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PETg woes

Posted by SupraGuy 
PETg woes
August 07, 2018 02:03PM
No pictures to support, but PETg is making me crazy.

I had high hopes for it, and my first attempt seemed to be going well. Unfortunately my gcode file was truncated, so it just stopped printing after about 7mm, but up to there, it looked perfect.

Then I tried again, and I got about 2 layers, then it jammed. I had to disassemble the extruder, since the filament bent and wouldn't go through the nozzle. I tried slowing down the print speed, same thing. bumped up the temp from 240 to 245... 250. Still no good. Printed (In ABS) a piece to go between the extruder gears and print throat. It stopped folding the filament and shoving it out to the side, but instead just jammed, and stopped extruding. (By 250 deg C, it was also really stringy, and wouldn't stop oozing, but at the same time wouldn't extrude.) The first layer or two seems to work fine, bed adhesion is good, layer adhesion is good, but it just stops extruding at all after that. (After putting int he part to make folding the filament impossible, it still extrudes a tiny amount, basically reduced to a constant ooze.

Printer works fine for ABS, and PLA but I had a part that I wanted to print in PETg.

I have a modified Mk10 nozzle setup. I was worried that the aluminum bar was getting too hot, but it doesn't seem to be adversely affecting the ABS part that I printed at the top of the nozzle, and there is a part cooling fan mount attached to it as well, which seems to be fine. My feeling is that it's related to having an all-metal hotend somehow jamming at the heat break where the temperature is settling to be hot enough to melt the PETg, but too cool to let it flow freely. I really want to resolve this though.

As I write this, I kind of come to the conclusion that hotter and slower doesn't seem to be the answer. I might try dropping the temperature a little to see how that does.

Of course if I could just solve the problem of large ABS prints warping like crazy, I might not need to use PETg at all.


MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts
Re: PETg woes
August 07, 2018 03:47PM
Doing some searching/reading here...

Heat creep may be the problem. I'm not using a lot of retraction. I'm getting some stringing, but generally, I think that the levels are acceptable. The one part that went fairly far looked pretty much acceptable as far as it went. (No idea why that one never had the problems that subsequent print attempts using the exact same settings do. This is also including when the printer was fired up from a complete 24 hour cooldown.) A little cleanup around holes may be needed.

My heat bed seems to be inconsistent when it comes to leveling. This printer uses 3 point leveling, utilizing a microswitch on the side of the extruder. I suspect that the glass on the heat bed isn't the flattest, so it changes sometimes as it heats. This causes some other problems. (I'm looking forward to getting the piezo sensors working on the other printer, which is what the part I'm trying to print in PETg is for.)

I can try changing out the aluminum throat for one that has a PTFE tube in it. I was a little concerned about printing temperatures greater than 240 deg C, but I don't think that I need to use higher temperatures than this. Of course filing the stainless steel tube down to fit in my print head is a bother, but I do have one.

The printer originally came with a PEEK tube directly connected to the hot end block, and the firmware configured to shut the printer down the instant that the hot end hit 245 deg C. I lifted that limit when I upgraded the firmware, since it would hit that sometimes when printing at 230 deg C, and I wanted to print ABS at 235 deg C. I apparently misconfigured the thermistor when I upgraded the firmware, and at an indicated 230 deg C, the PEEK tube melted a little. I replaced the PEEK tube, heat block (And thermistor for one of known calibration) with a Mk10 setup, but I needed to file down the tube in order to fit my printer. (This one has a 7mm opening for the throat, the Mk10 has a tube about 7.5mm in diameter.) I have one stainless steel throat that wants a piece of PTFE tubing inside, and one that's solid aluminum. I put the aluminum one in the lathe first, as it was much easier to do. I will file down the stainless steel one next, and try with the PTFE tubing inside to see if this resolves the issue. Kind of too bad, since it currently works very well with ABS and PLA.

Otherwise, the properties of PETg seem very desirable. What I've managed seems to be very warp resistant, layer adhesion is very good, if not excellent, and the finish seems good. A little stringing, but nothing that can't be easily cleaned up. I'm looking forward to getting good results.


MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts
Re: PETg woes
August 08, 2018 12:27AM
Maybe your extruder is pinching too much and squeezes the filament oval? That's typical for hot settings_still not passing the throat.
Re: PETg woes
August 08, 2018 01:54PM
Thanks, o_lampe, I don't think that's it though. When I pull the filament out, it definitely has marks from the extruder, but still seems round enough. I'll take a look at the stuff that I've cut off (where it got chewed up from the extruder gear) to see if this might be the case. I don't think I can really alter that pressure much though, There's a spring-loaded wheel that presses it against the gear. It's definitely another avenue of investigation.

I pulled the hot end apart. The beat break ... broke. It was full of melted plastic, past the constriction, and I'm fairly certain that was the problem. I'll have a replacement Friday.

I decided to bore out the aluminum block, instead of milling down the hot end throat, I put my GOOD calipers on the throat piece, and I get 7.76mm diameter. I bored out the block from having a 7mm diameter hole to a 5/16" (7.94mm) diameter mounting hole. The throat fits snugly with a little thermal grease to aid heat dissipation.At least now I can use obtainable standard parts if I decide to change it again. Hopefully the Wanhao Mk10 parts will continue to be available next time I need to do something about this. (Well, hopefully I get this solved, and never have to look at it again.)

Of course I also broke one of the wires to the thermistor in the heat block. It wasn't really under any strain, but just moving it seemed to be the last straw.

There was also a big hunk of melted plastic that had squeezed up from the heat block to the top beside the heat break. I may be wrong, but I think that this may be the reason why the first print seemed to go okay, and subsequent ones failed. Apparently I didn't have the nozzle appropriately cinched up against the heat break, leaving a bit of a gap. Not much, but enough to allow some plastic to work its way up past the threads. At some point there was enough there to no longer allow the heat break to cool, and the heat started creeping up the throat, melting the plastic a bit too high. Even though I've used a lot of ABS, the colour of the majority of that mass would indicate that it was mostly PETg. (Though there was definitely some of the ABS in it, too.)

So corrective measures to be taken:

Replace the broken parts. Note to self: Chances are that once installed, that heat break is probably never going to be removable from the heat block. Maybe if I hit the heat block with a propane torch...

New heat brake to be threaded in deeper to definitely meet the nozzle and seal. I suspect that this might work better if the heat block is at temperature when I tighten the nozzle to the heat brake. My fear is then that it may be difficult to ever get the nozzle off, if I need to, but if it works, then I should never need to, right? Well, ideally, I'd like to be able to change nozzle sizes, since I have a selection of them from 0.2mm to 0.5mm. Will probably require the application of heat, but then that might just be a good idea regardless. I should find a wrench that I can put on the heat block to hold it so not to strain the heat break.

New thermistor. I think that I'll grab the one in my E3D V6 hot end that I was planning for my rebuild. I had been considering the use of a PT1000 temperature sensor anyway, this may just be the impetus that seals the deal. Since this means that I'll be going back to a PTFE lined throat, I doubt that I'll be using this for temperatures over 250C anyhow. Hopefully the heat break works well enough to keep the PTFE in good condition.

My original run with PETg was terrible with this printer. I didn't have a heated bed, and the auto level was terrible. (It's still not great.) I ended up with nothing decent, and a lot of grief. It definitely needed hotter extrusion than what the printer would allow at that time too (pale, strained looking extrusion and terrible layer adhesion, even at painfully slow print speeds.) As the printer came to me, it was basically only good for PLA. Once I added the heated bet, it was okay for ABS, but anything thicker than about 3mm and larger than about 50mm to a side starts to curl. I might manage on a hot day with the A/C turned off, but that only goes so far, too.

This last attempt, I was so hopeful on the first run. Everything looked great, right up until the truncated file just stopped printing. I was about 6mm in, and no sign of curling, excellent layer adhesion, and a nice glossy part. I'm hoping to be able to replicate that experience once I get this sorted.


MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts
Re: PETg woes
August 22, 2018 10:09AM
So to date, I've run about a third of a spool of PET|g through this printer, and every single scrap of it has been garbage. I have yet to finish a single successful print. My best result to date has been that one where the file was truncated and it at least finished what was in the file.

The throat with the PTFE in it has not helped matters in the slightest, and has actually made for more problems with ABS than I had before I did it. I think that I'm ready to call that an abject failure and go back to the all-metal.

The printed surface looks terrible, kind of pale, like the plastic has been stressed if I print at even 3/4 of the speed that I routinely print ABS at, even if I'm printing at the limits of what the PTFE will allow (245-250 deg C) At least with the all-metal I could print hotter and the surface looked okay. It still will push the filament to the side of the gear instead of down the nozzle throat if there's a gap there wide enough for the filament there.

The one and only thing that I like about this so far is that the bed adhesion is nice. It doesn't seem to have the same warping issues that ABS is plagued with, but frankly, it's hard to tell when getting past about 1mm of thickness so far has been extremely rare. Layers do appear to adhere nicely, but again, when it's so rare to get more than 3 or 4 layers, it's hard to really know.

I'm about ready to give up on this for keeps. I think I'm going to reinstall the all-metal hotend. At least I was getting better ABS results with that.


MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts
Re: PETg woes
August 27, 2018 08:09AM
I'm surprised that your nozzle temp is so high - my PETG spool says 195C to 220C nozzle, and 35C - 60C bed. I'm using PETG as I type this, with a nozzle temp of 200C and the bed at 60C.

In other words, much like PLA, but I've found that I need to reduce the print speed a bit.

UPDATE: Here's what I was printing while I typed:



Black HobbyKing PETG so not the finest material, and I chose too small an infill value resulting in some patterning on the surface, but as a first attempt it's not so bad.

Edited 2 time(s). Last edit at 08/27/2018 09:04AM by David J.
Re: PETg woes
September 06, 2018 01:00PM
Quote
SupraGuy
No pictures to support, but PETg is making me crazy.

I had high hopes for it, and my first attempt seemed to be going well. Unfortunately my gcode file was truncated, so it just stopped printing after about 7mm, but up to there, it looked perfect.

Then I tried again, and I got about 2 layers, then it jammed. I had to disassemble the extruder, since the filament bent and wouldn't go through the nozzle. I tried slowing down the print speed, same thing. bumped up the temp from 240 to 245... 250. Still no good. Printed (In ABS) a piece to go between the extruder gears and print throat. It stopped folding the filament and shoving it out to the side, but instead just jammed, and stopped extruding. (By 250 deg C, it was also really stringy, and wouldn't stop oozing, but at the same time wouldn't extrude.) The first layer or two seems to work fine, bed adhesion is good, layer adhesion is good, but it just stops extruding at all after that. (After putting int he part to make folding the filament impossible, it still extrudes a tiny amount, basically reduced to a constant ooze.

Printer works fine for ABS, and PLA but I had a part that I wanted to print in PETg.

I have a modified Mk10 nozzle setup. I was worried that the aluminum bar was getting too hot, but it doesn't seem to be adversely affecting the ABS part that I printed at the top of the nozzle, and there is a part cooling fan mount attached to it as well, which seems to be fine. My feeling is that it's related to having an all-metal hotend somehow jamming at the heat break where the temperature is settling to be hot enough to melt the PETg, but too cool to let it flow freely. I really want to resolve this though.

As I write this, I kind of come to the conclusion that hotter and slower doesn't seem to be the answer. I might try dropping the temperature a little to see how that does.

Of course if I could just solve the problem of large ABS prints warping like crazy, I might not need to use PETg at all.

I had this same problem occur in the high summer on two printers, one using PLA, the other PETg.
Long story short, humidity and heat creep.
One printer was using a Chimera clone, the other a genuine E3Dv6. I replaced the 30mm fan on the E3Dv6 with a 40mm one that didn't clamp onto the heat sink: problem solved.
I enhanced the single 30mm on the Chimera by moving it over a bit and attaching a second 30mm fan: problem solved.

High humidity makes it harder to get the heat away, poor airflow does too. What works marginally in optimal conditions (usually humidity here is around 20% or less) does not work well when conditions change. It is so weird to see higher temps cause lower flow and drooling. When I had filament jam in both directions (unable to push in or pull out) I knew what was happening.

DLC


Kits: Folgertech Kossel 2020 upgraded E3Dv6, Anet A8 upgraded E3Dv6, Tevo Tarantula enhanced parts and dual-head, TronXY X5SA Pro(E3DHemera).
Scratch: Large bed Cartesian, exchangeable heads, Linear slide Delta, Maker-Beam XL Micro Delta, 220x220CoreXY.
Re: PETg woes
September 06, 2018 04:02PM
Well, I'm certainly not taking a lit of anti-humidity measures, but I'd think that a fresh spool straight out of the vacuum packaging shouldn't have had that problem. Of course it's been out of the plastic a few times in the intervening couple of months. Still, it's not very humid in my corner of the planet (come winter, my filaments will be drying out just by being indoors), it hasn't caused problems with other filaments. for poor airflow, that's certainly a possibility. Anyway, I'll probably be using that printer pretty exclusively for ABS from this point, since that's what it seems to do well as tweaked.

If all goes well with my new build, I'll be letting that handle PETg, but I'm not buying another spool until/unless I can get it working well. So far, it's certainly seemed to be more trouble than it's worth.

The printer I've been having trouble with started with a PEEK throat to heat-break, but I changed that to an all-metal setup for a Wanhao Mk10 when a tuning mishap destroyed the PEEK part. The new one that I hope works better uses an E3D V6 clone. I replaced the 30mm fan with another. It came prepared for 12V, but I'm running the printer on 24V. (Then added a second full-time 12V supply, because I have a few things that need fans, and 12V fans are both cheaper and tend to be longer lived.)

Anyhow, I hope that the new printer isn't going to give me the same grief with PETg. I keep hearing good things about it as a filament, and I hope to reap the benefits of it at some point.


MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts
Re: PETg woes
September 10, 2018 11:57AM
I've now managed my first successful print in PETg ever. Nothing much, a set of 5mm couplers to replace the PLA ones that I had made originally. It is. however a HUGE step forward as far as I'm concerned.

The print itself is tiny, but it's a fact that I had never managed to get them more than a few layers high before.


MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts
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