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Dual Filament Mixer Marble Effect
I'm looking for some software, that could create marble effect on product from two filaments, not just gradient, but evolving color change.
Do you know some slicer or some tool that can generate printer file like this from model?

E3D has a Cyclops product which mixes two filaments inside a melt chamber.  Clones of the E3D Cyclops can be found through the usual outlets.  E3D also has software recommendations for using their Cyclops product, which are found here.  They suggest cura as the slicer.
The RepRap firmware (and possibly others as well) allow two extruders steppers to be used in an extrusion move, proportionally mixing two filaments.
In case you want to go further, to get a broad color gamut, you will need five filaments mixed into one extrusion bead.  Cyan (sky-blue), magenta (or bright purple), yellow, white, and black filament can be mixed to make most colors.  "2D" printing is done with four colors (cyan, magenta, yellow, and black), but for 3D printing, you also need white.  2D printing uses white, but it is the white of the paper.  Black is needed to get dark colors, as well as to form neutral gray colors.
Based on the OPs comments, I understand that the software sought is a shader that creates a marble effect on the surface of a print.  I don't know of such software, but, as a software engineer, I imagine it would take roughly this form:

Slice the object conventionally, producing G-code for the object.  Identify all exterior extrusions with a special extruder number.  Multi-material slicers should provide this option (Slic3r-PE does).
Project a 2d image or synthetic pattern onto the 3D external surface of the object.
For each voxel (volume pixel) of the exterior extrusion, determine what it's color should be based on the shading.
With previously determined propagation delay from when the mix is set to when the color is extruded, back up along the extrusion path the correct distance.
Split the extrusion command at the point where the mix must be changed.  Insert new extrusion values.
Output the modified g-code.

I've left out many implementation details.
The scheme depends on how predictable is the delay (in extrusion distance) from when the extrusion mix is changed to when the change comes out of the nozzle.  The variation (if any) in that distance will make the output look jagged and fuzzy.  In some ways, that variations limits the 2D bandwidth of the color information.
Schemes that require sharp, line-to-line coherence may require a purging process.  I assume that for a marble pattern, which I characterize as having soft color changes on a scale that is larger than the extrusion width, purging on every change is not desired or possible.

I know that it mix, one of the "come in pocket" model on my printer has gradient, but I'm looking specificly for some marble shadder in 3D


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MKS Gen V1.4 won't work when connect to computer via USB
My board programmed OK using Arduino software and spoke back to me on the USB port.  I then installed it in the system.
The display worked fine selecting menu items when powered up.
However, when I plugged the USB connector in, it all went dead.
When I disconnected everything and connected up to the Arduino software, it spoke to me again.  Now if I connect it up to the power supply, with only other connection the display (Smart Controller), it seems OK, but display goes blank when I connect the USB.
Any ideas?

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Short circuit on RAMPS 1.6 board?
I have a RAMPS 1.6 board. After soldering my stepper drivers, I probed them for bridging and found a short where none should be. Digging deaper into it, my multimeter shows continuity between the 12V +/- connectors (on occasion).
I have scanned the whole board repeatedly for solder bridges, but could not find any. Are there any known weaknesses that I should look for or any specific place I should look at to repair it?

Can you switch your multi meter into Resistance measurement mode and report the measured resistance between 12V+ and 12V -

Your multimeter showing continuity doesn't necessarily mean there is a short.
All your multimeter is doing is applying a small voltage and then, if the current that flows is over a certain threshold, reporting that there is continuity.
The components (stepper drivers, microprocessor) on the board, draw current. That's normal. The current draw might be enough for your multimeter to report continuity. Because the multimeter is only using a small voltage to test (and not the required 12V), the current draw may be intermittent (not enough voltage for the microprocessor to actually start working), and capacitors getting (dis-)charged may also affect things.
The multimeter not reporting continuity is a guarantee of no short. However, the multimeter reporting continuity does not mean there is a short. The only way to find out is to apply 12V. If you use a current-limited power supply the possibility of damage if there is a short circuit is limited.

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Weird lines and smaller height
I finished my first print and it came out like this

I calibrated all my axis steps and manual movement gives perfect numbers.
I am printing with these slicer settings:

I don't even know where is the problem to begin searching for a solution. It's my very first print after a couple fails and a lot of calibration to Z axis and bed leveling.
Update the printer without the heatbed as it's an older picture:

The Z axis moves on 2 lead screws and 2 rods with bearings all of which attached to the plate.

please tell us the printer design or show a picture of it

It's a diy printer i am not near it rn to take a pic but i updated with a photo without the heatbed which is on the white plate basically

Your X belt needs more tension. Also you move a lot of weight (rods, aluminium plates, X stepper). The X belt does not power the carriage in the centre, you only have 2 bearings while you should use 3. All this adds to the (in)accuracy of the print. Also add a picture from the side please. It might be that the platform is too heavy that you are missing steps.

i will add a side picture once i go to the printer. what do you mean x belt doesn't power the carriage and how can i minimize all those errors for example if i added 3 bearings instead of 2 would it matter?

Using 2 small bearings and attaching the belt closer to one bearing may cause the carriage  to rotate and prevent smooth movement, a third bearing or a longer one prevents that. Please also explain by [edit] of your question in words how the platform moves; e.g. do you have 4 leadscrews raising the platform, how are they powered.

Ok are we talking about the same axis here: the axis with just 1 belt if yes then i dont understand where would i put a third bearing and nothing rotates there
if not then we are talking about the axis with 2 belts? and u are talking like there is just one belt so i think i am misunderstanding you a little

How do the  measured X, Y, and Z dimensions of your printed cube compare with the model? Is the Z shorter than anticipated?

yes Z is shorter by 2mm x and y are the expected sizes

I'd say that your axis aren't square, aren't tightened enough and you seem to have overextrusion as well. That would explain why all your layers are wobbly and not neatly stacked on top of each other, why your cube is far being being a cube (the picture of the X face shows it clearly) and the quality of surface finish on the top.
I do not know what kind of printer you are using, but I would advise you to check that the X and Y axis are correctly calibrated and that they're perfectly square, which would ensure that each layer is correctly stacked on top of the previous one to produce a nice cube. And make sure to tighten the axles to avoid the noise in the print due to the vibration produced by the printing.
As for the overextrusion, you'll need to make more test with your printer and the material you're using, changing temperature, and print speed until you find the right combination that will extrude just enough material through your nozzle.

Thank you i will make sure to check all of that
about the extrusion how exactly do i set that is it in marlin or is it from pronterface because it's confusing me a little

I'm sorry but I cannot help further as I do not use marlin or pronterface with my printer, thus I'm not familiar with how they work.

This looks like substantial amounts of overextrusion, I'd try fixing that problem before anything else. Change the steps/mm for the E axis in Marlin, there's extrusion tuning tutorials out there that can help you figure out how to get a good extrusion rate. Hint, you've got your steps/mm in the E axis set too high.

but when i searched regards the steps/mm every guide said cold extrude and measure the filament if it's the same number then the steps are fine and i am extruding exactly what i am giving the machine or is that can change sometimes?


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Laser LA03-5000 wiring to RAMPS 1.4
I'm totally lost. I have been searching about two days how to correctly wire Blue Laser LA03-5000 to RAMPS 1.4 board.
This laser has 12 V input and separates PWM/TTL wires. I have found out how to control laser with no PWM (just hook it to D9 same as a fan), but how do I correctly wire this type of laser? I really want to wire it correctly for safety reasons.

Please look into this question, this is a very similar question and also involves PWM and a RAMPS 1.4 shield.
In your case you connect the top red wire on the right bottom connector to the D4 pin and adjust the firmware accordingly as described in this answer.
The bottom 2 wires of the lower right connector should be connected to ground and 12 V (resp. black and red).


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Ender 3 X axis not level
I've been aware ever since I got it that my Ender 3's X-axis isn't level. Measuring from the top of it to the top of the frame, the right-hand (positive) side is about 4.7mm higher than the left.
During assembly, the vertical rails were not entirely parallel, and had to be pulled together to get the X axis on and to bolt the cross beam on the top. I suspect this is related, but I'm not sure.
Anyway, aside from the bed having to be tilted to be level with respect to the X axis, this never seemed to cause any problem, so I've left it alone until now. However I have measured almost exactly a 1% dimensional error in the X direction that I've now compensated for by setting the steps per mm, and wonder if the tilted axis could be the cause. Doing the trig, that doesn't make sense - a 4.7 mm error across the width of the bed should translate to something like one part in 2000, not 1%. But maybe something's wrong in my analysis so I'd like second opinions.
Aside from that, is this something I should try to correct, or just let be? I suspect it's the base that's warped or tapped/cut incorrectly where the vertical rails bolt on, in which case it seems unlikely there's any way to fix it without replacing that part, which is something I'd rather not get into as long as the printer is working. But if there are other possibilities that are non-invasive to try, I might.

Further update: if this is the cause of the dimensional error (which turned out to be more like 0.41% than 1%, thus closer to plausible) I probably need to fix it. Using firmware steps/mm adjustment is not viable because it produces aliasing patterns in skin layers presumably due to step width no longer dividing nozzle size/line width.

Could you add a picture to sustain the text?

0scar: Yes, I think it's sufficiently visibly obvious that I can take a good pic. Will do soon.

@0scar: added pics.

So I disassembled the printer and first found something very suspicious: the left (Z-motor side) vertical rail was not mounted flush against the base, because the edge of the control board cover panel was under the edge of it. Fixing this made the vertical rails parallel and made the X-axis unit easily slide back on, but it did not fix the issue; the X-axis was still non-level.
Next, I started playing with eccentric nuts, which was probably a mistake. They were already the appropriate tightness, and I might have messed them up, in which case I'll have to go back and tune them more later. I then found a second point of adjustment: the attachment of the roughly-triangular bracket that holds the three roller wheels on the right side to the X-axis aluminum extrusion rail. I as soon as I loosened the bolts, I was able to get a plenty play to level the axis. In order to get it level, with the top beam mounted, I raised both sides so that the top outer wheels would hit the plastic end caps of the top beam. This relied on a dubious assumption that the triangular roller wheel arrangements on both sides are symmetric, but it seems correct, and after re-tightening the bracket, lowering it to the bed, and re-leveling the bed, everything seems fully level.
Further, after the fix, my dimensional accuracy test piece is 119.6 mm instead of 119.5 mm, which works out to the difference before the fix being undersized by 0.084%, very close to my "1 part in 2000" estimate of the error that the non-level axis should cause. Sadly it still wasn't 120.0 mm like it should be, so I went looking for another source of the inaccuracy. Tensioning the X-axis belt seems to have done the job, and I'm now getting 120.0 mm.
I took some pictures in the process, which I'll try to attach later to improve this answer for others who may hit the same problem.
Caveats: In the process of doing this, I badly messed up the Z axis. I was getting prints coming out almost 1mm shorter than they should be and having to relevel the bed continually. The whole system is "over-constrained" by all the points at which it can be tightened, so if anything is inconsistent when it's tightened, everything goes catastrophically wrong. This entry on Maker Steve's blog was very helpful in figuring out how to get it back in order. After making the adjustments, however, I still had a problem: a horrible grinding squeal whenever the Z motor moved in the negative direction. It turned out I'd also over-tightened the screws holding the Z lead screw nut on the carriage (after mistakenly removing it during all this), forgetting that the assembly instructions specify that it shouldn't be tightened down. loosening both screws by about half a turn finally got everything working right again.

0.4 mm indeed sounds like it missed part of the movement from the slop in the belt.

@Trish: Yep. I think it just had enough slack that it would be off by about 0.2 mm in the opposite of whatever direction it had last traveled.

Thanks for the tip on not over tightening it fixed a z axis binding problem for me :)

i've just bought an Ender 3 Pro and on assembly I carefully checked and deburred the uprigh rails on their bottom faces to ensure they did not splay out or in etc.
Once the 2 uprights are loosely attached to the base rails I laid the assembly flat onto a table on the uprights to ensure the uprights were square to one another and tightened the screws.
Check the uprights are parallel to one another by placing the top crossbeam on the top of the uprights and check if the screw holes are alligned...….if the screws are tight to enter their holes the uprights are splayed out or in and need correcting etc......a small amount of pressure "can" make them line up.
The X axis rail slides up and down on the two uprights with two 3 wheeled brackets, one either side, that have 3 wheels on them, one wheel on each bracket is the adjuster and it is easy to have the X axis cross beam out of square if you tighten the one bracket to the rail before you test the rail for squareness.
Firstly, place only the 2 wheel brackets on their uprights and adjust the wheels for smooth running, then attach the X axis rail to each wheel bracket and just nip up the 2 screws loosely to hold them to the cross beam.
Now, check the cross beam for squareness by running it to the top of the uprights and measuring the gap left to right between the X axis rail and the top rail, then tighten the left hand wheel bracket screws to the X axis rail......and then tighten the right hand wheel bracket to the cross beam.
Leave the Z axis leadscrew off for the moment and run the crossbeam up and down on the uprights making sure there are no tight spots due to out of squareness.
if it's all freely moving.....fit the Z axis leadscrew.
The bed plate can only be set once you have the machine itself squared up.
Ian.

authors: webknjaz -- Слава Україні


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Are there practical reasons to NOT use a stepper motor with lead screw for the X and or Y axes?
After a few months of printing with my Prusa Mk3 (with plans to get a second one soon), I have been wondering about making my third printer a home-built one was a larger print bed than the Mk3. One thing I wondered about is perfectly expressed in the title question.
Are there practical reasons to not use a stepper motor with lead screw for the X and or Y axes?
I am certainly happy with the GT2 belts used in my current printer, but I wonder if the design might be simpler with lead-screws on all three axes.

Speed but you can use it with different pitch than 1mm/rev or 6.35mm/rev with special threads like 8.46mm/rev or 12.7mm/rev, I'm planning to use an standar 8mm acme thread.

Purely as a "fun experiment" , how about putting the stepper on the hotend assembly (or bed assembly) , attach a gear to the stepper motor, and place a Rack  in a fixed position  Sort of a funicular setup.  You'll still have backlash, I fear.

I am going to answer this as someone who actually did rework their Prusa i3 fleabay clone to use leadscrews for all axes. Before digging into the matter, the backlash issue can be solved easily with spring-loaded brass nuts, kinda like how ballscrews work. That's the simplest problem to solve though as there are a lot of other issues.
Short version / tl;dr

Hardware can't handle that many microsteps.

Crosstalk and motor inductance limit speeds and acceleration.

Print quality suffers in really weird ways because of (2).

Leadscrews are not made for quick movement over extended periods of time and will wear, even with grease.

You'll need additional bearing surfaces to prevent your motors from grinding themselves apart, and to eliminate backlash due to the flex couplings.

The system becomes a lot more prone to highly destructive failure modes.

Long explanations
First
You're going to notice is that you're constrained to horribly, horribly slow movement and acceleration rates. My screws are 8 mm screws, with 8mm pitch. That means it takes 200 steps to travel 8 mm. Multiply by 1/16th microstepping, and that's 3200 microsteps per 8 millimeter of travel. Multiply by whatever speed you're trying to print at, then the number of axes you're using, and you'll find that your RAMPS board starts to stutter on complex moves if you print fast enough.
Second
You'll quickly hit the inductance limits of your motors. At "standard" power levels (ones that don't fry my knockoff NEMA17 motors), even after switching to 24 V for the entire setup, the fastest I could spin my motors was about 5 revolutions per second, which translates to 16,000 microsteps per second with 8mm pitch screws. For reference that means that under ZERO load, the fastest my N17 w/ 8 mm pitch could travel, is about 40 mm/s.
You're basically running the motor coils at several kilohertz, which means you have to be really careful about keeping your wires separate and shielded to prevent crosstalk, in addition to the fact that as your step frequency goes up, your step torque goes down dramatically. Not only does this limit the weight of the bed that the motor is capable of pushing at a given speed, but you even have to worry about the inertia of the motor and bed much more than with a belt-driven system. So instead of 30 mm/s jerk with 200 mm/s2 acceleration, suddenly you're limited to, say, 5 mm/s jerk and 40 mm/s2 acceleration.
As mentioned, for best results, the whole system needs to be converted to 24 V, and not all boards are configured for this to be easily done. My cheap RAMPS clone only needed a single diode removed and everything else was fine, but YMMV in this regard.
You could solve this particular problem by gearing the motors down, but at that point you've now introduced a new source of backlash either between the gear teeth or in the belt drive system, and kinda defeated the point.
Third
Due to this effect, is that you run into extrusion pressure artifacts. Basically, the plastic in the nozzle is a fluid, a very viscous one, being forced through a small hole. The fluid pressure will "lag" somewhat behind what the extruder motor thinks is happening.
The end result is that while you're accelerating, the lines you're laying are thinner than they should be, and will be thicker than they should be while decelerating, and you tend to get weird "globs" on each corner when you come to a stop. For me, with a 0.4 mm nozzle, 0.8 mm line width, and 0.2 mm layer height, these artifacts actually completely offset the additional accuracy I was getting with a tightly-coupled leadscrew with spring loaded dual nuts on it. The parts ended up being even less dimensionally accurate than before, with very strange deformities.
There ARE settings you can use in the firmware to try and combat this specific effect, but the process is tedious and takes a lot of trial-and-error, and recompiling the firmware every 30 seconds is annoying, not to mention the variables are dependent on line width, speed and acceleration settings, and layer height, so you have to recompile your firmware any time you want to change the print quality. Super, super annoying.
Fourth
Leadscrews aren't actually designed for this. The constant back-and-forth motion will wear the brass nuts and even the steel threads of the screws over time. You end up with a black powdery residue on everything underneath the screw, which, in the X axis, typically also means your print. Nobody wants steel powder messing up their layer adhesion.
In my case I used Superlube, which is a silicone/PTFE grease, to help prevent this problem, but that only works so well when you've got spring-loaded brass nuts. Eventually they push most of the lube out. Additionally, the lube tends to grab and hold any metal powder that does form, accelerating wear in areas that are still lubricated.
Fifth
Bearings. Turns out motors have internal bearings, that generally suck and aren't made for heavy loads in any direction. I found that out when my Y-axis N17 motor failed because the bearing did, and spread powder all over the coils, some of which got pushed through the enamel and shorted the wires out.
Additionally, because tiny amounts of misalignment turn motors into shrapnel in a hurry, you're almost certainly going to be using flex couplings. Flex couplings have a certain amount of yield to them axially, and are primarily designed to be under compression loads, and tend to fail when stretched repeatedly.
For the Z axis this is normally not an issue because the whole system is held down by gravity, but in the X and Y axes, you'll get some weird offsets of even a millimeter or two each time the carriage or bed switches directions. So you'll want to make sure that the motors aren't load bearing themselves, and the screw remains locked relative to the frame while still being able to rotate.
You can accomplish this by having a ring fastened to each end of the leadscrew that either pushes on a thrust bearing or rides in a regular ball bearing. Ideally, you can do both, but this turns into an expensive venture with a whole lot of brackets in odd places that you may not have space for. I ended up losing about 20 mm of bed travel solving this problem.
Sixth
You need to think about what happens when a component fails. For me, it was my endstops. The first failure was from the crosstalk issue I mentioned above. Y-stops triggered, bed started shifting towards the front of the printer over time, and eventually the printer started trying to move the bed through the front of the printer frame.
It was successful.
The second time was simply the endstop switch failing mechanically. Belt travel stops at the pulley. Leadscrews go all the way to the end of the screw, and because they're geared so much lower than belts are, there's a lot more torque involved. I destroyed my printer frame three separate times because of this problem, and once more when the Y-axis flex coupling snapped. This allowed the motor to spin the screw easily in one direction but not in another - which this time forced the print bed backwards instead of forwards, yanking the Y motor through its bracket and the frame again.
Conclusion
X/Y screws are not necessarily a bad idea, simply an expensive and tedious one in 3D printing. They're much better suited to low-feedrate applications like CNC mills, mechanical engravers, and the like. You may notice that even high-accuracy applications like laser printers tend to have belt-fed carriages rather than screw-driven ones. Screws are much better suited to high load, low-speed applications, and printers tend to be the opposite of that.
If you're trying to eliminate backlash due to the belts not being tight enough, as I was, the answer is to make a better printer. I couldn't tighten the belts enough to get my prints accurate before the motors started failing, because I didn't have the motor-end pulley supported by a bearing. Start there, literally just support on either side of the pulley on the motor shaft with a small bearing braced against the frame to take the radial load off the motor. If your belts are stretching too much, use steel-core GT2 belt. If your system is overall just sloppy, build a more robust system. My current project is a Hypercube Evo, and I found a supplier that makes steel-core GT2 belt. I'm going to use that to maximize rigidity in the CoreXY belt system. The frame is made from 30x30 mm T-slot extrusions, with 12 mm Z-axis rods and 10 mm X/Y axis rods. Bigger, more expensive components that are way more robust and will flex much less than the 400 mm long 8 mm rods on my cheapo printer.
Hope this helps.
(edited to get my math right on the microsteps)

This is an example of an excellent answer as it covers a lot of bases that were lacking in the others, and discusses the pros and cons and the general "it can be done, but this is why it's not done". The only thing missing for a perfect answer is discussing combination machines (FDM/Laser and FDM/CNC combo).

Unfortunately I don't have any experience with combination machines, and I'd rather not speculate too far outside my little shenanigan bubble. Glad I could provide some illumination on the topic, and thanks to Trish and Greenonline for helping with formatting. My markdown ain't the best yet.

Great answer, can I suggest descriptive section titles rather than "First" to "Sixth" though, as it will make it easier to navigate this answer in the future.

Great, complete answer.  Like all engineering discussions, I'll suggest some mitigation measures.  Issue #1, the problem of firmware overhead with micro stepping,  can be addressed (with the right drivers) by reducing the micro-step ratio at higher speed so that fewer micro steps are required, even reverting to full steps.  Issue #2, the problem of stepper motor inductance is addressed by changing from stepper motors to servomotors, probably oversized so that the torque at low speed is high enough.

These are valid points, and I did in fact end up dropping my X/Y step/mm down to 1/4th rather than 1/16th. The downside there is that the beefy N23 motor I was using for the Y axis turned my entire desk into a sounding board while the printer sang us the song of its people. Never worked with servomotors though, how plug-and-play are those compared to regular steppers?

In addition to cost, backlash, which can be experienced in the Z-axis where threaded rods and leadscrews are mostly commonly used, would/could become an issue. The elasticity of GT2 belts generally avoids this issue for the X and Y axes.
It would be worth reading Tom's answer to Advantages of GT2 over a rack, which while the question was related to Rack and Pinion mechanisms, would also apply to leadscrews, in particular:

To avoid backlash and get the same kind of "tight" engagement, both the gear and the rack need to be made with very high precision. The carriage also needs to be very well constrained, because any wobble of the rack relative to the gear introduces backlash (or binding). Moreover, you also need to keep the rack and pinion well lubricated lest they wear out prematurely.

Cost would be the primary reason.  You can engineer a belt driven system that will be equally accurate, faster, and with longer travel for a lower cost.
Lead screws are comparatively expensive. The cost differential dramatically increases with length of travel and speed with equivalent accuracy.
Lead screws do have a significant advantage of being able to carry a much heavier load while maintaining rigidity which is important for something like a CNC mill but isn't as relevant for 3D printing.
This is on the assumption when you say:

Are there practical reasons to not use a stepper motor with lead screw for the X and or Y axes?

you meant that you are still planning on using stepper motors but considering a lead screw vs. belts.

While helpful, cost was not a big worry for a one off project. unless it was hundreds of dollars different. Prices I've seen for steppers with lead screws are not too outlandish.

It is possible to use lead screws; specifically 4 start leadscrews. The only drawback is that you need to be wary of heat.
Let's breakdown the concerns

Cost. Yes it costs more than belts, and it will last longer at higher speeds, whereas a belt may stretch. If cost is a factor then stick to belts.
Speed. Multi start screws offer a lower pitch than single start ones. As a result you less of a turn reduction. This can bring them on part with belts. The drivers you use will determine how fast you can spin your stepper motor. Voltage mode drivers are as used in 3d printers are good at high torque at low speed (sub 1000rpm). Current mode drivers are better at high rpm (e.g. STMicro's powerStep01)
Heat. When the lead screw heats, the metal expands. When the metal expands your positional accuracy disappears. Using a metal that has a low coefficient of thermal expansion would be best, however they may cost more.

Just from changing the drivers you should be able to get a speed increase without needing to resort to the heavier multi start lead screw. Increasing the voltage will also help, however you would need a driver that can let you vary the holding current, otherwise the motor will heat up and burn when it is not moving.


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Tronxy Marlin boards (two of them) reboot when asked to heat bed
I have two Tronxy 2.0 V5 Marlin boards that reboot whenever heat is applied to the bed. The bed has been swapped (because I thought that was the problem) for a new shiny one. The thermistors, too, of course.  The same boards (both) work when the beds remain unheated (setpoint = 0 °C).
Any ideas what might be causing this, or what I might do to figure it out?
Note: I really have no idea which Tronxy board this is;  the "2.0" is stenciled on the board, so that's all I can figure out. I shamefully admit I tagged it with Tronxy x1 to see if I could generate any interest, and because a "Tronxy" tag is not available.

What's the resistance of the bed and thermosensor? What is the resistance of the old bed and thermosensor? If they differ, you need to fix your firmware.

It might have something to do with the coefficient set in the firmware, or, similarly, the setting of the thermocouple/thermistor/thermosensor in the firmware. I vaguely recall a similar question asked in the past about the settings (but not necessarily for a Tronxy board, nor did it reset). Could you edit your question and paste in the firmware settings related to the thermocouple/thermistor? This might help you find the related settings, but it probably doesn't fix your issue.

Can you confirm that you have a Tronxy X1? We just need the confirmation about the Tronxy X1, because if that is the case, then Mick's answer is definitely correct. I wonder if the [trony-x1] tag was only selected as it was the closest thing to what you have. There doesn't seem to be a basic [tronxy] tag. So, I'm trying to both clarify whether the tags are sufficiently diverse and whether Mick's answer is the right one (which it would seem to be).

A Tronxy X1 does not have a heated bed in stock... Also, the stock firmware does not even have heated bed enabled for the X1. Sure you have an X1 and not an x3? Voting to close unclear till it is cleared up.

@Trish, I haven't measured the thermosensors (didn't think of it), but the beds are the same and they are 12V. However, a 24V bed gives the same result: reboot. So that's three different beds.  I like Mick 's idea that the PS is not up to the task; I will look into that tonight.

What kind of Printer do you use? reboot is usually a result of too little power.

Can you post a photo of the printer. It should be easy enough to work it out from the photo. A Tronxy X1 has only one upright bar, the X3 has two. Unless, you have re-used Tronxy boards for a different printer that you have built or modded yourself - Is that the case? If so, what did the donor printer look like? Also, any serial numbers, etc. Thanks.

I'm going to go with all 12V parts (including the PSU) and see what happens. I will post results and we shall see what we see.
Thanks to all for help and suggestions.

All righty then: a 12V power supply fixes everything. Even having a 24V hot end and it still works. Thanks to everyone for helping the ignorant cope with slow learning.

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.

The PS is 24V 13.5A = 324 W,  bit more than required, right?
This is NOT Tronxy X1; there is no tag for the Tomb of the Unknown Tronxy.

All righty then: a 12V power supply fixes everything.  Even having a 24V hot end and it still works.
Thanks to everyone for helping the ignorant cope with slow learning.

First, check the power supply.  Although it may be specified to deliver the required power, it is possible that the power supply has failed in a way that it can not deliver the rated power.  At lower load, the voltage may be correct, but under higher load, it either droops or cuts out completely.
To check this, use a voltmeter on the power as it enters the CPU board, not where it leaves the power supply.  This accomplishes one additional check.  If the voltage droops rather than cuts off, it may be that the connections have corroded and have a higher resistance.
If you have any kind of oscilloscope, I would recommend it over a simple voltmeter, because the power interruption or droop time may be very short.  When the CPU resets it will switch off the load that causes the problem, and the power may quickly resume the correct value.
Second, check that there is not a short in the bed wiring.  You might detect that with an ohm meter.  You have used two different CPU boards, to it is unlikely to be a common fault on both boards, but you might be using the same wiring.
Third, check the routing of the bed heater wires to see that they are not near other wires which connect with the CPU, including thermistor wires and wires to the UI.  High-current switching in the bed wires could be coupling into other wires and conducting a RESET signal to the CPU.  Ideally, the heater wires will be twisted together with about 3 (or more) twists per inch, and not twisted together with other wires.

I'm going to replace this one with a 12V PSU, and see where that takes me. I'm not really sure how I ended up with a 24V unit (a lot has happened in the last few months, and my memory is a shambles).

Is the bed spec'ed for 12V or 24V?  If 12V, then using 24V would result in the bed drawing 4 times as much power [computed as (24/12)^2]

All righty then: a 12V power supply fixes everything.  Even having a 24V hot end and it still works.
Thanks to everyone for helping the ignorant cope with slow learning. I'm not really sure who should get the Green Check, though.

Great!  You may be dissatisfied with the hot-end performance with a 24v heater.  Did you determine if the bed rated for 12V or 24V?

The one I'm using is 12V...currently (see watt I did there?).


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Prusa MK3 heatbed marks
I've got some curious marks on my heatbed.
It appears to be from my black Sunlu PLA+ (I can just feel it if I scrape my finger nail over it) but I can't scrape it off with the metal spatula.
When I try and print over it the filament won't stick.
Any suggestions as to what it is and how you get rid of it?

Try isopropyl (rubbing) alcohol. If that doesn't work, try acetone.

Have you tried naptha and a razor blade?

that's the PEI sheet, yes?

Prusa ships (or has shipped) with two types of PEI build plates.  The original (and what I was shipped in February 2019) is a PEI sheet held in place with an adhesive.  The marks I've gotten seem to be places where the adhesive has been displaced slightly from long term pressure by the object being printed.
In your case, it actually looks like scratches in the PEI.  If, after cleaning with water, then 95% Isopropyl alcohol, and finally acetone the scratches still appear, I'd check if they are a problem.  Do they transfer onto objects printed on the plate?
If you decide you have a problem, I would use a mild kitchen scrubby sponge to "sand" out the scratches.  I have two types in my kitchen.  The yellow ones are too abrasive.  The blue ones are better.  Gently use one to make the surface uniform.
If you have an adhesive based plate, Prusa sells replacement PEI sheets, with adhesive.  The process of changing them seems onerous.  Although I bought two spare sheets when I got the printer, I have never been tempted to use one.  When my build plate becomes unusable, I will buy another one.
Prusa3D also offers a textured build plate, which is more expensive and in short supply.  These are a powder-coating process and from pictures and their blog, I infer they are particles of PEI which are melted onto the steel surface.  I have no experience with these.
I don't know if they are making the current smooth plates with a powder coating process, or if they are still using the adhesive.
The adhesive is the weak link in the heated bed.  It is only rated for 110 degrees C, which is the temperature limit of the bed.  I find that when I print with a hot bed (such as for PETG), the visible ripples in the surface are worse than when printing PLA on a cooler bed.

Edit: As Trish noted, apparently Prusa printers don't ship with Buildtak stickers like the other printers I've used, so this is probably a bad idea in your specific case. For others reading this, only do the sanding shenanigans with buildtak or other stickers that you can easily replace and don't mind wearing down over time.
Used to happen to me printing PETG on Buildtak. I ended up using a medium grit sanding sponge to remove the PLA layer. Related, you might want to grab some 1k grit sandpaper for the same reason, it does a great job of freshening up your build surface once builds stop sticking well.

Prusa beds are not buildtak but either coated with PEI or powercoated. treating them like buildtak easily destroys them!

The last time I looked into it, Buildtak was listed as a PEI surface, I have no idea about the powdercoat though. I was under the impression Prusas shipped with the same sticker surfaces that basically everyone else was using - I'll edit accordingly.

BuildTak is not PEI at all. PEI is a smooth plastic surface, BuildTak has a distinct rough surface.

Duly noted, I've no idea why I thought it was this whole time.

I've just had this issue whilst writing the tag usage for PEI. If you google for PEI film, some sites (the first search item returned) call it BuildTak PEI, which, as @Trish states, would appear to be incorrect. Ultem PEI is the correct term.

Isn't the hammertone-like finish Prusa3d has on the new build plates also PEI that is fused with the surface rather than applied with an adhesive?   The smooth build plate I have on my i3m3 speed in February is specified as a PEI sheet with pressure sensitive adhesive made by 3M.

It looks like you may be a little bit too close with the nozzle. Does the first layer calibration look alright?
The steel sheet with coating is a consumable. It will get marks.
Even with long PLA prints. However, these will slowly fade and should not interfere with print quality.
I can still see my first benchy on my sheet.
When you're no longer satisfied with the state of your sheet, use some acetone to clean to bed.
Note: PETG will case bumps since this sticks a bit too much to IPA cleaned coating. Causing the coating to bubble on removal. These damages can fade. If not too bad. So don't clean with IPA for PETG, use window cleaner.
What you can do is move the print around, instead of always print in the center.

Prusa beds are PEI surfaced or Powder coated

@Trish Yes, I own one.


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Can commodity 3D printer extrusion hardware and filament be used for injection molding?
Assuming you have a suitable oven to maintain temperature at the filament melting point and a suitable mold that can handle the temperature, is a commodity 3D printer hotend and extruder, with large nozzle, suitable for injecting material into the mold? I'm thinking of a setup like having the hotend mounted through a wall of the oven, braced against a hole in the mold inside the oven, and feeding filament via motor or manual cranking outside. Or is much higher pressure needed to make something like this work?
Certainly there are better setups to do this for manufacturing at scale, but the point of this question is whether you can do it with minimal setup effort and cost using commodity parts and filaments rather than needing expensive or custom-built equipment and material sourcing.
For relevance to the site in case it's questionable: certainly if this technique is possible, it could be used along with initial 3D printing of a design and using that to produce a (e.g. high-temperature epoxy) mold.

This is interesting, considering the recent spate of 3-in-1 devices that can do FDM printing, CNC milling, and laser etching in the same device, depending on the attached head. With the right set-up you could add injection to the list and create a 4-in-1 maker powerhouse.

@JoelCoehoorn: Sounds nice, but I'm not sure how you'd make that practical - it needs an insulated oven.

@R.. you can use a filaextruder as molding injection, just need the mold to be cooled according your volume rate. you don't need as much pressure, you won't make diamonds; you just need more pipes for injection to distribute the material.

Injection molding requires two major components: pressure and heat. So your question can be broken down into those two halves: can your average extruder handle injection molding temperatures, and can it handle injection molding pressures?
Let's start with pressure.
Per this page on the University of Minnesota's site, plastic injection molding tends to require pressures of around 2 to 8 tons per square inch. Assuming you're using a 0.4 mm nozzle, which has a cross-section of 0.126 mm², that works out to be 0.000195 (1.95E-4) square inches, which translates to about 3 lb of pressure total at the nozzle assuming you're going for the high end of 8 tons (16,000 lb). However because of the way that you're treating the molten filament in the extruder as a hydraulic fluid, you've got to deal with the fact that the "piston" on one end is actually quite a lot larger area, which means you have to multiply the force by that difference in size. The cross-section of 1.75 mm filament is approx. 9.62 mm², or 0.149 in². That's 76.4 times larger, which means you need to be pushing on the end of that filament with roundabout 230 pounds, or 105 kg, of force.
For reference, the Nema 17 that's on my extruder is spec'd at 76 oz-in of torque, geared down 4:1 through a Wade's extruder, and then acting on a hobbed gear with a 6 mm effective diameter (3 mm radius). Much to my own surprise, as I write this, that means that my little plastic extruder is actually capable of just north of 160 lb of pressure force! All these numbers would need to be recalculated for 3 mm filament, and I have no experience with 3 mm, so we're going to skip that one for now.
Now, that being said, my extruder is also capable of shredding filament if conditions aren't just right. The main two problems you'll have to overcome is 1) gripping the filament hard enough without destroying it, and 2) keeping the filament from buckling. I think if you got clever with some gears keeping multiple hobbed gears synced up, and a polished aluminum or steel feed tube, you could absolutely make your own extruder that's capable of consistently putting 300+ pounds of force on your plastic filament without it buckling or stripping. The downside is that your feed rates are going to be fairly slow, so each injection molding is likely going to take you quite a bit of time. A larger motor such as a beefy NEMA23 might help offset that by giving you much higher torque at higher speeds, so long as you can melt the filament fast enough. However we'll need to revisit these pressure numbers in a few moments, after I explain a few things about temperature.
Next, let's look at temperatures. Obviously we know that we can melt the filament itself as it's moving through the extruder. Using a Volcano nozzle or something, you can even guarantee molten filament at a fairly high extrusion rate. However most printers are designed such that the filament cools to solid (60-80 °C normally) almost immediately. Injection molding designs require that the entire mass of plastic be kept molten. Fortunately, ABS and PLA melting temps are easily reached by literally any toaster oven, so stick your setup in there and you're golden, right?
But wait, there's more!
One of the problems you'll run into immediately is that extruders are carefully designed so that the plastic is molten for as little time as possible, because molten plastic against a metal tube introduces a bunch of friction, hence the need for super high pressures during injection molding. If the plastic melts too soon, then you'll clog up your heatsink (the "cold" side of the extruder), and won't be able to extrude at all. This is a fairly common source of jams in 3D printing, where you're extruding too slowly and there's not enough cooling on the heatsink. Fortunately, E3D sells a water-cooled Titan extruder that would keep the heatsink cool. However the rest of your gearing assembly, and the motor, will also need active cooling, as heat damages the permanent magnets in the rotors, and the printed geared assembly obviously will melt if put inside an oven. Your best bet might be a water-cooled Bowden setup, assuming you can find tube fittings that can withstand several hundred pounds of force. You might look into using solid tubes like brake line rather than your normal PTFE shenanigans.
TL;DR:
Get you a water-cooled extruder, make a super-strong Bowden setup, and gear down a huge motor with a bunch of synchronized hobbed gears, and you might actually pull it off! There's plenty of Thingiverse extruder files you can use as a starting point.
As far as commercially available extruders go, however, I don't think you're going to find anything that's immediately available that can handle what you need it to without some level of modification depending on your selected injection pressures.

An injection molding injector melts all the plastic needed for the shot and pushes it into the mold and through the sprue very quickly.  Perhaps that is why it is called a "shot".
Injection molding machines do not heat the mold to plastic-melting temperatures.  This works because the plastic is injected quickly, and fills the mold before the plastic cools.  Molds are designed so that this happens, and often include multiple thick sprues to direct plastic to all parts of the hold.
Injecting with a 3D printer extruder will be a slow process.  If the mold is not above the melting point, the plastic will cool and likely become a tangle of thread at the entrance of the mold.  To combat that, you could heat the mold.  This is doable, and will suitable insulation the temperature of the cold end and the extruder should be acceptable.
With the mold heated, you would inject plastic until the mold is full.  The mold heater would then be disabled and the mold would cool.  This would take a long time.
Injection molding machines typically have water-cooled molds to cool the plastic more quickly.  Time is money for an injection molding factory, and cooling quickly is key to productivity.
For the 3D printer injection molding machine, the time when the plastic is hot could be fairly long -- longer than would typically be found in injection molding.  I am concerned that some plastics, perhaps such as PLA, would degrade or burn during the long molten time.  Experience would be required.

Yes, technically you can but only for small parts.
However the size of the object would be limited (about the size of a button). It has to do with the power of the heater element. Its too small to deliver enough thermal energy to heat enough plastic fast enough to fill a large cavity (i.e. anything larger than a button in my humble opinion). The previous answers give a breakdown as to why. Normally in an injection molding machine, the plastic starts cooling when it hits the walls.  As the first set of plastic hits the wall of the mold, it sticks and starts cooling. You have to get the rest of the plastic in before that area cools back down and solidifies. Practical for a small part, but not for a large part.
As for your idea about keeping the mold itself hot, yes that would work, if you could keep the temp within range. Overheating the plastic destroys the bonds, weakening the part. Too cold and it will clog.
But I say try it with a Volcano hot end and an actual mold. The plastic will melt faster if you use a preheater (a second hot end, that is upstream), to print the plastic up to 80% temp before it enters the final extruder.

Why would it start cooling when it hits the wall of the mold? The mold is at the temperature of the oven.

Normally in an injection mold the plastic starts cooling when it hits the walls.


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How to effectively eliminate stringing in 3D print
I'm having this stringing problem that happens when the machine moves and when it's not supposed to print that I still haven't effectively solved. I will try exemplify with the following image.

We can see it leaves some prints when it's not supposed to.
I know we can try to solve it with the retraction properties, but is there a way to calculate the right levels of it?
How do you guys do it?
My setup is:

Ender3 printer
Ultimaker Cura sw
BQ filament

Info about this particular filament, from store.bq.com
DIMENSIONS AND WEIGHT

Weight - 1 kg
Filament diameter - 1.75 mm
Coil size (diameter x width) - 175 x 77 mm
Spool axle diameter - 44 mm
Enclosure - 187 x 187 x 83 mm

MATERIAL

Composition - 100% PLA (Polylactic acid).

PRINTING FEATURES

Optimum printing temperature - 205 ºC
Printing temperature range - 200-220 ºC

Add which material you are printing to your question by [edit]. Is this PETG? PETG is known for its stringing properties and is hard to completely get rid of. I've printed kilometers of 2.85 mm PETG and have reduced stringing to a minimum, but some models still show very fine strings.

Now that the image has changed, this question has turned in a "help me fight stringing" which has been asked multiple times. Please look into other questions and answers and try to define what is different to your situation. E.g. those very fine strings are common  for PETG.

This is getting confusing, due to the image change and probably should be closed as a duplicate now (unless the image gets reverted back and the question edited to address the issue in the original question). However, close it as a duplicate against which question, as there are a number to chose from?

@Greenonline sorry i could only provide the info now. The problem is that when i created the post i didnt had the right image to provide, but i said it on parentesis.

Excellent, thanks for the update. Yeah, it is true you did state that in the parentheses. Just out of interest, w.r.t. the original image, were those random thick orthogonal lines intentional?

Note: The image in the question was changed after the question was asked. This answer is out-of-date with respect to how the question has changed; I'll update it when more information is available.

These don't look like strings, which I'd define as material deposited outside of the model, but rather damage done by moving the hotend through already-printed material without retracting. In Cura, this is called "retraction combing", and it defaults to "all", which is way too aggressive and visibly harms the surface finish. Switching it to "noskin" or even "infill" only will make this go away and greatly improve your print quality, at the cost of some speed. The cost can be severe in worst case with certain kinds of fine detail, but usually "noskin" is cheap and suffices.

OK, this new image looks completely different from the old one and largely invalidates my answer. I may update it later.

Thanks, that might be another problem, I switched to an image where I show the stringing that is happening

You should reply to Oscar's comment asking about the material, and provide as much information as you can about your settings.

@Nmaster88 - IMHO, I think you should revert the image, via a roll back, and let this answer answer the original question, as it is a little unfair to change the question after someone has taken the time to answer it. Meanwhile, check the other stringing questions (provided by 0scar's link above) to see if they address your issue and if not, post an new different question. It's just a suggestion, but seems to make sense, given the current situation.


text:
Where did Marlin get its name?
Does anyone know how the developers of Marlin decided to name it that?

I saw I'd got an answer, and excitedly opened it up, but then realised that you were backing my question up! I was a bit disappointed that I didn't have an actual answer, but grateful for the backup, nevertheless :-) BTW, I'm quite impressed to see that you've been a member of the forum for over ten years already...!

As far as I know Erik van der Zalm started Marlin. He is from the Netherlands and Zalm translates to "salmon". One of the design goals of Marlin was to make it faster than the other firmware available at that time. And a marlin is a very fast swimming fish.
Some firmwares developed after Marlin also joined this fish theme: Sailfish, Minnow, ...

Should I just accept this? Any way to confirm it?

Does it answer your question?

Yes, it probably is totally off-topic, but fun too, so I'll try to get an answer in, before the question gets closed.
The best place to ask would be the Firmware - Marlin forum, on RepRap.org.
The question is there now, Why was it named Marlin? and I'll update this answer, if/when I get a response...


text:
Strange banding on first layer/skin
I've been printing for a while with a Creality CR-10S with Colorfabb black PETG economy and all was good.
Until today, where on a large, flat print (30x10cm - a small drawer) I can't manage to get a smooth first (or second) layer no matter how hard I try.
I tried so far:

calibrating the extruder
setting different temperatures (range 230-240 suggested by the manufacture is 235-250)
slowing down the print (I usually print skin at 80mm/s, I tried this one down to 40mm/s)
installing a brand new nozzle
levelling the bed

The print starts fine but then, randomly, some bands that look like under extrusion appear:

Here's a second example of the first layer - I've ripped it off the plate but as you can see the first 50% of it was fine. The problem appeared later in the process.

The extruder "clicks", the filament stalls and it's clear that the nozzle is not extruding plastic fast enough.
What can it be?
All other prints are fine, but I have to say this is the only one that has such a large horizontal surface.

Do you print with an all-metal hotend?

Underextrusion I see too.

No, stock CR-10s hot-end but I replaced the plastic tube with a unicorn PTFE one so no issues there at 230C. Other prints - ones that require less flat surface - are usually fine.

i'd say your extruder driver and/or motor is overheated - really
according to your description - when you've printed other things it was fine but this is the first with such big "flat" area
usually extruder motor works for some time then stops and starts and so on and again so it has some time when driver cools down but here it runs constantly for relatively long time
this overheats the driver and/or motor then is starts to clicks as there is not enough current delivered to the motor
what can you do?

try to take the cover off
check the driver temperature (use electronic thermometer as it can be even 100C)
try to cool it with some kind of fan while running the same printout

if the diagnosis is fine - you are at home and now you know what to do ;)

the one described as E is the one to check and cool down

I'll definitely check that but I have to say that when it "clicks" if I try to manually push the filament through I can't because there seems to be too much pressure inside the feeding tube. That's why I felt like it was more under extrusion at the nozzle than a problem with the feeder.

you cannot push the filament as same as you couldn't pull hard enough to prevent pulling the filament even when there is enough current. think it this way - the undercurrent motor is "almost working" but not "not working".

Right I see what you mean. I made another test and it looks like before/after the "click sound" the extruder motor is moving fine but the filament is not. The little cog that pushes the filament is literally grinding it because it moves but the filament is not. If I release the spring mechanism that keeps the extruder connected to the filament the filament bounces back by 1 inch like if it were spring loaded into the feeding tube. Would this still a side effect of the issue you describe or something else all together? (BTW I haven't checked the temp yet but will do asap)

hmmm... this sounds a bit like this "little cog" is plugged with scrapped filament but if it works well in other printouts... this get a bit crazy. could you examine if this notched bolster (little-cog) is not dirty (filled with filament debris) or even smoothed? but please check the temperature first

well i've found this - https://www.youtube.com/watch?v=x35aWmnZ_A0

ah! I saw that one - I don't have that problem - I've already replaced the tube and the holder

so my diagnosis earned some percentage of probability ;)

Finally got some time to check your theory - all the drivers seem to be running at the same temperature. I then raised the hot-end temperature to 255C and that seemed to alleviate the problem. is it perhaps because I'm printing too fast and 235C is not enough to melt all that plastic?

hmm... strange... you've said you tried slowing down and i think it should fix the problem or at least make it less nagging.


text:
Stuck filament in the extruder of Infitary M508
Model: Infitary M508
Details: The filament is stuck in the extruder preheated for PLA (the filament is PLA 1.75 white). The extruder's motor works and the filament is in the hole of the extruder (not somewhere else). I took the fan covering the motor apart, to show what is inside, so you might see it on the attached image:

You might also see this video for details: https://www.youtube.com/watch?v=R8rYGhuYWvc
I'm able to pull the filament out, when I uncouple the motor's gear, but it doesn't go through the extruder when I push it in.
What can I do to fix this? Thanks!
P.S. It's the first start of the printer.

Unfortunately you're going to have to tear the extruder head apart and clean the nozzle. There are kits like the following (found on Amazon - No affiliation):

This will give you everything you need to clear the nozzle. The only other solution is to replace the nozzle and extruder tube. The filament is stuck in either or both of these parts.
(As an aside ... a wise person < cough > @0scar < cough > once told me I should keep extras of these parts, as well as the thermister and heating elements on hand. Treat them as disposable parts ... once they're dead, just replace them.)
What you need to figure out though, is why it clogged in the first place. More than likely you tried to extrude filament before the nozzle was up to temperature. If your readout said it was good, then you need to get a no-touch thermometer and check the nozzle for the proper temperature prior to printing to ensure it's all good.

"Mind what you have learned. Save you it can." :)

Thanks, I've ordered a similar kit. Will try to clean first.

Cold extrusion won't give you a clog that needs fancy cleaning techniques -- get it up to proper operating temperature, and the clog will go away.

@Mark - It never hurts trying, but my experience with them is, once it's clogged, it won't unclog itself, even with heat.

Or perform a cold pull/atomic cleaning from e.g. this answer. Used this last week after someone tried to print PLA at 250 ℃ on our Ultimaker 3E...

The hot end can clog in two places.

Heat distortion can cause the filament above the nozzle, at the level of the cooling fins, to melt, expand and prevent further passage.
The nozzle itself may be clogged by impurities.

There are two methods available, depending on the type of clogging.

If the hot end is blocked at the level of the cooling fins, a so-called "Atomic Pull" helps. This is also a convenient method of changing filaments. The hot end is heated to approx. 90°C and the filament is pulled out of the hot end with a bold jerk. The filament does not melt completely and remains tough. Thus the complete plastic is pulled out of the hot end.
If the nozzle is clogged, an "Atomic Pull" only helps to a limited extent.
To clean a nozzle, the hot end should be removed from the holder and the heating block unscrewed. You need a gas burner. With the gas burner the brass nozzle is heated until the plastic is completely carbonized. Wait until it has cooled down and reassemble the hotend.

Post-cleaning advice:
Be sure that the hotend is cooled enough that no heat can creep up the hotend and melt the plastic before it enters the heat block. Without sufficient cooling clogging pre-nozzle is very likely.

authors: សំភ័ណ្ឌ សំភ័ណ្ឌ សំភ័ណ សំភ័ណ្ឌ


text:
TMC2130 External VM RAMPS 1.4
I'm attempting to replace my DRV8825's with TMC2130's on a Prusa i3 rework clone, 12 V RAMPS 1.4, motor currents have been accounted for. Since they don't work as well with 12 V than with higher voltages, I bought a 10-50 V, 10 A DC-DC converter to power the drivers (and steppers). On the RAMPS this is done simply by taking the VM pin out and soldering it on the other side to draw power from an external source.
It is stated everywhere that VM should be powered BEFORE VIO. Would it be valid to switch on a relay with the DC-DC converter and connect the VIO pin to RAMPS 5 V through it? Is it enough having both sources turn on at roughly the same time? I haven't found any indication on how much time there should be in between (or if there needs to be any).
Please tell me your own experience if you have attempted something similar, or any alternatives (aside from buying a new board, because I'll eventually build a CoreXY or something else) that may be valid.

I think it's more of an issue for when you have the board powered from USB, firmware and drivers active, and then consider turning on the power supply.
I used pretty much the same setup for a while - a MKS Gen 1.4 board at 12V, a 12-36V boost converter to 24V, which then went onto the driver ICs.
I did solder a 100µF capacitor to each driver though.

@towe well, i did this almost a month ago, and yes, if you connect usb before turning the supply on then the drivers misbehave. But I'm happy enough, because I use a makeshift 6m USB cable that I didn't put the 5v line to anyways, so i only have this problem when I forget to turn the supply on and use another cable. I have it with the 50v 10a boost converter set at 36v (i could actually go higher, but my drivers are the high current type so it's nonsense) and a 2200uf electrolytic paired with a 1uf polyester for all of the steppers.

I cannot find any such requirement in the datasheet. The only requirement that I can find is to power VCC before V_IO and/or 5VOUT, but this has nothing to do with the motor supply voltage.

First of all, I'm not talking on a first-hand experience: I don't own a RAMPS based printer.
If I were you and wish to be 100 % sure the setup you are describing doesn't blow up in my face I would use a spare pin on the Mega to drive the relay which, in turn, drive the 24 V source line. In terms of delay I would use a couple of seconds after power on: enough time to have the bootscreen completes and all the pins being set as per firmware configuration.

It's the other way around, the 24V have to be switched on first, but it's the same since I could switch the 5v with a relay. I'll consider doing this


text:
What is the functional difference between an e3D-Style nozzle, Makerbot MK8 and M6 Chinesium Nozzles?
There is pretty much an ecosystem of two Nozzle designs out there that share the M6 thread on the coupler to the Heating block:

the e3D "snub nose" or "shouldered" design.
the "Chinesium" nozzle that is often claimed to be some "MK8" or "MK10" without naming what item of which manufacturer is actually iterated there.

They seem to be derived from the Makerbot MK8 Hotend which uses M6 threading and not the MK10, as that uses M7 threading.

What differentiates the two and can one swap one for the other?

related, but not a duplicate (as focussing on the layer adhesion effects)

Differentiation
The main differences between the e3D-Nozzle family and the "simple" Nozzle are the wrench size, body length and thread length of the nozzle. In fact, I have come across 2 different "Chinese" styles of nozzle, a "big" and a "small" one.
Comparison
For comparison, take a look at this photo, where I aligned the lower ends of the bodies to line up under the wrench needed to handle them.

In words, left to right:

Chinese Big M6 Nozzle - Aka "Creality Mk8"

size 8 metric wrench, 4 mm M6x1 thread length, 1 mm clearance, extends a minimum of 8 mm from the heater block

Chinese Small M6 Nozzle

size 7 metric wrench, 4 mm M6x1 thread length, 1 mm clearance, extends a minimum of 8 mm from the heater block

e3D v6 normal (aka NOT volcano etc)

size 7 metric wrench, 6 mm M6x1 thread length, 2 mm clearance, extends a minimum of 5 mm from the heater block

To differentiate from Makerbot nozzles:

Makerbot Mk6

size unspecified wrench, 7 mm M6x1 thread + clearance, extends a minimum of 5.5 mm from the heater block, 12.5 mm overall.

Makerbot Mk7

size 1/4 inch imperial wrench (6.36 mm), 5 mm M6x1 thread + clearance, extends a minimum of 8 mm from the heater block.

Makerbot Mk8

size 7 mm metric wrench, otherwise as Mk7 - making this almost identical to Creality Mk8 but for no specified clearance between thread and head

Makerbot Mk10

size 9 mm metric wrench, 4.5 mm M7x1 thread, 1.5 mm clearing + dia 7.5 mm shelf, extends a minimum of 7 mm from the heater block

Replaceability
Chinese big to Chinese small nozzles in either hotend
Due to the dimensions, one can easily swap the big and small Chinese nozzles for one another. They are virtually interchangeable but differ in the wear patterns.
Chinese nozzles in e3D Hotend
The 3 mm shorter snout and deeper butting with the heatbreak of the e3D nozzle in its designed hotend make it hard to swap a Chinese nozzle into an e3D setup: neither does the thread allow to screw the nozzle in the right length sometimes, it also extends much further. To accommodate, the whole heater block has to be screwed about 3 mm more onto the heatbreak, then the nozzle gets screwed in. The result is equal in overall length.
Makerbot Mk7/Mk8 to Chinese Nozzles
But for the different wrench, those generally will fit, but
###e3D Nozzle in Chinese Hotend
However, the long thread of the e3D Nozzle allows it to be mounted in a hotend designed to hold a Chinese nozzle without trouble - the 3 mm of difference in the body are used for a longer thread and clearance between thread and body, resulting in the same overall length without changing the mounting position of the heater block on the heatbreak.
Internals
Stefan of CNC-Kitchen recently tortured a couple of nozzles for science and investigating wear and tear (video). He found out a couple of differences on the internals:

The Chinese nozzle had a non-straight pattern on the inside
The angle in the feeding cone is 60° in an e3D and 90° in the Chinese sample

Conclusion
The Chinese Style nozzles can be interchanged for one another. an e3D style nozzle with standard length (aka not-volcano) can be swapped in for any Chinese Style nozzle. A Chinese Style nozzle needs to have the heater block shifted if mounted into an e3D hotend.


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3d printer set up
I am not very used to 3D printers and I just bought my first 3D printer today (Creality3D Ender 3). But I am unable to assemble it. The 3D printer doesn't contain instruction on how to built it which I found very weird. I searched a couple of things on the Internet and I found this website, but after some steps I couldn't read it , I didn't understand what I was reading.

What printer did you buy? Usually, the build instructions in kits are on the Micro-SD card in the parcel, if you buy a Chinese printer.

I have never linked to a Google link as this is considered very impolite, but such instructions are very easy to find, you can get them from the manufacturer website.

The website you looked at is for an entirely different printer and in general.
Your instructions are in a PDF file on the mini-SD card that came with the printer. The official Ender 3 support site is https://creality3d.cn/download/produktdatei_c0002 and it also contains the Official Assembly Instructions (to me, the lower right corner). An alternate setup instruction is in a PDF distributed by Sain Smart.


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What makes an extruder right handed?
I have been looking to buy a new extruder. One of the options I have seen comes in "right handed" and "left handed".  What does this mean? How can I tell what my current extruder is, so I get the right replacement?

can you provie a link to such a setup? It might be a case of mirrored setup (If mounted with the motor in Y and the gripping side going "down", is the motor left or right?) or it might be a case of the pinning (does the motor rotate clockwise or counterclockwise with this pinning?)

Opposed to some some views, the orientation sometimes does matter. E.g. it depends on the access to and positioning of the extruder motor. I guess you operate remotely considering you tagged [tag:bowden], so look at the current extruder and how the shaft turns to extrude filament. Please add your machine and extruder setup and a photo would be very welcome!

Quick clarification on my end: gripping side means the side that moves the filament.

The short answer to identify what extruder type you have is the rotation of the extruder gear.
CCW rotation to extrude = right-handed extruder
Detailed explanation is below.

In addition to the other answers, the right-handed designation comes from math and pysics convention that has become a well known mnemonic in engineering practice:

or in its physics coat,

The Right Hand Rule: Figure (a) shows a disk is rotating counterclockwise when viewed from above. Figure (b) shows the right-hand rule. The direction of angular velocity ω size and angular momentum L are defined to be the direction in which the thumb of your right hand points when you curl your fingers in the direction of the disk’s rotation as shown.
  reference

In a right-handed extruder,

you place your thumb of your right hand in the direction of the shaft (so pointing it towards yourself in the image of the extruder above) to see that rotation in the direction of your curved fingers leads to extrusion of filament (in counterclockwise direction).
For a mirrored extruder they call it left-handed extruder.

i'm not quite sure why "the right hand rule" should have any meaning here

@darthpixel because it is a math/physics convention: a rotation is given as the rotational axis and the speed of it. "10° per second around X" means it rotates with that speed counterclockwise around the X-vector. A "lefthanded" extruder spins - mathematically speaking - around the -X vector.

but it's not connected to left or right handed extruder. L, I and omega are also not very needed in terms of the question - What makes an extruder right handed? you could also incluse 2pir as it's also loosely connected but it won't help here. left handed means this and right handed means this - why to make things overcomplicated? rotation direction is not really what defines left/right handed extruder

Sorry but it is. Do you think it is called because you operate a right-handed one with your right hand? :)

:D i claim that pictures in your answer make it even more curly and they are not making the subject clear. the RHR doesn't explain anything here, the thumb doesn't represent anything so this picture is misleading rather than explaining - that's what i think

@darthpixel I'll try to find a better picture. The thumb is the "shaft", I'll try to clarify that with an edit!

Righthanded: The shaft of the motor and the rotation vector (According to right hand rule!) both point out. Lefthanded: the shaft poinsts out while the rotation vector points in.

@Oscar and Trish please try to imagine a person who is not very familiar with physics - i think such person won't get much from your explanations. What is rotation vector for such person? I'm really trying to imagine the contaxtual meaning of the RHR based on your answers and comments but this still leads me nowhere. and believe me - i'm familiar with physics and at least a bit with 3d printing.

This is an example of a right handed extruder setup:

And this is an example of a left handed extruder setup:

I believe that you can can choose whatever one you favor. With the right handed setup, you will be pushing down the red part with your right hand when inserting filament. With the left handed setup, you will be doing the same thing but then with your left hand. Personally, I favor the right handed setup (my right hand is my dominant and stronger hand). But, you should be able to choose whatever one you like! Be sure to check it will work with your printer though (extruder holder & hotend).

It seems to me that if the stepper is rotating clockwise, then the right handed setup would "push", and the left handed would "pull". Depending on how the stepper is mounted and the layout of the machine, this could be important when choosing which to go with, as it might only be feasible to mount the stepper one way.

With an un-keyed cable, the stepper wiring can be rotated (at one end pins 1-4 mapping to 4-1), to reverse the direction. Of course, it can be done in software too.

when thinking about righ-handed extruder or left-handed extruder it's good to know that there is no magic or any other science rule behind this naming convention. it's just an arbitrary explanation which can be unfortunately misleading. in fact there is visual explanation of this left / right handed name and it doesn't have anything to any "the right handed rule" mentioned in other answers.
it's just this

no physics... no magnetism... no induction... no vectors and no formulas
the other answers present pictures of LH and RH extruders which are of course fine but be careful - there are universal extruders which can be both L or R handed.
like this one

as this extruder has fully fixed filament path and there is no restriction which direction the filament should go - there is no way to describe it arbitrarily
it is left-handed when it works as left-handed and it is RH when it works as RH

@Greenonline thanx :) in terms of the answer - the picture is worth 1000 words so it was obvious to have both on one picture. as i tried to explain in my other comments in this thread - why to add unnecessary and misleading pseudo-scientific value if just such simple picture will explain it all

Hmmm... I think both explanations are good. It's nice to have a simple explanation, but it is always handy to have a scientific one too, for greater depth, when needed. :-) Sorry, I got so carried away writing my first comment that I forgot to vote. LOL.

It usually doesn't matter whether you get a right-handed or left-handed one. The reason the two different variations exist is because some people use a dual extruder setup. If you have two extruders it is convenient to have them be mirror images of each other (as this makes them easier to install in use with the filament release lever pointing out to the side). If you have only a single extruder, it doesn't really matter, unless there are other construction restraints.


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How does this Martian habitat 3D printer built for NASA work?
The ArchDaily article AI SpaceFactory Wins NASA's 3D-Printed Mars Habitat Challenge shows a working 3D printing apparatus using an unusual material containing

basalt fiber extracted from Marian rock (simulant) and renewable plant-based bioplastic.

The photo below shows part of the printer. Is this printer just leaving a slurry to dry, or does the mixture somehow catalyze or harden spontaneously? I'm also wondering what the (looks like) twelve black hoses are around the central nozzle.

Let's start with the general design look and feel: This printer contains a robotic arm with a toolhead, pretty similar to a welding robot, and probably is controlled with a similar CAM software.
 Picture by Robotics.org
Tool head
The really interesting part here is the tool head. So let's look at it and try to reverse engineer the use of some parts by how they are placed and what one can see about them, together with the information given by OP.
Black pipes
There's a bundle of 12 black pipes that go from the main body to the print head, ending at the side of some distance disk. To me, these look suspiciously like a system to deliver an airstream, so most likely some sort of cooling system. This is further supported by the huge fans at the base of the machine, pumping air into the flexible pipe.
Silver Tank
The first picture shows a silver tank with the label V7 (version 7?) or VT (as in Virginia Tech) or something similar on it. This is connected via a grey hose to the base of the printer. The mounting of it over the extruder hints, that this is a hopper, most likely holding the print material in pelletized or powder form, and that it is fed via the grey hose. From the information given in the question, it might be some sort of PLA (synthesized from cornstarch) or other bioplastic using the Martian dust as a filler material. From here, the print material falls into the central column...
Central Column
...which goes down through the distance disk into the thick nozzle, so it must be the extruder and heater combo. At its top, there is a large stepper motor in Z orientation, which hints that inside of the matte grey tube is an arbor, pressing down the melting pellets past a heating element into the nozzle below.
Print material and further information
The last picture shows proudly "Autodesk" on the side of the printer. Autodesk has an own article about printing in space from August 2018, where Nathan Golino of the NASA owned GMRO states this:

Abrasion has been an issue with the 3D printer we use. It’s very rough on the feed screw and the barrel and nozzle as the material is extruded through the system.

This confirms the general makeup akin to a pellet-style extruder.

Combining a small amount of waste plastic with crushed rock known as regolith can form an additive construction material that’s stronger than concrete. (on a picture caption)
The material we’ve been using in our additive-construction experiments is regolith mixed with waste polymers. You can get polymers in the form of astronaut trash and shipping containers, or you can synthesize polymers. You can use that as a binder for regolith, with a relatively low ratio of polymer to regolith, to make a construction material pretty similar to Portland cement in compression and 20 times stronger in tensile strength.

"Waste polymer" could be anything from ABS to PETG, from ASA over PC to PLA, but it seems that the plastic-to-regolith mix is on the high regolith side. It seems that it behaves more like a plastic than concrete, hardening/solidifying from a molten paste to its hard concrete as it cools.
As an interesting extra tidbit: Golino also states, that the mars-printers are at the moment on level 2 to 3, where 0 is "general concept" and 9 "ready to fly", so in early development.
Further reading into the background of the project - a design competition in 2015 - hinted, that the software for the arm might even be Autodesk PowerMill.
Looking back at the question if that is V7 or VT on the printer's hopper, an article with the same dome printed in OP's question popped up: Virginia Tech had been part of the crews that were taken to the finals of the aforementioned design competition and was part of the finals. They worked with the AI Space Factory team, which came out winning. In a related article, the printer OP showed us can be seen from a different angle and stripped of the cooling pipes and with a different, longer extruder. It tells us a little more about the work distribution of the teams and participants:

Large format vessel printed by AI SpaceFactory in the Autodesk BUILD Space for the construction phase of the competition. The tooling was developed in collaboration with Virginia Tech and Autodesk.

The main company behind it, AI SpaceFactory, showed a different version - the one without cooling pipes - in motion on a YouTube video on April 10th 2019 and the performance of the air-cooled version during the competition finals on May 3rd 2019 (warning, 10 hours of 3D printing galore!) At 9:52:12 we also start to learn what that disk is in picture 1: It is the endcap of the structure which sadly fell through the hole due to navigation issues.
In the following shorter and commented video, we see that the printer also contains some sort of gripper to place the window frames and skylight just as well as the load bearing test performed after the print. Apparently, the material they use is engineered to a point where it can be reused after regrinding it to dust again.

Wow, thank you for investigating and putting together such a thorough and interesting answer!

That "V7" label looks a lot like "VT" to me - https://vt.edu/

@DigitalTrauma your hint actually uncovered even more about this printer! THANKS!


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Selective reinforcement of some places in my part
I have a part that experiences larger than average forces in some of its protrusions. It would make sense to reinforce walls, and in particular strengthen infill in those areas. But to save material and printing time, I would like to use thinner walls etc for the rest of the part.
Are there any tricks for how to do this, other than printing two parts with different parameters and joining them somehow?
This is Prusa i3 with slic3r.

Welcome to 3dPrinting.SE! There's two things I can think of off the top of my head: 1) use a stronger material (such as ABS instead of PLA) to print your part; 2) use fillet radii where you can which will help reduce/eliminate stress risers (areas where the part can break easier). I'm sure there's ways to make certain areas more resilient, but I personally don't have an answer for you there :o)

There is an answer that does exactly what you want, e.g. have multiple infill percentages; I'm pretty sure you can change wall count as well. I can't test it at the moment. Note that this is advanced slicing!


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precise transformation using meshmixer
I am trying to do some edits on an STL file. I am trying to use meshmixer for this. I am essentially trying to move a hole in the following picture

and widen the hole on the bottom of the part. I was playing around with meshmixer and it seems that it can do this by sculpting rather than precise measures. I would appreciate comments if my observation is correct and if so, what other STL editor would you suggest to do these edits. Thanks!

It's possible to close over a hole using Meshmixer. I've done exactly that recently, although the "hole" was a depression, the process would be the same. As you've discovered, Meshmixer can be considered somewhat imprecise.
Fusion 360 will import the model you wish to modify. You would then turn off edit history, convert the model to BREP, then perform the edits you require.
Once you are satisfied with the results, it's an easy matter to export the model as an STL file.
I've summarized the steps, which are almost as easy as my description. You'd have to combine Google-Fu with the summary for the detailed portions, but it's something I've done in the past.
Fusion 360 is free for hobbyists, renewable each year. There are many YouTube tutorials and text-referenced solutions for the steps required to accomplish your edit.
Some will consider Blender to be an alternative method and I agree that it's a viable option, but it's not quite as intuitive as Fusion 360 and was more challenging for me to embrace.

Done! Thanks for your advice. Fusion 360 looks very similar to SolidWorks. (I apparently can't upvote until I have 15 reputations, but you have my upvote :-bd)

For those who stick with Meshmixer: you can do some "interesting" things by duplicating an object, or a sliced portion of the object, moving that duplicated piece in one axis, and doing a Combination.  That avoids surface mismatches.  Or, to duplicate one of the hex-countersunk holes, slice out and copy that chunk, do a Make Solid on both parts, and do a Boolean Intersection.


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Is iron oxide a suitable material for use in SLS/SLM 3d printing?
I recently asked a question in the space section of stackexchange as to if Martian soil, with its decent iron oxide content, could be mined (with magnets) for its iron oxide and the iron oxide used as building material for an SLS/SLM 3d printer.
Is this possible? The final result doesn't have to be pure iron, I'm just looking to see if iron oxide is a suitable building material for a SLS/SLM 3d printer.

First of all, let's start with the basics:
Iron oxide aka rust
The University of Illinois hosts a "Ask the Van", where the question "is rust magnetic" has been asked, and I will quote from Tom J. and Mike W.:

There are several different oxides of iron, with different fractions of oxygen. They are Fe0, Fe2O3, and Fe3O4. Rust consists mostly of Fe2O3, with additional water molecules attached. There are several forms of Fe2O3, and a common mineral composed of Fe2O3 is called hematite, which is a shiny-blackish mineral. Hematite is not ferromagnetic, but it does still respond to a magnetic field and will be attracted to the poles of a permanent magnet.[...] FeO is also not ferromagnetic, but it is pulled about twice as much as Fe2O3 towards the poles of a magnet. Magnetite, Fe3O4, is ferromagnetic, and is about 1/4 as strong as pure iron.

In a followup answer by Mike W., it gets more explicit:

Rust (a collection of some iron oxides) is virtually non-magnetic, unlike plain iron or most types of steel.

This means pretty much, that unlike pure iron, you can't pick up (most) rust particles with a magnet. From all that we know about the Martian soil, we know for sure that it has a very fine grain, so the particles in itself are tiny. This again hints that any exposed iron on Mars has been thoroughly rusted through over the last million years, leaving only non-magnetic rust dust on the surface - dust that is not suitable to be mined with magnets.
We have an analysis of the chemical composition of Mars from some landers, hinting that Martian regolith indeed is colored from its high content of iron in various bonds. So, what we do with that data? We create Maritan regolith simulant, which has been checked back against the findings of the probes. And low and behold: there is not a single percentile of iron in either the findings or the probes or the regolith simulants. Just about 16-18 % rust.
Regolith for SLS?
Now, we have regolith with a somewhat even distribution of rust in it. And we have a stimulant that can be acquired from Huston. To my knowledge, it has not yet been tested for SLM, but it has been used in powder based extruders, as explored in How does this Martian habitat 3D printer built for NASA work?
With the lack of testing and the relatively low iron oxide content, I am hesitant to say that it will work to print in the usual way. However, with the addition of some polymer, one could create a fast regolith-plastic compound that shows similar behavior to concrete. This material could be made suitable for 3D printing in SLS machines. Another idea might be to go from SLM (selective laser melting) to the older SLS (selective laser sintering) or even simple sintering, in which a compound is pretty much "baked" into shape without fully melting it. We understand well how to sinter materials we have trouble with melting otherwise, and one of the prime examples is tungsten carbide.
Conclusion
While I see problems with mining iron from Martian regolith without a chemical refining process or refining it akin to iron sand, I don't see how martian regolith can't be refined into a suitable SLM or SLS material by addition of some kind of polymer or a thermal and mechanical process to achieve sinterable material. Instead of a polymer, a pure metal (magnesium or aluminium) could be added as a binder too. With the availability of regolith simulant for research, it only takes a research group that is interested in researching the suitability of this material for such applications.

Bravo. One of the most straightforward yet eloquent answers I have ever seen. Perfectly answers my question.

In other words: we can't print structures from the material on Mars alone, but maybe the material there could be suitable if we add a relatively small quantity of polymer. Thus, a habitation mission to Mars might not need to lift and transport an entire structure, but only a machine big enough to print the structure... and some polymer... and the regolith mining and processing equipment... so still a very significant move, but probably worth it if we think in terms of creating many smaller buildings in a continuously expanding settlement, rather than one big one for a single mission.


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Nozzle insulation gone, can the printer be damaged?
During a print a lot of plastic ended up ripping the nozzle's yellow insulation strap.
Can printing without this insulation around the fusion chamber damage the printer?
If there is no chance of damaging the printer, how likely is it that the prints will be affected by the absence of this insulation

Removing the insulation will not damage the printer, although it may affect the quality of the prints. The insulation is, after all, there for a purpose.
Allowing too much heat to escape radiatively from the heater block will reduce the maximum flow rate, since less energy will be available to heat the filament, and you may need to reduce your printing speeds or increase your nozzle temperature.
A bigger problem is that heat radiating from the heater block can cause already extruded filament to sag, especially when printing details and intricate infill. If the nozzle remains too long in any area, already extruded filament is likely to soften and deform. Without adequate insulation, the only way to counteract this is by increasing part cooling, and this will remove even more energy from the heater block.
Either fit new insulating tape or buy some silicone socks, since they are readily available for MK7/8/9 heater blocks. Then print a couple of Benchies, both with and without a sock, and compare the results.

There is not less energy available unless the block is excessively cooled by the part cooler. The thermistor will read the temperature, when it drops below a certain temperature the heater will heat up. It also does that with the insulation on. It is expected that the heater will be scheduled more without insulation.

@0scar You're right. I was speaking too much from personal experience. I'll edit my answer.

Thank you, I'll look into silicon socks. According to what I read it's thermal conductivity is far higher than that of the former insulation material but it'll still be better than just air, and it'll avoir PLA buildup around the nozzle which is basically what destroyed the insulation band.

The second paragraph is incorrect. That is only happening when the block is cooled too much, more than the heater can supply. I've been printing with (cotton and silicon) and without insulation for years, works just fine.

No, without the insulation you can print without a problem. I've been printing for years with (cotton or silicone) and without insulation, works perfectly. Although heat radiates from the heater block, I've never experienced issues that it causes overheating of your printed parts.
Note that the insulation tries to contain the heat in the nozzle preventing heat to leak to the surroundings (less energy is used/wasted). As such you may need to do a new PID tuning (certainly when the print cooling fan is incorrectly positioned as such that it cools the hotend heater block), but printing should just work fine if the print cooling fan is in the correct position.

I consider both answers deserved to be tagged as "the one", but I can't flag both

@MathieuVIALES No problem, it is good to have multiple answers! Mine does not address the damage side.

Insulation of the nozzle is crucial. I removed it and put a silicon sock on a CR-10. I constantly got heat creeps even at 10C lower temp. Then I removed the sock and printed a 12 hour part with significant quality loss. It did finish the job. With silicon it stopped after 5-6 hours. I suppose that with the sock the upper part of the heat block which is uninsulated leaves more energy go up than without a silicon sock. Then I put cotton all around the heat block. I even put the cotton at the side of the thermistor. And kapton tape. The results are really really perfect. Always talking for the CR-10 stock nozzle and fans. If you don't have insulation you need better fans. All the heat goes up to the heatbreak and softens the fillament.


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Heater cartridge with 7.2 ohms - 12 or 24 V?
I have a heater cartridge here that measures 7.2 Ω.

At 12 V that would amount to 20 W
At 24 V that would amount to 80 W

The cartridge itself is 2 cm long
Could it handle both voltages or is this clearly an under-powered 12 V cartridge?

Just give it 15V, what controller board are you using?

The question is what voltage, and/or continuous power level, is the cartridge rated for?  You're going to dump roughly the same total energy to reach a given temperature setpoint regardless of input voltage. ("Roughly" because there is heat loss from the hotend to air)

any way I can figure that out?

The same total energy given a set temperature, but a higher wattage will have a higher max temp and be able to heat up quicker. Regardless I don't see how we can determine the rated voltage with the information provided. We would be better off looking at the source of the heater cartridge, from a pre assembled printer, printer kit, preassembled hotend, or sourced individually. If it was sourced with the rest of the printer what voltage of the PSU?

@user1282931 as my answer explains, you might need to supply photos - both possible types exist.

e3D Heater Cartridges are documented to be around 4.8 Ω for 12 V & 30 W, 3.6 Ω for 12 V & 40 W, 19.2 Ω for 24 V 30 W and 14.4 Ω for 24 V 40 W.
7.2 Ω is a value quite far away from these values - about double of what the 12 V versions are listed and about a third/half of a 24 V heater cartridge. So it is not a cartridge that is similar to those. I have contacted e3D about updating the specs of their High Precision Heater Cartridges to include the nominal resistances to get more references, but that information is pending.
However, we don't need that. A variant of Ohm's law can help us estimate what this cartridge could be: Power is the square of Voltage (U) divided by Resistance.
$P=\frac {U^2} R = \frac {144\ \text V^2}{7.2\ \Omega} = 20\ \text W$
$P=\frac {U^2} R = \frac {576\ \text V^2}{7.2\ \Omega} = 80\ \text W$
Mounted in a 12 V Machine this should act work at 20 W, in a 24 V it would work at 80 W. It does not say, however, if it is designed to get powered with 12 V or 24 V. It doesn't help, that both types exist: I was able to find 12 V 20 W heater cartridges just as well as 24 V 80 W heater cartridges. If it is an underpowered 20 W one and mounted in a 24 V machine, you risk burning it though, but not the other way round.
To differentiate what exactly you have, a photo of the heater cartridge would be needed - it should bear at least a marking of what it's nominal wattage or voltage is.