Mini does great with PLA, but repeated failures with PETG (jams!)
 
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Mini does great with PLA, but repeated failures with PETG (jams!)  

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BillyK
(@billyk)
Active Member
Mini does great with PLA, but repeated failures with PETG (jams!)

I have great luck with PLA, and usually also with PETG, but now I have repeated failures after about 2 hours with PETG.

The symptom is that the filament stops being extruded (hotend continues working as if everything is ok). The filament (Prusament) is stuck in the extruder, and requires multiple tries (and a lot of pulling) to unload. 

Once I get it out, there's an obvious 1-2cm bad (worn down, like it was filed) patch on the filament. Once I get it unloaded and cut off the bad part, it loads/unloads perfectly, but retrying the print again fails after a couple of hours.

There's some dust visible in the viewing door, but nothing bigger.

I saw a hint here about adjusting the screw just below the PTFE tube in the extruder. The manual says "You can use this screw to increase or decrease the idler’s pressure." Mine was super-loose. I assume my first move should be to tighten it ... but how much?

I'd really appreciate some advice rather than printing for 2 hours to see another failure. Thanks.

This topic was modified 1 month ago 2 times by BillyK
Posted : 19/09/2021 10:41 pm
fuchsr
(@fuchsr)
Noble Member

The Mini shouldn't have a problem with PETG. From your description it sounds like the idler screw is too tight and chewing up the filament but that doesn't jibe with your saying the screw was very loose. I assume you're looking at the correct screw (purple arrow):

 

I did experience issues with several types of filament—not necessarily PLA vs PETG, even within PLA different brands required different adjustments to the idler screw. In the end I had enough of that sensitive behavior and spent $30 on the Trianglelab clone of the Bondtech dual drive extruder  (on Aliexpress). Never had to adjust the screw again for anything, works like a charm. Okay, TPU, but that's to be expected. Best money I spent on the Mini, and the only upgrade I unconditionally recommend.

Posted : 20/09/2021 12:32 am
BillyK liked
fortinmike
(@fortinmike)
Trusted Member
Suggestions

I recently fixed the exact same issue on mine using the procedure I'll outline below.

BTW it doesn't look like an extruder issue to me. The MINI is plenty capable of printing lots of types of filament (including flex, depending on Shore Hardness) with the stock extruder.

It's normal for the idler screw to feel quite loose; it's not like a screw that needs tightening until you feel resistance, more like a tension adjustment. If you tighten it until you feel resistance the extruder is going to grind down your filament and that may lead to other issues. The screw head should be flush with the extruder casing (should be perfect for both PLA and PETG).

As for the clogs at approximately the same time (after 2 hours in your case), I'd first suggest to do a few cold pulls to clean the hot end as much as possible, then follow this procedure (no need to replace the PTFE tube unless it's much shorter than 43.4mm or visibly damaged) and pay special attention to steps 8 and up. Don't skimp on those as they will make sure that the PTFE tube in the hotend is compressed properly (bad compression, sometimes due to a heat-shrunk PTFE tube, is often the root cause of partial or full clogs).

Afterwards, depending on how much higher your heater block was moved upwards, you may need to move your PINDA up a bit. Just make sure that there is approximately the thickness of a credit card between the sensor and the heat bed.

Finally, make sure to do first layer calibration again before printing (starting from zero offset).

Then try printing again and tell us if you can get your part to finish printing!

Hope this helps.

Posted : 20/09/2021 4:12 am
BillyK liked
fuchsr
(@fuchsr)
Noble Member

I agree with everything @fortinmike said but I wouldn't use a credit card to adjust the PINDA. There's a huge difference between a thin Bank of America card and a thick, metal Amex Platinum card.…. The SuperPINDA should have a distance of about 1.5mm from the heatbed, so I created this little tool to help adjust it to proper distance. It should get you into the -1 range for Live Z for a good first layer. 

 

Posted : 20/09/2021 10:26 am
BillyK liked
BillyK
(@billyk)
Active Member
Topic starter answered:
Re:

Thanks, guys!

Yes, @fuchsr, it's the same screw you point to. The head of mine is about 1mm into the casing (I haven't touched it in a year of use), so I will adjust it out, not in as I had thought.

I will try the procedures @fortinmike suggests.

Really appreciate this advice.

Posted : 20/09/2021 1:57 pm
BillyK
(@billyk)
Active Member
Topic starter answered:
RE: Re:

I tried the easy thing of adjusting the idler screw out per @fortinmike 's suggestion. The print ran perfectly 9hours 53min before failing in the same way: print head kept moving as if it was printing, but nothing came out the nozzle.

Then unload fails, even when I unscrew both ends of the PTFE tube. I see that the filament goes cleanly through the PTFE tube when I unscrewed both ends: nothing stuck there, but it will not respond to unload without a lot of hard pulling.

I'm starting to agree with @fortinmike 's remark "BTW it doesn't look like an extruder issue to me". If the problem is a clogged print head that would explain these symptoms, right?

I'll do the cold pull next. Thanks for the instruction link.

This post was modified 1 month ago by BillyK
Posted : 21/09/2021 3:58 am
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