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PETG Filament Crimping In Extruder

Posted by mpmumau 
PETG Filament Crimping In Extruder
May 11, 2016 04:00AM
I've been having an awful time getting PETG to print properly in my Mendelmax 1.5.

It seems like the hotend is getting too "full" with filament, causing the filament strand to crimp up after the hobbed bolt in my extruder.

I keep getting the same, consistent type of jam, as exemplified in the attached screenshots of atomic pulls.

I've tried a variety of settings at this point, including slowing down my print speed dramatically, as low as 30-40% (I normally print at 60mm/s), reducing retraction amount and speed, increasing and playing with different temperatures in the 240-250 degree range, increasing my bed height, reducing my extrusion multiplier to about .98 as well as saying a little prayer to the PETG gods. I've also tried both tensioning and untensioning the screws that determine the tension on my bolt to the filament. I'm using a standard Greg's Wade extruder.

Any ideas or suggestions as to why I'm getting these horrible jams? Thanks so much in advance for any advice!

Edited 2 time(s). Last edit at 05/11/2016 04:01AM by mpmumau.
open | download - petg_problems.jpg (246.1 KB)
Re: PETG Filament Crimping In Extruder
May 11, 2016 05:39AM
crimp up between bolt and extruder normally is a sign there is to much space between the two, The entry has to be as close as possible to the bolt. The filament getting stuck could point to either the tension of the idler is not being high enough or there is a small section of the filament that is larger then the ID of the hotend
Re: PETG Filament Crimping In Extruder
May 11, 2016 08:36AM
In some cases it can help to drillout the extruder so a teflon tube of the right ID can be fitted.
Requires some careful drilling though as you want a really tight fit preventing slipping.
The area around the bolt can be cut free once the tube is in place.
Re: PETG Filament Crimping In Extruder
May 11, 2016 02:18PM
The relative sizes of the filament and melt zone suggest you are using 1.75mm filament with a 3mm nozzle. The pressure that the extruder has to generate is determined by the cross sectional area of the melt zone, so will be roughly 3x greater for a 3mm nozzle, and that's really hard to push with 1.75mm filament - I know, I tried smiling smiley
Re: PETG Filament Crimping In Extruder
May 11, 2016 02:49PM
Thanks to all for the responses! I think I'm getting the idea here, especially with JamesK's response. If I'm following what you guys are saying, basically because the filament is too thin (1.75mm is correct) and my nozzle is capable of holding 3mm filament, the extruder gear is pushing, but the remaining bit of the filament doesn't have the force it needs to actually extrude? I typically print ABS and PLA 1.75mm filament fine, so perhaps I'm just noticing the problem now because of the fact that PETG is harder to extrude.

I'm not sure I'm ready or willing to take a drill to my extruder yet, haha, so perhaps I'll start by just dramatically increasing the tension between the hobbed bolt and the gear on my Wade's extruder. I'll let you guys know if that works.
Re: PETG Filament Crimping In Extruder
May 11, 2016 06:49PM

I'll start by just dramatically increasing the tension between the hobbed bolt and the gear on my Wade's extruder

I wouldn't hold out a lot of hope for that working. The best option is to replace the nozzle and throat with 1.75mm versions which will reduce the force needed to extrude the filament. Next best is to minimize the space between the extruder gear and the top of the throat so that there's less unsupported path for the filament to buckle.
Re: PETG Filament Crimping In Extruder
May 11, 2016 09:56PM
JamesK, I hear you. Unfortunately I have no practical way of doing that that I am aware of; I have a Greg's Wade direct drive extruder, so there's no real adjusting I can do to make the distance between the gear and the throat of my hotend smaller. It just is what it is. Other than printing a new type of extruder I don't believe there's any other way.

It's just the one material I'm having trouble with; been printing with PLA and ABS fine for years. So, if I have to do anything too dramatic with the printer itself, I might just chalk the ability to print PETG up to a loss. I was just wondering if there were any tricks or settings that might help, but sounds like that isn't the case.
Re: PETG Filament Crimping In Extruder
May 11, 2016 10:15PM
I've seen photos where people use a piece of ptfe tubing between the top of the throat and just below the gear to act as a filament guide. Is the top of the throat wide enough to take a piece of ptfe? Some of the Greg's/Wade derivatives have a filament guide built in, so printing a new extruder might not be a bad idea.

The only tricks I can think of are things that reduce the extrusion pressure - using a larger diameter nozzle and printing more slowly. Possibly running a higher temperature, but petg can be fussy about hotend temp. Interesting that it's been working with pla and abs. I guess it's the extra flex of the petg that's causing the trouble.

I hope you find a solution - it hurts to have filament you can't use.
Re: PETG Filament Crimping In Extruder
May 19, 2016 11:35PM
Just as an update to this, more or less for posterity, I did follow what JamesK and others had said about 1.75mm filament not being properly supported in my Wade's extruder. I ended up buying an E3D hotend specifically for 1.75mm filament, as well as some PTFE tubing to run through my extruder in order to properly ensure that my filament would be supported, and low and behold I'm now able to print PETG no problem. So, the RepRap gurus prevail yet again smiling smiley Thanks to all you guys for the support, and to anyone who's experiencing something similar down the line, they ain't lyin' when they say you really do need a 1.75mm extruder/hotend setup to work with 1.75mm filament. How I was able to get my printer to run ABS and PLA up until now is a bit of a miracle!

Edited 1 time(s). Last edit at 05/21/2016 01:48AM by mpmumau.
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