Many manufactures list their filaments as being food safe, but I would not treat this as "gospel truth". Apparently, the FDA considers PETG to be safe for food contact, but they are probably thinking about injection-moulded and vacuum-formed parts. Unfortunately, an initial search of the FDA's website did not yield any definitive information.

Even if a particular filament is genuinely food safe, that does not mean that a 3D-printed part made from it will be food safe, since there will be an abundance of nooks and crannies where bacteria can lodge and reproduce. You would have to sterilise a utensil before and after every use to be absolutely safe.

Anyway, good luck with making a water-tight mug with an FDM printer. You will probably have to seal it to make it water-tight, and then it will be the food-safety of the sealant that you will need to worry about. I would give it a miss, if I were you (at least, for other people's use). Items intended for one-time use would be OK, I suppose.


Ender 3 build surface is sticking up in the middle

So your (clone) BuildTak bed surface is not sticking to the bed anymore, time to remove the surface and clean the heatbed and apply a new one. These build surfaces (usually) have a sticky 3M sticker to stick it to the bed (or the surface bottom is covered with a sticky surface). When this sticking layer fails of subsequent heating cycles you need to replace the build surface. The higher the temperature the more the build surface expands the higher the surface gets when it doesn't stick in certain places.

Note that the build surface is a consumable, it needs to be replaced once in a while.


Extruder prints fine up until further down the print

I used a different heat break with a PFTE lining inside. After that it ran smoothly.

Probably what was happening was that my filament was getting too hot and started to stick on the full metal heat break.


How do PLA, PETG, TPU, ABS and/or nylon work together in a single print?

The answers are

yes
yes
probably

Which is to say, if you only want to use MaterialNumberTwo for disposable supports, then you should be fine. Presumably the slicer software is material-aware and adjusts the feed so the layer heights are the same for both materials. BUTbe careful that the support material isn't higher-temp than the object material, or supports which start from the object rather than the bed may cause local melting or distortion when the first layer is deposited on the cooler-melt material.

But if you want to try to intertwine two materials for the final product, then certainly bonding will be a major risk, as will shrinkage during cooling (not to mention the risk of melting the lower-temp material while depositing the higher-temp material on top of it!).  If at all possible I'd recommend printing such parts separately and fitting them together post-print.


CR6-SE fails to heat hotend to set point

Perform PID calibration procedure for hotend using G-code 'M303' with nozzle fans turned off completely.
You may use detailed guidelines from AK Eric's blog, RepRap wiki or 3DMaker Engineering.
If this will improve or clearly change the situation, but you still observe some issues during or after tuning, review other posts for troubleshooting. For example: large initial overshoot, no oscillations, struggle to fit into functional range or narrowed down hardware issues of incorrect heating cartridges.
When succeeded, you should repeat the procedure with fans enabled at the regular speed you use during printing.
PID calibration can be performed from Marlin's LCD menu (Configuration > Advanced Settings > Temperature > PID Autotune E1). It will allow to select target temperature, but not number of tuning cycles. It is only accessible when PID_AUTOTUNE_MENU is enabled in firmware settings (Configuration.h):
//#define PID_EDIT_MENU         // Add PID editing to the "Advanced Settings" menu. (~700 bytes of PROGMEM)
#define PID_AUTOTUNE_MENU     // Add PID auto-tuning to the "Advanced Settings" menu. (~250 bytes of PROGMEM)


Issue is solved!
Root cause was a broken thermistor circuit at board and broken thermistor.
I disconnected all wires and power, measured board and thermistors resistance: E0 = ~120 Ω, (E1 and Bed) = ~700 Ω. I swapped pins for TEMP_0_PIN and TEMP_1_PIN within Marlin for Tevo firmware at pins_RAMPS.h as described in answer on question Change hotend thermistor input in Marlin, changed thermistor and everything prints fine.


Nozzle heats while autoleveling (or before)

I am using CURA as my slicer, and it sets the bed and nozzle temp before printer start code is executed.
You can easily check that by opening a file in a notepad and see, that there will be a few lines describing the job, nozzle and bed setting temperature and the user code that is inserted in printer properties screen.

To change that behavior - you need to open the file and move the M commands down after leveling is executed.

;FLAVOR:Marlin
;TIME:45
;Filament used: 0.0187665m
;Layer height: 0.2
;Generated with Cura_SteamEngine 3.3.1
M190 S60
M104 S200
M109 S200M82 ;absolute extrusion mode

lines above are added by slicer so temperature is set before instritions from START G-Code section:

G21 ;metric values
G90 ;absolute positioning
M82 ;set extruder to absolute mode
M107 ;start with the fan off
G28;
G92 E0 ;zero the extruded length
G1 F20 E3 ;extrude 3mm of feed stock
G92 E0 ;zero the extruded length again


Why the Anet A6 can't do .05 layer height

I'm not familiar with the Anet A6 specifically, but as many other things in a 3D printer, the minimum layer height is co-determined by a number of factors.  For the Z-axis the factors I am aware of are:

The number of steps in the stepper motor
The geometry of the lead screw
The tolerance with which the lead screw has been machined
The microstep settings
The quality of the stepper drivers
The amount of play and flexibility of the X-axis gantry
The ration between filament and nozzle diameter
The precision of the extruder's stepper motor
...

Many printers that claim to have ridiculously low minimum Z-layer height do so by relying on the mathematical model only.  It goes something like this: the lead screw has an offset of 1mm per revolution, the stepper motor makes 200 steps and is set for 32 microsteps per step so the minimum resolution should be...

1mm / (200 * 32) = 0.0002mm

The reality is however different.  For example: the lead screw may have been machined with a tolerance of 0.002mm, so to make sure a layer has a thickness >0mm its heigh should be >0.004mm (20 times the theoretical limit computed with the microsteps).  But to make sure layers have the same height ±10% you would need to increase the minimum layer heigh of an order of magnitude, bringing it to 0.04mm.  A similar reasoning applies for the amount of play in the gantry, while the ratio between filament and nozzle influences the minimum volume of plastic that can be extruded per step (for very thin layers you want to be able to extrude a minimal amount of it).

At the end of the day this is a typical case of "a chain is only as strong as its weakest link": the minimum layer height of a printer is affected much more dramatically by the limitations of the most imprecise component in the printer than by the performance of its best one.

As for your question about breaking the printer by issuing g-code with very thin layers: should you issue gcode that requires layers below that limit, the firmware will simply print at the same z-height (see comments, credits to Tom).

I'm unaware of people having permanently damaged their machines by issuing code with too thin Z-layers.  But given how the firmware operates, I'd expect the quality of the print to be negatively affected, the filament to be possibly chewed by the cobbed wheel and in extreme cases cloggig of the printer head.


Why does infill percentage stop the print from sticking to the bed?

The more infill, the more material. The more material, the more stress is inside the part while it cools down from printing temperature to ambient temperature. Parts with higher infill density tend to warp more (the edges curl up).
But 20 % should be fine, you shouldn't have any issue at that percentage (unless you're printing with ABS/ASA).
I think it's a first layer issue, the 0.2 mm first layer gets more 'squished' onto the bed, thats why you get better adhesion. I'm using PrusaSlicer, every default print profile in PrusaSlicer uses a 0.2 mm first layer, maybe there is something like that in Cura too?
For example the 0.1 mm PrusaSlicer profile will squish a 0.2 mm first layer onto the bed and changes to 0.1 mm layers for the rest of the print.


Can I repair my microwave with a PLA part?

I would say PLA itself should not be heated up by microwave. It's because microwave oven creates oscilations which excites water particles (see microwave explanation here) so assuming PLA doesn't contain water, it won't heat up. (removed to not mislead as the water is not only material which heats up by microwaves. Thanx to Tom van der Zanden for being vigilant)

But as usual, it's more complicated.

First. PLA can contain water as while producing it can be cooled down in water bath. Of course well made PLA will have as less water as possible as water has an influence on printing process.

Second. PLA is absorbing humidity so in fact it gets water inside right from the air. This unfortunately causes problems in microwave oven.

Water can be overheated and oven can overheat water above 100C. But even at 100C, PLA will not be hard anymore so your 3 arm star would "collapse". Wheels could get oval or start sticking to their axis.

Eventually if high power is delivered to very "wet" PLA, I think it can... well maybe not explode but break.

Here goes a test which shows it can be used to defrost things on PLA plate in microwave

But here Daan Snijders claims PLA gets soft in microwave during the test

Will it be a disaster?

In my opinion it will work only for short uses of MW. Heating up a glass of milk or so. But for longer sessions when there will be much more heat (out of heating dish) it won't work.

SHORT TEST

20sec and 950W gives no effect on my sample (hotend cooling fan duct)
40sec and 950W caused the sample became a bit warm

Inspite that it's not a good idea to run MW without "proper-absorber" this little test confirmes my suspisious - short sessions are ok.


One feature of Cura is the ability to set supports to build plate only. This would remove any supports internal to the model, as your model has a base that is not considered the build plate or raft. In the image provided, you would have some complications, I believe, as there would be no supports on the outside of the model if it was directly over the base.

As you are not eliminating other options, you can also turn off supports in Cura, load your model into Meshmixer and make use of their support feature, which allows you to adjust placement, size and other parameters in order to get a good result.

The flexibility is limited only by your imagination:


E3D have a blog post on the subject of hardened nozzles. The common abrasive materials are carbon fibre, wood impregnated filament (or any other particulate fill), and some pigments. The blog describes that as little as 250g of the more abrasive filaments can wreck a brass nozzle.

For wear resistance, different manufacturers will have different options. Stainless steel is a little harder than brass, and hardened steel is a big step forward. If you fancy spending more money, aluminium oxide (i.e. Ruby) is an option.

The downside is printability and cost. Specifically thermal conductivity of brass (or copper) is very good when compared to steel. However, this may not be the limiting factor for your printing unless you're running a very large machine. The various materials may also give different friction/wetting performance which can affect jams.

Depending on the printer and the type of hardened nozzle, it probably makes sense to avoid swapping between hardened and standard nozzles most of the time.

Hardened nozzles cost between 3 and 20 times what you will pay for a branded brass nozzle (and arguably a bag of no-name brass nozzles can be treated as near enough free disposables in comparison).


How to edit G-code created in Cura to begin printing at a specified layer height?

Well this is a little complicated since nozzle height could collides with the part if the line 1169 has had started to be printed (part of the line), so the overlap will be the main problem, however adding the initial parameters to heat the extruder and getting the X0 and Y0 with G1 X0 y0 Z385 I recommend to increase Z by 3 or 5 mm, so the extruder will travel from a higher position to avoid the crash going for example, from Z390 to Z385.


It’s either because you haven’t connected it properly or you have not  mounted it the correct way. This could lead to the damaging of the part and failure to work again.

Check your connections with the stepper motors and hotend power wires. Make sure the connectors are in fine condition and cords are not frayed. Ensure all power is completely off and mains cable is unplugged.


What is causing this "ribbed" texture on my circular prints?

Any deviation from smoothness is caused by irregularity in the material feed, the motion, or both.  In this case, I would suggest both.

The problem is that current 3D printer control firmware (If someone has a counter-example in the hobbiest space, please add it) prints in linear segments.  This starts as @senthil-j-prakash shows in the conversion of the CAD object to an STL file.  STL files are made of triangles, which are linear structures.  There is no curvature in a triangle, only straight edges and flat faces.  Making the triangles as small as possible helps, but it exacerbates the next problem.

The second problem is that each line segment is passed as a separate command to the control firmware.  No matter if this is stored on an SD card, or transmitted through USB from the PC to the control firmware, each command defines a short, linear movement.  In an ideal world, the printer would precisely reproduce each of this short, linear motions, which would flow smoothly from one to the next.

Unfortunately, the "flowing smoothly" part is difficult to implement, and in some cases isn't actually what you want.  If the angle between segments is sharp enough, you don't want to round the corner.  When printing approximations to circles, however, one could move continuously, if the commands were sent enough ahead to analyze, and the firmware were clever enough to combine two segments into one smooth, curving motion.

This computation is very difficult to perform on an 8-bit microcontroller, and historically has not been done.

I am using a 32-bit ARM microcontroller and the RepRap firmware, which also does not smoothly merge motion between two low-angle linear motions into one smoother motion.

But, it's not just merging two into one.  One must merge a long series of short, linear moves into a long sequence of curved moves.  We could be doing motion planning based on splines rather than segments.

But then, we need to cap how much the control processor may change the path because the slicing software needs to predict very closely where each extruded element will lie. Adjacent elements (additional perimeters and infill) must be placed to touch those elements for bonding and strength.  if the control processor has moved an element too far, it could either not connect with, or interfere with, an element that is placed later.

But, enough of that rant about the technical difficulties.

For your particular machine, it is likely to be moving in fits and starts because of the short, linear commands.  Anything you do that improves the print quality will help with the ribs, and make them look more like facets.

Check the belt tension, the backlash, and the stiffness of the whole machine.  Try using slower speed and acceleration settings.  If you are printing from a PC through USB or the network, try printing from an SD card.  (If printing from an SD card, try printing over USB or the network).

Good luck, and keep printing!  Tell others of your experiences.


Problem in 3D printing of an empty model

You have modeled your bird. So far so good, but you likely only modeled a single surface and not a closed surface body. The crucial step was forgotten, as your pictures 1 and 2 show: you have designed a single surface for most of the object, not a body. To turn the bird into a printable object needs it not to be a single surface but a surface enclosing a volume that has some thickness.

At the moment, it looks like this: 640 vertices, NO enclosed space.

To achieve an even thickness object in blender:

A to choose the whole model
E for extrude Region
Z Z to constrain movement to Z axis
type in the wanted thickness

remember, that the grid in Blender is usually in cm, while slicing programs reference in mm!

close the edges by creating faces there (chose 3 and F)

A to grab everything
W then R to remove doubles, increase the merging distance to 0.05 (it takes away hundreds of superfluous, slightly shifted vertices!)
CTRL+N to recalculate normals

Make sure to check the slicer, because we have some strays, visible in red... where are those? They are faces hidden in the body!

Hide the underside (Select nothing, allow viewing through the object, 3 > B > draw a box around the lowest layer > H)

If you have the normals visible, you'll see the iffy areas now. Fix them by removing the superfluous faces and flipping those that are not superfuous but just inside out (W>F). One example area I highlight in the next picture

In the end, it should look like this in cura:

Make sure to check layer view and possibly thicken some areas manually - or make a box-part for the top, so you can ensure printability. As you'll see, at some scales, some walls are too thin due to how we extruded along Z only.

Alternate ways

As noted in the comments, instead of the Z-Extrude, a model with very vertical walls could benefit from using the solidify modifier. You will have to add it via object mode, modifiers and then choosing solidify and setting a positive thickness. To properly convert the visible modifier into an actual change of the model for the export, you will have to Apply the modifier.

Afterwards, go back to hunting stray internal surfaces and flipped faces.


It is hard to tell whether you personally should enclose your printer. However, you asked for the advantages and I will name some of them on which one can base a decision.

A 3D printer enclosure

helps to keep the temperature of the whole print at controlled levels, if you use a heating element, thermocouple and pid regulator. This is one of the most direct uses of the enclosure, which can be achieved by almost no other means. One could sloppily say it does for the whole print what the heatbed does for the initial layers. Controlling the temperature can be beneficial for layer adhesion and can help against delamination problems. This can go as far as fixing cracks and complete delamination (Thanks to @J. Roibal for bringing these cracks to my attention in the comments)
keeps dangerous fumes controlled. Here you can find a scientific study about it, published in Atmospheric Environment 79, titled 'ultrafine particle emission from desktop 3D printers, on exactly that topic. You can embed a filter with a fan in your housing to filter the air from all dangerous fumes that are created when melting certain plastic types. It could just circulate the air inside the chamber or get the filtered air out of the housing. This is another use which cannot be achieved otherwise (afaik).
can keep humidity away from your printer. This is helpful for filaments that attract water (and don't print well under that circumstance). This should be realized separately for stored filament, too, adding some silica gel to regulate humidity. (Thanks to @Obmerk Kronen in the comments)
minimizes losses of your heatbed. This happens in at least two ways, - the heated bed will also heat the surroundings, that is the inside of the enclosure. By raising its temperature, the temperature difference and hence heat loss is minimized. Also wind, introducing high fluctuations in the transfered (i.e. lost) heat is minimized. In that sense, it also
shuts out any wind for print temperature stability. Also dust and particles that could be blown on the print will be shut out (thanks to the addition of dust/particles: @Obmerk Kronen). This is a benefit that comes without having a heated chamber or filter.
helps to keep the printer clean in between use. Your axes will thank you being free from dust.
reduces smell and noise. If you use the printer in you living area, that alone can be a great benefit.
makes sure that your printer is safe during storage, nothing will fall on it.
can look pretty nice and add to the style of your printer, even if selfmade ;-)

There are obviously also downsides, as: connected work/money to make it, increased space used for the printer, and, if not well made for that purpose (which it should be), increased difficulty in repairs and maintenance of the printer itself (i.e. to get the printer out of the enclosure).


Cura has some options in this area that might or might not help. I've had mixed results. You should make sure Enable Bridge Settings is on, and try adjusting Bridge Skin Support Threshold. By default bridge settings are only used if 50% or more of the area is unsupported. Area is an utterly ridiculous/meaningless metric for whether bridging is needed, so you probably need to set this to just a really high value like 90% or 95%. You may also want to check that Bridge Has Multiple Layers is on.

With that said, for your model I would just use supports with a support interface (roof) below the bridges. You could reduce the material cost of them with Support Tree mode. But there are of course places where you can't use supports in similar models (bridge is over another part of the model and there's no access to remove the support material), so having working bridge settings is still desirable.


The question changed after I answered, so I'll answer the new question.

My answers are based on seeing the results of 3D printing deployed in a nearby school system, and my own experience as a FIRST Robotics mentor in my son's school system.

Current question's answer

K-8

You are ambitious.  At the K level, I can see a group project to change a design (such as bracelets), and print the result.  This would be done by an adult operating the design software and managing the printer.

At some point, maybe G4-G5, the students would be in more control, with assistance at hand to help jump past barriers that appear (software bugs, clogged nozzles, ...).  By G8 the students should be able to handle the whole workflow if they have come up through the program.

It would be great if there were a version of Logo for 3D printing.  Maybe there is.

CAD

You will need some form of CAD software to make 3D printing useful.  Depending on the students, and assuming a small budget, you could look at OpenSCAD (or SolidPython) and OnShape.

OpenSCAD uses a simple language to specify and transform geometric shapes and to perform union, intersection, and subtraction functions.  SolidPython is built atop OpenSCAD works with Python IDEs.  With the Python language, loops and conditionals are more natural.  OpenSCAD is pretty simple, but some people prefer Python.  Designs are not "drawn", but are programmed.

OnShape is a cloud-based, traditional 3D design and modeling tool.  Free user licenses are available with the caveat that all designs are publicly accessible and copiable, but others may not change your copy. It will be familiar to users of AutoDesk and SolidWorks systems, although the dialect will be strange.

Both produce STL files for 3D printing the designs.

What is the purpose of 3D printing at the school?

Other training really depends on how 3D printing is integrated into the core curriculum.  If 3D printing is part of a class in the static analysis of structures, then the class would be providing the training about strength.

IMO, the best training is accomplished by giving students access to the equipment with a mentor available to answer questions.  Each student comes to 3D modeling and printing with their own curiosity and motivation, and those are best served by smoothing their chosen path with information and advise.

What can go wrong?

The worst outcome is where money is raised, equipment is purchased, and no one is available to make it work.  Or, it works great until the inevitable problem arises, and no one can resolve it.  I've seen this happen in a large, well-funded school system.  The students get frustrated, and the program loses credibility.  The well-off students buy their own equipment and carry on, while those who can't dismiss 3D printing.  3D printing becomes another failed adventure.

Typical Problems

Working in any school system is complicated.  CORI checks are required.  Special certifications and permissions are needed to work on school property.  Insurance and liability are raised as problems which block progress.  Often nothing is possible without a teacher-on-staff taking personal responsibility and directly supervising activities.

Scheduling prints which take over a few hours may be impossible.

Most problems can be overcome with strong support from teachers and administration.

Training Required

The most important persons to be trained are the teachers and/or mentors.  They will train the students, and the students will train themselves and each other.

The teachers/mentors should be familiar with the general operation of the CAD software, know how to operate the 3D printing devices, and be able to resolve all common problems.  Keeping the equipment available is important.  Going down for a month is a long time in a school semester.

If 3D printing is integrated into a specific part of the curriculum, the teacher of that curriculum will provide the subject matter training that is being demonstrated through printing.  The physics teacher, the math teacher, or the art teacher will use the 3D printing to teach their domain.

Supporting Components

Look to the chemistry department for a fume hood to use for ventilation and a fire-proof enclosure.

Consult with the responsible authorities in the school to determine if special ventilation is required for occasional classroom use.  Whatever they say, it may not be enough because of parents' fear of plastics.

Have spare parts on hand to quickly bring a printer back online.  The ideal spare part is an extra printer -- plus other parts to restore the broken one when it fails.  Consider the latency in the supply chain for replacement parts.

Have a purchasing flow authorized that allows spare parts and operating supplies to be purchased quickly.  In some school systems, it can take months to purchase materials because such purchases are handled on a semester-by-semester basis.  That won't work when you really need a spool of a special color by yesterday.  If necessary, look to PTA-like organizations because they may be able to operate more quickly.

Consider using PLA in the classrooms.  There is friendly web content about PLA being sustainable, "natural", and biodegradable, rather than the ABS stigma of being petrochemical.

If the upper grades have a community service requirement, allow the 3D savvy students to volunteer as 3D printing mentors to the younger grades.

Previous answer

If your question is about what equipment to buy, it would be off topic as being a question of opinion and recommending specific vendor's equipment.  I am answering the question about determining what should be in a proposal.

Like any consideration of acquiring a 3d printing capability, there is some data that must be known before you can determine such a list of equipment.

First, what will the capability be used for?  In a school context, it could be used as part of a curriculum, probably not on the topic of 3d printing, but perhaps something else. Or, it could be part of a school machine shop or hobby shop.  It could be used by a robotics club, a rocket club, or a theater club.  Based on how it will be used at the school, you can determine the next data.

Second, what will be capability be used to print?  Based on that, you can judge which devices meet the need.

Third, based on the "what", and a sense of "how much", you can judge the type and quantity of supplies you will need.  Supplies for the first two or three years should be included in the proposal.

Fourth, estimate the amount of special staff time that should be needed, find a sponsor within the school who will commit to that time, and estimate the funds required to compensate them.

Finally, roll up a sales document, ideally based on a rubric from the granting agency, which included the benefits, allignment with the grant guidelines, and the costs.  Validate the proposal, especially the cost and the staff requirements, with whoever invited you to submit a proposal.

... and remember to actually submit the proposal by the deadline.

Bringing 3d printing into school is a great addition to other educational and engineering tools.  With the right support from the existing school staff and a clear vision of how it will fit into the school activities and existing culture, 3d printing succeed in a school setting.


You don't get a more accurate Z height when you heat the printer and let it settle. You get a different value that will work perfectly. E.g. I've got printers that do bed leveling cold but print with the correct initial Z height to get a perfect first layer. This is also valid for manually trammed beds. The only settling you might need if for thick glass beds so that the heat can be spread evenly, but operating thick glass beds I've never had to settle the bed, just heat up and start. But since ABS is prone to shrink, heating the bed first and then the hotend might prove valuable, at the time the hotend reaches it's temperature, the bed had time to evenly distribute the heat.

Oozing isn't good, maybe retracting filament at the end of a print might stop oozing for the next print. Most higher end printers therefore have a purge/prime, wipe and retract procedure prior to printing.


Adventurer 3 3D Printer doesn't extrude correctly

There are a number of different ways to narrow down the problem.

Your printing temperature is likely too low. Raise it up about ten degrees, but don't try a print just yet.

Ensure that the Bowden tube is firmly pressed into the hot end assembly. A gap below the tube is asking for future problems. If the tube is clear, remove it and examine for a squarely cut end and re-insert firmly.

I'm not familiar with the specifics of your model, but you should be able to disengage the Bowden tube from the extruder motor and manually push filament through the hot end and out the nozzle. For obvious reasons, raise the carriage above the bed before doing this.

Start with the 205 °C temperature and heat the nozzle. When it reaches stable temperature, push filament through. If it moves smoothly and extrudes cleanly, you're more than half-way home. If not, raise the temperature by another five degrees. At some point, you'll have a good idea of the temperature to use for that brand and color of filament.

Once you've checked those two items, you may have it solved, or you can edit your question to address any new developments.

Once you have the temperature determined, note that it may have to be increased to match a higher print speed. It is easy enough to push filament manually at the equivalent of a slow print, which allows the hot end to transfer the heat at a sufficient rate.

When printing normal speeds, if it can't move the heat fast enough, you have to raise the temperature or lower the speed. The former is preferable, of course. Who wants a print that takes two or three times longer?

EDIT: more info added

You may have more than one problem. I think your next step is to focus on the hot end/nozzle area. With the Bowden tube removed, insert a length of filament and raise the temperature to around 200 °C and push the filament downward.

You probably won't have filament passing through the nozzle, based on the limited information in the video. Once you've confirmed that, reduce the temperature in the nozzle to about 125 °C, let it hold there for a bit. You should note that the additional filament has now fused with that in the heat sink/heat break area. Increase the temperature again to 200 °C and apply gentle upwards pressure.

This is not a typical cold-pull process, but close to it. If you had nylon filament available, I'd recommend to use the nylon cleaning method.

I suspect that your hot end is clogged at the point where the bowden tube should have been flush into the bore.

I did not see both ends free on your Bowden tube. Your second problem may be related to that aspect. Consider to manually feed filament through the tube (after first clearing it) and if that doesn't work, the bowden tube is internally damaged.

The additional videos are helpful. Two items come to mind. The temperature may be too low at 200°C. You can't hurt things by going a bit too high, even as high as 225°C or 230°C but don't make big jumps to get there. Bring the temperature up to 210°C and see if you can force filament smoothly through the nozzle by hand. Keep on this practice until you find a good temperature.

For the second item, it's possible that your e-steps need to be checked. Feed filament through the bowden tube with the tube removed from the nozzle assembly. Feed a few centimeters beyond the end and make a mark where the filament is at the edge of the tube.

Using a terminal program or your printer control software, command a 100 millimeter filament feed. When it is completed, mark the filament and determine if you have extruded the correct amount.

The second part of the second video certainly presents well the frustration you are experiencing. Many of the people in the 3D printing community have had similar frustrations.

For the lock-up portion, check the manufacturer's web site for firmware upgrades, as sometimes there will be a correction to a problem such as yours.


What to do with failed/unwanted 3D prints?

The "obvious" answer is re-grinding the prints and making more filament. Unfortunately, this isn't yet a very economical or simple operation. A decent filament extruder capable of holding acceptable diameter tolerances is around $1000, and even then they can be pretty fidgety to operate. You have to have a LOT of volume throughput in your filament extruder for regrinding to be an economical proposition.

Some of the reasons why recycling prints into filament can be difficult:

Most plastics will degrade to some extent each time they are extruded. (Both by the 3d printer and by the filament extruder.) PLA will thermally degrade with extended exposure to heat. PET will hydrolyze and break down if not meticulously dried to remove moisture prior to heating to the melting temp. (PETG seems to be less prone to hydrolysis damage than plastic bottle PET, but it still happens to a limited degree.) ABS holds up to extrusion conditions better than most, which is part of why it's favored for injection molding, but there's still the potential to affect properties by depleting additives or cooking out plasticizers. In practice, this means regrinds generally need to be mixed with fresh pellets at some ratio. That dilutes the degraded or additive-depleted polymer with good material so you can maintain the material properties and performance.
If you print a variety of different colors, and don't want all your recycled filament to mix and end up a muddy brownish color, it can be difficult to manage the color sorting and matching. Most people don't want different colors along the length of a spool, either. So the regrind has to be mixed evenly in with virgin pellets and a suitable amount of masterbatch colorant to get a reasonable color output. You're not going to run off a new spool with 95% virgin pellets just to recycle a 50 gram failed print, are you? Likewise for material matching. Mixing materials is a bad idea. If you only print white PLA, this is all pretty easy to manage. But if you print a variety of colors and materials, you've got to set up a material tracking, sorting, and storage operation. You can do it... it's just a hassle.
Diameter control is difficult. 3D printers need a fairly tight diameter control for reliable performance and good quality. This is really the key challenge in any filament extrusion process. Extruded polymers like to change shape as they extrude and cool due to molecular alignment effects. You can't just push molten plastic out a 1.75mm nozzle -- "die swell" will make the extrudate bulge to a larger diameter immediately upon exiting the nozzle. Then you have to actually pull on the soft filament as it cools to carefully draw it down to the right diameter. The way the filament extruder measures diameter and controls tension is the key to getting acceptable results. Most hobbyist/desktop filament extruders have not succeeded at this.

Those are just the major issues. Filament extrusion is a complex subject with a lot of depth. For a home user of 3d printers, making filament basically becomes a whole second hobby. In my opinion, it only really makes sense in a commercial production printing environment where paid technicians can run the extruder(s) and a very large print throughput makes the pellets+regrind economics much more favorable than just buying new filament.

Reducing and reusing are preferable to recycling. Making your printer more reliable and gaining experience with calibration/configuration will reduce the volume of waste produced.

There are also some productive uses that let you reuse unwanted prints as-is or "downcycle" them for productive uses.

I personally keep a box of failed prints (and calibration prints and
no-longer-needed prototypes) as showpieces for people who want to
learn about 3D printing, and as toys for my nieces and nephews. I strongly recommend doing your calibration prints with a "toy" calibration model like Benchy or CaliBlocks. 3D printing is still new enough that people will happily take dozens of Benchies off your hands for the novelty value.
Failed and unwanted prints can also be used around the workshop for shims, sacrificial
cushions when clamping or hammering or drilling, or as scrap for experimenting
with adhesives or post-processing techniques.
ABS scraps are good for making ABS-slurry as a print bed adhesion treatment
layer, or for solvent-painting and filling gaps in other prints. Unfortunately, most other filaments do not have such convenient and safe solvents.
Some people have experimented with putting piles of scrap prints on a cookie sheet in an oven and melting them into multicolor cutting boards. There's a lot you can do with this sort of heavy remelt plate if you get creative. (I personally wouldn't use cheap Asian filaments for food contact though, they often have unpleasant contaminants.)


To my knowledge, OpenSCAD does not have any such feature. However, a related feature might help you: the debugging aid modifier characters. By inserting %, #, !, or * before an object (including aggregate objects), you can control how it renders in relation to the whole file; this makes it possible to do "binary search" type operations to figure out where the object you're seeing is.


Can snap-fit connector be designed for 3D Printing?

yes
You can totally print snap-fit connectors for 3D printing, but you need to keep some things in mind. I assume that since you have looked at these connectors, you have a good idea about the matter, but I nevertheless suggest Angus (MakersMuse) discussion locking devices at the beginning of a tutorial Video on designing buckles.
Your tabs thickness will need to be at least one line width wide at the most narrow point to be printable at all.
Print-Orientation
Another thing besides thickness is orientation. For the strongest tabs, you might want to print the tabs like a C for maximum part strength. Just modeling the part with the tabs, it should print in this orientation then:

This way the bending is not applying stress against layer boundaries but 90° to them, giving even force on each layer. This means that you will need to print parts in awkward orientations just for the tabs usually. You will need lots of support.
You can certainly print in a less awkward position at the expense of strength of the tab, acknowledging that "this is a prototype, we can show you that it closes perfectly like this, though due to FDM limitations we might break the tabs opening it again. So we'll be careful."
prototype-variation of model
Snaples tabs
It might be however easier to print the tabs flat and without the hooks, allowing to do a fitting test, but not a snap-connection. Your benefit is, that you won't have to watch for print orientation, but it won't be locking. Make sure to work with workflow and put the modifications for easy printing/not-locking at the end. Alterations to the general design should come all before this point. Then turn off these steps to create the model that is sent to machining for the mold.
Modular intermediate design
If you need to have working, strong tabs AND a good print, it can pay off to print separate parts that combine into a single piece with a little glue. Maybe the C-clamp is actually a thin bar that is put into the back plate and glued into place or secured with a little friction weld.


What are the changes between BLtouch 3.0 and 3.1?

Best reference would be the original equipment manufacturer (Antclabs). It appears their sensor has had many versions:

So, from 3.0 to 3.1 is a software upgrade. Reported highlights are:

★ Smart V3.0 (Mar. 2019 ~ ) : S10, S60, S90, S120, S140, S150, S160,
PWM Wiring defect indication(Blue LED), QR, Molex 1.25, Plastic
Push-pin(PC), Power Wiring defect indication(Red LED)
★ Smart V3.1 (Mar. 2019 ~ ) : S10, S60, S90, S120, S130, S140, S150,
S160, PWM Wiring defect indication(Blue LED), QR, Molex 1.25, Plastic
Push-pin(PC), Power Wiring defect indication(Red LED)

If you look at the manuals you will see the differences:
V3.0

V3.1

As can be seen, timings are different and more PWM position G-code options are available in the V3.1.


Repetier Host stops sending commands to printer when switching Windows user

Is it possible that in updating Repetier you inadvertently installed it for a single user rather than for everyone? If so, that might account for its stopping when the user is changed.


You are not taking into account die swell.

When printing with a 3D printer hot plastic is forced through a nozzle, which leads to the expansion of the material. The result is, that with 0.4 mm nozzle and 0.4 mm intended line width, the material will actually deposit some fraction of a millimeter wider. In your test case, that is 0.22%. If you'd print a double-sized test piece, I expect 0.11%, and in case of a half-sized 0.44% - in other words, it is a static offset.

Because of this, it is usually better to demand wider lines than the nozzle is, forcing the die swell effect to become negligible in the wider line. I managed this with about 110% of the nozzle width on my machines.

Further Reading: Why is it conventional to set line width > nozzle diameter?


Making a 3D printed surface easily cleanable

There is a huge difference between "Certified food -safe" and "is actually perfectly safe for you to use at home" . – Carl Witthoft Sep 18 '18 at 14:54

Regarding certified food safe I point to Ender 3 is capable of food safe printing? - you probably can't get the certification with a 3D printer, but, as Carl said, you might manage a pretty safe at home. So let's assume you go for that.

To make a surface easily cleanable, it is best to make sure that the imperfections of the print are filled up and that there are no undercuts that are not easily cleanable. If you need it smoothed, do it mechanically (e.g. sanding)! Heat or chemicals as a smoothing method are to be avoided, as they can damage the print and accumulate the chemicals used in smoothing in the plastic from where they are released over time.

To make the material both smooth and more safe at the same time, a generous coating with a food-safe lacquer or similar coating would be possible. This also might alleviate the problems with possibly having contaminants in the printing material - we don't know always what is in the printed plastic.


3D printing source material and superglue

CA glue works on PLA, especially if you're gluing parts that fit together rather than small surfaces that just touch, but I'd encourage you to consider alternatives just because there are so many more ways to attach things when you have freedom to design the parts, and non-glue approaches admit disassembly, repair, etc.
Some possibilities include:

snap fits
parts sliding into grooves
threaded holes and bolts
threaded interfaces.


XYZPrinting printers use a .3w file format vs GCode on all opensource printer designs.  I have used Simplify3D since the first month I obtained my Da Vinci Pro 3 in 1 which also has WiFi enabled.

Simplify3D does not connect very well to my Da Vinci WiFi so a 25ft ActiveUSB extension makes the connection for uploading and monitoring the progress of the print.

All the XYZPrinting Da Vinci series are available on the printer configuration wizard if not then sending a request to Simplify3D will obtain a response with the printer configuration file.


Removing test print from magnetic flexible paper coated build plate

You could try freezing your bed with cooling spray around the print and then wait some seconds and try peel it off.
I had the problem once on my PEI sheet and it did help. I used this spray: Spray
But make sure you don't break any electric parts on your printer.


Resin basics
Resins are tricky, but probably less tricky than FDM as the manufacturing process is much less likely to include contaminants in the shape of contaminated air, particles, or adding lead into the print. This is all due to the whole process of creating the polymer happening under the protection of the resin, which in its monomeric liquid state is so toxic that it is unlikely any bacteria can survive in it. But before going out on a spending spree, you need to be aware that there are basically 3 kinds of resins on the market, only one of them is for SLA. To know exactly what you get you'd need to read the MSDS, which is usually available by the manufacturer of the resin.

Two-component resins as you found in the lower half of the question. You might know them as Epoxy or Polyurethane resins. They have a base material and a hardener, sometimes called Component A and B. If mixed perfectly, they cure fully, neither hardener nor resin remains. This means it is chemically inert.
Air-curing resins. These two come as Polyurethanes and also Acrylates and you might know them better under the terms paint, lacquer or coating.
Light-cured resins, as you find them in SLA resins and all coatings that are not air-curing. These are for SLA a strange chemical mixture of a photoinitiator and then some monomers that create a copolymer while coatings can be as easy as having some initiators and the rest is a single type of monomer.

Food safety?
There are some resins is on the list of FDA approved plastics for food contact. The list is exclusive: if your plastic doesn't fit one of the listed ones, you can not use it. One example would be polyacrylate, which is defined as being "formed by melt polycondensation of bisphenol-A with diphenylisophthalate and diphenylterephthalate" - which excludes any other method of getting a polyacrylate and it prescribes exactly what basic materials are allowed.
As a result, many two-component resins and light-cured resins that don't match the exact chemistry and method to create an approved plastic/coating will not match the FDA approval list and won't get approval on their own.
Coating
But there is often a way out by applying a proper coating, for example with a sufficiently thick food-grade Polyurethane coating for dry foods. This would render the item food safe under FDA standards for the approved appication. You'd need to adhere to the proper method to apply this coating (manufacturers add those to the labeling usually), which can at times be somewhat complicated.
Insert
Another way might be to add an insert that does follow FDA standards, for example, a steel cup for liquids.


Should you use hairspray on a metal bed 3D printer?

I have been using a sort of a very strong hairspray called 3DLAC for about 2 years directly onto the aluminium heat bed of the Anet A8 printer I have.

Basically, all those sprays contain copolymer constituents, PVA (PolyVinyl Alcohol), Vinyl or Acetate.  These are also found in  certain glue sticks or wood glues. For me this spray works perfectly! On day one I assembled the printer, the paper tape tore and I was too anxious to wait for new tape to arrive. This worked so well that I have not changed it for that printer.

Cleaning is very easy as PVA or any of those constituents are solvable in water, so a moist cloth or paper towel over the plate is all to clean it. Furthermore, you do not require to spray before every print.

To answer your question if you should use a PVA based spray like hairspray directly onto the metal build plate is a matter of preference, but you definitely could use it as I have been doing it for about 2 years.

To address the comments:
I spray the heat bed platform whilst it is attached to the printer. I do pull it forward and gently spray the bed or just the location where the print is going to be build. Note that you do not need to do that for every print. I recently did notice very little spray on the X guide rods (maybe I have been careless once or twice), but that has not been a problem for my Chinesium iGus ripoff plastic bearings. It is very easy to clean with a damp cloth. It also works great on the glass bed of my Ultimaker 3E, but I usually (unless when I'm lazy ;) ) remove the slate of glass before printing. You could consider shielding the rods with a piece of paper, but it has not been necessary for 2 years.


Are parentheses allowed within a G-code comment?

This is not universally valid G-code, and how it is handled depends on the implementation. You can use this style of comment on some machines, but not all.

The way parsing used to be implemented in Marlin (a very common 3D printer firmware), it would work fine unless the comment string included a X, Y, Z, E or F character. The parser simply looks for the first occurrence of X/Y/Z/E/F and then tries to parse the bit of text appearing after that character into a number. If the string cannot be parsed as a number, it defaults to 0 instead. For example,

 G0 (Some comment containing the character Y) Y10 Z-5

would be interpreted as G0 Y0 Z-5 and not as G0 Y10 Z-5, because ") " (the string appearing after the first occurrence of "Y") does not parse to any valid number. Your example happens to work fine because the comment string doesn't contain any special characters.

Marlin does support end-of-line comments, which should start with a semicolon and continue until the end of the line.

This is how it used to work in older Marlin versions. Newer Marlin versions have a more advanced parser, but it still would not play well with these parentheses-style comments. It is best to avoid them, as compatibility is not guaranteed.


Ender 3 distance between nozzle and bed changing on Y-axis

Your video shows that your bed seems warped somewhat.
Ammount of error
As I assume you did level the bed with a sheet of paper to be 0.1 mm thick, we can estimate the change of thickness. The thickest point seems to be 0.2 mm, the thinnest 0.05. that's in average an error of 0.075 mm for the first layer. If you can live with that, no need to touch it.
Fixing the issue
Basically, if the error is too large for your liking, you need to fix it. To fix it, there are pretty much 2 ways. Remember that the Ender-3 uses 24V when ordering parts!
Fix the part or install a replacement part
If you feel like you need to get it even flatter, you'll need to try to flatten the bed mechanically or replace it. You'll need to be comfortable to remove the BuildTak-clone surface, then remove the leveling screws, open the electronics enclosure, remove some hot glue, unhook the bed.
Then you will need to flatten the bed in some way (grinding the upper side perfectly flat or bending it, replacing it for an entirely flat one).
Then reinstall it, going through the uninstallation backward, and add a new build surface on it.
Switch to alternate leveling method: Mesh Bed Leveling
If you consider yourself to be able to do some intermediate to advanced modification of your printer, you can change the hotend carriage to one that allows mounting a distance sensor and changing the firmware to mesh-bed-leveling.
You'll need to get an induction or capacity sensor (common operation ranges for those are 6-36V, so perfectly fine with 24V) and some way to couple that to the board, most likely an optocoupler. Print a new mounting for sensor and fans.
To install you open the electronics compartment, hook up your chosen 24V-5V coupler as extra to the Z-switch, hook the power supply of the sensor up and run it up to the printhead. Replace the mounting for the hotend cooling fan and part cooling fan and change your firmware. Calibrate the height of the sensor to trigger correctly.
I did flash a bootloader via the ISP on my ender-3 since then, so I can just flash the new firmware via a direct connection.
Last words
In either way, after fixing, you should run a PID-tune on the machine.
Thermal Runaway might or might not be active, depending on your firmware iteration, so you should update it anyway, which might make Mesh Bed Leveling the slightly easier way to go.
This has nothing to do with the bed carriage wheels, as the bed hangs onto the carriage only via the screws in the corners.


This looks a bit like your build plate isn't level. I'd suggest re-leveling using feeler gauges.


Is there a well-tested Ender 3 printer profile for PrusaSlicer available for download?

Open PrusaSlicer, go to Configuration -> Configuration wizard, then go to page named "Other Vendors", tick the checkbox next to the name "Creality", then click "Next" at the bottom right of the window. A page with a handful of Creality printers should appear including Ender 3. Tick the checkbox under Creality Ender 3. Then click "Finish" at the bottom right. The profile should appear in the selection.
It imports various print settings (from 0.3 mm to 0.08 mm I believe) as well as some basic material presets. You can import more materials by just going to the "Filaments" page in the Configuration wizard and ticking the desired options.
The profiles are tested by PrusaResearch themselves I believe and I think they are based on other profiles found online with some tweaks and adjustments to better fit to PrusaSlicer.
I am using PrusaSlicer 2.3.0
Here is an image, what it should look like. Your colors might be different, I asume you are using Windows, wheras I am using Linux Mint.


Is there a way to get more horizontal coverage out of "Vase Mode" in Simplify3D?

Version 4 allows you to have multi-process vase mode prints -- do the vertical surfaces in vase mode, then switch over to normal mode for the horizontals. This lets you have the best of both worlds in the same print. :)


Makerbot Replicator 2X - restarts after heating

"Im guessing its the mightyboard or the power pack."

Right track there.
Usually this symptom suggests your heaters are overtaxing your power supplies.
Since you swapped extruders already, the heating elements and sensors in those are not likely to be an issue.  That leaves the bed heating element and power supply.

A resistance measurement can help rule out the bed heater but since it works without the extruder, its probably not a severe issue there.

If I had to guess, I'd say power supply.  If you can, rig up a meter to measure its output and cause the issue.  If the voltage drops drastically in tune with your screen going dark, try to replace with a beefier (higher amperage) one.


Automatic bed leveling probes outside of bed despite NOZZLE_TO_PROBE_OFFSET

The problem is that, although you have set the offsets correctly, the boundary limits for the probe to "probe the area" have not been adjusted. It is my belief that this is a flaw in ABL of Marlin 2.0.x. If the user has set the probe offsets, the firmware already knows that the probe area is limited!

This answer on question "How to set Z-probe boundary limits in firmware when using automatic bed leveling?" describes in detail what the boundaries of the probe are for Marlin firmware 1.1.x and 2.0.x.

Basically, you need to set the boundaries of the probe using some extra definitions in your Configuration_adv.h file:

  constexpr int nozzle_to_probe_offset[] = NOZZLE_TO_PROBE_OFFSET;
  #define PROBE_X_OFFSET_FROM_EXTRUDER nozzle_to_probe_offset[0]
  #define PROBE_Y_OFFSET_FROM_EXTRUDER nozzle_to_probe_offset[1]

When including the MIN_PROBE_EDGE this means that the area is defined as:

  #define MIN_PROBE_EDGE_LEFT (MIN_PROBE_EDGE)
  #define MIN_PROBE_EDGE_RIGHT (MIN_PROBE_EDGE - PROBE_X_OFFSET_FROM_EXTRUDER)
  #define MIN_PROBE_EDGE_FRONT (MIN_PROBE_EDGE)
  #define MIN_PROBE_EDGE_BACK (MIN_PROBE_EDGE - PROBE_Y_OFFSET_FROM_EXTRUDER)

(Since the offsets are negative in your probe setup, we need to subtract the values in order to add up the absolute value to the edge...)


What causes ripples on part of first layer?

First layer rippling is usually caused by a too low of a first layer height (for the amount of extruded filament).

Are you sure that:

Your bed is leveled as good as possible, and
the initial height between the nozzle and the bed is correct when Z=0 (A4 paper thickness, when moved should be giving some drag), and
the bed is flat. (This is most probably your actual problem!)

To minimize the effects, you could try to:

increase the first layer height, or
set an additional Z offset in the slicer, or
reduce the filament flow for the first layer, or
install an automatic bed leveling sensor, or
perform a manual bed levelling mesh procedure (if you have Marlin Firmware).

This usually helps fighting these ripples.


When dwelling G4, my printer is oozing, how can i stop that?

Ooze is virtually unstoppable. This becomes apparent once you understand why an nozzle oozes. As the filament melts, its viscosity drops and the free flowing filament slowly makes it way out of the nozzle due to the action of gravity (and sometimes thermal expansion). If you make the throat air tight then you can use air pressure to keep the plastic from oozing out. Further you would have to immediately turn off the heat to the nozzle and cool the nozzle as fast as possible (possibly with a blower). Even if you retract the filament all the way out of the throat, there could still be some plastic left inside that will ooze out.


Printing multiple prints stacked on top of each other

If you can get it to work reliably and with decent quality, it would be a good solution. However, you might find it unreliable and the bottom surfaces of the objects might not turn out very nice (as is usually the case with overhangs that needs support). How well this will work is strongly dependent on the object being printed, and this probably will only work for a very small class of objects.

You don't gain much by doing this, as printing multiples "at once" isn't much faster compared to printing them sequentially (that is, if you have time to check on your printer and reset it between prints).


There seems to be an issue with these cheap controllers with the timing.
With reference to the next reported issues:
https://github.com/MarlinFirmware/Marlin/issues/5703
https://github.com/MarlinFirmware/Marlin/issues/5720
Add these 3 lines after the #define ENDER5_PLUS in the firmware files:
#define ST7920_DELAY_1 DELAY_NS(250)
#define ST7920_DELAY_2 DELAY_NS(250)
#define ST7920_DELAY_3 DELAY_NS(250)


PMMA print distortion and inconsistencies

Commercial PMMA may soften already at 85 °C.
The higher you go away from the bed, the colder the air is, so the issues solves itself.
Try lowering the bed temperature, at least to exclude that as cause.
The second cylinder shows the very common issue related to uneven cooling. Probably your part cooling fan is blowing only from one side. Try using a better fan shroud or add a second part cooling fan.


Bolt hole terminology for "tight" and "loose" bolt holes

A hole designed for a screw/bolt to slide freely through is called a clearance hole. A hole that is designed to be tapped could be called a pilot hole.


What is the best 3D modeling software for a beginner on a 3D printed mini barrel project?

Your question begins in an inappropriate format for StackExchange, but you've ended it with one more appropriate by asking if Blender would work.
If you are willing to take the time to learn Blender, you are certain to discover that it will do as you require, and much much more. Your referenced model could be created using engineering-type design software such as Fusion 360 or SolidWorks or many of the free packages, but the free-form aspect is more suited to the flexibility of Blender.

2020 UPDATE: Fusion 360 now supports a sculpt feature, which combines organic modeling with the engineering-type for which it is previously known.

Even though Blender is not an engineering-type program, it has internal support for precise modeling. Should you learn to use those features, you get the best of both types of software.
If you construct your model in the software in segments/pieces as you suggest, your result will have greater flexibility at the printing stage, specifically with respect to color and filament choices. Instead of wood-colored sides, you can use wood-simulated PLA filament! Depending on the printer at the library, you could also use filamet, a filament containing 88 percent metal for the hoops.
I use Blender for some aspects of modeling, often importing the STL into Meshmixer to address things I've not yet learned in Blender.
I hope your reference to 5 liter is the original size and that your model will be a miniature of it. A 3d printer with 5 liter capacity would be a wonderful asset at the public library!


PID autotune fails 'Temp too high' with 12 V heater cartridge but works with 24 V?

It is all about resistance.

This requires some formulae:

$U = Voltage$
$I = Current$
$R = Resistance$
$P = Power$

$U = I \times R$

$P = U \times R$

$ R = \dfrac{P}{I^2} = \dfrac{U^2}{P} $

The 12 V, 40 W cartridge has a resistance of about 3.6 Ω.

If you use this cartridge at 24 V, this caculates to a power of 160 W!

This means that there is an enormous influx of heat that is hard to control, hence the overshoot.


3d printer not printing circles correctly

Possible causes for the printer not printing correct dimensions:

Incorrect number of steps/mm in firmware settings
Belts are not tight enough
Pulley slips on the shaft

Looking at the picture, I would go for the first case, because distortion looks regular. Try checking microstep settings on your board, and settings in the firmware.


Tronxy Marlin boards (two of them) reboot when asked to heat bed

It sounds like a power-related problem. Always use an external MOSFET to drive a heated bed, and consider investing in a decent power supply. Inevitably, the Tronxy PSU will be barely adequate.

Edit: I've just noticed the tronxy-x1 tag. Be aware that the stock (60 Watt) PSU for the Tronxy X1 cannot power a heated bed (the printer does not have one). Trying to do so will overload the PSU and cause an immediate reset.


Through what methods and mechanisms can a multi-material FDM printer operate?

Let's look at various methods:

Multiple Hotends

The oldest version and one of the best to print materials at vastly different print temperatures (like printing a cheaper PLA infill into a Polycarbonate shell - the print temperature difference is 60-100 °C) is to have 2 or more hotends. This way also avoids the need for purging towers. It does, however, limit the maximum size of the used printbed and few 2-printhead machines are cheap.

Y-Coupler

Using a bowden setup, a Y-coupler could be used to feed the filament from 2 extruders into one hotend. On the switching tool command, E0 would pull the filament back some couple millimeters beyond the coupler and then E1 would push forward back into the meltzone. One will need a purging tower/object.

Special, multi-entry hotend

Some Hotends had been concieved that have 2 or more ways into the meltzone and the multiple extruders push along them. They generally are quite complex and hard to clean, but they allow to seamlessly blend between two filaments of the same material and create pretty much a controlled fade by precisely directing how much of either side is used on any layer. For clean cuts, a purging tower is necessary.

Splicing filament

This is what the Palette 2 and the Prusa MMU do: they push pieces of filament into a feeder tube that then are consumed by the printer via its own extruder. If they melt the filaments together like in the PAlette, it's proper splicing, if they just line up the next filament piece without merging into a spliced filament it's more like instant color switching.

This method is good for multi-color prints or using materials that have the same or similar1 melting temperatures. It might or might not need a purge tower/object to get rid of the residue in the zones between the filaments.

This could btw also be done manually but should be avoided.

1 - or rather not too dissimilar, if the slicer is set up to do it right. By setting up the slicer cleverly, one can have the extruder retract the filament, then adjust the heat over the purge tower and then resume extruding in the purge object at the changed temperature. PLA/PVA from a Prusa MMU is known and advertised to be doable, PLA/ABS might be possible this way. For extreme dissimilarities like PLA/PC (60-100 °C) I have my doubts though.

Usability

All of these variants are basically viable, but some have benefits over others. Service is in this comparison meant as repairing a broken extruder, maintaining as the operations needed to keep it in printing order.

multiple fully independent hotends is among the easiest to services. It could be direct drive (good for flexible filaments) or bowden. It is however heavy and usually not an option for delta printers. It has a downside that you have to perfectly level two hotend nozzles to be exactly on the same height, putting it in the hard to maintain category.

multiple hotends on the same carrier is harder to service and maintain in comparison to multiple independent hotends as the components are very close together. Especially nozzle height adjustments can be more finicky.

Y-Coupler needs to be a bowden and has problem with materials that are very stringy. That makes it especially bad for flexible materials. Maintaining is like a normal hotend and servicing is almost the same.
Special hotends are hard to come by but could be available for direct drive, making them possible for flexible filaments. They are, as already noticed, very hard to service.
Splicing filament can be done with either direct drive or bowden setups. It is probaby the most convenient to use after setup and has the maintenance and serviceability of a single hotend and a fully separate machine. Their biggest downside is price and setup time needed.


I am not too sure what you're searching for, but I imagine it to be a kind of thermistor housing to distribute pressure from the screw while maintaining good heat conductance.

I first have to say that I'd be afraid to damage the glass droplet of the typical thermistor design by putting pressure to them, especially including later thermal expansion. However, I never tried and we might find some valuable experience on that in other answers here.

If what I assumed in the first paragraph is true, I would suggest forming some housing yourself with copper foil or copper sheets, since the heat conductance of copper is good and it is more or less soft.
However, as a more simple solution, you might just cut the metal part of a 'wire ferrule', if you got some lying around. (Wikipedia has no english article for this, so I link the german one for the images: Aderendhülse)

Additional info: Can't you clamp the thermistor the way it is done in the E3D V6 hotend, see this image?

Thermal contact should be quite good and you don't have any problems which could lead to damage of the thermistor.


Looks like under extrusion, here's a extreme example.

I would check your feed rate by marking out 100 mm on the filament then manually extruding 100 mm. You can use this to verify if you are under extruding due to your feeder. If you find that the printer only fed say 90 mm when you asked for 100 mm, you will need to change your feed rate in Cura to 110 %.
If you confirm that the printer is pulling 100 mm through when you manually ask for that much, then it could be a combination of speed, cooling & jitter. I would slow down the print speed and see if it improves the print quality. I've experienced issues where the nozzle is moving fast around small bends and wobbling slightly, the filament is struggling to land on the previous layer and the resulting effect looked a bit like your photo.
I can't think of anything else that might be causing this issue.


How long can you leave filament in the extruder

Most filaments you can leave in the extruder indefinitely without any ill effects.

There are some filaments that need to be stored away from moisture, particularly Nylon, because they absorb moisture from the air and don't print well if they contain a lot of absorbed moisture. However, this isn't an inherent issue with having the filaments in the extruder (if you had some setup that protected the filament from moisture while in the extruder, that would be fine as well - but in most cases it is more practical to store such filament in an airtight box).

Most commodity filaments (ABS/PLA/PETG) don't suffer from this as much (PLA supposedly also absorbs moisture but I haven't noticed this to be a problem, perhaps it depends on the conditions of the room in which your printer is kept) so they're fine to leave in the extruder.


Do hygroscopic filaments (PVA, Nylon) absorb moisture while in a heated enclosure

The concept that relative humidity decreases with an air temperature increase runs consistent with the concept of using a food dehydrator to purge moisture from filament spools. As the filament heats up, energy is imparted to the water molecules within. The dryer air around the spool will accept the moisture and "distribute" it to the environment. A warmed enclosed chamber will not have much humidity to endanger the filament.
I have a Sigma R16 and have moved the spools to the outside of the enclosure, but I don't plan to print hygroscopic materials in the near future. I suppose I'd have to build some form of drying enclosure around the spools, particularly for nylon and PVA.
My Qidi3D X-Max has both internal and external spool mounts and it is recommended to use the internal mount for nylon, as even an hour's exposure to humidity can deteriorate print quality.
PLA is safe for days, ABS is safe for perhaps less, but PVA is not a good overnight exposure material and nylon is definitely an inside-the-box condition.
I suspect that having the filament inside your Sigma, especially if you plan to fully enclose it, is not going to be problematic. I created a front panel for my Sigma to reduce ABS warping and the internal temperatures reached 37 °C. That's warm enough to keep the water clear of the filament, unless you have an extremely humid environment.
Before you add an additional heater, consider to place a perforated container of color-change desiccant inside the build chamber and observe over time the color change. Obviously when not printing, seal the desiccant from collecting non-test humidity, but I think you'll find it's pretty dry while you're printing.


Yes this is possible. For an FDM/FFF printer, you'll need to print with supports. I might also recommend printing in PLA to minimize the chance of warping during the print (from experience).
It might also help to slow down the feedrate to ensure smooth surface finish and avoiding delamination on such small layers.
You'll probably see a decrease in the surface quality on the inside due to the printing of support scaffolding depending on the slicing engine you use.
However
You'll want to pay attention to the strength of the case. If you print the case upright then it will be more susceptible to breaking without post-processing.
Conclusion
Ultimately, if you can get away with it, it would be better to subtract the star instead of extruding it in the model. Then you can simply print the case back face down on the plate with much better results.


One technique is to add your own custom brims to the model. A couple of "Mickey Mouse ears", attached to each end of the piece, may be enough to keep it in place (and will also be easy to remove).


As the filament in the melt chamber heats up, it's going to inevitably ooze a little bit.  Make sure you watch for this and clean it off as the hot-end heats up, and setup you slicing software to print a skirt, which will print a few loops around the outside of your print, separated by a few mm, to deal with ooze and get filament flowing properly.

If it oozes a lot, try reducing your print temperature a bit.


This sort of failure is best diagnosed by observing the failure. It probably isn't underextrusion, there is no reason to get variation in extrusion just along one edge.

Did you really get a proper vase-mode? You can check in your slicer, or with gcode.ws and make sure that each layer only occupies a fraction of the part, with many small steps (rather than one step after printing a slice of the whole part)

It seems the failure is close to a sharp transition in the wall. Have you got enough cooling, or a low enough extrusion temperature? It could be that the plastic viscosity and surface tension are conspiring against the shape. Printing slower might possibly help too (both on the failure, and to allow the part to cool between layers).

Finally, you might have a mechanical problem which is interfering with the print just at this point, and that might include the extruder binding in some way. This could be hard to spot during the print, so check over all the moving parts, and all the fixings.


Filament lifts from the hot bed while printing

Check the following:

Is the print bed clean? On glass, you can use a few squirts of window cleaner.
Is the print bed actually reaching the correct temperature?
Have you manually calibrated the printer (at both the center and the edges), such that you can just about get a sheet of paper between the print bed and the hotend nozzle, at z = 0? This last check ensures that the first printed layer of extruded filament is actually touching and "presses on" to the print bed. See the video #18:Calibration for a great explanation on the use of the paper. Whilst this video is for a Delta printer, it clearly demonstrates the height that the zeroed print head should be at, and how to check using a sheet paper.
Maybe the filament, for the first few layers, should be heated at a high temperature, than the rest of the print, to ensure adhesion.

If all of the above are checked and OK, then (as electrophile points out in their answer) try making the print head more grippy. This can be achieved by simply adding a thin coating to the glass with one of the following:

Wiping the glass with a glue stick or wood glue
Using hairspray

Both use PVA as an adhesive/stiffener.

Or by adding an additional print surface, such as:

Using blue painters tape
Using PEI tape
Using Kapton tape
Using BuildTak

If adding tape, then the printer may require a small re-calibration, due to the thickness of the tape adding a few microns to the print bed height. This can be done in the firmware.


What are the downsides of high stepper current OR power?

There is a downside.

If the current is too high, you lose the linearity of micro-stepping.  If the highest current exceeds the maximum, then the highest current micro-stepping positions will collapse on each other.

If you are within the specs of the motors, there are no motor-related problems caused by higher currents.

But other problems can be caused by increasing the current.  The current must be within the capacity of the motor drivers and their heat sink.  If the drivers overheat, many will simply shut off, causing the motors to not move when they should, which will appear as misalignment on X, Y, or Y.

Another problem could be higher vibration, which would show as stronger ringing when going around corners.  The higher current will give higher torque and higher acceleration, which will cause more vibration.

If you are increasing the current to support a bigger and heavier print bed, you will possibly have other troubles.  Although the higher torque will be countered by the higher bed mass, the higher bed mass may be coupled with longer belts, which will be more stretchy.  You may also be imposing forces over longer frame components, which may cause them to flex more.


Auto bed leveling with BL Touch sensor crashing to bed

As it turns out, my Z-axis carriage mount to the X-axis was bent, causing the nozzle to touch the bed before the proble could get a chance to detect anything. Manually bending it back to the correct angle solved the problem.


Custom 3D printer printing dimensions has changed because of a .gcode file

Your printer is an Ultimaker clone or something else?  All of the original firmwares located on TinkerGnome's Github are configured for Ultimaker printers so if you are using them on something different you will need to configure it before using it.  The easiest option would be editing this print file that changed your settings to your desired settings and then reloading it.

How to find your actual Z? Well that's a bit difficult without more information.  I'm guessing from your description that your printer homes at Z max?  If it's homing at Z max you need to home the machine, jog the Z axis to where you want 0 to be (usually using a piece of paper between the nozzle and bed), then record the Z axis position and enter that as your travel limit in the firmware.  If your printer homes at Z min this could be as simple as changing the homing offset.


Steppers stuck with Klipper but work with Marlin

It seems the pinout scheme changed on the Creality board between the versions V4.2.2 and 4.2.8. For example, PB9 & PC2 were inverted between step_pin and dir_pin.
Using the following Klipper config (found here) allows the motors to do their job again.
[stepper_x]
step_pin: PB9
dir_pin: PC2
enable_pin: !PC3
step_distance: .0125
endstop_pin: ^PA5
position_endstop: 0
position_max: 235
homing_speed: 50

[stepper_y]
step_pin: PB7
dir_pin: PB8
enable_pin: !PC3
step_distance: .0125
endstop_pin: ^PA6
position_endstop: 0
position_max: 235
homing_speed: 50

[stepper_z]
step_pin: PB5
dir_pin: !PB6
enable_pin: !PC3
step_distance: .0025
endstop_pin: ^PA7
position_endstop: 0.0
position_max: 250

[extruder]
max_extrude_only_distance: 100.0
step_pin: PB3
dir_pin: PB4
enable_pin: !PC3
step_distance: 0.010752
nozzle_diameter: 0.400
filament_diameter: 1.750
heater_pin: PA1
sensor_type: EPCOS 100K B57560G104F
sensor_pin: PC5
control: pid
# tuned for stock hardware with 200 degree Celsius target
pid_Kp: 21.527
pid_Ki: 1.063
pid_Kd: 108.982
min_temp: 0
max_temp: 250

[heater_bed]
heater_pin: PA2
sensor_type: EPCOS 100K B57560G104F
sensor_pin: PC4
control: pid
# tuned for stock hardware with 50 degree Celsius target
pid_Kp: 54.027
pid_Ki: 0.770
pid_Kd: 948.182
min_temp: 0
max_temp: 130

[fan]
pin: PA0

[mcu]
serial: /dev/serial/by-id/usb-1a86_USB_Serial-if00-port0

[printer]
kinematics: cartesian
max_velocity: 300
max_accel: 3000
max_z_velocity: 5
max_z_accel: 100

[display]
lcd_type: st7920
cs_pin: PB12
sclk_pin: PB13
sid_pin: PB15
encoder_pins: ^PB14, ^PB10
click_pin: ^!PB2
```


Switched to a Bowden setup. Should I retract the filament out at the end of a print?

It's okay to leave the filament in the hot end, as long as you let it cool down with the hot end cooling fan running.

From comment:

  That's not an issue, you can simply leave it in the hot end. The only "end of print" clogs usually occur when leaving the hot end hot for a while - allowing the filament to drip out - and then retract the filament without feeding it against the nozzle once more. That creates a plug that's larger than the filament diameter that might get stuck in the bowden tube


What are the long term material properties of VeroWhitePlus 3D printer material?

In our experience, the parts will continue to cure. I don't have the chemical science background to provide proof or evidence, but I operate from an assumption that if the part requires UV rays to cure, it will continue to be reactive to UV rays after it is considered "cured".

I too have found the same brittleness over long periods of time. The only experience I have with the moisture issue would be a small component designed and built for a cable pulley in the tail section of an aircraft as a temporary solution (acting on a non-critical trim control surface). The aircraft is based down here in Houston, Texas where we get some pretty gnarly humidity. The part did begin warping after a few months but we don't have definitive information indicating it was a moisture problem, or something more structural.

I do know however, that if you aren't absolutely meticulous about cleaning ALL of that gelatin-like support material off of the part, it does wind up being more susceptible to slight deformities, and when you DO remove it all thoroughly,  it is then slightly more susceptible to the brittleness issue. Not sure if I'm the only one finding this, and apologies for not having the chemical background to provide more quantitative support.


How to log more than 300 lines of the OctoPrint terminal?

Yes, you can show more than 300 lines in the terminal; just disable auto scrolling (reference).

  Disabling Autoscroll now completely disables cutting off the lines (so
  you can have way more than 300 lines while that's disabled), filtering
  has been improved too and doesn't cause scrolling anymore.

Note that with disabled autoscrolling, you will be able to see more lines up to the point that the buffer is full. If you need even more lines to monitor, just enable the logging the data to file serial.log. If you open the options page (OctoPrint Settings), just tick the box for "Log communication to serial.log" under "Serial logging" of the "Serial connection" options.

This serial logging file is typically used for debug purposes, but as can be read from the options, it comes with a warning:

  While this can negatively impact performance, a serial.log can be
  incredibly useful for debugging any issues observed in the
  communication between OctoPrint and your printer.

You can either access the log file through the OctoPrint options/setting through the "Logging" options tab, or direct download/copy from the logging directory:

  on Linux: ~/.octoprint/logs
  on Windows: %APPDATA%\OctoPrint\logs
  on MacOSX: ~/Library/Application Support/OctoPrint/logs


The easiest way to freshen up filament is hot air, although there are other options.

There is an optimal melt processing moisture level for every plastic, typically in the range of 0.1-0.2% water content by weight. But the equilibrium moisture content of most plastics in humid air can be more like 1%. As a consequence, hot air dehydration is standard practice to prepare plastic pellets for extrusion in industry. Pretty much every injection-molded and extruded plastic product in the world -- including 3d printer filament -- is made with pre-dried pellets. Hot air is blown through the pellets until they are below the moisture limit.

Different plastics tolerate extrusion with different amounts of moisture, and absorb different amounts of moisture. They can also tolerate different drying temperatures. So the ideal storage and drying conditions vary by material.

PLA absorbs relatively little moisture, but in humid environments can accumulate enough water content to cause steam bubbles during extrusion. In some cases, steam bubbles can contribute to hot end jamming. Extreme wetness has been known to cause swelling that can increase filament feed drag. It's arguable whether wetness actually causes brittleness, or if that is a separate aging issue. People who keep their homes below ~50% relative humidity usually don't have any problems. Leaving PLA in a dry environment for a week or two should adequately re-dry it, or it can be gently heated to about 120F / 50C for a couple hours. (Some people dry it hotter. but that risks deforming the filament.)
ABS also doesn't absorb very much water, but perhaps a little more than PLA. It also experiences steam bubbles, but that's typically the only issue. Homes below ~45% RH usually don't have problems. Storing ABS with fresh silica gel for a couple weeks will dry it. Or it can be oven-dried up to about 180F / 80C for an couple hours. HIPS can be treated the same.
The kind of PET used in plastic bottles is rapidly degraded into tar by hydrolysis when melted with any significant water content. So PETG filaments are specially blended to absorb less water and to be less damaged by water than PET. But there is still the possibility of bubbles and cloudy strands due to steam expansion at higher temperatures, and there is some evidence that wet PETG produces weaker, more brittle prints than dry PETG. Different manufacturers' blends require different conditions: some people report Taulman t-glase needs oven-drying and careful storage while Esun PETG is fairly tolerant of normal home humidity levels. Oven-drying at 150F / 65C should work well.
Nylon absorbs a huge amount of water, which causes it to swell considerably, produce massive steam bubbles, look cloudy, warp more, and adhere less than properly-dried nylon. It's nearly unprintable when wet. It should be oven-dried at around 150F / 65C for 4+ hours -- desiccant will not strip enough moisture from it. In fact, nylon will pull water out of used silica gel! Once dry, it should be stored with an aggressive desiccant (either bone-dry silica or preferably calcium chloride). It only takes a few hours of exposure to air for it to become excessively moist. Building a sealed drybox feed system is highly recommended to avoid exposed time during and between prints.
Polycarbonate is similar to nylon in that is is an aggressive water-absorber. It will look cloudy, produce steam bubbles, warp more, and provide very poor layer bonding when wet. It should be oven-dried at 180F / 80C if on a plastic spool (up to 250F / 120C if dried alone) for 4+ hours and then stored in a drybox with aggressive desiccant just like nylon. Note that some modern PC blends like Esun ePC are less prone to water absorption, at the cost of some decrease in mechanical properties.
PVA is basically destroyed by airborne humidity, since it literally dissolves in water. Store in a drybox with an aggressive desiccant at all times.

Composite filaments should be treated like the base material.

Some drying and prevention options:

Oven: The "warm" setting will usually work pretty well. Let the oven preheat and settle out for a while, and measure temperature with a good oven thermometer or thermocouple. Shield the filament from direct radiant heating and hot spots with aluminum foil, cookie sheets, etc. Electric ovens will dry faster than gas ovens, because burning natural gas produces some additional moisture. Do not leave the oven unattended if using temperatures above the glass point of the filament, or bad things may happen!
"Light bucket": A 5-gallon plastic bucket with an incandescent lightbulb inside is a pretty effective way to gently warm low-temp filament like PLA for drying or medium-term storage. Leave the lid slightly open if drying.
Food dehydrator: Works great. Set temperatures as per the oven temps above. The main challenge is getting a large enough space inside for a filament spool.
Desiccant: In order for desiccant to actively dry filament, it must be significantly more attractive to water than the filament is. And affinity for water is a function of how wet the material already is. That means dry desiccant can easily pull some water out of very wet filament, but wet desiccant can actually give water TO the filament! Rechargeable indicator desiccant (such as an Eva-Dry E-333 unit) is ideal. It's also important to have ENOUGH desiccant: silica gel can only absorb 10% of its weight in water at 20% RH. That means to pull 1% moisture content out of a wet 1kg spool, you would need to start with at least 100g of bone-dry, fresh-baked silica! "Used" silica is basically useless, it already contains too much water to pull any more from the filament. But you can re-dry the silica in an oven. 250F / 120C for 6 hours should be safe for all types of silica gel, but more aggressive drying (including microwave drying) is possible for some silica gels. Follow the gel manufacturer instructions.
Rice: Does not work. It's basically a myth that rice has drying power. A bag of rice you buy at the store is already pretty close to moisture equilibrium with the air, so it has minimal capacity to pull water from filament (or a soaked iPhone, for that matter). If you dry the rice in an oven to drive out its water first, it will work to some degree, but silica gel is considerably more effective.
Kitty litter: Silica gel style kitty litter is nearly identical to desiccant silica gel. Like rice, it is fairly close to saturated when you open the container, but can be dried in the oven to be a good cheap bulk desiccant. Clay type kitty litter is not as effective. Be careful of getting kitty litter dust all over your filament.
Dry storage A thick plastic box with an airtight seal is preferable. Look for recycling code 2 (HDPE) or 5 (PP) on the box. 5 gallon buckets with sealing lids also work fine. Ziplocks and other thin plastic bags are better than nothing, but are permeable to water (yes, really) and can only be relied on as long as there is fresh desiccant in the bag. Acrylic/plexiglas dryboxes have been sold by various people, but acrylic is very permeable to water, so I don't recommend that option.
Air conditioning: Simply keeping the air in your printing environment reasonably dry will protect PLA and ABS and other low-absorption filaments. It may help to buy a humidity monitor to get an understanding of your ambient humidity.

Now, considering the original question here, it's important to note that moisture content is not the only way filament can age or be damaged. PLA in particular is prone to becoming brittle over time. There are different theories for why this occurs. One is gradual chemical aging because poly(lactic acid) simply is not a very stable polymer. Moisture could contribute to that aging process, but true chemical aging would be irreversible even if the filament is later dried. How much this occurs should depend on the specific polymer blend and storage conditions.

Another theory for PLA aging is that the residual filament extrusion stresses (from being drawn down to the correct diameter and rapidly quenched in a water bath) are slowly creeping over time. Anyone who has placed a PLA part under heavy load for more than a few weeks will see PLA creep. It's a rather odd polymer in that it will "creep to failure" and crack at very low creep elongations rather than progressively deform in a ductile manner like most creep-prone materials. So if the PLA has significant stresses locked-in from the initial extrusion process (which is very common) it may be creeping into a more brittle arrangement of polymer molecules over time. That would explain the aging effect, and it would explain why "drying" sometimes rejuvenates the PLA: heating the filament near its glass point will allow the polymer molecules to gently relax and basically anneal to a less brittle state.


Entwined fiber-filled filament stops extruding after a few layers

I've managed to get a successful print! The key was to keep the material moving quickly. The settings I've customized are as follows:

Print Speed: 70 mm/s
Layer Height: 0.4 mm
Default Printing Temperature: 215C

...and perhaps not as necessarily:

Shell Wall Thickness: 0.8 mm
Wall Line Count: 3
Alternate Extra Wall: True

Also, I've found it important to print a skirt (perhaps a double-walled one), and watch the first-layer closely and be willing to push more material through and restart: The material in the hotend can easily form a partial clog while the printer runs through its auto-leveling / head-cleaning routine, thus needing to have more material pushed through before the job starts in earnest.

By the way, the model is https://www.thingiverse.com/thing:1993747, by Holodrio on Thingiverse.


From the printer...
Non-post-processed surface smoothness of a print is mainly a function of the Layer height during print: it is smoother if one reduces the height of the steps taken between the layers. A very good FDM machine can achieve down to 0.05 mm layer height, but 0.1 mm is what most hobbyist machines can achieve if well dialed in. SLA printers cure resin in layers down to 25 micron reliably and some can get down to 12.5 micron - a quarter of the best achievable FDM.
Reducing the layer height in FDM comes at the cost of mainly three factors:

Print time increases roughly antiproportional to the layer height. 0.1 mm is about double the print time of 0.2 mm and so on.
The prints tensile strength gets reduced by increasing the number of layers increases, creating additional possible weakpoints.
The thinner the layer, the more susceptible the print is to errors like clogged nozzles or variations of the filament thickness.

SLA printers are not affected by the print strength loss and the errors from clogged nozzles and can print entirely clear material without air inclusions. They are affected by the print time increase though. Usually, SLA prints come out of the vat covered in residual resin and curing them in the proper post-processing method results in this resin smoothing over the surface perfectly.
Simple Postprocessing...
Many prints can easily be post-processed.
Sanding
PLA and ABS can be easily sanded down to somewhat smooth, but you'll need to spend time and muscle grease or go electric. A sander with 300+ grit can help a lot. If you have a rotational body, you could sand the vase on a lathe.
Putty
A plastic putty could be smeared over the stepped surface to smooth it and then sanded smooth. I personally like Valejo plastic putty, as it doesn't shrink, but Tamya putty also is a good alternative, bonding strong.
Primer-Filler
Independent of the base material, using a spray coating can easily fill in the notches and crannies left behind during printing. Printing in 0.15 mm and giving it a short spray coat of primer-filler twice, sanding over rough spots between did a good job of smoothing prints for me.
Vapor Smoothing
If you chose ABS, you could use Acetone vapor to smooth over the surface of a print in almost an instant. This can achieve Super smooth results with tall layer heights, as you practically melt the plastic over, but it comes at the loss of small surface details.
Exposure time is the limiting factor here: the longer the exposure to the acetone vapor, the more the surface is smoothed and the less details remain. Think of exposure time like running the smooth filter in blender once or twice each second.

Similarly, ethylacetate or propylene carbonate could be used for PLA prints, though timing might differ from the well established "a couple of seconds" for acetone vapor. Note that these two chemicals are much more expensive.
Costs
Checking prices, I was quoted about 90 €/l for (chemical grade) Ethyl Acetate and 130 €/l for (chemical grade) Propylene Carbonate via a laboratory supply. Useable Acetone (not chemical grade) comes about 3.70 €/l in home depot. For comparison: chemical-grade Acetone comes with a price tag of about 50 €/l.
Considering that ABS filaments and PLA filaments typically price similarily,  ABS+Acetone Vapor is the least costly chemical Vapor smoothing.


Which choices do we have on Daylight Resins?

It looks like Ono may fit what you are looking for.
They have several colors listed on their site.

Red     Blue

Yellow   Black

Clear  Creamy White

They also have a flexible resin and a low temperature "casting" resin.

It is unclear if the resin is available now or if it is preorder.


How to re-program Prusa firmware to accept a taller Z axis?

A .hex file is of no use to you, because it consists of compiled firmware which is very difficult to edit. You need to go to Prusa's GitHub and download the source code. Then, find the header file for your model of printer, and change Z_max_pos to the correct value. Finally, you need to compile and upload the firmware to your printer following the build instructions (see README.md). You will need to have the Arduino IDE installed to do this.


Because my research shows that LAS files are point cloud data, you would first have to convert the point cloud to a mesh. Point clouds are just that, data references to points in 3d space. A printing service works with files that represent planar surfaces, properly joined (watertight, aka manifold) to form a solid or solid surface model.

The only resource I was able to find involves using Meshlab. There are two reasonably practical references for this process.

The first is somewhat generic and provides the conceptual information:
Point Clouds to Mesh

The second appears to be a more step-by-step method:

Point Clouds to Mesh (2)

I would expect that if you are successful in creating a mesh from your data, you would then want to use a program suitable to determine (and repair) any non-manifold portions of the model. There are many available, including Meshmixer, although the others have escaped my alleged mind at this moment.


Anet A8 extruder motor moves back and forth

Check the continuity of the wires on the cable. Sometimes, they are not crimped correctly. Another common fault is crossed wires. In either case, the easiest diagnostic test is to substitute another cable, but please note the color coding of this replacement wire to match the cable you replace.


Is it possible to upgrade the CR10-S Pro to CR10-S Pro v2?

Print recovery can be achieved by changing the firmware.

Here is some information on how to do that: Marlin documentation

Also, this another stackoverflow post about that: Stackoverflow Post