PLA filament quickly jams, PETG is fine  

RE: PLA filament quickly jams, PETG is fine

You will discover some flecks of old PETG inside your nozzle or near hot end of heat break upon your tear down. At PLA print temperatures, a flake of PETG won't melt, particularly if it has been "cooked" for a while. This results in a clog while printing PLA.

This is always a risk when switching from a higher temp filament to a colder one. When changing from hotter to colder filament, always do a very thorough cleaning at the higher temperature by running through cleaning filament and preferably also an atomic pull. If any higher temp filament residua is left, it will eventually create a clog during colder filament printing.

RE: PLA filament quickly jams, PETG is fine

My printer has identical issues (Documented here) that have proved nearly impossible to fix. I have not printed in PETG so I am not sure if our printers jam due to the same reason but all of the symptoms of your jams fit well. I believe that a lot of the problems are caused by a design flaw relating to the heating as lots of people are having inconsistent extrusion problems and jams but I believe somehow the problem could be more severe possibly due to a defective part. I agree with guy-k2 that the next logical step is to clean the nozzle to check for PETG residue but if that fails I would advise to start considering your unit might have a larger underlying issue relating to the hotend and reaching out to Prusa research. Also does your extruder motor heat up significantly, I have noticed the motor on my units easily gets to high temperature almost enough to burn and suspect that could cause a momentary stop in printing triggering a jam as the filament bakes.

thanks

RE: PLA filament quickly jams, PETG is fine

I had some time to dive into this over the weekend. 

• I took apart the hot end, cleaned the nozzle and heat break to make sure there was no clog or particles, etc.  Visually examined them, used a heat gun to heat them up then clean them out with a needle, a brass rod and a Q-tip.
• Reapplied the thermal paste between the heat break and heat sink. 
• Reassembled the hot end, made sure the nozzle and heat break were snug together, and there is a gap between the nozzle and the heat block. 
• Replaced the PTFE tube and added the clip to hold the collet. 
• Cleaned and adjusted the bondtech gears to make sure everything was tight, aligned properly, the idler side moves freely, etc. 

After re-assembly, I started doing a Live Z calibration using one of the models with multiple squares across the build plate.  I was doing it with PLA to see if the maintenance had fixed the issue with PLA jamming.  I hadn't even finished the Live Z before it just stopped extruding.  The extruder motor was still moving, but the filament was no longer feeding.  I unloaded the filament - it came out easily, the end of the filament was normal sized and looked fine.  Reloaded the same filament without even clipping the end, and it loaded correctly and extruded fine.  

I next started a extrusion calibration test file, which has two pieces that print sequentially.  The first one started fine.  The bottom layers were clean, and most of the object printed fine, but as it neared the top (about 10 minutes into the print) it started under extruding badly.  Once it finished the first part, it started the second which almost immediately failed in a rats nest then stopped extruding entirely.  

I switched to PETG, and like always, it prints cleanly.  I'm now doing some other prints in PETG and they look fine so far too.  It is definitely only a problem with PLA.  I had been printing with PLA for a month or two without seeing this type of jam, so something changed, either in the environment or the printer.  It doesn't appear to be anything in the hot end itself, as far as I can tell.  Unless it is possible that the nozzle could work for PETG but not PLA for some reason?  That seems unlikely to me, but maybe I'll try switching the nozzle next.

It seems more likely to be an issue in the filament feed path.  The obvious answer is heat in the extruder causing the PLA to soften above the PTFE tube.  But I'm in a very cold basement, with no enclosure around the printer, and I didn't have this problem initially for the first month or two after setting up the printer.  I can put my hand on the extruder motor and it is warm but not hot. 

I don't have any way to check the temperature inside the bondtech chamber, so how can I prove or disprove if heat in the bondtech gears is the issue?  I don't think I have any tools to help with that - the closest I have is an electronic meat thermometer - but I'd be willing to buy something if it isn't too expensive.  Can I quickly unload the filament and measure the temperature of it before it cools enough to make the measurement useless?  What do people use to measure temperatures around the bondtech while it is running?  

And if it is not heat, what else could it be?  Could something around the filament sensor be causing it for PLA, while consistently working with PETG?  Is there something else that could be causing it?

Thanks for any advice you can share!

PLA test - 1st part - bottom surface

PLA test - 1st part - side - starting to under extrude near the top surface

PLA test - 1st part - top surface - badly under extruded

PLA test - 2nd part - total fail

PETG test - both parts print cleanly

RE: PLA filament quickly jams, PETG is fine

The extruder motor was still moving, but the filament was no longer feeding.

You mention neither any clicking nor chewing/deformation of the filament at or just below the Bondtechs.

There should be at least either clicking or chewing of the filament when the motor spins but moves no filament. In the absence of both those signs, the only thing left is the idler Bondtech not engaging with good alignment or with insufficient tension.

Presuming you did get either clicking but not deformation of the filament I am thinking about...

Classic Prusa heat break problem with their stepped heat break. Is PrusaSlicer set to have an unusually high retraction distance? Is it worth testing with an std straight through E3D heat break?

I think we can rule out thermal deformation of the PLA with such an early failure.

Could this be a hot end thermistor that is reading higher than normal and thus creating actual nozzle temps that are lower than normal? Lacking a contact thermistor, you could test by printing with PLA, but with nozzle temp cranked up another 10-15C.  If PETG prints OK under those conditions then you have a suspicious thermistor. 

RE: PLA filament quickly jams, PETG is fine

Hi Guy,

There was no clicking from the extruder.  As for deformation, I think it depends on how much you'd expect.  I'll post some pictures of the end of the filament after I unloaded it.  This is what the filament looked like after the failed prints I posted pictures of earlier today.  

The first picture has it lying flat, and you can't see the marks where the bondtech gears engage, so the surface is fairly clean and smooth.  I don't see any deformation in that one.  The second picture I'm holding it so that the gear marks are visible.  On the left side, near my fingers, is the area where the bondtech gears were chewing at it during the jam.  

I don't have much experience with 3D printing yet, but to me it doesn't look deformed.  The surface of the filament shows minor, regularly shaped, evenly spaced gear marks up the filament (from right to left in the pic) until the jam.  When it jammed, it looks like the gears were still spinning and gripping, with enough tension to kind of blur or wear away the surface of the filament so you can't see distinct gear marks anymore, just a general scarring of the surface.  But there wasn't so much tension that it was gouging into the filament either - the filament is not particularly thinner in that spot.  A while ago I had the bondtech idler tension screw tighter and had a jam, and the gears basically gouged a concave cavity into the filament on both sides.  But today, at my current tension, it just sort of wears away the surface a bit without really deforming it. 

I have already replaced the Prusa heatbreak with an E3D.  I used to get jams where the tip of the filament would have a pronounced bulge that was 2.2mm.  Since I swapped the heatbreak, that problem has gone away.  And I was able to print PLA successfully for at least a week or two after I swapped the heatbreak, so hopefully that means the new heatbreak is okay.  It was a couple weeks later that I started having the PLA jam with the current symptoms.  

I will try printing at different temperatures with PLA and see what happens.  I'm in the middle of a print with PETG right now, but I'll do some testing when it is done.

Thanks again for taking the time to help!

RE: PLA filament quickly jams, PETG is fine

If you have PLA print issues after printing PETG without issue, it's pointing to PETG still being in the hot end.  Try some cleaning filament or a few cold pulls with PETG until you get a clean pull - no warts at the nozzle cone. Then retry the PLA print.

. 

RE: PLA filament quickly jams, PETG is fine

I agree that PTFE residual in the system is still the most likely cause. However did pretty complete clear out of hotend. Could possibly be in the NOZZLE which wasn't mentioned as being replaced or cleared out. Atomic pulls for cleaning the nozzle whenever going from hotter filament to a colder one is essential practice.

Then there is the "zebra" of thermistor misreading temperature to rule out.

RE: PLA filament quickly jams, PETG is fine

I'm thinking it might be your "zebra".  I tried printing the sample tree frog with PLA at 215, and it failed within 30 minutes.  Tried again printing it at 230 (same gcode, but using the tune menu on the LCD to override the nozzle temp) and it printed cleanly.  Tried it again at 215 and it failed again, at almost the same layer as the first failure.  Now I am printing the Nefertiti at 230, which is a 7 hour print.  It is about 2 hours in and looks good so far.  Assuming it finishes, I will try one more tree frog at 215.  If that fails, then I'll have a pretty solid alternating pattern of success and failure at 230 vs 215.  I should know later today.  

Assuming it is temperature, here are the factors I can think of:

• Possibly a bad thermistor.  I don't really understand this one though.  If it is reading artificially high, wouldn't it be worse with PETG than PLA?
• I do have a hardened steel nozzle in the printer at the moment.  I can try swapping back to the original brass and see if that matters.
• I do have a silicon sock on the nozzle.
• I replaced the Prusa heat break with a straight through E3D heat break.  At that point I added thermal paste to the heat break / heat sink.  My printer was shipped just before Prusa started doing that, I think, since my original heat break did not appear to have any thermal paste.

Regarding the timing of when I started having PLA failures, I know that I had successful PLA prints when I first switched to the steel nozzle.  I read that steel may need some extra heat compared to brass nozzles, but I didn't see an effect initially.  I switched to the steel nozzle because I wanted to print some wood PLA, and that worked fine for several medium-large prints, so everything was good then (as long as it didn't do the heat break jam). 

Then I replaced the heat break.  I know I had several successful PLA prints after that, but I can't recall which nozzle was used - it might have been a brass .25 mm.  It may be that the PLA temperature related failures started after replacing the heatbreak and only with the steel nozzle.  I'll try switching back to the brass nozzle and see what happens.  

So, maybe I damaged the thermistor during the heatbreak replacement? What tool do I need to buy to verify if the thermistor is good or bad?  

Also, would the nozzle's depth of insertion into the heat block affect this?  There were two versions of the E3D instructions that I saw.  Each version had me screw the nozzle in flush to the heat block, then unscrew it a little, then insert the new heat break until it touched.  The older instructions only had me unscrew the nozzle a partial turn (forget if it was 1/4 or 1/2).  The latest instructions had me unscrew it a full turn.  I followed the latest version, so there is now more of a gap between the nozzle and heat block than it used to have with the original.  That would mean less of the nozzle's screw is within the block, so that might be affecting how it is transferring heat into the body of the nozzle?  Combined with steel instead of brass, maybe that is the issue?

Take home message:   I need to keep a journal with the dates of any part or nozzle changes, and when errors occur, so I can look back at what combinations cause issues... 😀 

RE: PLA filament quickly jams, PETG is fine

One final data point to get is test with a new brass nozzle. 

If old nozzle has residual PETG causing clogs, 230C is high enough to melt PETG and make things work again.

If you put in a fresh new nozzle, print at 215 with PLA --> fail, but print at 230C -->succeed, then we eliminate PETG residue as cause.

That would cinch the thermistor as root cause instead of PETG residue. 

Steel nozzle complicates things because effective print temp is about 10C to 20C lower at nozzle tip than thermistor setting.

RE: PLA filament quickly jams, PETG is fine

yep i bet the steel nozzle is the cause - 230 w/steel is probably close to 215 w/brass

RE: PLA filament quickly jams, PETG is fine

There should be a requirement for users to post configuration, like printer model, FW version, filament type and age, nozzle size and type, print source, slicer used, and any user mods ... It would really save folks helping others a lot of time.

RE: PLA filament quickly jams, PETG is fine

Over the weekend I swapped the steel nozzle for the original Prusa brass nozzle.  At first, it looked like that fixed it.  I was able to print the sample tree frog on the SD card at the standard temperature, which had failed 3 times in a row with the steel nozzle.  However, that may have been a fluke, as virtually everything else I've tried since that first print has failed, even when I raise the temperature to 230 again.  If I had to compare the success rates with the steel and brass nozzles, it seems like the brass is actually failing more often and at the higher temperature, which makes no sense to me. 

I do have a brand new brass nozzle from Amazon.  It came in a selection of nozzles included with a tool kit that I bought, so I assume it is probably a low quality nozzle, which is why I haven't tried it yet.  Maybe I'll try that next though, just for comparison.

Assuming that doesn't solve it, any recommendations on what tool I should get to verify the temperature and see if the thermistor is accurate? 

Do you think that having the nozzle not inserted far enough into the heat block could be the issue?  I could take it apart and unscrew the heat break a little so the nozzle is just half a turn out of the block instead of the full turn described in the new E3D instructions.  

RE: PLA filament quickly jams, PETG is fine

Ohm meter for test thermistor: a high quality DVM / DMM is worth the cost.  And they can be purchased pretty cheap:

https://www.amazon.com/Fluke-101-Multimeter-Equipment-Industrial/dp/B00JT5RUUU

And this is a good in between if measuring AC current is in your future:

https://www.amazon.com/Fluke-107-Current-Handheld-Multimeter/dp/B00HEAMMIC

But this is a bit better for reasons I don't want to go into:

https://www.amazon.com/Fluke-True-RMS-Multimeter-Polyester-Carrying/dp/B01EWFB9FI

RE: PLA filament quickly jams, PETG is fine

Did you ever solve this issue? I’m having the same problem where petg prints perfectly and pla is causing me lots of headache. Getting better results at around 230, at least when it comes to extrusion, but I keep trying to lower it since using a higher temp than needed can cause other issues, but always run into problems. Seems strange that it’s easier to print petg than pla.