MK3 Extruder Skipping  

Re: MK3 Extruder Skipping

may be he also does not know what it means.... 😀 😀 😀 just copy paste from his script 😀 😀 😀

Re: MK3 Extruder Skipping

Aloha folks,

Okay I have good news I emailed the tech that had been helping us all along and let me know I was posting his response to the forums to help others.

He replied
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Hi there.

It means, that the cable management wasn't assembled properly and had to be corrected.

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I will tell you the person I dealt with via email at Tech Support is a super guy and really took the time to try to solve the problem, gave me options and did in fact solve the problem.

So if you trouble shooting your own printer double check the cable management. At Mystic-Realm we don't want to work on printers or mod printers we just need them to work. We are so very thankful that Prusa folks took good care of us.

Be blessed!

Re: MK3 Extruder Skipping

@MysticRealm, thank you very much for the sharing.

For me, I have fixed mine yesterday. As I have tried many things including rebuild the extruder with all new components. End up, I have to downgrade the firmware from 3.5.1 to 3.4.1 As someone told me that start 3.5.1some printers experience the Temperature drop randomly. I have not connected my printer with Octoprint yet, so I can't show if it effects on my printer. But, once I downgrade the firmware it works as it supposed to be.

Re: MK3 Extruder Skipping

I have 10 Mk3 printers, and I'm also running into the same extruder clicking issue on a couple of machines (not all of them, yet).

I have tried:
- Increasing hotend temp,
- Lowering print speed,
- Lubricating bondtech gears,
- Repositioning/calibrating bondtech gears with piece of filament,
- Adjusted filament idler tension multiple times, from weak to strong,
- Stealth mode, normal mode,
- Different filament colors, brands and even materials (PETG and PLA).

None of these worked so far.

Could linear advance have something to do with it?
If yes, is linear advance value stored in the printer's memory until it gets overwritten?

Re: MK3 Extruder Skipping

If someone hasn't already posted this, it looks like one of the reasons that slowing a print down and turning up the temperature can also reduce or eliminate clicking/under-extrusion issues is that the “custom” PRUSA e3D heatbreak changes bore size from 2.2 to 2 close to the heat zone. Proto-Pasta did a bunch of testing that showed that this was probably the major cause of the click (stepper slips) and under-extrusion sometimes leading to jams. If this is your problem, the solution is to by the non PRUSA custom e3D heatbreak

Re: MK3 Extruder Skipping

Another common cause for the jamming/skipping extruder is the idler shaft for the bondtech idler backing out. It happened to me after about a month of perfect printing. The press fit on it is pretty poor, but they fixed it in the MK3S release.

The "Prusa" heatbreak is definitely another cause for jamming. There's a long thread somewhere around here where the OP swapped out to the Nickle coated MicroSwiss heatbreak and never looked back. He said it resolved all of his jamming issues.

Despite the MicroSwiss heatbreaks being out of stock, I think any straight through or non-step-down heat break will work. If you don't use MMU, I highly recommend swapping out that step-down heat break. The MicroSwiss heatbreak is actually step UP, but the step is above the heat break zone. I wonder why MicroSwiss thinks this Step Up style is better. All they say is "Stepped inside bore to improve PLA printing."

MICROSWISS HEATBREAK CUTAWAY

RE: MK3 Extruder Skipping

I have also been struggling with the extruder of my MK3S.  First it started slipping and searching around it was only when I tried to fasten the tension screw some more that I found that the tension screw's hex head has started pulling through the extruder body.  I guess the small surface between the screw and the extruder body, combined with the heat of the extruder was just too much.

I have then tried different methods to work around this as I do not currently have black PETG with borders being closed for anything non-essential and secondly I am not quite able to print anything with the extruder not working properly.  So I have ended up with a 3mm washer on the screw, but it seems with the hole already enlarge this also did not last long.  Then I ended up taking a thin but much larger diameter washer which I have beaten to some kind of convex shape to fit partially over the hole and prevent it from pulling through again.  This has brought some improvement.

Soon afterwards I started experiencing the skipping issue as mentioned above where the extruder motor would just click instead of feeding the filament.  From reading several forum posts I realised that this time my issue might be slightly different.  It might well be, with the screw not pulling into the hole as deep as it used to, that this time I am over tightening the screw.  So I have loosened it up a bit and I am trying again now.  So far so good.  Looks like it is working so I am crossing my fingers that things will start to work again.  I should probably start working on getting myself some black filament to reprint the extruder body while it seems to work now.

RE: MK3 Extruder Skipping

I'm getting the same issue where the motor is micro-stalling. I have tried most troubleshooting steps that others have. Fortunately, I have another Mk3S (machine #2) so I can confirm that prints, which fail on machine #1, work perfectly on machine #2 (using the same material, same g-code). The stalling affects about 10% of the print, which is enough to fail any print and it seems to be getting worse. I've tried a wide variety of prints and the timing of the stall seems to coincide with more material being extruded. The motor does not get unusually hot and it has even happened on the initial purge of a print after being switched on.

Additionally, I have replaced all printable parts for the extruder, and used the hot end and gears from machine #2. Didn’t help. I contacted support about this and they weren't able to help beyond advice for preventing filament skipping, which is not what’s happening here. 

This video shows the micro-stalling over about 10 seconds (from about 22 seconds in), when you can hear the stall noise but the extruder isn't moving. Previously, when filament skips, the motor has the power to chew a chunk out of the filament but it doesn’t have the power to do that anymore. I have set the gear tension from very tight to very loose and it makes no noticeable difference. The gears have been cleaned, aligned, changed over from #2 and no matter what, machine #1 still micro-stalls while #2 still works perfectly. 

It seems clear that, under load, the motor is not delivering the power needed. I assume the voltage is good because the self-test is good. But I am no electrical or software specialist so I'm hoping that someone out there can advise what else to try to determine which component is faulty. The machine is now 5 years old and it won't be a surprise if something needs replacing, but what? I'm guessing the PSU or EINSY but who knows, might be a faulty connector.

Any help is greatly appreciated - I really need this machine to be running again!

Thanks, Tom @3DPC

RE: MK3 Extruder Skipping

Posted by: @sven-d3

[...] Could linear advance have something to do with it?

Under very specific circumstances, possibly. I started getting extruder skips while printing the prime line. Since the prime line is generated with 'raw' gcode, it pushes a big blob out quickly without regard to printer capabilities. With LA enabled, this would cause skips. With LA disabled (M900 K0) at the start of the prime line gcode, this problem went away. You could try disabling LA to see if it helps, but you really do want LA for print quality.

One thing I don't see on your list that might cause problems mid-print: If cooling kicks on mid-print and the fan duct is not oriented properly, it can cool the heater block which might explain why some printers have the problem and not others. Check your cooling fan orientation, consider another duct design, and add a silicone sock to protect the heater block from thermal shock.

RE: MK3 Extruder Skipping

@bobstro

I think you may be confusing the filament skipping and motor stalling. Both sound the same but filament skipping is usually caused by a filament jam, due to exceeding speed limits, under temperature, dirty gears, over cooling and so on - the gear turns but doesn't advance the filament, which usually gets chewed up by the spinning gear. Motor stalling is where the motor misses steps and can be identified by a visualizer that shows the motor shaft isn't turning when it should be. I am no expert on this but the causes are probably excess load on the motor, maybe due to friction with another component, very tight gear tension in combo with with jammed filament or some electrical issue that's causing the motor to loose torque. I have pretty much eliminated everything but the loss of torque.  

As to your suggestions, I tried disabling linear advance and it didn't help - in fact there was a micro stall on the prime line. I stopped the print when stalling continued. The cooling fan is well aligned. I use a silicone sock on most prints, although it's off at the moment since I'm printing PLA where any benefit is marginal at best and because I'm trying different things. 

RE: MK3 Extruder Skipping

Posted by: @3dpc-2

I think you may be confusing the filament skipping and motor stalling. Both sound the same but filament skipping is usually caused by a filament jam, due to exceeding speed limits, under temperature, dirty gears, over cooling and so on - the gear turns but doesn't advance the filament, which usually gets chewed up by the spinning gear.

No, not confused. Motor stalling is a common symptom of exactly the issues you listed. It's clearly visible with an extruder visualizer installed. The extruder motor may shred the filament if the tension is sufficient, or simply slip when it cannot overcome the backpressure when the filament can't be advanced. You'll see the visualizer jump and hear the clicks when this happens.

Motor stalling is where the motor misses steps and can be identified by a visualizer that shows the motor shaft isn't turning when it should be.

Yes, that is the effect. I'm understanding you're after the cause. It sounds like you've done most of the basic troubleshooting steps. Personally, I'd take as much out of the equation as possible by doing something like:

1. On one of the Mk3s that is not exhibiting the problem, raise Z, heat the nozzle, and manually extrude a length filament. Repeat, increasing speeds until you the motor begins to skip/extruder begins to chew filament (both of which you can usually hear clearly). Note your upper-end speed. 
2. Repeat the procedure on one of the Mk3s exhibiting the problem.

Then compare results:

• If the speeds are close, you have reasonable assurance that your motors are generating sufficient torque and the basic printer hardware is functioning. (This is essentially the same procedure for calibrating your hotend maximum volumetric flow. Notes here.)
• If the speeds vary and the affected Mk3 can only handle lower speeds, you may have a hardware problem. You might try using the M907 Exx gcode command to adjust extruder motor current as is done in the latest PrusaSlicer start gcode. You can use the Prusa presets as a starting point:

{if print_settings_id=~/.*(DETAIL @MK3|QUALITY @MK3).*/}M907 E430 ; set extruder motor current{endif}
{if print_settings_id=~/.*(SPEED @MK3|DRAFT @MK3).*/}M907 E538 ; set extruder motor current{endif}

Prusa's presets use a higher motor current for faster print profiles. Unfortunately, M907 settings don't seem to be displayed with an M503 settings dump. I'm not aware of a way to view what a printer is set to, and presumably, it has changed with firmware updates. Are your printers all on the same firmware version? I'm also unaware of any way to save this setting, or whether it is saved with M500. Is it possible you printed with a Prusa detail profile at one point, or do so periodically? I've had problems when Prusa presets made setting changes that were still in memory when I switched to a custom profile.

You're using the same filament on all printers, correct? 

RE: MK3 Extruder Skipping

1. ... manually extrude a length filament. Repeat, increasing speeds until you the motor begins to skip/extruder begins to chew filament (both of which you can usually hear clearly). Note your upper-end speed. 

How do I do this? I can manually extrude (settings/ move axis/ extruder) but tuning the speed has no effect while doing this, so need an insight here. 

Both machines are on firmware level 3.9.0-3421

RE: MK3 Extruder Skipping

Posted by: @3dpc-2

How do I do this? I can manually extrude (settings/ move axis/ extruder) but tuning the speed has no effect while doing this, so need an insight here. 

The linked notes on calculating maximum volumetric rate show the details of how to do this. You need some sort of serial terminal program to interface directly with the printer. I use OctoPrint. Pronterface is another option. Any serial communications program (e.g., screen on MacOS) should work.

RE: MK3 Extruder Skipping

@bobstro

Thanks, it's interesting to quantify the effect. Using Pronterface and extruding PLA (from the same spool) at 210 C. Both machines fitted with 0.4 nozzle X. Results:

Mk3S #1 Okay at 250 mm/min, Starts clicking at 275 mm/min. MVS ~10. I played with the idler tension it but didn't make an substantive difference.

Mk3S #2. Okay at 400 mm/min, Starts clicking at 425 mm/min. MVS ~ 16. I felt this is normal so I didn't adjust anything.

I don't feel comfortable with adjusting the motor current and I'm no good at gcode programming, so without a clear objective of where the desult would lead, I didn't adjust the motor current.

I thought your MVS tests were interesting, BTW, particularly the MVS of PETG being higher than PLA. The limiting factor is probably quality in that case rather than torque/ resistance. 

RE: MK3 Extruder Skipping

Posted by: @3dpc-2

Thanks, it's interesting to quantify the effect. Using Pronterface and extruding PLA (from the same spool) at 210 C. Both machines fitted with 0.4 nozzle X. Results:

Mk3S #1 Okay at 250 mm/min, Starts clicking at 275 mm/min. MVS ~10. I played with the idler tension it but didn't make an substantive difference.

Mk3S #2. Okay at 400 mm/min, Starts clicking at 425 mm/min. MVS ~ 16. I felt this is normal so I didn't adjust anything.

I'm assuming Mk3S #1 is the problem child with clicking?

I don't feel comfortable with adjusting the motor current and I'm no good at gcode programming, so without a clear objective of where the desult would lead, I didn't adjust the motor current.

I'm not crazy about the idea myself, so don't include it in my gcode. Unfortunately, I'm not aware of a way to determine what it's currently set to, or if changes are persistent.

Interesting that you're finding a significant difference between printers of the same type. I'd be interested to know if your other "clicky" printer(s) show similar results.

I've got a quick checklist for extruder or hotend issues here. It would be interesting to replace the heatbreak and nozzle on the clicky printer, or better, swap those parts (or the entire hotend) with a non-clicky printer. Have you done a PID tune on all of them? Temperature variations might cause problems. 

I thought your MVS tests were interesting, BTW, particularly the MVS of PETG being higher than PLA. The limiting factor is probably quality in that case rather than torque/ resistance. 

It was a real surprise for me as well. I started testing in earnest when trying to maximize PPE print output last year. I took the PETG MVS settings for granted, assuming "PETG is always lower than PLA". I was surprised at how much faster PETG could flow. Quality does suffer, but that doesn't always matter, especially if you're not printing with infill or fine details. If I plan on working with a filament much, I'll use that procedure as a quick test to determine the "redline" value, then back quite a bit off from there for actual printing.

I'd be going nuts with one printer acting differently than another. Good luck hunting the problem down and please update if you find a solution.

RE: MK3 Extruder Skipping

@bobstro

Yes, Machine #1 is the problem.

Yes, I'm going nuts about this.

  - I  have swapped the whole hotend & gears with machine #2 (where they is working just fine)

  - I have installed all new printable parts in the extruder

The only relevant components I haven't changed are the motor, EINSY & PSU. I believe one of these is faulty but waiting on a response from PRUSA to determine which. I could swap over from machine #2 again but these are bigger changes and I am now down a machine so it's difficult. I believe a specialist in the motor controllers could instantly say what to do.

Machine #1 is about 5 years old and has given excellent service until this began to happen for no apparent reason. I think it is getting worse. At first I just lived with it but now it is effectively not working. Whilst your work suggests I might get away with using it for PETG, I had to give up on the last PETG print I was doing, but I might play with that when I'm desperate enough. 

Machine #2 is about 1 year old is working perfectly with all the old parts from machine #1

RE: MK3 Extruder Skipping

Posted by: @3dpc-2

[...] The only relevant components I haven't changed are the motor, EINSY & PSU. 

You've eliminated all of the obvious choices.

• The extruder motor is a good candidate. This might be a good opportunity to read up on replacing steppers with Moons 0.9° steppers, although you probably don't want any unicorns for mass production.
• Can you use OctoPrint or something similar to monitor temperature stability over time? That might help determine if the PSU is a concern. Turn up the bed, nozzle, and fans and observe, possibly with a meter.

RE: MK3 Extruder Skipping

SOLVED!

The replacement motor finally arrived and made an immediate improvement. The extruded now works normally and can extrude that same amount of material as the good machine using the Pronterface test. So I'm back up and running. 

There was some interaction with PRUSA techs on the way where potentially useful troubleshooting steps performed along the way helped to eliminate the PSU and EINSY:

    1. Measure thermistor resistance when cold. Mine measured 90.3 kOhm. I have a spare that measures 86.5 kOhm. Okay

    2. Measure cartridge heater resistance when cold. Mine measured 15.8 Ohm. I have a spare that measures 14.8 Ohm. Okay

    3. Compare voltages of the cartridge heater and heat bed during heat-up, should ~24V. Okay

    4. Compare voltages of the cartridge heater and heat bed once heated and stable. After a few minutes at PLA temps, cartridge was varying between about 3 and 5 V. The heatbed varied between about 2 and 7 V, which was considered normal.

WARNING. Measuring these is a bit tricky, and I strongly recommend you get advice from tech support before you create bigger problems.

There is no direct test of the motor. It was really a case of eliminate everything else.

I hope this helps someone to avoid a fairly tortuous few weeks/ months where it seemed no-one at Prusa believed the motor could possibly be at fault. Clearly it can go bad!

.

RE: MK3 Extruder Skipping

@3dpc-2

To be clear - this was the extruder motor?

RE: MK3 Extruder Skipping

Posted by: @tim-2

@3dpc-2

To be clear - this was the extruder motor?

Yes