I've looked into doing something similar to this before and love the idea, never had the chance to follow  through on it yet. This is sort of a hybrid method between cast molding and 3D printing.

The accepted answer to a question I had a while back had some very good points by fred_dot_u

Post processing FDM for strengrh

Short version, Epoxy is a good option but you may have to consider heat generated from it. Urethane is another really good option (cast urethane is a pretty standard process). Chem-Eng isn't my area of expertise but there is a huge range of material options out there that can be mixed as two parts. I think there are enough options out there right now that you can choose your material properties you need and then select the material from there.

You  could also consider going the chopped-fiber composite route. (carbon, glass, etc) and then combine with whatever the appropriate resin is for those materials.

I see the most difficult part of this is getting the shells to print properly. When I had looked into doing this, I considered modeling my part then hollowing it out completely. Then going back into the hollow part and designing in minimal internal structures for the purpose of supporting the thin-walled shell model. Printing that, and then drilling and filling the part after the fact. This approach I see as being a good option however the location of the drill points would be critical otherwise you could get voids as your fill material is injected in. And, the additional modeling time wouldn't be insignificant, however the saving I expected would come from having a ridiculously strong part, with complex geometry and be significantly cheaper than even a cast-urethane part.

If you get some good results, please post a link to them! This is a huge interest of mine!


G-code (M-code?) for Get Bed Temperature

M105 should give you the bed temperature.

For future reference you can find a general list of G/M codes here - RepRap Wiki - G-code.

Most firmware files include a list, Marlin has it in Marlin_main.  I have no idea how often the list is updated but they don't change often.


How to avoid nozzle from hitting the model?

It seems the problem was because of Z-axis leveling (level of the X-axis), I found out that the right side was more than 3-4 mm below the left side when the Z-axis height exceeds around 8-10 cm. Below 8-10 cm, the two sides were even. I calibrated the X-axis by turning the eccentric nuts of the wheels and tighten them. I will try printing soon with some test objects.


Increase hotend temperature on Monoprice Ultimate 2

Ok, first of all you need to understand why the limit is given at 250 °C: that's when the hotend design chosen by the Monoprice starts to destroy its PETG liner. To print hotter, you'd need an unlined hotend, which means you'd need a proper all metal hotend.
A proper all metal hodend is a tradeoff, not an upgrade: you sacrifice some ease of printing and risk some clogs in the lower temperature band for being able to print higher temperatures.
When you want to buy an e3D hotend, you should go for a genuine one, as many clones are actually not all metal. Also note, that there are other all-metal hotends around.
If you get an e3D v6, you should make sure to buy the right variant for your machine! Monoprice tells us, that this is a 24 V Machine, so you'll need to get the 24 V Variant! As you also will swap the temperature sensor, you might need to update your firmware according to the e3D installation manual. Since a genuine hotend comes with all the cabling and a new thermosensor, you'll need to rewire the whole machine - and you might need to make new fittings before installing. The standard e3D Thermistor that comes with the hotend is good up to 285 °C, which will be your new ceiling temperature. Take careful note of these two parts that appear in the before assembly notes section of the manual:

The standard V6 is capable of printing up to 285°C, do not exceed these temperatures unless you have replaced the Thermistor cartridge with a PT100, the Aluminium heater block with a Plated copper heater block, and the Brass nozzle for a Plated copper, Hardened steel or Nozzle X.
Firmware modification is not optional it is a mandatory step.


When to use an anti-backlash bolt for a Z drive gear?

First of all, let's look at the geometry: We have a static XY and changing Z on our build plate. This mitigates several problems we might have faced in a different setup, mainly that our lead screw has loads changing from one face to the other: all loads always go into $-Z$, so the lower surface of the Trapezoidal threads in the brass nut of the bed carrier and the upper surface of the screw will always rub against each other.

However, let's talk about your lead. Tr8x8(p2) is not a Metric ISO-Trapezoidal pattern that is commonly recognized - the only 8 mm diameter one in that standard is Tr8x1.5, very flat and very well suited for putting high loads onto it because there are several engagement surfaces in the nut and a low pitch angle - the thread only has about a 5° (+-1°)to the horizontal. Assuming a 15 mm nut, that's 10 times the projected engagement surface for a total area of about 214 mm².

A Tr8x8 is a very common oddball as in, it's not in the metric tables but available everywhere. It is considerably steeper, and with a 16 mm nut (for easier calculation) would result in 2 times the projected surfaceof a single engagement per thread. But that's only a projected area of 42.8 mm² per thread - about 1/5th of the Tr8x1.5, which correlates directly into that much less friction, because the friction is linear with the surface, which is linear to the length of the nut.

Taking an "intermediary" TR8x4 gets us about 1/2.5th of the Tr8.1.5's holding power per thread at the cost of half of the speed. From a physical standpoint, I'd  take this one, also increasing the precision of the Z-movement by a factor of 2 in comparison to the Tr8x8.

Tradeoffs

Generally speaking, we have a tradeoff here:

Pitch is proportional to the movement speed

double the pitch and you move twice as fast

Pitch is anti-proportional to holding power/torque and Z-position accuracy

half the pitch gives twice the torque and the Z-position error is in average reduced by half

holding power is proportional to the diameter of the rod and the number of threads engaging with the nut
Z-position accuracy is anti-proportional to the effective step-size of the motor

Z-position accuracy can be increased by using a reduction gearset: a 2:1 reduction gear halves the step-size and doubles the torque at the price of halving the movement speed. However, it can and will introduce slop and backlash.

Due to the geometry, the slop in the nut should not be an issue, as the relevant engagement surfaces never change. Further, the heavier the bed, the fewer problems you'll have with fast movements, as gravity will prevent the bed from going "airborne" at the end of travel towards the printhead. Travel away from the printhead, as it will do during printing, should never experience such.


Can the filament tube be outside of the nozzle?

Let me clean up a little nomenclature
The PTFE tube is either a Bowden Style Setup delivering the filament from the extruder down through the cool-end and to the heatbreak or just a liner in the cool-end and heatbreak for direct drive. In both cases they are to prevent clogs. In most setups it is not pushed into the nozzle which is in the heater block (they exist, see below).
The liner/Bowden tube guides the filament through the heatsink and into the proper Hotend/Meltzone. In the better designs intended for higher temperature like ABS (see left half), it ends in the heatbreak. This also has the added benefit of having less chance to leak if the tube slips a little bit.
Simple setups (see right half) butt it against the nozzle and thus limit the temperature range. This kind of butted setup can lead to leakage if the tube slips up. In either case, it is no problem to reuse the PTFE tube when changing nozzles, it is even advisable in the case of a Bowden setup as it might change the length of the path.
The nozzle is usually screwed into the heater block from below, and for best use, one screws it against the heatbreak in a heated state - this is called hot-tightening.

If you somehow end up destroying your PTFE Tube, you can get them under the keyword PTFE tube, Bowden tube or Pneumatic PTFE tube on the internet.
PTFE inside the nozzle?
Yes, these exist, OP has them, they look like this, and are not what has become the industry standard.
I can think of no good reason to put an PTFE Sleeve into the nozzle, but someone did it, and it sis a valid approach. However, I see several problems with it:

the PTFE tube degrades if pushed deep into the melt zone and can lead to clogs.
the added PTFE is not a very good at transmitting heat, thus reducing the effectiveness of the melt zone. This can lead to needing either much lower printing speeds or a much higher printing temperature to achieve good prints

It should be of no issue to convert from this style into the butted-style (right) just by using a short length of PTFE in the heatbreak. I would prefer though to combine it with a heatbreak where the PTFE ends and making this what is commonly referred to as an "all metal hotend" (left).


Is there any way to shrink 3 mm filaments down to 2.85 mm?

I would not recommend you to try and somehow re-size the filament, since even the smallest of irregularities and error in diameter occurring from such a process would ruin your prints with sporadic over and under extrusion. Rather, if you have the tools available, you could grind the filament into pellets, and use a filament extruder to make it anew with your desired diameter.

Alternatively, depending on your printer setup, you might very well extrude true 3.00 filament with your 2.85 mm filament printer. If you try to do that, make sure to:

Adjust filament diameter in your slicer
Check that your filament isn't getting squashed by the extruder wheel
Check that all mechanical parts actually can pass through your filament freely

I do not own a 2.85 mm printer myself, and therefore have not tried this procedure. There are, however, several people who seem to have done this successfully.


What causes my Bowden tube to melt on the side?

If the tube is PTFE, the tube is not likely to be melting unless your hotend temperature is out of control.  You would probably notice the PLA cooking.

So, perhaps they aren't PTFE, or perhaps it is wear.

If it wasn't PTFE, you should be able to tell by the texture, slipperiness, and bending force.

The four thinned faces look like they would correspond to four of the barbs in the connector.  The thinned ring below the four thinned faces look like a wear line where the tube is pressing against the exit of the connector.  It looks to me as if the tube is moving or flexing in the connector.  The barbs act as little chisels cutting into the tube, which is how they restrain such a slippery material as PTFE.

It might work better if the tube were a little longer.  This might reduce the forces at the limits of movement which may be placing strain on the tubes.  If you can, you might also fashion a strain relief for the tube so that it doesn't bend right as it exist from the connector. If you can cut down on the movement, you will help with the external wear.

It is also possible that the tubes are being strained by a high filament pressure.  All the drive to push filament into the hot end is matched by an equivalent reverse pressure from the tube onto the connector.  If you can stand a higher print temperature, the life of the tube may be increased.

@towe added a comment:

  I don't think those are marks from the teeth of the pneumatic coupler. The questions states "where it pushes against the nozzle", and the Ender 3 Pro seems to have a hot-end where the Bowden tube reaches all the way through the cold end and heat break to the nozzle.

A mechanical drawing of what may be a MK-10 hot-end as used on the Ender 3 Pro also suggests that the Ender 3 Pro has a PTFE lined hot end.  Lets accept that drawing as confirming that @towe is right.  Never-the-less, the marks you show in the photo look like the types of cuts I have seen from a pneumatic coupler.  How can we reconcile this contradiction?

The most direct answer would be that the tube is not reaching through to the nozzle.  In the photo you don't show enough of the blue tube to show the coupler scars which should be a little further up the tube.  Suppose that, in fact, the tube is not pressing against the nozzle.  This might not be the case if any of these are true:

There is a separate piece of PTFE that is permanently in hot end.
The Creality Ender 3 Pro looks as if
it is not configured for a Bowden feed.  A PTFE lined hot-end for a
direct extruder would have a piece of PTFE cut to length in the
hot-end.  A simple mod to make that a Bowden would leave that
sculpted PTFE tube in place.
The pneumatic couplers have been replaced.  Many couplers do not
permit the tube to pass through them, although the hole in the end
can be drilled to 4mm diameter.  In fact, preventing the tube from
passing through a pneumatic coupler is a feature in the intended
application of coupling to air tubes in moderate pressure
applications.
There is a bump in the path that is catching the  tube and
preventing it from extending through to the cold end and onward.


How much plastic pellets does it take to make 1 kg of filament? (making my own 3D filaments)

If you ignore losses due to production machinery, your one kilogram of pellets will provide you with nearly one kilogram of filament. There may be some small loss of material stuck in the auger and drips from the nozzle and any place you discover plastic that is not on the spool.

How many plastic pellets does it take to make one kilogram of filament? One kilogram plus a bit more. If you are asking about the numerical quantity of pellets, how much does one pellet weigh? Are they large pellets or small pellets?


There are several ways to get the Z0 into a position the sotware can account for it without needing to write your own firmware if needed:

Remove the build-tak-clone under your glass sheet to get the better heat transfer and remove a couple millimeters.
Tighten the bed leveling to account for some millimeters.
Move the physical endstop to account for the thicker build platform.


To speed up the probing for a touch sensor, a "High Speed" option is available in Configuration_adv.h which is by default disabled (//#define BLTOUCH_HS_MODE) as not all printers/sensors are able to use this.
You can also increase the homing speeds in your Configuration.h file.
// Homing speeds (mm/min)
#define HOMING_FEEDRATE_XY (50*60)
#define HOMING_FEEDRATE_Z  (4*60)

.
..
...
..
.
// Feedrate (mm/min) for the first approach when double-probing (MULTIPLE_PROBING == 2)
#define Z_PROBE_SPEED_FAST HOMING_FEEDRATE_Z

// Feedrate (mm/min) for the "accurate" probe of each point
#define Z_PROBE_SPEED_SLOW (Z_PROBE_SPEED_FAST / 2)

However, you can simply speed up the movement between probe locations by setting the movement speed directly through G-code. The G29 code, used for automatic probing of the bed surface is described in "G29 Auto Bed Leveling (Marlin - MK4duo)". The S parameter in G29 can be used to set the movement speed between probes, where the units are specified in "units/min", e.g. mm/min.
Note that you potentially can change the Z-height for deployment:
/**
 * Z probes require clearance when deploying, stowing, and moving between
 * probe points to avoid hitting the bed and other hardware.
 * Servo-mounted probes require extra space for the arm to rotate.
 * Inductive probes need space to keep from triggering early.
 *
 * Use these settings to specify the distance (mm) to raise the probe (or
 * lower the bed). The values set here apply over and above any (negative)
 * probe Z Offset set with NOZZLE_TO_PROBE_OFFSET, M851, or the LCD.
 * Only integer values >= 1 are valid here.
 *
 * Example: `M851 Z-5` with a CLEARANCE of 4  =>  9mm from bed to nozzle.
 *     But: `M851 Z+1` with a CLEARANCE of 2  =>  2mm from bed to nozzle.
 */
#define Z_CLEARANCE_DEPLOY_PROBE   10 // Z Clearance for Deploy/Stow
#define Z_CLEARANCE_BETWEEN_PROBES  5 // Z Clearance between probe points
#define Z_CLEARANCE_MULTI_PROBE     5 // Z Clearance between multiple probes
//#define Z_AFTER_PROBING           5 // Z position after probing is done


I have worked with PLA and paints before. I use mainly acryl-based paints as well as spray lacquers.
Sealent is not necessary.
While a sealant is not necessary, you might prefer to use a spray on, smooth drying lacquer to get a smooth surface. PLA does not "soak in" paints or colors like resins.


What type of fire alarm/smoke alarm should my printer have?

Since some prints can take literally days, I would use a combination of techniques if you're worried about a fire.  According to The Internets, firefighters are willing to inspect your stuff to see if they pose fire hazards.  You could ask your local firefighters what they think of your risk with yoru 3D printer.

Keep your workplace free of dangers

Don't keep flammables, explosives, or similar stuff near your printer.  If it does catch fire, these kinds of things will make it worse.  There are plenty of valid 3D printer supplies that fall in this category: alcohol, alcohol pads, acetone, acetone pads, various glues, various cleaners, hairspray, etc.

Periodically inspect the high amperage parts of the system

Inspect crimps, but splices, solder joints, relays, etc for burn marks, loose connections, or other problems.  Solve the problems before they catch fire.

Alarm

One or more smoke alarms should detect a fire.  However, they may give false positives for ABS, because ABS gives off that burning plastic smell.  I would experiment with the super-cheap ones and one or two more expensive models to see what kinds of false positives you get.  You'll probably want to put at least one of them directly above the printer.  If your printer is enclosed, put a sensor in the enclosed area.

I think smoke alarms should be sufficient, but I'm not an expert (or even hobbyist) on fire alarms.  I have not come across any information that states Carbon Monoxide or Radon are a worries with 3D printers.  Area-affect heat sensors may give many false alarms because of how hot printer stuff gets.  However, you could use contact heat sensors for parts that should not get too hot and monitor them with a microcontroller or Raspberry Pi.  Reading this article, it seems you may want some ionization sensors for the printer, and not photoelectric.  My WAG (link) is that the plastic (or electronics) would smolder long before catching fire, so you want sensors that would detect the smoldering.

Camera

OctoPrint/OctoPi make it easy to use a webcam to monitor your printer.  However, if your printer is on fire and you're remote, it may or may not be able to shut the printer down.  Even if successful, you still have a fire to deal with.

Fire extinguisher

You should have a fire extinguisher available to someone to put out your printer should it catch fire.  Printers will need at least an extuingsher of Class C rating, and since we're working with plastics, you probably want Class B as well.  Most of the fire extinguishers you can find in consumer stores are going to be ABC rated, and powder based.  The powder will make a mess and wreak havoc on electronics.  CO2 or Halon will not themselves damage the electronics, but are substantially more expensive than their powder based brethren.  For example, I get 5lb Fire Extinguishers for ~$30 at Costco, but an equivalent in CO2 would be several hundred.

Automatic suppression system

As a maker, you could build a reactionary fire suppression system.  I imagine it would be cost prohibitive to hire someone to do it for you.  Basically, you would use the alarms or special sensors to activate one or more fire extinguishers.  You should over-engineer this so that your fire suppression system completely overwhelms any fire that occurs.  According to The Internets, firefighters are willing to inspect your stuff to see if they pose fire hazards.  You could ask your local firefighters what they think of your risk and suppression system.

Firefighting Robot

You could build a robot to detect fires about put them out, as sort of an advanced automatic suppression system.  Something like Tony Stark's robot, or something emulating what is actually in service (US Navy (CNN), Australia tracked firefighter).


Printing non-commercial model to make money

Intellectual property law is complex, so you might want to consider getting proper legal advice. However, to respect the original designer's intent you need to look at what their license permits and try not to find a loophole in the process. There is nothing to stop you asking the designer (in public or private) to clarify their intent.

The biggest 'non-commercial' restriction reason is to protect the design idea, and stop someone mass-producing a clever design for profit. This applies irrespective of the original designer's intent to monetise their work.

Another big reason might be to 'hold back' the time invested in the design. Maybe the designer wants to share something they spent a lot of time on, for individuals to appreciate rather than profit from. The designer would presumably gain reputation as a result of wider knowledge of their work.

Sometimes, a design inherits licensing restrictions from a 3rd party (even maybe from the design tools used). For example, Fusion360 can be used for free by small companies, students, or for hobbies and personal learning, but has restrictions on commercial, professional or for-profit use. In that case, you would need to ask clarification from the tool provider.

The case you describe is complicated. You can't sell the printed part, but a 3rd party can probably contract you to print the part (or rent time/access to a printer). However, your contract rate can't include any element of value derived from the model. Assuming there is no explicit license condition, you should be OK if you charge for your direct costs. As soon as you include time, profit, or any modification to the model, you are on less solid ground.

To consider a non-obvious use-case of the Fusion 360 license, a student may well not have their own printer (particularly for an exotic material, or living in university accommodation). Can they contract a fabrication company to commercially produce or evaluate their model for the purposes of education or not?

I don't expect you will find a definitive answer to this question since there are too many variables. Creative Commons have a page about their Non Commercial license which identifies some things to consider when you interpret a license.

As noted in the comments, you can divide your time and professional contribution (and thus billable items) into several steps. By providing a model, the customer skips step 1:

making the digital model
preproduction (slicing)
printing
postproduction (cleaning off support)

A clear license would refer to all of these.


Access uncapped 5 V output on 3D printer controller board

Any pin that is labeled as "5 V" can supply the full amount of current. Looking at, for example, the Arduino MEGA pinout, we can see several pins labeled in red with "5 V". These are the pins you can use. Most 3D printer boards will expose the 5 V pins at several points. For example, the endstop connectors often have a 5 V pin that can be used.

The pins that are limited to 40 mA that you are thinking of are the digital pins, i.e. the pins that can be switched on/off by the microcontroller. These are actually more limited than this, and while in some cases drawing 40 mA from them may be possible, it is not a good idea.


Ultimaker 2 ticking sound coming from feeder

Ultimately, your stepper motor is unsuccessful in driving the filament through the extruder. A couple potential reasons:

extruder temperature isn't high enough. This could either be operator error from not setting the temperature correctly or your machine is getting a false reading. Typically, for ABS/PLA, you can get away with a low extruding temperature of about 210c.
filament tension is too high. This happens if, say, your spool of filament gets kinked or wrapped around the spool spindle.
your nozzle is clogged. I've encountered where I had back flow coming out of the nozzle (filaments oozed around from the hotend at the threads). This was a result of not putting the hotend back together correctly. There was a enough hardened plastic backed up in the hotend that when I threaded the nozzle back on, it technically didn't fit back on all the way.


Considerations for storing resin include using a light-tight bottle, preventing stray ultraviolet radiation from prematurely curing the resin.
You'll also note that users will filter the resin through a fine mesh filter. I've seen some videos in which the user pours through coffee filters to remove as many particulates as possible.
Left-over resin that has been carefully filtered is effectively the same as fresh-from-the-bottle material, from a purely technical view, but you can pick up contaminants that bypass the filter.


Don't use grease, it is better to use a light oil to lubricate the rods.  A light oil will help flush out any dust and filament debris, grease will trap it.

I've used both light machine oil (like used for sewing machines) and PTFE based spray (Teflon). Grease is thick and will collect and trap dust and particles more easily than light machine oil.

Even high-end consumer printers use light machine oil, e.g. the Ultimaker 3 Extended I got came with a bottle of light machine oil for the linear guide rails. Their advice is to regularly add a drop of oil on each shaft once in a while (how frequent depends on how much your printer prints).


I am getting bubbles and a bulge at the bottom layer of my 3D print

I think that your bed is too hot because the bubbling is only on the bottom layer, if it was through out the entire print, I would say that it is your nozzle temp and you should do a temp tower, but because that isn't the case try lowering your bed temp


Issue was with PID tuning nothing to do with the hardware. I switched to a duet wifi and used the auto tuning of the reprap firmware and now it is just working beautifully. I guess I was doing the manually tuning in such a bad way and the auto tuning on marlin was not working correctly for me.


How is a Thermistor supposed to be installed between Heated Bed and the Glass?

Try to use a silicone heat conductive pad between heater and glass, where you can make a hole for the sensor. It also helps to improve the contact between aluminium heater and glass, which otherwise may be inhomogeneous (as expected between two quite rigid materials).

They sell them in rolls and you can choose a 1 mm thick one or even 0.5 mm. They are "sticky" but they don't have glue, so you will be able to separate the glass from the pad, even if not so easily as it would be with a clip.


Your steps/mm settings are very high. Assuming you are running an ATMEGA based controller, like RAMPS, you will only be able to move at very slow feed rates (<20mm/s). There are also many hardware factors that influence your maximum speed at a given steps/mm (which is typically referred to a your maximum step rate):

Supplied voltage. Using too high/low voltage can cause poor stepper performance or create unexpected faults at high/low step rates.
Motor specifications. Stepper motors come in a dizzying number of models with varying specifications. This is because each one is tailored to a specific use case.
Stepper Driver. There are a bunch of driver designs and manufacturers out there and none of them should be considered equal. It also matters how you setup the driver in terms of current/voltage limits, microstepping, decay modes, heat syncing, etc.
Wiring. At high step rates the inductance of the wires between your controller and motors start to matter more, as does interference to/from other electrical devices.

If you aren't sure how to set/select/tune the things above it's best to just mimic what is done on common printers like the Prusa i3, which have robust designs.

In more direct regard to your Marlin settings, your acceleration and feedrate values are very high for an untested printer. It's best to start with conservative values (Accel ~500mm/s^2, Feedrate <10mm/s) and work your way up 10% at a time until you start having issues, then back off ~20% from there.


How to make symmetric Low-Poly objects in meshmixer?

The best way would be to follow a four-step workflow:

Reduce complexity.
Cut the object along the symmetry plane.
Discard one half of the object.
Mirror the cut object along the cut symmetry plane.


With the model file available, I was able to use Edit, Generate Face Groups. This allows one to continue with Select, {set small cursor}, select reversed panels, Edit, Flip Normals.

The above steps resolve the cockpit windows, but meshmixer's Analysis, Inspector shows a sea-urchin-presentation of other flaws, including what appears to be zero thickness walls in some locations.


e-steps are wrong only during printing moves

Annoyingly, this went away with a replacement board.  I don't have a better fix.


Extruder stepper motor problem, what can be wrong?

Your controller board probably requires calibration.
It sounds like, maybe, the extruder's stepper motor is not receiving sufficient current, to make it turn. Or, somewhat confusingly, maybe the stepper is receiving too much current, and overheating.
You don't say which controller board you are using, but regardless, there should be an adjustable potentiometer on the board, next to each of the stepper drivers, or on the stepper driver daughter boards.  Like so,

This potentiomenter adjusts the reference voltage used to control the stepper motor. From this reference voltage, and the resistance of the stepper coils, one can determine the current, which is used to drive the stepper motor.
For the stepper driver of the extruder, you could try turning this adjustable potentiometer slightly, in order to provide more current to the stepper, in turn to provide sufficient torque such that the motor is able to turn. Or, less current to stop the stepper from overheating.
The adjustments can be made whilst the power is on, but a non-ferrous (i..e. plastic) screw driver should be used, so as to avoid short circuits. Also care needs to be taken, when turning the potentiometer, as they have been known to just fall apart whilst being turned. If you are paranoid, then make micro adjustments with the power turned off, and then turn back on to check the behaviour.
Note: it should go without saying that one should never disconnect a stepper whilst the power is on, as both the driver and the stepper motor may be irrevocably damaged.

The photo above is taken from POTs Calibration – RAMPS 1.4.

If a POT is set too high then the associated stepper driver will tend to overheat and go into over-temperature thermal shutdown (to prevent damage to its components). The first sign of overheating is erratic stepper motor behavior. Typically, this can be recognized by the sounds of the stepper motor suddenly losing power (thermal shutdown). If no load or movement is required of the motor, it is hard to detect whether it is over-powered as the driver is barely producing any heat.

and

Conversely, if the POT is set too low, the stepper motor can enter an underpowered state. This can be recognized by a lack of holding torque and a stepper motor that is skipping steps because the necessary movement  requires a higher power demand than the POT setting allows for.

Driver cooling
In addition to the possibility of the stepper motor over heating, it could be possible that the stepper driver is overheating, although the symptoms may be different, to those that you are experiencing. Regardless, you may still find it advantageous to cooler the controller/driver board with a fan that is always on (not temperature controlled).
Additional reading

RigidWiki - Stepper Driver Adjustment, which goes into further detail about the adjustment of the potentiometers, that I outlined above, as well as the reference voltage and the adjustment thereof.

RepRap Wiki - RepRapPro Setting Motor Currents describes a different controller to yours, but goes into the process of adjustment, and description of the reference voltage (which is applicable to all boards):

The wiper on each potentiometer generates a DC voltage that is sent to the chip. This is the reference voltage; it defines how much current the stepping motor driver chip supplies to the motor. The bigger the reference voltage (VREF), the higher the current (A) that the chip will send to the motor. For most NEMA14 motors, the current maximum is 1A, but this will generally cause it to get warm, so a setting of 750mA is recommended. For NEMA17 motors, depending on size, the limit on current is generally between 1.3A and 1.7A. If you drive stepper motors with more current than they were designed for, the motor will get hot, and may be damaged.

Pololu - A4988 Stepper Motor Driver Carrier with Voltage Regulators - this is a very common stepper driver.

MyHomeFab - DRV8825 Adjust Stepper Current goes into the adjustment of the reference voltage, for the commonly used DRV8825, which is an alternative to the popular A4988.

This thread, about non-actuating steppers, may also be useful, Motors, which mentions setting the trimpots and points the OP to RepRap Wiki - Pololu stepper driver board, which, in turn, refers to this thread, Strange stepper behavior and this video, video-2012-02-02-16-37-26.mp4, which describes a jitter in the stepper behaviour.


As mentioned by Matt - PVA glues work perfect for both filaments.
It works well because it's softening temperature is between 45..85C so it's more or less temperature of HB.

Advantages:

cheap
easy to apply on HB
can be applied on cold as same as on hot HB
sticks model very well
non toxic, no solvent, odorless
easy to wash (from HB) (just wash it under water or scrape with sharp tool)
works very well even with old and dry layer of glue

Disadvantages:

quite hard to detach model (I use paper knife)
first layer is not glass-perfect
after detaching, model is a bit sticky (first layer)

I use Scotch Glue Stick by 3M.


Can you print at 0.3 mm with a 0.2 mm nozzle?

To get the best results, the plastic coming out of the nozzle needs to be squished/ironed down by the nozzle. If you are using a higher layer height than nozzle size, this does not happen. Instead, you are taking a 0.2mm diameter string of plastic and folding it back onto itself to create a thicker 0.3mm bead.

Triffid_Hunter's calibration guide recommends using a layer height that is not higher than 80% of your nozzle size, so with a 0.4mm nozzle you should not print layers thicker than 0.32mm, and with a 0.2mm nozzle you should not print layers thicker than 0.16mm.

While it is not impossible to print thicker layers with a smaller nozzle, the results won't be as good. Moreover, if you are used to working with a 0.4mm nozzle then swapping to a 0.2mm nozzle may take some getting used to, as printing with smaller nozzles is more difficult (for example, the smaller the nozzle, the higher the likelihood of clogs).


You can print it laying flat on the bed with supports. It will be very laborious to clean up, but it will probably work. supports usually are thin enough to strip away, but they leave marks which you need to cut off to get a clean result.

You can also buy a printer with dual extruders and then use dissolvable supports. That would probably be easier to clean up and provide a cleaner result.

If you're using PLA to print, you might get away with turning up the part cooling fan to the maximum level and hope for the best. Overhangs are very much prone to dropping though. I'm not sure if a stock MP Select mini will get the job done. You might want to consider an upgrade to the part cooling fan. You can look for fan duct related upgrades which allow you to mount bigger fans on Thingiverse

With PETG you can possibly get away with longer overhangs, as it cools quicker. However, PETG is much harder to print well, as it's much more prone to stringing, which can cause issues like artifacts and clogging.

All in all I'd start out with getting a good benchy before you start on engineering projects. This will make sure that you have your printer calibrated to perform for your chosen filament. Every brand and type has their own quirks and differences, so you'll have to fine tune your settings to get the best result.

A CNC-like finish will not be easy to achieve. A CNC type finish will be unachievable without extensive post processing if you're using supports. In any case, getting a good finish requires some practice with finding the right settings for your filament.

Learn how to print and to get your printer dialled in to achieve the required result, which, in the case of it having to be CNC-like, is quite high-end. The fact you're laying down filament means that you'll be able to see lines, even at top quality. Maybe this guide will help you get on your way.

Getting a $1000 printer mainly inproves reliability of the print. The quality of the print is in the skill of dialling in the right settings in your slicer for a given filament choice, plus recognising the type of supports necessary. This takes practice to achieve.


No, the bed does not look too close to the nozzle, it could well be that it is too far from the nozzle. However, the brim looks okay, but the method you follow is questionable.

Using a feeler gauge of 0.2 mm is larger than the recommended paper method which is in the order of half that value (0.1 mm). You compensate this larger leveling gap with an over-extrusion of 130 %. The preferred method is using a thinner feeler gauge or a sheet of paper without over-extrusion. The reasoning is that if you have a 0.2 mm to start with, adding the first layer thickness (e.g. 0.2 mm) would imply that you are already starting at a 0.4 mm gap on your first layer. You now try to push out more filament to fill that gap (resulting in not really pressing the filament to the plate).

Furthermore, your tape does not look like it is laid down next to each other, it looks as though it is laid over each other. This creates an uneven bed surface.

Finalizing, you should do whatever you do to get the filament to stick to the build plate, if it works for you, use it. If it doesn't produce viable prints, or you are not satisfied with the surface finish, change it.


Are the thermsistors identical for both the heatbed and the extruder head?

This depends on how you ended up with your finished printer. If it was a kit, then there is a chance that the thermistors might be the same, however, even a kit manufacturer might buy parts that come preassembled as I could imagine being the case for the hotend.

To find out about the actual thermistor you would need to look up the spec sheet of the manufacturer of your printer or the individual parts, afaik there is no way to identify them by having them in your hand beyond identifying the resistivity and the coefficient type by using a multimeter.

You could, of course, check the resistivity for a whole temperature range to compare the table of your thermistor to the tables which are listed in firmware, but then you could compile your own tables right away.


How can I fix First Layer Adhesion with BL Touch - Tevo Tarantula

I have the same kind of issues I'm also using Sunlu white filament 210 °C and bed at 60 °C on a CR-10S also original BLtouch v3.1

On some parts of the bed it's okay but in the middle and some corners it's too high and doesn't stick (really annoying). I bought the BLtouch to avoid this kind of issues.

I have printed many things with no issues and with this filament It's making some trouble.

Ok I have solved the issue, the problem is Sunlu pla+ filament.

It seems that their filament is really hard to adhere to bed.

I found on another forum that you need to increase bed temperature up to 70° and head to 220 °c at least for the few first layers and don't go under 215°.

also moving the head a bit lower to skish the filament on bed.

I tried and got much better adhesion.

Hope it will help other people


What type of kinamatics is 3D Gence One using?

I'm can't say for sure, since this is my first time seeing this type of 3D printer configuration too, but I think this is a cartesian style printer. If you think about it, it is similar to a Prusa-style printer, but instead of an x-gantry being raised and lowered by a leadscrew, the heated bed is being lowered and raised with two leadscrews. Software-wise, the printer you mentioned should be configured exactly like a Prusa-style printer, but with a reversed Z-axis, since to make the heated bed move closer to the hotend, it must be raised instead of lowered.
I personally do not think this printer is a CoreXY configuration since a CoreXY printer relies on two motors that work simultaneously to move the X and Y axis, while the printer you showed has the X and Y-axis moving independently of each other (as can be seen by the belt under the heated bed and the belt that moves the hotend left and right). At least, in my opinion, the way the X and Y-axis operate on a CoreXY is what makes the CoreXY unique, instead of the raising and lowering of the heated bed.
You can read about the variations of Cartesian 3D printers here. If you are interested in other styles of 3D printers, you can check the Delta and Polar style printer section of this article.
Hope I piqued your interest in 3D printing :D
Feel free to comment on this if you have more things to ask, and I'll get back to you as soon as I can :)


This can be caused by various problems, of which an aforementioned filament diameter is only one of multiple possible causes.

The observed phenomenon is called under-extrusion. Temporary under-extrusion can also be caused by filament friction on the spool, too low or too high filament extruder gear friction (pressure on the filament by the roller), or friction in a Bowden tube (dust particles).

Please ensure your spool unrolls freely (not entangled; entangled filament is audible like "ker-chunk" when the filament is rearranged on the spool by force of the extruder pulling) and check the extruder for friction or slip. If the extruder gear slips, this is also accompanied by an audible "click" that is called clicking. This generally implies that there is too much friction in the hot end, or an obstruction/clog.

Considering that your print recovers from the problem, and that it occurs randomly, the best guess is that your filament in entangled now and then.


It's extremely unlikely that belt tension is actually your problem. I've never heard of anyone using a gauge to measure their belt tension. Typically you just pull your belt tight by hand so that it produces a low note when plucked. It's far more likely that you're experiencing shifts due to too high or too low stepper current.

Unless your belt is so loose that it easily skips over the pulley (which should be obvious without using a gauge) or so tight that it completely binds up (it would be impossible to get it that tight without some kind of superhuman force) it's definitely not the problem.


You'll need to do some calculation to figure out how long of a lead screw you need. The best solution would be to mock up the entire printer in CAD so you can visualize how everything fits together. Not only is the coupler going to take up some space, but the nut also takes up some space, and perhaps (due to design constraints) you won't be able to have the nut go up right against the coupler so you'll need some more space. Unfortunately, there isn't a general "just take the length of your Z-axis and add X millimeters"-type formula.


Anet A8 Marlin BLtouch moves up instead of down during homing

SOLVED -- The problem turned out to be that the BLtouch was set up for 3.3 V and my Anet board is 5 V. The docs were not clear on what the BL defaulted to and I mistakenly thought 5 V. After I did a M280 P0 S140 command, the carriage would home properly with G28. Why it was going up instead of down was a Red Herring. I changed the settings in configuration_adv.h to force 5 V and did the EEPROM one time write. Now the A8 works correctly. Thank you for your help Oscar.


Levelling issues with BLTouch sensor; unlevel and weak adhesion

I have the same printer, but what are you printing, is it an stl that you created yourself or that came standard with the printer?
In the beginning, I had the same when printing the models that were delivered with the SD card. Can you check your settings as well on Cura, maybe the adhesion type is set to raft then the first layers are like that.
If not then see what nozzle you are using and see what settings you have them on, I noticed also that the initial nozzle that was on my printer was a 0.8 mm and not a 0.4 mm.
Also, did you check your Z-offset settings on the printer, when printing you click on adjust and then normally in the left top you see Z-offset if you go in minus (try with 0.5) every time and see if it sticks better.
Can you try and check this. These things I also had, still figuring out the settings for the CR-10 Max so I'm not an expert, just sharing my things where I also struggled with.


Cooling fan noise when head is moving in the X axis

As discussed in the comments...

The problem with the fan seems to be its flimsy attachment to the printer head.  The fact the fan chassis is not firmly kept in place allows for it to act as a soundboard, amplyfing whatever vibration nomally occurs in the motor.

You could probably get a fan that is more silent in the first place (noctua is a known brand for silent fans, and it is used on the Original Prusa MK3 for example), but since there's nothing inherently wrong with your current fan, I would simply design a custom, more beefy mount for it.  For added dampening effect you could also use small o-rings as washers for the screws.


Three RAMPS boards wasted by plugging in a heated bed

It could be a couple of issues:

the heated bed tries to use more power than the ramps board is capable of because the traces on the board aren't big enough to get rid of the heat.

the thermistor is broken / not properly connected or configured, and it keeps on heating the bed forever.

a short somewhere in the wiring.

My advice:
Check the wiring. If there is no short, check your thermistor. Is it reporting the right temperature? If it reports the right temperature, try using a external mosfet module for the heated bed. These are fairly cheap, and easy to connect.


A problem I have come across when using Pronterface is that the operating system starves the resources of the program if the program's window is not in the front.

If I, for instance, started a print, then started browsing the web, it would sometimes suddenly stop. When bringing Pronterface back to the front, it would take a few seconds, and then continue (if I remember correctly).

On OS X - which I am using - I believe this is called app nap, while a similar mechanism exist for Windows. I ended up printing form an SD card myself after this, but you might want to try manually setting the resource priority for Pronterface in your OS.

In Windows, you could trying to increase the resource allocation for Pronterface by going to Task Manager -> Details -> Right click the Pronterface process -> Set Priority. I would be careful to set it too high, since you are basically allowing the program more juice to potentially do something wrong.

In OS X you could try to disable app nap for Pronterface.


Connector Suggestion for Extruder and Heatbed

You might be able to use one of the connectors (Deans Ultra, EC3, XT-60/30, Bullet) that are normally used for RC models. They're made for very high currents. The XT60 connectors depicted below are rated for 60A continuous (well above what you'd need for any heated bed); their smaller XT30 cousins are good for 30A but less commonly available.

(Photo by Mark Fickett)

For your extruder you wouldn't need anything quite as drastic as an XT60, even a simple JST connector would suffice (though if you are going to source XT60/30's for your heated bed anyway, you might use them here as well).

(Wikimedia Commons, Mike Mahoney)


CR-10 Ignoring Z-Stop Switch, Keeps Trying to Lower

I had this same issue with my CR-10s. My black and white wires were reversed where I plugged them in to the motherboard in place of the stock z stop wires. I had to take apart the connector and swap them, as they came backwards from the mfg. Once I did that it worked perfectly.

The image I'm attaching helped me solve my issue. It is not mine, after much searching I found kenneycp's reply on this comment thread
https://www.thingiverse.com/thing:2975949/comments


Will the TMC2130 V3.0 stepper driver work with the Ramps 1.6 Plus board?

Well I found that I can use a DuPont cable to connect the diag1 pin to the right endstop

There is also a beta functionality in the Marlin firmware I haven't tried: Just uncommenting SPI_ENDSTOPS definition

    * SPI_ENDSTOPS  *** Beta feature! *** TMC2130 Only ***
    * Poll the driver through SPI to determine load when homing.
    * Removes the need for a wire from DIAG1 to an endstop pin.
    *
    * IMPROVE_HOMING_RELIABILITY tunes acceleration and jerk when
    * homing and adds a guard period for endstop triggering.
*/
#define SENSORLESS_HOMING // StallGuard capable drivers only

#if EITHER(SENSORLESS_HOMING, SENSORLESS_PROBING)
    // TMC2209: 0...255. TMC2130: -64...63
    #define X_STALL_SENSITIVITY  8
    #define X2_STALL_SENSITIVITY X_STALL_SENSITIVITY
    #define Y_STALL_SENSITIVITY  8
    //#define Z_STALL_SENSITIVITY  8
    //#define SPI_ENDSTOPS              // TMC2130 only
    //#define IMPROVE_HOMING_RELIABILITY
#endif


It is indeed more related to the blender forum  than the 3d printing one.

You can start by looking at this post from blender.stackexchange.com which explain how to unwrap and paint on a 3d object. You can also paint the texture on a 2d software like Gimp and then put it in the UV Image editor of Blender. Then you should be able to export your project (with the texture) in a suitable format for 3d print.


Stringy first layer (possible extruder issue?)

The first photo shows under extrusion. This could indicate either a bad filament, a massive clog or the wrong filament diameter in the slicer.
I have experienced, that small demo-reels of filament that come with printers come damaged from the shipping: I have experienced some of them having been exposed to moisture in their zip-lock bags and one time I had no clue what kind of filament that was supposed to be, but it was not PLA, as it didn't properly melt at 200 °C. That might not be the case with your printer, but it leads me to caution towards those 20 g demo reels, so I always test with a known good reel of filament with a known melting point. If it was the wrong material (e.g. ABS), under extrusion due to a too low temperature would be normal. Damaged or bad filament can create several problems: non-uniform thickness can result in random stops in the extruder or underextrusion, waterlogged ("wet") filament can print stringy, hissing, or even with underextrusion, brittle filament might break and result in aborted lines.
A clog in the nozzle could lead to under extrusion but should also show clicking in the extruder (the motor moving the filament). Checking the whole filament path (nozzle, heat break, liner & Bowden tube) for clogs should be done. However, that would be a massive clog to get your depicted prints. It might be a factor impacting it though.
Sometimes, setting up a printer in a slicer is not perfect: You need to make sure the filament diameter fits! 1.75 mm might be the de facto standard, but most slicers are set up with 2.75 mm as filament diameter in the presets for a self-configured printer! That means you only extrude about a third of the filament you actually want! That would be super consistent with your picture but doesn't need to be the only factor.


What kind of thermal paste do I need for a heatbed thermistor?

If you need it to hold the thermistor in place, there are thermally conductive electrically insulating potting compounds, such as Appli-Thane® 7300 Urethane that have a temperature range of -100 to 160 °C.
The newest CPU thermal pastes contain silver particles and will conduct electricity. So, it needs to stay away from leads and pads that don't want to be shorted


Comparative design methods for joints that will be joined together

One of my favorite techniques is to join pieces with screws, and include a tapered feature that helps align the parts. A single screw can give a very strong joint, that is well-aligned and won't twist. Another advantage is that such joints can be printed in any orientation, since the tapered feature can be designed with 45 degree angles.

Here is a cross-section example of such a joint:


What can I do to remove the rounded corners using Junction Deviation?

Contrary to what's implied by its name, junction deviation does not produce rounded corners. It merely allows violations of the acceleration profile at corners that would be allowed if the corner were rounded by the deviation. So you should not expect changes to it to create or eliminate unwanted "rounded corners".
However I don't think what you're seeing are rounded corners. They're bulging corners, likely produced as a consequence of the toolhead moving slower just before and after the corner in order to honor the acceleration profile. My guess is that your acceleration limits in Marlin 2.0 (500 mm/s² if I recall correctly) are a lot lower than on the original Creality firmware.
You can and probably should increase the acceleration limits. The machine should handle 1000 mm/s² easily and up to 3000 mm/s² or even higher with some ringing; I use lower acceleration for the outer walls and let it run wild for inner walls and infill. But the real solution to your bulging corners problem is to enable and calibrate Linear Advance to get a consistent extrusion rate with varing speed. For my Ender 3, the right constant is around 0.5-0.6 s (yes the units are seconds - it's mm/(mm/s)) for PLA. You can use the calibration pattern generator to run the calibration yourself, but I would expect the same results.
This will significantly impact your print speed, since Marlin applies E-axis speed, acceleration, and jerk limits to the advance offsets. You can get a lot of it back though by increasing those limits though; the defaults are a whole lot lower than what the machine can handle. 200 mm/s speed limit and 10000-15000 mm/s² acceleration limit (vs 25 and 5000 defaults in Marlin, respectively) are within reason.


I have no experience with either GRBL or DLP printers, but the

M7
M8
M9

coolant control codes should be able to be sent by NanoDLP to GRBL. Those seem to allow for direct digital output.
Apparently you can set the pin you want them to use in the cpu_map.h file, with the standard being Analog Pins 3 and 4 for the M8 and M7 commands respectively.

// Define flood and mist coolant enable output pins.
#define COOLANT_FLOOD_DDR   DDRC
#define COOLANT_FLOOD_PORT  PORTC
#define COOLANT_FLOOD_BIT   3  // Uno Analog Pin 3
#define COOLANT_MIST_DDR   DDRC
#define COOLANT_MIST_PORT  PORTC
#define COOLANT_MIST_BIT   4  // Uno Analog Pin 4

Hope this helps!
Source: https://github.com/gnea/grbl


How should I go about printing easily removable rafts?

As comments suggest,  a raft is not all that popular.  Consider using a brim/skirt instead.  I've had excellent luck with a 4-mm skirt, printing onto blue painter's tape. (Unless you consider it bad luck when I have a devil of a time getting some parts to release :-) ).   Skirts are trivial to cut free from the object.

In a similar vein, if you run into trouble getting support structures to pop off the object cleanly, try to make them as thin-walled as possible.


As a software developer and 3D printing enthousiast I can tell you that indeed, like Trish said, the limit is your memory (RAM) and loading/slicing time depends on the cpu power.
RAM: keep an eye on the memory usage in the task manager/performance/memory tab. When it reaches the top of the graph, the application will suddenly crash and disappear.
CPU: The application (cura/slicer/prusaslicer) can become "not responsive". This does not always mean that the process hangs. It just means that the cpu is very busy and the program is not reporting the progress to windows. Most probably the application will recover from this if you just choose to wait.
Files do not get dumbed down when imported afaik in cura. They are shown exactly like in the STL. Don't know about other software though, but I doubt this happens.
Like you noted, this has nothing to do with Gcode, which is loaded serially.


Can I use Araldite to stick PLA to metal frame?

Araldite is a brand that refers to a range of structural epoxy, acrylic and polyurethane adhesives. Among the vast number of products marketed under the name are also "metal repair" paste and what seems to be silicone based glues. Depending on what Araldite you have on hand, all of these types can be useful for PLA and any other 3D-printing material, as I had elaborated here. I suggest grabbing either an epoxy or PU variant or some kind of silicone for this use. You should make sure several things though if you go with epoxy or PU:

make a small sample print and clamp down one side, then put a small weight on the other side. Apply the glue in the center of it. If it sags considerably during the bonding, the heat of the glue curing is warm enough to soften the print. If this happens, you should take precautions to prevent it from deforming during the bonding, e.g. not apply too much pressure onto the bond.
The MOSFET can get rather hot. Make sure that the clamp holding the MOSFET still holds the item as it gets hot, as PLA starts to get malleable enough to deform under stress at 50 °C and usually fails quickly at about 100 °C.

Silicone-based glues depend on an area to force ratio to stick but offer a flexible bond that is somewhat thermal resistant and very gap filling.


It looks like a sensor issue.  Maybe a temporary resistance in a contact of the sensor circuit made the temperature look low to the controler, so it applies power to raise the temperature.  When the contection recovers, the temperature is too high, so the controller lowers the power to restore the temperature.


When installing a glass bed, what do you change?

The most common way to install a glass bed (assuming it's literally a piece of borosilicate glass) is with binder clips. Glass is an insulator, so you may need to adjust your bed temps by a few degrees, and it will take somewhat longer to warm up.

You shouldn't need any firmware changes, but will need to adjust whatever z homing you do. If you have a limit switch currently, you'll need to move it by the thickness of the glass. If you have an inductive probe, it should still continue to work, but your z-offset will need to be adjusted. If you have BLTouch or a piezo, nothing should need to change there.


Building 3D printer: LM8UU bearing can't fit into

Bearing on a shaft
An 8 mm (ID, Internal Diameter) bearing should always fit on an 8 mm (OD, Outer Diameter) shaft. If it does not fit, one of the 2 is of a different size. Please use a caliper to determine the size of both.
Bearing in a housing
If it is the outer size of the bearing, i.e. fitting in a printed carriage or a bearing housing (e.g. SCxxUU), you should be aware of the different sizes of polymer bearings. E.g. there are RJMP-01-xx and RJ4JP-01-xx types of polymer bearings (xx denotes the shaft diameter, e.g. 08 for 8 mm shafts).
For RJMP-01-xx bearings (not compatible with LMxxUU bearings):

// Parameters for RJMP-01-xx (shaft size xx, all dimensions in [mm])
// Designation  d1  d2  B   B1      s   dn
//-------------------------------------------
// RJMP-01-08   8   16  25  16.2    1.1  15.2

For RJ4JP-01-xx bearings (compatible with LMxxUU bearings):

// Parameters for RJ4JP-01-xx (shaft size xx, all dimensions in [mm])
// Designation  d1  d2  B   B1      s   dn
//-------------------------------------------
// RJ4JP-01-08  8   15  24  17.5    1.1  14.3

d1 is the inner diameter, d2 the outer diameter and B the length of the bearing
The RJ4JP-01-08 bearings are drop-in replacements for the LM8UU linear bearings. Note that the RJMP-01-08 have a larger outer diameter and do not fit into the regular bearing housings. The increased thickness gives the bearings more rigidity.


What hotend designs exist as paired all-metal and PTFE-lined versions?

Hotend Designes in General
Lined
Makerbot Mk8 & e3D Lite6
The Makerbot Mk8 seen on many Chinese machines and the E3D Lite6 are both lined hotends, which means the PTFE liner goes down into the heartbreak and butts against the nozzle. This style is very easy to print PLA with, but can't print hotter than about 240 °C.
Makerbot MK10
A variant of the lined hotend is the Makerbot MK10, where the PTFE goes a bit into the nozzle. These nozzles have a larger diameter, the melt zone is very short.
All Metal
There are mainly two designs of consumer all-metal hotend out there at the moment.
E3D v6
Stereotypical by now, the All Metal hotend typically means E3D v6. The liner ends at the end of the heartbreak, the heartbreak of the original is necked down to reduce heat creep. The design is flawed in that heat creep can't be mitigated completely. While this design can print much higher temperatures than lined hotends, the heat creep can create trouble with PLA.
E3D Hermea
The dreamchild of the v6 is the Hermea (formerly Hermes), which fights the problem of heat creep by drastically altering the coolend design: The heartbreak is even slimmer than the v6 and has very little area outside of the cooling block. This cooling block is fitted with a somewhat stronger fan. In theory this leads to much better cooling in the upper filament path and getting heat creep under control. However, due to the manufacturing stop induced by COVID-19, there are not too many Hermea out in the wild. Some early to mid development information could be gained from Joel and Thomas Sanladerer.
Among the still few reviews I have found is Thomas Sanladerer.
Slice Engineering Mosquito Hotend
Slice engineering went a different way to fight heatcreep in an unined all metal hotend: The heatsink is mode away from the filament path and serves as its own structure. As a downsize, each and every part is pretty much precision machined, making it comparably expensive: without heater, thermosensor, and extruder the bare item clocks in 145$. Claimed benefits are, that the thinner filament path (as it doesn't need to be structural) from a low heat-conducting material reduces heat creep and because we have an unlined filament path it can print at 450 °C, making it one o the highest-rated hotends.
Slice Engineering Copperhead
Currently, the same company is working on the Copperhead, in which they introduce a dual metal construction on necked heatbreak. The name Bi-Metal for this however would be a misnomer: Bimetal is a standing technical term for a strip of metals that, when heated, starts to tilt into one direction because of dissimilar heat expansion. The correct term, which they properly use on their website is Bimetallic, not Bimetal.
Because of the dissimilar thermal behavior, such a setup needs to be designed and machined very carefully, but could, help to dissipate the heat from the filament path and massively reduce heatcreep. The Copperhead as shown currently is offered for preorder with two mounting options, one of them the e3D style groove., which might allow drop-in replacement of a full hotend.
The heartbreak however alone could suffice to get some of the effects, and as the website shows, it would be available as a drop-in replacement part. However, pricing and effectivity remain still to be seen.
Paired?!
At the time of this writing in May 2020, the combination of e3D v6 and Lite6 using the same outer form factor is pretty much unique to them and their clones. The Trianglelab Dragon hotend (a review of it here) uses the e3D v6 Style connector on a Slice Enginering Mosquito Hotend design, making it pretty much paired to the two.
However the main functioning parts of the distinction is the heartbreak being either part of the cooling body and lined or a separate piece. The e3D v6 does use the same M6 threading that is also used in a Makerbot Mk8 and many Chinese clones on many machines [Some are M7, so beware!], and thus one can easily make a Frankenstein Hotend by combining the pre-mounted cooling body with a proper e3D v6 heartbreak and turn the lined into an All Metal hotend.


SLA printing: piece does not stick to supporting structures

I have tried to print the piece upside-down with the cave part facing down and it worked.
Since the printer prints upside down, positioning the cave part facing up creates a suction-cup effect on the printer display that makes the whole structure stick to the lcd and detach from the supporting structure, thus making the print fail.


From your comments can be read that you print infill at 200 mm/s.

Know that 200 mm/s is ridiculously fast (like high travelling speed), close to the limits of printing on certain machines (for an AtMega)! It is hard for the filament to keep up at this speed. A value of 60 mm/s would be a good value to start experimenting. Your infill is not rough, it just failed printing. I have printed kilometers of PETG, normal print speeds for my PETG are recommended at 30-50 mm/s by my manufacturer; I get good results at 50-60 mm/s. On my Ultimaker 3, 70 mm/s is also feasible.

Note that the filament you use seems to have rather low printing temperatures (195-225 °C) as opposed to the PETG filament (co-polymer) I'm used to. The manufacturer does not specify advised print speeds (other than "high", but what defines "high"?), but this user posted some of his print settings for this material. The overall speed of 60 mm/s seems to support lower than 200 mm/s print speeds.


There are two areas of this design which seem to pose a risk of connectors overheating, the hot end and the heated bed. The heated bed runs at about 6 amps, 12 Volts. The hot end runs at a lower current, but can itself overheat if the thermistor stops providing feedback.

The problem in this design with the heated bed is mainly the connectors - they work OK when they are good, but can easily come a bit loose. This has two side effects. The bed heats less well, and the connector itself heats instead. Replacing the 2mm plug connector, and 2mm molex with direct soldered connections will help (the on-board mosfet seems OK with the current, unless you increase the power rail voltage).

A mosfet is a good solution for high current switching, the modules available have good screw terminals which should be OK for maybe 25A (well in excess of what you need). Mosfets are efficient when switched fully on, so there won't be much heating.

You would also use a relay (rated for at least 10A), but this will be noisy since the heater is switched repeatedly to maintain the target temperature. A relay also takes more power itself and will ear out if repeatedly switched under load.

Bottom line, if you have a good relay already, it is OK as a temporary (safe) solution. Longer-term a mosfet is better. Pay attention to the connectors at power supply, board (in and out) and heated bed. Using an additional mosfet for the hotend is maybe overkill.


How to solve burnt blobs on Prusa MK3S (PETG)?

I saw PETG printed at 100 mm/s, but 150! That's a lot.

One solution to avoid blobs may be to limit the maximum speed to a value you can actually achieve with reliable results.

Simple test to find your machine limits (each combination filament brand + nozzle + temperature has a different value): extrude filament in the air at increasing speeds, see how the flow changes, and when you see more than 5% decrease, that's it.

M83
mark the filament as if you were calibrating the E steps
calculate filament speed: speed = volum/s / filament surface * 60 = mm^3/s * 25 (this factor is valid for 1.75 mm filament)
set extrusion speed for 2 mm^3/s: G1 F50
extrude 50 mm: G1 E50
measure actual length extruded
repeat 2.-6. but increase the speed by 2 mm^3/s each time: 2, 4, 6, 8, 10, 12, ...
at a certain speed you will see that the actual filament length starts to decrease. When you see that the underextrusion reaches 5-10% (depending how much underextrusion you accept), write down that volumetric speed (mm^3/s) somewhere, it's your limit for THAT filament + THAT nozzle + THAT temperature
Either a) calculate the max print speed = volumetric speed / layer height / line width or b) set the maximum volumetric flow rate in the slicing software so that the speed will be automatically capped taking into account layer height and line width. Prusaslicer allows to set that in the "Print" or in "Filament" settings, I recommend it for "Filament" settings, since it's a filament-dependent parameter.

Example data from CNC Kitchen:

You can increase the max print speed, at the price of a little loss of quality around edges, if you calibrate the E steps at a speed corresponding to 2-3% underextrusion (alternative: to the speed of outer perimeters).

This way you know that when you print slower than that (uncommon... typically only sharp corners and small perimeters) you'll get up to 2-3% overextrusion, and you extend by 2-3% the maximum print speed, since your max speed is the one where you get 5-10% underextrusion compared to your E steps calibration speed.


At the intersection of the top and bottom planes of the cross-piece and the cylinder, there are non-manifold edges. Meshmixer is able to identify this problem but cannot repair it. My slicer, Simplify3D also identifies the faults and prints a solid cylinder between the planes. Prusa Slicer 2 also creates a solid at that location.

As you've indicated that you are the creator, consider to use the 3D printing features within Blender to assist you with repairing the problem locations.

  File ‣ User Preferences (or Ctrl-Alt-U)
  to open the User Preferences menu.

  In the Add-ons tab, start typing 3d print into the search bar. Once
  the “Mesh: 3D Print Toolbox” shows up, click the checkbox on the far
  right to enable this add-on.

  Close the User Preferences window.

  In the Tool Shelf, there should be a new 3D Printing tab.


I don't believe that slicing engines create any sort of solid model that would be useful for CAD simulation. When a slicing engine slices a 3D model, it's goal is to spit out the preferred machine paths in G-Code (of some kind). However, I've read a few articles, done some tests, and heard through the grape vine that anywhere between 10%-35% is good enough for most applications. I once watched a webinar for understanding the new MakerWare interface that explained how they chose such settings. Although I can't find the clip directly, here is the page for all of MakerBot's webinars. I think this webinar was the one I watched explaining a little bit about preferred infill percentages.

From experience, anything over 35% doesn't yield much more strength from infill side of things. Beyond 35% and you're going to want to reconsider how you're orienting the print when you print it and what you're printing to utilize the grain structure for proper strength.

However, infill percentage/patterns are not the only variable for creating strong parts. Infill is really just a way to save time and material. Here are some other ways to potentially increase strength:

Increase your shell. Shell is the number of profile patterns per layer. Typically (in FDM/FFF), each shell is about the diameter of your extruder nozzle.
Increase your floor/roof. Similar to shell, floor/roof refers to the number of layers that make up the "bottom" and "top" of the part with regard to the build plate.
Print orientation. Pay attention to which areas of the part are susceptible to strain along the "grain" of the layers. Try to rotate your part on the build plate in a way that minimizes potential failure both in print and post-print use.
Post process. Don't be afraid to do some post-processing to increase the strength. There are some 3D printers on the market that go as far as including Kevlar strands in the printing process to beef up their prints. However, it may be as simple as just coating the part in an epoxy with some basic finishing techniques. It's a bit more work, but it turns weak 3D printed parts into full production quality prints.

Update:
Based on some of the comments, it sounds like your best bet might be to find a custom application that can either convert the g-code file into a solid model (try CAM software?), or create a plugin for your CAD software (I know Unigraphics NX and Solidworks allow for this) and essentially recreate your own slicing engine that takes your solid model and generates the same infill pattern dynamically inside.

Perhaps look into the works of Simlab or similar which has a lot of 3D software plugins. I'm not promoting them and I don't work for them, this is just a reference of what to look for.


I have used a standard soldering iron to modify and fix 3D prints in the past. You have to keep some things in mind when doing so:

Don't overheat your material. PLA can take a soldering iron of about 230 °C before charring.
Don't use a tip with solder, or you will get grey deposits in the plastic.
Round tips or flat tips both work fine, but you want to not dump too much heat into the model or you start to deform the print as it needs to cool again.
Using snippets from the end of the spool for soldering is a good way to recycle the "waste".


Is Tetrahydrofuran viable for dissolving PLA and sticking PLA objects together?

According to Shuichi Sato, Daiki Gondo, Takayuki Wada, Shinji Kanehashi & Kazukiyo Nagai: Effects of various liquid organic solvents on solvent‐induced crystallization of amorphous poly(lactic acid) film in Journal of Applied Polymer Science, Volume 129 Issue 3 (2013), p1607-1617source, Tetrahydrofuran is classified as a solvent for PLA. The specific entry on page 1608:
Group  Solvent          Solvent type    dd   dp   dh   dt   Result
Ether  Tetrahydrofuran  Polar aprotic  16.8  5.7  8   19.4  soluble

The values dd dp dh and dt are explained on page 1607:

The effects of 60 liquid organic solvents on PLA are systematically
investigated using the Hansen solubility parameter (HSP). The HSP
is one of the digitizing methods for analyzing the interaction
between polymer materials and organic solvents. In HSP analysis,
all solvents have three parameters: energy from dispersion bonds
between molecules (dd), dipolar intermolecular force between molecules
(dp), and the hydrogen bonds between molecules (dh). All solvents
were characterized by a point in a three-dimensional structure
at which dd, dp, and dh are plotted on three mutually perpendicular
axes. Generally, if the HSP values of the various organic solvents
are near that of the given polymer, the solvent is considered compatible
with the polymer material.

The factor dt is the total Hansen solubility parameter - the bigger this is, the better it is a solvent.
19.4 is a rather good solvent but extremely explosive: in air 20000 ppm (2%) are explosive and thus the allowable concentration in an area is 2000 ppmsource
Alternatives
A similar potent solvent would be Benzene (dt = 18.6) which more easily available and less explosive, but more deadly (10000-20000 ppm fumes) and has an allowable concentration of 500 ppmsource
Ethyl-acetate is also a solvent (dt = 18.2) and more available. It is explosive at an equal concentration as Tetrahydrofuransource, but it has just about half of its vapor pressure (73 mmHgsource  vs. 132 mmHgsource), so can be stored more safely, and is less aggressive on the body. It is sometimes used to Smooth PLA via vapor chambersource, and only comes at a price tag of ca. 90 €/l for the pure stuff and also is used in some nail polish removers, put into a safe mix.
Acetone is classified as a better solvent (dt = 20.1), and it is known to act as a glue and to soften PLA with some exposure time, but from experience, it can't smooth it. It is available most easy (nail polish remover and in the home depot), and is the least deadly option.
Propylene-1,2-carbonate is classed as solvent and a far better at it with dt = 27.2. It has been used as an alternative to Ethyl-Acetatesource and its MSDS is rather gentlesource. It comes at a price tag of 130 €/l for the chemical-grade liquid.
Conclusion
Tetrahydrofuran is not a viable replacement due to its explosive properties. It is not an improvement above Benzene, which at least can be stored safely.
Using Acetone as a benchmark, Tetrahydrofuran should not smooth the surface in a vapor chamber, as it is a worse solvent than Acetone. It should also take longer to soften and dissolve objects than Acetone, but a heated bath or coating the surface with it could help to generate the needed exposure times.
However, its comparable ethyl-acetate has been claimed to be used as a cleaning, vapor smoothing, and brush on surface smoothing agent successfully and can be used better by helping the solubility via heating, which can be done much safer with ethyl-acetate than THF. In a proper chemical mix, its storage problem can be solved too.
A better alternative is propylene-1,2-carbonate, which is a better solvent, and much less dangerous.
tl;dr: No, Tetrahydrofuran is not able to dissolve PLA in a reasonable time1 without heat activation and it has worse characteristics than Acetone. It could arguably be used to weld parts, but Dichloromethane would be more effective.

1 - Sato, Gondo et al. in the aforementioned paper: Solubility tests were performed for 24 h at 35+-1 °C. which means we have a prolonged exposure of a thin film to a huge amount of solvent. how thin a film? Very thin: The PLA films
were prepared by casting 2 wt % dichloromethane solution onto a
flat-bottomed glass Petri dish in a glass bell-type vessel and by drying
under atmospheric pressure at room temperature. Each solvent
was allowed to evaporate for 48 h. The dried PLA films were then
thermally treated under a vacuum for 48 h at 70 °C to eliminate
the residual solvent and to obtain amorphous PLA films. Afterwards,
the thermally treated PLA films were cooled at room temperature
under atmospheric pressure.


Extruder always clogs up almost immediately after cleaning

I have had one roll of filament that did this.  I'd get a jam, clean it out, and immediately jam again.

I got the filament from a friend who had reported problems using it, but I thought, "I have a Prusa3D i3m3-mmu2, I can print with anything."  Unfortunately, I could not.

I threw away the filament (first I've ever jetisoned so callously), replaced the nozzle, and was back in business.

So, some filament just doesn't work.

But, there is another possible problem to check -- you might have a problem with stepper driver.  Even with low current from a blown driver or badly adjusted driver, the extruder motor may spin.  It may even be able to extrude filament into the air through the hot nozzle.  But, the torque may not be sufficient to force the molten plastic as it pushes against the build plate.

Pushing the molten plastic against the build plate so that it "smooshes" well requires pressure, which comes from the push on the filament from the extruder gear, which comes from the torque of the motor, which comes from the current from the driver, which may be either blown or seriously mal-adjusted.


Building a cheap 3d printer with DC Motors?

To use DC-motors instead of stepper motors, you would need to have some sort of encoder that tells the controlling machine where the printhead has moved.

On the arduino Forums they have discussed the problems and difficulties. The main problem is, that currently, there is little firmware for Arduino or similar chips that can do this. Another big problem is, that such a machine might need a different type of G-code, unless well done.

That is not to say that there is no firmware that does control DC motors via an encoder. Printers do so since ages. But to reverse engineer printer firmware is really really hard. It took a pair of hackers the better part of a half year to dissect the printer & Fax firmware for one printer, and they had mainly looked to dissect the fax protocol and had not looked at all at the motor controlDefcon talk about it.

Luckily, as the RepRap tells though, somebody did hack together a DC motor control: Miguel Sanchez has a GitHub about it. You DO need proper encoders though.


Are the Makerbot 5th generation's initial issues resolved

Makerbot claims the problems are fixed. I have heard from a number of resellers that the problems are fixed. Unfortunately, both of those are somewhat biased sources. It's surprisingly hard to get good info on the subject -- very few credible people are talking about recent experiences with the product line.

Issue #1: The main surviving user forum (https://groups.google.com/forum/#!forum/makerbot-users) has had the torrent of people reporting 5th gen issues more or less dry up. There ARE still people posting issues, but at a fairly low level that is not far outside what you would expect for an average hobbyist printer. What we DON'T know is whether the flood of complaints has slowed because they're working better, or because very few people are actually buying them any more.

Issue #2: The power-users and community leaders that typically evaluate and review 3d printers are all avoiding the 5th gen line like the plague. Makerbot burned up a lot of community good-will by going closed source with the Replicator 2, and lost more good-will through a series of misunderstandings over patent applications and the Thingiverse terms of service (Takerbot scandals), and put the nail in the coffin by knowingly releasing a non-functional 5th gen product line. Very few credible people are willing to give them a chance at this point, so there is a severe shortage of unbiased reviews.

Issue #3: Makerbot has a proven history of buying off journalists and reviewers to get positive 5th gen press. Some verifiable examples:

Hundreds of fake 5-star Amazon reviews from paid review accounts. A relevant analysis: http://www.amazon.com/review/R2JI8LRRXZYNX1/ (Not verified, but related: a widely-believed rumor states that the German Amazon site actually wiped all of Makerbot's 5th Gen reviews because of blatant tampering: http://www.amazon.de/MakerBot-MP05825-Replicator-5th-H%C3%B6he/dp/B0183TP806/)
The CES awards initially given to the 5th Gen line were given before Makerbot had functional firmware. None of the 5th Gens at the CES launch were functional. All demo prints shown were made on Replicator 2s. How could a non-functional product win awards? Not hard to figure that one out.
Historical positive press in the 3DP journalism media (3ders, Make Magazine, etc) has been directly proportional to the volume of ad-buys from Makerbot or the parent company Stratasys.

I could keep going, but you get the idea.

So it's hard to evaluate the reality of the situation. But even IF the Smart Extruder issues are truly all fixed (jams, leveling issues, thermocouple connection, filament encoder failures, etc), there are still meaningful problems with the product line.

The print quality is not impressive. The motion mechanics, which have not been appreciably changed to my knowledge, are not great. The Smart Extruder is basically a giant pendulum wobbling off the side of a non-optimal gantry selection of an H-bot architecture. Makerbot has addressed the floppy construction via firmware tweaks to significantly slow down the machine to give marginally-acceptable print quality. According to most reports I have seen, a Replicator 5th Gen will print significantly slower than a Replicator 2, for example. Expect in the neighborhood of perhaps 30-40% longer print times than comparable printers.
The price tag is roughly double or even triple the current market price for the size and print quality output of the machine. There are so many great printers on the market now for significantly less money that it's kind of nuts to drop the cash on a Makerbot.
It is marketed as a PLA-only machine. That's fine if you're printing art and trinkets, but it's not a great option for mechanical parts. While you CAN print other materials, this is not technically supported.
The support plan structure has quite frankly become abusive. Makerbot used to have really helpful phone tech support, but the crushingly massive volume of 5th gen troubleshooting requests forced them into a paid tech support model. Around the same time, Makerbot shut down their user community forum and deleted links to external technical resources off their website. So unless you know the right places to go, support is scarce. For official tech support you must buy "Makercare" or pay for each help ticket. This is completely out of line with industry norms for a hobbyist/consumer 3d printer. They essentially took their biggest liability -- unreliable printers -- and tried to twist it into a profit center. I personally think this is a significant reason to avoid the company entirely.

Is it possible to get good results from a Replicator 5th Gen? Sure. But it's a poor value for the cost, from a company that has spent the last few years systematically driving away its former loyal user base. I would recommend staying away until there's some significant change in the product line at minimum.


RAMPS won't PID tune and shows unreal temps

This can come from several sources:
Hardware
The thermistor or its connections might be damaged, and the fault is only observable when the hotend is hot or moved to a certain area. Start by checking the wiring! You may be able to repair a bad connection easily, but depending what was broken, you may need to replace something. In some cases squishing a thermistor cartridge too much can destroy the internals, so a replacement is needed.
A mainboard failure is more likely to just show a static temperature, and a heater failure would show as maybe not getting past a certain point.
Firmware
If it had not worked before or you changed the firmware, the firmware should also be a suspect. The firmware can 'fail' when using the wrong thermistor type/table which can result in a very big offset or bad slope, resulting in wrong or unaccurate readings.


3D printed part sticking to the support layer

I finally found out two causes:

The 3D printer has default settings for ABS, and since there is no printer bed settings in ReplicatorG, the bed temperature was set to 110 °C instead of  60°C. I fixed the setting directly on the printer itself.
It seems that one side of the printer bed was little closer to the nozzle than other sides (relatively to the extruder) and this added a pressure on the support layer. I found this by observing the structure of the support layer that was little more compressed in one side. That was easy to fix by iteratively tightening/loosening the screw of that side and observing the support layer (and canceling the print if it is not homogeneous).

I installed Ultimaker Cura and Slic3r to try them and I found that Ultimaker Cura was not adapted to my printer (I did not found a complying model), Slic3r seems to be okay but I was not able to fit my big part inside of it.
I am trying to use the maximum available space for my part, perhaps I need to change some settings for Slic3r and anyway it is already working on ReplicatorG.


PEEK may well be the strongest filament out there (and it has other interesting properties to recommend it), but it is very difficult to print and requires a printer designed to operate at high temperatures. If you are still using PLA, your next port of call should be PETG. It is a lot stronger than PLA (although it will shatter if hit hard enough) and it is almost as easy to print. It also gives off hardly any fumes and it can be printed without an enclosure.


What are the other materials which can be used in DLP Printing, other than polymers?

DLP doesn't use "melted polymer". It uses a photosenstive resin which is at room temperature and polymerizes when exposed to (UV) light. At no point is any material melted.

As such, steel or carbon fiber can not be used as these materials are not photosensitive.


A Bowden tube is by design fairly small diameter to match the filament within, constraining the forces applied by the remote extruder mechanism. As you've noted, friction is a consideration.
For your application, you would not have to have such a tightly constrained diameter. You could use a Bowden tube for 2.85 mm filament, if your direct drive extruder is made for 1.75 mm filament.
You'd have the environmental control of the smaller tube, the path control and all of the other benefits, but none (or little) of the friction.
Additionally, you would not have the complexity of managing retraction or synchronizing feed that a dual motor system presents.


Here is a set of options you can get:

print the object on multi color printer

Unfortunately we got some limitations here (on the market). Printers have limited set of heads which are in fact printing in one color at a time. So we usually have 2 colors, there are also 4 color heads. If there are more then they are rare, expensive or rare and expensive.

here are examples of such color printouts:

project
project

print object splitted

In this case you can have single color printer. You print parts in one color then you change filament and print other color and so on. The issue here is to have well formed object which is designed for such print method (it's connectable in some way) or you can stick printed parts with the glue.

here are examples of such puzzled printouts:

project
project

print and paint

here are examples of such painted printouts:

project
project

NOTE:

All above assumes that you are gonna print your object in FDM technology. You can also take a look on other technologies such as:

Stereolithography(SLA)
Digital Light Processing(DLP)
Selective Laser Sintering (SLS)
Selective laser melting (SLM)
Electronic Beam Melting (EBM)
Laminated object manufacturing (LOM)


it seems like retraction issue

i would say you should experiment with

retraction length - so it would retract more
extra extrusion after retraction - so the printer could put some material before it will start your next hole :)

unfortunately there is no good guide how much it should retract and how much it should additionally extrude as it depends on "all your printing circumstances" but here is my arbitrary list in order of importance

filament (density - type and producer)
temperature (viscosity - hotter filament flows easier)
nozzle diam (as filament escapes easier through big hole ;)
heat barrier (cooling efficiency - filament should be cool as long as possible up to (or down to) the nozzle)
extruder gearing quality (good coupling makes precise retraction and extra-extrusion)
cooling (fan and duct should cool your printing right after it sticks to the surface)

and one more thing worth to mention

usually the first layer is not cooled which makes whole system hotter (so filament flows easier)

you could experiment with it too especially for big printouts

so

overextrude first layer AND
turn on cooling first layer

it seems like there is a bunch of things you can do to master it :)

good luck - it's definitely manageable


You'll probably be fine printing TPU with no fan. I just started printing with TPU, and did a lot of test prints to find out what settings work. Fan made little difference. With hotend at 230 °C, which I started out with, 0-20% fan was fine. I eventually increased temperature to 250 °C, which made extrusion more consistent and allowed me to reduce linear advance K-factor somewhat, and at that temperature having a bit more fan (I'm using 40% now) seems to help the material hold its shape, but it mainly made a difference at higher print speeds (over 35 mm/s) where the motion of the nozzle was "pulling on" the still-very-soft material just extruded. At 30 mm/s and below, fan still doesn't seem very important.

All of this is likely to vary somewhat with the properties of your machine. However I think it's safe to say you should be able to find a combination of print speed and temperature that make it possible to get by with no fan.

Follow-up: Upon further experimentation with TPU, I would say you really don't want any fan at all, except possibly for bridges. I've found significant distortion to shape just from air pressure from the fan, and at higher speeds the fan makes the print brittle just like what happens with PETG. Layers of TPU really seem to want time to melt together to bond, and without a fan blowing on them they don't seem to lose their shape during that time.


Converting / measuring bottle threads for creating an adapter to it

It's really unlikely that a bottle is using nonstandard threads; the engineering and tooling cost for doing so would not make sense. Most plastic drink bottles use PCO 1881 or PCO 1810 threads. If not, it should be one of a number of other less widely used standards.
The industry term for drink bottle thread is "neck finish". Searching on that, or on one of the standard names like PCO 1881, will find you a lot of information. You can then try to find a match for your threads. Note that the breaks 120 degrees apart do not affect the thread design, and may or may not be part of the neck finish standard, so you can ignore them.
There are existing OpenSCAD libraries for some of these, including

threadlib
IoP-satellite

And some related articles on Hackaday about their development and use:

Learn The Secrets Of Matching Bottle Cap Threads To One Another
Generating Nice Threads in OpenSCAD


Filament starts extruding as soon as hotend reaches melting point

Any ideas what to do to prevent this from happening?

You cannot prevent it entirely, but you can probably mitigate the problem by depressing the lever that squashes the filament against the hobbed gear of the extruder before starting to heat the nozzle.

In bowden extruders, the long portion of filament between the stepper motor and the nozzle is subject to compression during the print.  Because of the hysteresis in the filament, and of the slack between filament and PTFE tube, this filament acts like a slow-releasing compression spring.  When the nozzle cools down, the potential energy stored in the filament is "frozen" in place.

By depressing the lever, you allow the spring to extend "backward" towards the spool, rather than "forward" through the nozzle.

Some oozing is still bound to happen because of gravity and - as highlighted by others - thermal expansion, but it should be significantly less.

If you adopt the lever trick, remember to print with a skirt, as you will want the printer to recreate that "compression" in the filament before the model proper begins.

Another way to address the issue would be to add a little bit of retraction in the closing stanza of your GCODE (the part where you also tell the printer to unpower the steppers and stop heating).  This will prevent any "compression" to be "frozen" in the first place.

This anwer is based on the assumption that the stepper motor is not actively spinning (i.e.: yours is not a hardware/firmware issue).


This has nothing to do with the infill overlap, the image you've added looks as if the issue is related to non-bonding perimeters (it looks as if it is in between the 2nd and the 3rd perimeter). If that is the case look into this question.

I've had this same issue, the problem is that if the perimeters do not touch, this is most probably caused by insufficient filament flow which can be a result of a too high of a print speed (or too low print temperature) of the inner perimeters.


Which are the strongest and most durable materials?

So, as you say you want to materials for printing robotics parts. And as you have not given any budget constraint, I would give you a list of materials which would help you achieve the task, and you can choose amongst them accordingly.

Plastics: Basically used for building prototypes. Nylon Polyamide should be a choice for you.

  Polyamide 3D printing is achieved through SLS 3D printing. It offers
  strong and flexible prints. The upside of this material is that the
  printing technology requires minimum preparation of the 3D file before
  printing. There is no need for support. And it also offers the
  possibility to create intricate shapes and moving part in just one go.
  After the print the polyamide can be polished and dyed.

Metals: Metals like Brass, Alumunium and Steel should be a good choice.

But, if I were to achieve your task, I would select carbon fiber. some details about it:

  Carbon fiber consists of 90% carbon atoms, each fiber is 10 times
  thinner than a human hair. Carbon is especially prized for its lack of
  combustibility and infusability but also by its incredible strength
  (stronger than steel) and ability to create flexible structure, light
  weight and corrosion resistance. Its melting temperature is 1500, this
  heat there are only carbon.


Switch nozzle contact probe auto leveling with Marlin 2.0

Basically, you are also using a probe, the nozzle is the probe. So this is very similar to an auto levelling setup using a capacitive or inductive sensor, the difference is that your M851 nozzle to probe distance is zero, and may receive a positive value to slightly raise it to get a sheet of paper in between the nozzle and printing surface.
Please note that below only changes for levelling are addressed, not other specifics in Marlin 2.x for the Robo R1+!
First you define the nozzle offset in Configuration.h, which is exactly at the nozzle, so X and Y (and Z) are zero.
#define NOZZLE_TO_PROBE_OFFSET { 0, 0, 0 }

You can also set:
define NOZZLE_AS_PROBE

Furthermore, you need to define a levelling method in the same configuration file:

//#define AUTO_BED_LEVELING_3POINT
//#define AUTO_BED_LEVELING_LINEAR
#define AUTO_BED_LEVELING_BILINEAR
//#define AUTO_BED_LEVELING_UBL
//#define MESH_BED_LEVELING

For safety, we usually home Z at the center of the printing surface:
#define Z_SAFE_HOMING

Also be sure the following statement is active:
#define Z_MIN_PROBE_USES_Z_MIN_ENDSTOP_PIN

Next, you need to define the boundaries of the "probe", which is exactly where the nozzle may come (apart from a small safety offset at all edges called MIN_PROBE_EDGE); how you do that is described in question "How to set Z-probe boundary limits in firmware when using automatic bed leveling?", in Marlin 2.x this needs to be set in Configuration_adv.h:

#if PROBE_SELECTED && !IS_KINEMATIC
  #define MIN_PROBE_EDGE_LEFT MIN_PROBE_EDGE
  #define MIN_PROBE_EDGE_RIGHT MIN_PROBE_EDGE
  #define MIN_PROBE_EDGE_FRONT MIN_PROBE_EDGE
  #define MIN_PROBE_EDGE_BACK MIN_PROBE_EDGE
#endif