the most part not relevant to the accuracy of extrusion; that's pretty much all on the filament diameter and extruder motor motion, which determine the volume of material extruded. In practice you can produce 0.4 mm extrusions pretty much equally well with an 0.3 mm orifice or an 0.5 mm orifice; at most you'll have some minor differences in behavior on overhangs. And presumably your error is not going to be anywhere near 25%.
As Trish noted, the threads do have to interface with another rigid part. However they're governed by ISO standards for metric threads not this particular design. I use this tolerance calculator site: https://amesweb.info/Screws/metric-thread-dimensions-calculator.aspx


How to work with PETG? Settings, caveats, etc

Slow down!

80 mm/s is much too fast for PETG. Try 45 or 50 mm/s instead, even for infill, supports, and other less-visible areas.


The "shock" is likely from noise filtering circuitry at the power supply's input. For filtering, every power supply has a small capacitor that connects the live input wire to ground (a so-called "class Y capacitor"). A small amount of current can flow through this capacitor, which can give an annoying, but otherwise harmless shock/tingle. Grounding the power supply would solve the problem (which you should do anyways, because it is dangerous to run electronics that are supposed to be grounded without ground).


PLA infill/perimeter-layer to mimic real bone hardness

Generally, if you care about achieving a specific structure inside the "interior" part of a model to be printed, that structure needs to be part of your model rather than generated by a slicer. If it were me, I would programmatically generate a generic pattern for the pockets of hollowness in OpenSCAD over a region slightly larger than the bone, then subtract it from the solid bone. After that, slicer settings will be mostly irrelevant since it will be constrained by reproducing the layer outlines with lots of holes in them.

I haven't done this, or anything really comparable, but it should work.


Anet A8 - hot end temperature still same

In my case, I had a bad resistor on my board. R41 had only 2.2 kΩ instead of 4.7. I replaced it and everything works now.


The cr10s has a filament run-out sensor. If the microswitch doesn't function properly, or you have issues with the wiring, the print pauses.


This is the result of travel moves passing through/over the top surface. The combing setting can prevent this type of move (for walls, infill or top), and z-hop can avoid making any mark during these travels.

Both settings will affect speed. Z-hop will be active on every layer, for example.


Ghosting is an artefact in the print due to the vibrations in the printer that are induced by rapid changes of direction.  It is important not to confuse them with inherent vibrations in the printer due for example to the belts being loose or the bearings not being in perfect order.

The good news is that it is relatively easy to tell them apart: ghosting (also known as "ringing" or "ripples" or "waves" or a number of other names...) is always downstream of a change of direction, and fades rapidly.

Inherent vibrations - on the other hand - tend to be consistently present when printing along a given direction, and do not fade.

Mechanically, ghosting works like this:

The moving part is travelling along - for example - the x-axis, when suddenly the direction of movement becomes the y-axis.
At that moment, the stepper motor of the x-axis stop rotating, but the momentum of the moving part stretches the belt even so slightly past the intended stop point.
At this moment the belt becomes like a rubber bend / spring, absorbs the kinetic energy of the moving mass and releases it by "throwing" it past the intended stop point in the other direction.
This keeps on repeating a number of times, but at each pass, some of the energy is dissipated, and the moving mass moves less end less away from the ideal stopping point.
While all of the above is happening, the object has also begun to move along the y-axis, so the extruded plastic looks "weavey" along the y-axis.

Understanding how this process works, makes it possible to understan why the three main factors affecting ghosting are:

The amount of mass being moved
The speed, acceleration and jerk settings
The elasticity of the mechanical components

Namely, mass and speed are important because their product is the momentum.  That in turn means that diminishing either one of the two will reduce the amount of "overshooting" past the stopping point.

Elasticity of the mechanical components is important as the more flex/stretch the part can take for a given amount of force, the more overshooting a given momentum will result in.

Finally, acceleration and jerk are important because - simplifying things a bit - the faster the change of direction happens, the less time the system has to adjust without vibrating.

So, concretely... what can you do to fix/reduce ghosting?  Three things, of course! :)

Reduce the mass being moved.  Depending on the geometry of your printer, the mass being moved could be the bed+print, the printing head, or an entire gantry.  These are normally considerations done when designing the printer itself, and engineers normally mitigate problems by using lighter materials (plastic over metal, aluminium or carbon fiber over steel, etc...), or adopting different designs (like using a Bowden extruder instead of a direct one, to save the weight of the stepper motor).
Reduce speed, acceleration and/or jerk.  Speed is normally the safest bet, as - besides your prints taking longer - there is really no penalty for it.  Acceleration and jerk - on the other hand - can cause overestrusion at sharp corners.
Reduce the elasticity of the system.  This is commonly achieved by tightening the belts and eventually switching to more rigid rods / tracks / rails.

A couple of resources that may come in handy for you to understand and solve the problem better:

A really nice article with illustrations (two of which I "stole" for this post)
A test model specifically designed to highlight any possible ringing problem with the printer.
A video showing lots of different test prints done with various settings (very useful to understand how changing the above parameters affects the print).


Recognizing that the posting party feels that FDM constructed parts are of insufficient strength for his purpose and allowing for proper layer bonding, one can understand that the model can be perfectly constructed and not reach the strength objective.

Filling a model with an epoxy or a casting resin will provide additional strength. Testing smaller, non-critical models is recommended to determine the level of increase. The design has to be re-engineered to provide for resin/epoxy flow within the model. Some epoxy and resin formulations generate heat when curing and may soften the model. The solution in such cases is to mix and pour small amounts, allowing for a pause between pours.

An alternative to filling a model is to reduce the perimeter (if applicable)  and apply a reinforcing layer. I've constructed satisfactorily printed models with insufficient strength for my purposes, but then applied fiberglass cloth and epoxy resin to the outside. A single layer provided the necessary strength in my case.

One could apply sufficient layers to provide all the necessary strength, effectively turning the model into a positive mold. This is commonly done with amateur-built aircraft of the Burt Rutan design style. More recently, an article appeared on the internet of a model being printed with wash-away support material only, covered in carbon fiber. The wash-away was washed away and the wing structure became the product. For your application, it may not be necessary or practical to remove the inner model.

Just as with the injection concept, one must re-engineer the model to allow for this type of reinforcement. Edges will have to be radiused or the sharp termination of reinforcement layer will become a weak point. Tight inside angles will have a similar problem.

Fiberglass cloth comes in various weights, measured in ounces per square foot (US). The lighter cloth is more capable of "turning corners" and fitting into tight angles.


Z axis no longer working on a working printer

It could be caused by software or configuration issue.
Possibility 1: just worked after re-installation of Marlin
You could have Z steps/mm set to 0 in EEPROM, and did not notice that fact.
It is possible to fix this unconsciously with Marlin software reinstallation, following the upgrade procedure which included reset of EEPROM settings - like "Step 4: Finishing touches" described in community wiki's guide for Updating Marlin Firmware. This is described in more details in another post No stepper motor movement on Ender 3 Pro.
Possibility 2: Marlin configuration is not correct
When you recompiled Marlin, did you use already proven configuration for Marlin? When saying "Motors will not turn" you mean only Z? Are your other motors are still functional now after Marlin was deployed?
Among other Marlin settings, you may want to check that this line is disabled in Configuration_adv.h:
  /**
   * Software enable
   *
   * Use for drivers that do not use a dedicated enable pin, but rather handle the same
   * function through a communication line such as SPI or UART.
   */
  //#define SOFTWARE_DRIVER_ENABLE

(I took this advice from No Motor Power With TMC2209 on RepRap forum.)


How do I add auto bed levelling to my Marlin-based CNC?

Auto bed leveling requires some settings (constants) in the configuration of your Marlin firmware.

It is recommended to read about the implementation of automatic bed leveling first. There are a few options to choose the kind of leveling, for 3D printers a commonly chosen option is AUTO_BED_LEVELING_BILINEAR which is the best option if you do not know if your bed is flat or not. If you are certain it is flat but tilted (e.g. when you have a milled bed or a glass plate in 3D printing) you could go for AUTO_BED_LEVELING_3POINT or AUTO_BED_LEVELING_LINEAR.

What further is important is the sensor type you choose. Do you want a touch or a proximity sensor. The latter is your preference (as specified in your question), which is a little simpler as you do not need to configure for servos for deploying and stowing.

You need to set:

#define FIX_MOUNTED_PROBE

for using a fixed proximity sensor.

In the configuration file you also need to specify the position of the probe in relation to the nozzle (in your case tool center):

#define X_PROBE_OFFSET_FROM_EXTRUDER 10  // X offset: -left  +right  [of the nozzle]
#define Y_PROBE_OFFSET_FROM_EXTRUDER 10  // Y offset: -front +behind [the nozzle]

and optionally:

#define Z_PROBE_OFFSET_FROM_EXTRUDER 0   // Z offset: -below +above  [the nozzle]

This latter is not necessary as you can always set the distance of the sensor trigger point to the nozzle/tool plane by G-code command M851 Z-x.xx

You would also need to set the boundaries of the probe area to prevent the tool to hit unwanted positions (fill out values or leave the constants):

// Set the boundaries for probing (where the probe can reach).
#define LEFT_PROBE_BED_POSITION MIN_PROBE_EDGE
#define RIGHT_PROBE_BED_POSITION (X_BED_SIZE - MIN_PROBE_EDGE)
#define FRONT_PROBE_BED_POSITION MIN_PROBE_EDGE
#define BACK_PROBE_BED_POSITION (Y_BED_SIZE - MIN_PROBE_EDGE)

Once properly setup, command G29 runs the leveling of the bed, options are available for that command to store the bed mesh to EEPROM.

Enabling LCD_BED_LEVELING constant in the configuration file will add a Bed Leveling sub-menu to the LCD. But you could also work with SD-card stored files that load these codes.

This reference explains the automatic leveling in more detail, but there are many more detailed guides to follow from the internet. Be sure that you get a recent guide to that is easier to set in the latest firmware.


Printer with 50 microns or close to 50 micron (z resolution)

I assume you mean a resolution of 50 microns (0.05 mm step size)
Most FDM printers can produce something useful upto 100 microns. If you want to print with more precision, try resin printers.
The reason for this is that an FDM printer uses an extruder with a specific nozzle diameter (typically around 0.4mm and minimum around 0.25 mm). plastic has too much viscosity to fit through a smaller diameter nozzle easy.


Uneven motion in X and Y directions after attempting to adjust Z motion in ADVI3++

Found the problem.

The screws connecting the carriage plate to the assembly that connects to the Y-axis belt had loosened, allowing some free play for movements in the Y direction and vibration for movements in the X direction. It just happened to go from nothing to unprintable all at once at the same time I was experimenting with the Z settings.


Good (preferably free) Beginner Software for Part Creation?

I don't have a heavy math background, but enjoy using such skills when applicable.

If you've not yet explored OpenSCAD, you may find that it meets your qualifications. It's more or less a scripting/descriptive language "compiler" that takes ordinary text and converts it to your model design. I use quotes, because I'm not skilled enough to qualify it as a true compiler, although it works in a similar manner and may indeed be a compiler.

It meets another qualification of yours in that it's free and there's quite a supportive mailing list/forum for any questions or difficulties that arise. If you look on Thingiverse using OpenSCAD as a search term, you'll find others' code available for examination and integration into your own models.

For the folks who are not so much into the math and text and logic, there's a GUI of sorts for OpenSCAD called BlocksCAD that allows drag and drop of various modules in a manner akin to Scratch programming.

I'd been using OpenSCAD long enough that I found BlocksCAD to overly complicate the creation of models by obscuring details. It may be better suited for younger model makers in that respect.

Syntax and punctuation errors would be eliminated with BlocksCAD, while it's far too easy to create such errors in the editor for OpenSCAD. One gets used to it and error count quickly is reduced.


Opening .STL to scale in Print Studio (Dremel)

The STL file format does not provide any way to provide the units of measurement for an object. The majority of FDM printers use millimeters so most people export objects with the assumption the values in the STL file are in millimeters.

As you found out that's not always true. The second most common assumption is to export in inches.

Most of the slicers I've used provide a scaling option if you can't edit the STL file yourself. Some will even offer to do the inches to mm conversion for you. Scale to suit when you print or use a 3d editor. I've gotten specific sizes by creating a temporary cube the size I wanted and scaling the object using the cube as a reference.


If we think about drying as a process, then we need to consider some factors:

we need to get same humidity level on the spool
that will require a good stable temperature and an air rotation (fan)
then we need to store  spool in a dry area (a bag and silicone sachets will do the work)

As energy consumption by owen could be the case, if we will run it for 4h full steam, then considering that we shall have about 60 degC, will turn down the usage by at least 70%, so we could assume that 2kW heater will be on only 30% of the time (so it will be 2kw*0.3 = 0.6kW, multiply by 4h -> we have 2.4kWh, so that is about 50 cents).

If you consider the price of wasted filament - then adding 50 cents to the drying process is something that is cheap enough to save precious nylon.


What are the benefits to using 128X microstepping drivers on the X and Y axis of a FFF printer?

You will likely not see a noticeable improvement by upgrading from a 16x or 32x to a 64x or 128x microstepping driver. Depending on the motors you're driving and the size of the load you could actually see a decrease in quality.

Although microstepping increases theoretical resolution it does not necessarily increase accuracy. The reason is that microstepping significantly limits the incremental torque of the motor. This means that you may ask for a step but not get one because the torque of the step won't be enough to actually turn the shaft.

As an example: a motor running in full steps will have 100% of its rated holding torque. Moving to 16 microsteps/full steps drops this to ~10%, 128 drops it to ~1%.

The practical effect of this is that in high torque situations (such as printing at fast speeds) the motor may end up skipping some of the steps. In this way the increase in resolution can actually lead to a decrease in accuracy (smaller steps but they may not actually be taken).

A relevant calculation to do would be to work out what the different number of microsteps to full steps works out to in terms of horizontal, vertical, or whatever movement the motor drives. You can do this by measuring how far the stepper moves said surface in one revolution provided you know the number of steps it takes per revolution.

Example:

With no microstepping: 1 turn/inch * 200 steps/turn = 200 steps/inch or .005 inch/step (127 micron resolution)

With 16x microstepping: 16 * 200 steps/inch or .0003 inch / step (8 micron resolution)

In this example 128x microstepping would be absolutely foolish. Every situation is different and you should use this information to make a decision based on your setup. Many manufacturers have recommendations on how far their motors can be microstepped.


Yes this is expected, with M206 you set a relative offset!

  The values specified are added to the endstop position when the axes are referenced.

reference: G-code wiki M206

So when you issue the command M206 X-10 Y-10 twice (or already have an offset set), the offset is 20, 20 (X, Y) and when instructed to move "nothing" (G1 X0 Y0) the printer moves "nothing" from (thus to!) the newly defined origin at (20, 20). Basically it is relative movement from the set coordinate system, not the position of the carriage. In effect you have changed the reference frame, the printer just responds to that action.


Strategy to stream large gcode file from serial port

Well, after some research I found something about Buffering on the RepRap documentation. I didn't see it before.

Works like this:

You send a command. An "ok" response it's received immediatly, that means that the command was successsfuly added to the buffer.
Then you can send another command. When the buffer is full, the "ok" response will be delayed until a new command it's received.

Some commands, for example M190: Wait for bed temperature to reach target temp will cause that the "ok" response will be delayed until the command finish his execution. That means that the printer won't accept more commands in the meantime.

I still have to check how many commands the buffer can save approximately, and if it's convenient to fill it entirely. I guess not, because let's say you want to pause the print. If you added a lot of commands to the buffer, you'll not able to pause it until all of them finished.

This thread on the RepRap forum was also useful.


Does a 5 axis 3D printer have any benefits over a regular 3 axis printer?

One aspect of having this level of control with 3d printing of a model is the removal of the need for supports and the attendant post-processing. In the case of the model shown in the video, some effects are created by printing the continents in a conformal manner that would otherwise be impossible with conventional 3d printing. Cosmetically, the results of the "5d" printer are superior in this example.

There would also be some structural benefit for models with high organic content, that is curves and bulges, as opposed to orthogonal designs. Even with orthogonal designs, one can achieve stronger parts with cross-layered plastic in all directions, rather than being limited by x and y filament layers.

I see on the web site that one can exchange tool heads as well. One could print a 3d model, layering the filament on all the surfaces, then use a tool head change to a milling bit and smooth the surface under CAD control.  Alternatively, one could use foam or wood and mill a model shape to be covered with a 3d printed material.

Considering the relative novelty of this product, it's likely that many aspects of the creative utility have yet to be discovered!


It is worthwhile to protect electronics with a 3D printed PLA case?

As pointed out by Ryan Carlyle, not all 3D printing filament is flammable (such as PET and PETG), and the question therefore rather becomes:

Can 3D printing be used to make proper electronic cases?

And the short answer to that is yes. 3D printing allows to make customized cases of all varieties. Also, since there is huge variety of materials available, you not only restricted to cases of plastic filaments - should this be of interest.

Then again, it all depends on what you are protecting your electronics from. If you plan on submerging your electronics into water or throw them into a fire, 3D printing might not work for you at all. If dust protection is your only concern, however, 3D printed cases should do just fine in most cases.


Provided that the print hasn't come loose from the bed and you know the layer height or layer number, you can edit the original G-code file. The following hints should be taken into account:

Don't use G28 or G29 instead use G28 X Y (please )
Manually position the printhead at the correct Z height and instruct the printer to use that height for reference: e.g. when the print stopped at layer 12 with a 0.2 mm layer height (2.4 mm height or use the measured height with a caliper) define G92 Z2.4
Make sure the hotend is primed before resuming printing
Cut all the G-code present in the file prior to the layer you want to start printing (e.g. search for G1 Z2.2), but do add bed and hotend heating, e.g. respectively M190 S60 and M109 S200

What you can also do is:

Reprint the whole print
Reslice the print where you have sunk the print 2.4 mm into the bed in the slicer just printing the top face which you glue on later.


Does cheap "plasticy" blue painter tape actually melt when printed upon?

It really depends on the tape. In my case, I've used various types of blue painters tape in bed adhesion situations and have only had one occasion where it sticks to the part. (All experience is with PLA) Best advice I can give is give it a shot, and be sure to wait for the part to cool before removing it from the bed for the best chance at not having tape stuck to the part.


What grade of wire is required for the heating element on a J-Head extruder?

There are a number of things to consider:

Wire Gauge: a typical 40W, 12V heater draws around 3A. 24 AWG or lower would be appropriate (copper wire, CCA will require thicker gauge).
Insulation: the part of the wire close to the resistor leads might get too hot for conventional PVC installation. Consider using silicone, teflon or glass fiber insulation instead, especially near the heating element. If the resistor's leads are long enough they might stay cool enough for regular PVC insulation, but make sure you insulate the part of the leads closer to the resistor appropriately.
Solder: if close to the heater itself, the solder might melt. Consider using silver solder, or using a mechanical connection (ferrule/crimp) instead. Again, this might not be a concern if the leads of the resistor are long enough.
Flexibility: given that the extruder (probably) moves a lot, use flexible wire (stranded, not solid core) and provide strain relief (especially near the connections, and avoid creating too sharp bends).

Finally, resistors have fallen out of favor compared to ceramic heating elements. Since they are inexpensive and solve all of the above problems (the leads are already attached and appropriately insulated) consider using a ceramic heater instead.


How are SLS printers able to print multiple colours?

The Z-corp/3D systems printers lay down what is essentially ink in each layer (only around the perimeters) much like an inkjet printer, dying the powder as the parts are made. This means they can make almost any color at any point in the model. The down size is these models are pretty fragile, at least the last ones that I have handled. This can be helped by dipping them in cyanoacrylate and letting them dry.

As pointed out in the comments, this is not an SLS process, but looks very similar. The printer lays down a binder (clear or colored) on each layer, and is why these models are much more fragile than SLS models, which are very strong.

Here is an example of some prints: http://mcad3dprintingandprototyping.blogspot.com/


How do you remove rough edges from completed prints?

To remove unwanted residual material:

You can scrape with a knife
Use sand paper
use files
Very fine sandpaper or files can smooth out the rough surfaces left from filing or sanding.
Dremel tools tend to be aggressive.  They tend to melt the surface if too fast.  Buffing wheels are probably the most useful on a Dremel.  Dremel tools are good for cutting.

A deburring tool can remove sharp edges such as parts of the brim that don't want to come loose.  However, it's not unusually to need to scrape off flat surfaces as well.

If you want to smooth out the surfaces left from layers, you can:

Carefully use a heat gun or heat from other soldering tools; not spending too long in one spot.  The difficulty with using heat is most prints have fill rather than being solid; so, with only two or three outside layers, it's easy to get the surface to deform into the fill. Also the print material will tend to stick to solid surfaces hot enough to melt the material.
Use acetone on ABS.  Don't breath the fumes or dissolve your print.
Paint the surface as the comment from user77232


Large 3D printer 10'x10'x4' - Need G-code to tell when it stops extruding and to stop machine

G-code is likely not the solution to your problem. G-code are simple commands that are executed by the printer (e.g. "heat up the hotend to this temperature" or "move the extruder to this position") but there is no G-code for "detect whether the pusher is still running" (and besides, how could the printer possibly detect whether the pusher is running without hardware to do so?

You'll likely want to configure your pusher to somehow act as a filament runout sensor. This is a feature in Marlin (smoothieware has something similar) that allows you to pause the print by making an input on one of the control board's pins. You'll need to build hardware that detects the motion of the pusher, and if the motion is interrupted, pulls the FIL_RUNOUT_PIN low (in the case of Marlin). You can then configure what should happen next (e.g. raising the head and stopping the print) using FILAMENT_RUNOUT_SCRIPT (again, only if you're using Marlin).


Can UV cure inside opaque or more massive printed object?

From what I know about the various resins, once they are printed they are cured enough. Some of the transparent ones require additional curing, however the manufactures of the machines only test based on the max size that their machines can print.

The resin never stops curing apparently, going into diminishing returns; curing slower and slower as time goes on. Only way you will know for sure is by experimentation. You should get a poly-carbonate tube, place black tape along one side then spray paint the rest black. This will leave a window that you can use for future observation. Seal the bottom, and pour in uncured resin. Leave it under a UV source for 2 weeks then peal the tape off to see how much of it has cured. Then come back here and ask Trish to do the math on what the co-efficients of absorption are for the material :)


This is not a definitive answer (and has turned into a ramble), as I have not yet had to change my filament size.

However, initially, I would have thought that only the hotend and the hotend's nozzle would need to be changed, from one that can handle the 1.75 mm filament to 3 mm. If the extruder is spring loaded, then it should adjust itself to the thicker filament, without a problem. If not, then you may have to do a slight manual adjustment.

However, after doing some further reading, there may be other factors that need to be considered, such as:

Extruder gearing;
Melt time (which would imply a different feed rate)

It could be worth having a close look at the aperture of your hotend. If, in the unlikely situation, it looks as if the hotend would accept 3 mm (or if you could remove the lining so that it can), you may not need to actually change any hardware, but instead just try tweeking the feedrate in the software, because as your nozzle is less than the width of the filament anyway, then it will be fine for both 1.75 mm and 3 mm. A 3 mm filament would require more heating, and therefore a slower feedrate than a 1.75 mm feedrate. Once the filament has melted, so long as the pressure from the extruder is sufficient, then the molten filament should come out of the nozzle. However, this may be a less than satisafctory method and result in some dubious prints.

There is an interesting thread on the RepRap wiki, 1.75mm Filament vs 3mm Filament, that discusses most of the points above.

It should be noted that the advantages of 3 mm filament has over 1.75 mm are that it is:

cheaper
stiffer (less flexible) and thus "easier" to push through the hotend.

As an aside, one interesting point raised in the thread, is that maybe a smaller extruder can be used, for the narrower 1.75 mm filament, thus resulting in a lighter print head. I am not sure how true that is.

This article, Converting a 3D printer from 3mm to 1.75mm, does the reverse of what you want, and comes with a video. It states that, as you have already found, that the hotend needs to be changed:

  The printer [Thomas] is changing out to accept 1.75mm is the Lulzbot
  Mini, one of the most popular printers that would ever need this
  modification. The only required materials is a new hot end suitable
  for 1.75mm filament, a 4mm drill, and a few wrenches and allen keys.
  It would be a smart idea to get a hot end that uses the same
  thermistor as the old one, but that’s not a deal-breaker as the
  problem can be fixed in the firmware.

Alternatively, you could leave your printer as it is and use a 3mm to 1.75mm filament converter, which may be a bit of overkill for just one reel of filament1.

The bottomline

To be honest, is it worth the hassle, time and expense of having to modify and re-calibrate your printer (or worst case, change the model of the printer), just for the price of a reel of filament (assuming that you did not bulk purchase a bunch of reels)? It may be better to stick to one filament size (i.e. your original size) for all of your projects, and so resell the reel of 3 mm and stick with the 1.75 mm printer and buy the correct filament2.

1 See also Conversion of 3mm ABS filament to 1.75mm

2 See also Tom's answer to Conversion of 3mm ABS filament to 1.75mm

See also Can 1.75mm filament be used in a printer that takes 3mm filament?


What are the ideal print conditions for polypropylene?

Polypropylene CAN be printed with excellent results, you just need a good filament roll and good printing setup.
A few days ago I read this topic and was kind of afraid of testing it, now I am so happy I tried it.

I am printing the PP filament from the brand Smart Materials 3D (search on google).

I am using a Prusa i3 Mk2, bed heated to 70ºC and hotend to 210ºC. I ventilate the printer as much as possible: room windows open and fan at 100% after second layer.

IMPORTANT: apply some cheap brown packaging adhesive strips to the bed, where the part is going to touch the bed, with adhesive facing down. I tried many other solutions but none worked.

I have printed so far at 20mm/s constant, with 0.2 mm layer heigth, 0.4 mm extrusion width, 0.8mm retraction, flow 125%. Still optimizing setings.
Parts come out very nice, with good flexibility and amazing inter layer bonding. Density is a bit lower than ABS, so excellent, and impact resistance is awesome.
Check some parts I printed today:


When is kapton tape useful as a bed adhesive?

I tested Kapton tape for PLA, ABS, PETG and XT. I know it works for other materials as well. What you need to keep in mind is that many materials only stick to Kapton tape well if you use a heated bed.

The advantage of Kapton tape in comparison to other materials is its heat endurance and mechanical stability. It protects the glass underneath, while you remove the print from the surface. Some filaments stick so well to glass that you may break chunks out of it.

The major disadvantage of Kapton tape is the time to apply the tape to the print surface and its very smooth surface pattern which seems odd in comparison to the rest of the print.


Are Fusion 360 drawings sufficient to design and enforce tolerance in a hole of a solid?

Besides offsetting the clearances you want into models, you can and should also calibrate your printer to compensate for included holes - because often inner holes are solved to be smaller than actually designed out of necessity.
However, the option can also be used to fix problems that stem from the slicing and printing itself, and thus offers to fix some problems that are endemic to your setup or where you can't easily fix the model by setting an offset to create the wanted clearances in it.
In Ultimaker Cura, the option for this fix is called Hole horizontal expansion since 4.6 in April 2020, which only affects internal perimeters as I know from testing.
SuperSlicer, a PrusaSlicer branch offers hole_XY_compensation, though I can't quite pinpoint the time when it was added. I guesstimate sometime before October 2020.
PrusaSlicer offers XY size compensation, which does affect outer perimeters. A hole-only is requested almost since that option was available the first time. An attempt to implement a hole-only compensation again appears to be worked on since mid-2020. It seems that in the beginning of March some implementation has been tested.
The first work for such a function was tried by Slic3r before PrusaSlicer was started on, using an Arc-compensation formula in at latest 2009, but the function proved to be overcompensating. As Prusa-Slicer is a fork of Slic3r, some of this work might remain in the code.


How do I repeat the layers of Slic3r for every 3 infill layers with different angles? (Might need some programming knowledge)

Slic3r is available on Github.

I think the section you'd be looking for is here


What is stepper motor binding? (When belts are too tight)

I think the RepRap wiki is using the word "binding", which translates to "stick together or cause to stick together in a single mass" (from Google dictionary), to indicate that some sort of friction is experienced (as you experience when things are sticking together).

When there is too much tension in the belt, pulleys and bearings experience a larger radial force stressing the balls of the bearings and pulley shafts. This causes extra friction for the stepper motor to overcome (as the friction force, tangential, is related to the radial force); this means that the stepper has to work harder and can skip steps (for more insight please read below).

While ball bearings are used to reduce friction (opposed to a bush bearing), each ball has a little friction from a couple of sources according to this reference:

  The sources of this friction are: slight deformation of the rolling elements and raceways under load, sliding friction of the rolling elements against the cage and guiding surfaces.

These effects are generally captured in a single friction coefficient called "μ". The relation between friction force (tangential) and bearing loading (radial) is written by $$P_{friction}=P_{load} \times \mu$$ so the higher the belt tension ($P_{load}$), the higher the frictional force ($P_{friction}$), the harder the stepper has to work.


Why does jerk have units of mm/s rather than mm/s³?

The jerk setting in 3D printing G-code and firmware represents a concept similar to, but distinct from, the physical definition of jerk. Rather, it's a [limit on] instantaneous change of speed.
Mathematically, one way to make sense of this is to think that, rather than being the second derivative of speed with respect to time, this "jerk" is the entire remainder of the first-order expansion of speed with respect to time - it corresponds to the second-order term and all higher order terms. Such terms cannot be combined just as coefficients, since they all have different units corresponding to different powers of time; rather, they can be combined only with their corresponding powers of time, in which case the resulting unit is mm/s.


I suggest your objective can best be accomplished by converting the image to a single color vector file. You can do this with Inkscape (free, Linux, Windows, Mac) by combining the built-in bitmap tracing feature with some manual editing. I attempted to do so, but the coarseness of the image would result in excessive manual edit time. It may even be faster to reduce the opacity of the image and create a manual tracing on a second layer.

Once you have a vector file, you can use any number of 3D modeling programs to convert the file to a 3D STL. Fusion 360, Tinkercad and OpenSCAD allow import of SVG files to be extruded to user-specified thickness.


How to set a new homing position using software and/or slicer without changing hardware end-stop?

The Y-Max setting does not help, because it is the software end stop for the  other end of the axis.

The Y Home position also doesn't help as it only changes the coordinate that the printer assumes for when it hits the home position. That is used for printers (like deltas) that home to the max end switches.

What could help is a little bit of G-Code right after the Homing. The Homing is a G28. Just add a G1Y10 after that. That will move your Y Axis 10 mm right after homing. So it will then be in the position that you want. If you then add a G92 then this position will become the home position for the print. So adding these two lines should fix it. Cura lets you edit these start G-Codes so that it then will automatically add the modified codes to all your prints.

You can also try a G10 (with a firmware that supports it.

For Details on G-Codes see:  http://reprap.org/wiki/Gcode


Can I print jewelry without any loss of the precious metal?

The jewelry industry typically uses printers that print in wax, and transform the models into precious metal by lost wax casting. Statasys offers wax printing in their Solidscape line, 3D systems offers ProJet. With this process there is basically no waste, since you can remelt the casting sprues.

I am not aware of printers that print directly in precious metal. It might technically be possible with DMLS but you have to fill up the entire machine with metal powder, which is cost prohibitive (and potentially more wasteful).


You only need 3 switches to determine/fix the position of the carriage (carrying the hotend) with respect to the printer frame (for X, Y and Z i.e. 3 dimensions). Firmware setup, by defining the offset and the traveling distance on each axis, determines the minimum and maximum displacement. By default the printer carriage will not go outside the boundaries and will not damage anything. That is sufficient for most printers, but, for those printers that have weak steppers and printers that produce prints that suffer from layer shifting, the coordinate system might be messed up, and the carriage may travel outside the initial boundaries, this can damage your printer, using maximum endstops will prevent the printer from destroying itself.
Why use only 3 switches? The reason for this could also be related to costs, you need half the amount of switches, cables and a less extended printer controller board.

I've had one printer setup with max limit switches, but they never got triggered (unless self triggered for testing), never had a layer shifting either.


Black goo from only one linear bearing - serious issue?

After completion of the print job, I was able to perform a closer inspection. The black goo contains metallic particles, and the rail the bearings are riding on has a visible groove - which means replacing both the bearings and the rail.


The "springs" connected to the stepper motors aren't a problem.  They are special shaft couplers which allow some relief if the motor mounts are not strictly perpendicular to the lead screws.  They are very rotationally stiff and allow just a little bit of misalignment between the shafts.

The first two prints were from the SD card.  You didn't talk about slicing from an STL file, so it is possible that they were pre-sliced for this machine.  Every G-code file has introductory code that initializes some aspects of the operation.  Check the "preamble" code at the front of the files you have sliced.  Are there commands that look different?  Is the Z parameter for the first layer different from the pre-sliced files?  Are there G-codes missing from the files you sliced?

If you are trying to understand what the G-codes do, this resource may be helpful.  Some possible commands could be commands to limit acceleration, jerk, speed, or introduce offsets.  Also check that the temperatures are being set correctly in the G-code you generated.

If you had sliced the files on the SD card, then double check that the parameters were the same.  Try re-slicing the object and comparing the G-code that is generated.


Ender 3 Pro Extruder Stepper Skipping with a Chunk sound

UPDATE 3-May-2020: I have now confirmed that the problem was the extruder. Specifically, the input port which was causing the filament to bind. The front of the input port is a metal ring but the back is just plastic and and has worn from the PLA filament, as seen in this photo:

After some delay (see my other question here) I have installed the new, all-metal extruder (original stepper), the clacking is gone as well as the significant under-extrusion. (I also replaced the Bowden tube and print bed springs but I don't believe these were the problem).

Having seen what a few km of PLA did, I highly recommend upgrading the extruder.

Side point: immediately after the replacement, I started getting corners lifting off the bed which I hadn't seen before. I realized that the new drive gear was slightly smaller than the old so I checked the extruder calibration and it was about 10% low. I adjusted the extruder steps/mm from 93 to 99 to correct for this.

Original:

It appears the problem was the filament binding in the entry to the extruder assembly. I did start seeing signs of under extrudement such as the outer layer of a rectangular object separating of the rest of the body. Later, the problem became worse, with a lot of clanking, to the point that prints became quite fragile.

I have ordered a all-metal extruder assembly and will update as I get new results.

By the way, I'm really not sure why it's binding but running a strip of filament through the entrance hole, it sure seem to be binding. But in trying to disassemble the extruder and starting by removing the filament, I managed to get molten filament in the bowden tube. Without thinking about it, I pulled the blob all the way into the fitting for the extruder, plugging it so much that I cannot get the fitting off nor push it back into the tube. Anyway, I'm taking the opportunity to upgrade the extruder, tube and springs.


photogrammetry with partially translucent objects

I found at least 2 online pages that'll create a 3D stl from an image, basically using intensity (brightness) to determine depth.

selva3d.com  and   embossify.com

I used it with success on a binary (black or white) image, at least.


How to split a model in SketchUp for printing

SketchUp is likely to not work well for you if your objective is to create a printable STL file in pieces. You would want to determine initially that the un-segmented model is manifold and 3d printer ready. Once that is determined, consider using an alternate program for your chop-up actions.

You do not specify the size of the printer you intend to use, but that is obviously a factor in the segmentation of the model.

I have some experience with Meshmixer, which has an edit feature named "plane cut" which will do as you require. The plane is placed on the model and the options are selected to keep both pieces after the slice is performed.

For a huge model of the type you describe, one would hope you have access to a printer with a one meter print bed or larger, although such printers are rare and of course, expensive.

My printer has a 200 x 300 mm build plate, up to 200 mm high, which would entail substantial segmenting.

If your model is mostly a shell, your segments would have to have wall thickness. It would be best accomplished, again in Meshmixer, by using the hollow or shell features. Those are a bit more challenging to understand, but there are plenty of videos and tutorials specific to creating hollow shells from a solid model. Once the shell is created, segments would be managed easily enough.

I suggested that your segments would "have to have" wall thickness, but it isn't a requirement. Solid segments would be like bricks and you may have a large number of rectangular solids that compose your model. Lego models are difficult or impossible to create with only an outer shell, so the interiors are often solid bricks, but 3d printers are a bit more flexible. Not using solid interiors would save money, of course.

I envision a jigsaw puzzle in three dimensions. Taking a nearly six meter dimension and chopping it into 20 slices multiplied by width and height means a carton of 3d puzzle pieces.


Apply X-offset to gcode (re-slicing not possible)

You can use G92 to change the coordinates the machine "thinks" it's at. If just after homing, you apply

G92 X-10

the machine now thinks it's at X = -10, while in reality it's at X = 0. This results in everything thereafter behaving as if it is shifted in the positive X direction by 10 mm (since if you then commanded a move to X = 1 the machine would move to what is physically X = 11).


Ender 3 is capable of food safe printing?

Food packaging needs to comply with regulations. One certification agency informing about these (and their service to certify for them) is TÜV Süd, another is SAI global. A summary of the GFSI can be found here. Inform yourself about the standards you wish to apply! The stack can not give legally binding answers.

No

The Ender 3 is not approved to produce food products (and not usable for them out of the box) for lack of certification. In the design it comes from the box, you need to replace a lot of parts for food rated ones:

The whole print head/bed need to be swapped out for food rated parts due to the exact composition being not known. They might contain banned materials. As a result:

You'll need an all-metal hot end that can be taken apart for cleaning up to the standards if needed.
You'll need a food rated PTFE tube.
You'll need a stainless steel nozzle that complies with food grade manufacturing demands.
The extruder gear should be stainless steel as well.
You'll need to add some part to prevent filament shreds/flakes from the extruder to enter the print area as they might act as contaminants or carry germs.
Similar measures have to be taken for the wheels on the hot end carriage, as it might shred.
As you include a volume of air into the print, you are likely to be demanded to print under a protective atmosphere to make sure no germs are inside the print.
We do not know the composition of the build platform, so you'd need to replace the back surface with something that is food rated.

You'll need to post-process your prints as smooth as possible, especially because of the small edges at the layer boundaries, which can and will act as spots where germs can grow.

This can be achieved with a material that is smoothable in some way.
Alternatively, a sealing lacquer/coating that is food safe might help here.

Remember, safety first:

Printed plastics that are rated for food are not necessarily food safe because of the quality or blend of the material. PLA and ABS can be made food safe, but that is usually pure material. We usually don't know what kinds of fillers or coloring is in our filament. The heating process might destroy the colors or fillers, which in turn might make it unsafe.

Indirect manufacturing

If you are stone set you want/need, you can use indirect manufacturing: you don't print the actual object, you print a mold that makes the actual object. Clay and other ceramics can be made food safe very easily and they can be shaped with plastic molds.

Boxing

There is also another way to facilitate food safety in a 3D printed container, and that is checking where the food will actually make contact. For a lunch box, that is the inside. We could line this inside with a food safe surface, for example placing a steel cup in our plastic cup-holder. Accessories like a cup holder or a decorative container for the actual food container do not need to adhere to the food packaging regulations themselves.

Exposure time

I know this is all looking at industrial food rated production. The Primer given in the question does include a point about time the product gets into contact with the food - if there is just a short exposure, you might get away with it, but it doesn't make it certified food safe. Another good read in this regard is this short discussion about the Pros and Cons.


The correct/good method to achieve this is called "rigging", but it is not an easy feat (as pointed out by others), as it requires plenty of knowledge about the software being used to edit the model, and a good understanding of the theory behind it.

Skeletal animation requires the designer to set up a skeleton (also called "rig", hence the slang term "rigging") for the mesh and define the variables controlling the motion range of the joints and and the geometry and deformation of the mesh.

It's quite some job to perform, so - unless this assignment is the first in a series of assignments having to do mesh movement for this model, or you have a keen interest in the topic - I would suggest you to take a shortcut and edit the mesh directly in a "one off" not reusable fashion.

(Rigging would conversely allow you to create a "rag doll" or at least a "rag arm" to freely and intuitively move around as you please).

The tool I would use for either task is blender.  If you want to take the shortcut, maybe a less complex software like meshmixer could also do the job (I don't have direct experience with it, though, so I'm not 100% sure).

The blender foundation have a nice series of videos on the topic, called "humane rigging".


Best practices to fix a threaded nut inside a print

One good option would be to - if possible - change the design, so the nut is inserted from the opposite side, so that the bolt just pulls it in tighter rather than pulling it out.

Another option would be to instead of using a nut, use a brass threaded insert. These are like nuts, except they have ridges that are specifically aimed at locking it inside the plastic.


Without testing the board(s) completely, by probing each component, it would be a bit hard to tell precisely. Your best bet might be to try it and see if it works ok, and if not, you'll see exactly what doesn't work... if that makes sense. Whilst not exactly the same issue, this answer, to the question How drastic is reversing the polarity of the power supply to a RAMPS board?, might help.

Now, after having correctly read your question (:-D), I see that you've already done the above, that I mentioned. Maybe these links will help:

No power to heatbed, how to test ramps for problem??, and;
(RAMPS)Hotend change pin from D8 to D10.

There are other similar links on the RepRap Wiki. You might need to check the power MOSFET and/or the fuse. The problem is knowing whether the Arduino Mega is damaged, or the RAMPS board, or both.

However, perform some of the relatively simple checks, listed below, for the:

Outputs;
MOSFETs - in particular Q3 which is switched by D8, and;
Fuses - in particular, F2 (MFR1100 - refer to schematic below) as it is this fuse alone which provides 12V2 which, in turn, is used by D8/Q3 for the heated bed. It should be noted that there are two 12 V supply lines and it is the latter which concerns the heated bed:

12V, and;
12V2

Salient points from (RAMPS)Hotend change pin from D8 to D10

  Also... There is something else to be aware of. Depending on what you claim you are attaching to the RAMPS board, the pins move around. You have 3 High Power MOS-FET's. You can use the RAMPS board to drive some combination of heat bed, fan and 2 extruders. Depending on what you claim you have on your printer, the pin numbers for things move around.

  I kind of doubt that is what is causing you problems... But it might be...

and check the config (bit of a long shot)

  Have you checked that you don't have any error condition (such as MAXTEMP or MINTEMP) which prevents the hotend from being switched on?

Be wary of randomly switching outputs for high current draw devices (such as the heated bed)

  Your topic says "D8 to D10" but if this is your heated bed, you can't
  do this. D8 is on the 11amp circuit. plugging the heated bed into D9
  or D10 goes threw the 5amp fuse and it will blow.

To test the outputs:

  But basically test the io ports

  Remove the ramps

  Setup a led and resistor in the D port you which to use (make sure led
  is the correct polarity)

  load up the blink demo program, change the port it uses to the port
  you testing.  Upload firmware (this will overwrite you current
  firmware) Does it blink? yes the IO pin is ok, no, The IO pin is dead.

  repeat for all io pins you which to test

  See learn.adafruit.com for more information

Salient points from No power to heatbed, how to test ramps for problem??:

Check the fuses

  Check the fuse (the big yellow thing). Connect you meter to ground and both sides of the fuse in turn. You should get about 12v on both.

Continuity check

  continuity test the heated bed with it not plugged in. is it possible you have an open in your circuit?

and

  Have you checked the cables? Also is the led coming on for D8?

The next section of the thread deals with an overheated (50 A?) MOSFET. Check the condition of that:

  ok think i found the culprit, any ideas why that blew?

A couple of good points

  With the bed I found there are 2 issues at play here.

  The standard MOSFET that is typically found in theese kits have an RDS that creates a fair amount of heat at 10A and at this level the
  datasheet says stick a heatsink on. Screwing a piece of metal to the
  MOSFET cures the issue I use an aluminium bracket because thats what I
  had laying around, thermal compound helps too if you have that laying
  around from a PC.
  A lot of heat beds state that they are 1.2ohms but aren't ( just a variance in manufacturing prehaps? ) sticking a cheap multimeter
  across it says this but in practice it may not be reading correctly. I
  found this out because my bed kept tripping a 11A polyfuse but was
  fine with a 12A meaning its somewhere around 1.1ohms. good news is it
  means my bed heats up slightly faster!

  but seeming as your transistor blew I imagine the polyfuse is ok,
  watch out though you may find it slowly does kick in when the MOSFET
  works properly because if its near its tripping point it can gently
  heat up and stop the current.

A good test procedure - this is probably the most relevant check for your case

  That's not the way it's wired. Check the schematic.

  12V input on RAMPS -- fuse -- (PS1) + output to BED

  GND -- Source[MOSFET]Drain -- (PS2) - output to BED D8
  ---------------- Gate

  As you can see, the MOSFET is switching the GND connection to the bed.
  There will always be +12V on the + bed terminal whenever power is on
  as long as the fuse is good. There's an LED across the + and - BED
  terminal on RAMPS to indicate voltage. If that LED is turning on when
  you turn the heated bed on from the host software, then the MOSFET is
  good. If it's not coming on, they you might have a bad MOSFET or your
  +12V supply is bad. Verify using a voltmeter across the bed terminals and across the 12V bed supply input in RAMPS.

  The Prusa heated bed PCB should have a resistance around 1.1 ohm.

Then there are some tests for the fuses. Looking at fuse F2 (the main culprit, which protects the 12V2 circuit):

  You haven't mentioned checking the fuse yet. You should make sure that
  it's not blown. If RAMPS is still wired to the 12V power supply for
  the bed, you can check this easily witn a voltmeter between the + bed
  terminal and the ground wire from your power supply (any of the -
  terminal between the power supply and RAMPS). You should read 12V if
  the fuse is still good. If not, then the fuse is probably blown. If
  the fuse is good, then it's a problem with the MOSFET.

  You should visually check the solder pads for the MOSFET to make sure
  that all the 3 pins are still soldered well. The chip can get hot
  enough to melt the solder resulting in broken connection. Then with
  the power on, turn on the bed heater in the host software and measure
  the voltage going into the gate pin of the MOSFET. That should be the
  outside pin on the same side of the MOSFET as the + D8 terminal. You
  should see TTL voltage there (probably close to 5V). If you do, then
  it confirms that the MOSFET is bad.

  BTW, 1.5 ohm is probably too high for the bed resistance. You need to
  subtract the resistance that you measure when you touch your
  multimeter leads together. There could easily be 0.4 ohms there.

and

  As far as checking the fuse, another way would be to turn off all the 12V power to RAMPS and check for continuity between the + bed power supply input and the + bed output on RAMPS. If the fuse is still good, this should be a short (near 0 ohms). If you disconnect the + lead to the bed, then this would be more accurate.

For fuse F1, you can do the following, although it is extremely unlikely that this has blown as the rest of the circuit is working from the 12V circuit:

  There's also a separate fuse for the other 12V supply input to RAMPS that powers the rest of the controller, including the AT Mega. You should check that too in a similar way. With all the power off, measure the resistance between the leads of F1 on RAMPS. You can also double check the resistance on F2 (bed 12V fuse) right next to it.

That should give you something to get started on. Without knowing more details, it's hard to be more precise.


Order of a HEPA filter and Carbon filter in a filter-stack

The easiest way is to look at a profesional dry filter stack first to learn how a filter stack is usually made. So, let me grab my Dyson vacuum cleaner. On the intake side I get the following stack:

large particle trap
foam filter for medium particles
HEPA filter

Incidentally, that's the same setup as my Shop-Vaccum has (though the foam filter gets replaced by a paper bag)
When I googled other dry filters, I found these filter stacks as common:

large particle wavy paper filter then combined Carbon-HEPA filter (carbon first)
2 x Nylon-Mesh, Carbon, HEPA

The idea is to reduce the particulate grain the deeper you go into the filter. The rough filter is cleanable, the carbon filter traps chemicals and odor that might damage the HEPA filter, the HEPA filter catches any remaining particles.
If you want to know more about various filter types and applications, you might want to read an article on engineering 360.
Safety pointer
Carbon dust is not not harmful - it is both flammable to explosive, as well as resulting in Black Lung (Coalworker's pneumoconiosis) if it is thrown into the air like in a mine.
However, commercially produced carbon filters don't usually release any coal dust: after making the activated coal, the product is shaped (as you can see in this manufacturer video) and sorted into various grains, like in the photo below. These granulate are then put into the carbon filter and trapped in a mesh that is small enough to keep them even after having been broken apart some. Very fine grains like the Bead Barbon are usually used in wet applications.

In a kitchen, you have sticks of 3-4 mm diameter, often trapped in a metal mesh. ABC-Mask filters usually use very porous carbon-grains in the half to millimeter grain size, trapped between paper sheets.


ABS is a plastic type that has a relatively large shrinkage when cooling down compared to other filaments;e.g. much more than the popular replacement PETG (which prints similarly as PLA but has properties like ABS).

As of this shrinkage, it is the operator of the slicer to produce an environment to properly print ABS. This not only implies that correct settings for the slicer itself need to be chosen (depending on the brand: high hotend temperature; about 220-240 °C, high heated bed temperature; 90-110 °C, using a large brim), but also that the printing environment is optimally setup to allow printing successful prints. You should think of adhesion to the build plate, modifying parts to include so-called Mickey Mouse ears and an enclosed printer space to regulate the temperature. ABS doesn't like temperature changes as that will result in split layers. This is why ABS is difficult to print for most people, it is best not to choose this when you just starting printing, nowadays much better alternatives are available called Co-polymers like PETG.


When homing the printer, the hot end carriage will be instructed to hit the (mechanical or optical) end stops. From this point a well configured firmware knows where to find the origin of the heat bed.

For the printer to know the origin of the bed, offsets are defined in the firmware from the end stop locations to the actual origin of the heat bed.

E.g. in Marlin Firmware this is defined by

 #define X_MIN_POS -35 ; move the head 35 mm to the right to place the
                       ; nozzle at X = 0
 #define Y_MIN_POS -8  ; move the head 8 mm to the back (or the plate
                       ; forward) to place the nozzle at Y = 0

When you change the hardware (e.g. carriage), you need to re-calibrate the movement from the end stop location to the origin of the bed. Note that any arbitrary point on the heat bed can be used to re-calibrate this. E.g. the center of the bed can also be used, and is frequently much more easy to re-calibrate as the heated beds usually have rounded corners or are slightly larger than the actual print area (e.g. I have a 300 x 300 mm heat bed that actually measures 315 x 315 mm). Printing a large square on the heat bed will therefore give you a good impression of the offset of the nozzle due to your new carriage design.

Note that, if you cannot or will not flash new firmware, an alternative solution exists to set new incremental offset values using the M206 command IF your current firmware supports this.

A detailed description to re-calibrate is found in answer How to center my prints on the build platform? or in external link Bed center calibration.


3 Extruders on SKR V1.1, how set up 2 in 1 out (Y piece), and 1 single extruder in latest Marlin?

The latest Marlin, version 2.0.8, allows for multiple extruders (albeit with a single or multiple stepper motors) through a single nozzle, or multiple extruders with multiple nozzles, it is not possible with the current compiler definitions to configure a mixed extruder nozzle concept; this would require more changes to the sources.


Ultimaker Cura is adding redundant top/bottom layers

It would appear that your model does not conform properly to STL standards. I base this conclusion on a couple of factors. When I loaded the model into Simplify3D slicer, it displayed fine, but when sliced, displayed nothing. Using the onboard repair feature, it presented the entire model as being composed of non-manifold surfaces.

Meshmixer's Analysis/Inspector feature also highlighted the entire model as flawed.

Another observation is that there is an extraordinary amount of facets/triangles/faces to this model. Nearly three-quarters of a million triangles for something that should be much simpler.

The most recent version of Prusa Slicer 2.0 presents an error message indicating that no layers were detected. This is peculiar indeed.

All of the above points to a problem with the source file or the software used to create it.

Please consider to add to your post the program you used or the source of the model.


I believe printing directly on aluminium is unwise, simply because it will expand when heated, typically giving the bed a concave or convex shape. Glass, on the other hand, does not (at least not significantly).

As pointed out in the comments below, the heat expansion of aluminium could potentially be mitigated by increasing the thickness of the bed, as well as heating it evenly. Also, a common solution is to place a glass plate on top of an aluminium bed, at the cost of a slightly longer heat-up time.

In my experience, printing directly on heated glass can be very practical and give a nice surface finish for some PLA variants and other materials that support it. I don't know if printing directly on aluminium can give similar benefits.


Why does OpenSCAD fail to cut holes in polygon sides that are exactly the width of the wall?

openSCAD simply allows having surface solutions that result in a wall of 0 thickness. The walls appear to clip in those areas and can at times be seen from both sides, like in your example:

A 0 thickness wall is also exportable into an STL as a set of triangles spun up by vertices that are in each other's plane but have inverted normal vectors for the two sides - which means that the construct exists for the computer - and I have used this in 3D designs for a hologram-effect, even if it does not result in a physically possible property set.
An example of that effect is this cube (made in blender), that has the back wall purple, all others are grey - and the internal wall is at the same X-value as the back wall. You see the grey wall clipping despite the normal of it pointing to +X while the normal of the purple wall is into -X.

By having your cookie-cutter extrude not just to but through the back wall, you force a solution that disallows the 0-surface solution and thus solves the problem of creating those artifact walls.
Note that the 0-surface wall persists in the slicer preview:

But rest assured: almost all slicers ignore walls that are too thin to be printed, and a 0 thickness wall especially is ignored:


Main board heated bed connectors aren't powering up

Considering:

  Multimeter shows zero across the board's heat bed contacts

this implies that

If you measured resistance, the heated bed has no resistance. Basically this implies that the bed has a short. This might be the reason why it is not working. If you would power it as such you create a short. Instead of replacing the board, you need to replace the heated bed. Typical values for a heated bed of about 200 x 200 mm are in the order of 1.2 Ω (measurements between 0.9 and 1.5 Ω are reasonable to be expected).
If you measured voltage, the heated bed does not receive power for heating, or the power does not reach the bed (not turned on or broken wire?). It would then be wise to measure the resistance (of the bed and the wires). If the resistance is in the order of about 1.2 Ω (see above) for the bed, you could try to connect the heated bed directly to the PSU to see if it gets warm, if so, please disconnect immediately to prevent damage. From this experiment you can find whether the heated bed is broken (or the cables), or that the board is not functioning correctly, this is, however, strange as you tried 2 boards. A possible suspect could be the MOSFET that schedules the powering of the heated bed if you use an external MOSFET board that it.
If you measured current, then you found out that no power is delivered to the board, but you also might have broken your board in the process, as measuring current is a (close to) 0 Ω connection and has to be done in line of a circuit.


single point z-correction after 3-point auto-leveling

There is no "standard" g-code, especially for the auxiliary functions of calibration, and even more so for the calibration of delta-class printers.  I find that the Reprap Wiki includes a fairly comprehensive list: http://reprap.org/wiki/RepRap_Firmware_G-Codes and http://reprap.org/wiki/G-code.  These lists address the RepRap firmware, although they include some g-code functions which are specific to other types of applications.

If the Monoprice Delta firmware is based on the RepRap firmware, the lists might be helpful, although detailed documention from Monoprice would be the best reference.

Assuming there is no available or known g-code to adjust this, you work from the hypothesis that your three switches are not responding identically.  If possible, use a micrometer to measure the difference between the "idle" position of the bed and the point where the switch actuates.  It could be that the front switch requires more travel before actuation, which would then cause the leveling calculation to have a lower point for the front switch.  In the alternative to measuring, it may be possible to exchange the front switch with a rear/side switch and see if the problem moves.

Delta machines are more difficult to calibrate because everything interacts.  The three actuator delta machine is a simplification of a more complex 6-axis Stewart platform.  As I see it, a delta machine is a 6-actuator machine in which pairs of actuators operate "identically", except that minor variations cause unexpected positioning errors.  Sometimes these are modeled as a bowl shape with positive or negative curvature, although measurements I've made on my home-brew delta show an error that looks more like a carpet in a high wind.  Some factors improve the design, such as longer actuator arm pairs and smaller build diameter, which may help you with the Monoprice.


Multi-color printing with desktop 3D printer?

The most obvious solution is to pause the print and swap filament for another color.

Another option is to splice pieces of filament together, though this does not allow very precise control of when the switch happens. There is also a device that can automatically slice filament this way.

Finally, another option that uses very little external equipment is to use (permanent) markers to colorize light-colored filament.

Other options include upgrading to a printer with more hotends, or installing a hotend with multiple filament inputs and one outputs, but these options would involve significantly changing your printer setup.


Which are the food-safe materials and how do I recognize them?

Food safety is a property of both the process and the material. You can't stick food-safe material in a printer that has previously been used to print something food-dangerous and expect the result to be food safe.

The only way to know if a given material is food-safe is to ask your supplier, but a lot depends on how you then process it. For instance, FDM printers often have brass nozzles, which contain lead. To print food-safe materials, you need to use a stainless steel nozzle.

Food safe materials can be identified by mean of an universal symbol.

Moreover, to ensure food-safety of a 3D printed model you may need to further process it (for instance, by vapor smoothing or coating with a food-safe lacquer). Some claims circulate on the internet that 3D printed models may have surface porosity in which bacteria can grow, but I've not been able to find a reliable source for this claim. Still, you need to be cautious.


It looks like you are not extruding at the correct rate. I would check your slicer settings for nozzle and filament size. Also check and calibrate for your filament diameter.

It looks like you could be getting better adhesion too. Lulzbot recommends a 110C bed temperature. That might help. (lulzbot.com/store/filament/abs under specifications)

These are some good resources to troubleshoot prints,

RepRap

All3DP

Simplify3D