Can't print PETG without damaging bed, now X axis is shot?
 

Can't print PETG without damaging bed, now X axis is shot?  

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Kate
 Kate
(@kate-4)
Active Member

Hi all.

Ive been using my MK3S happily with PLA for two months or so now. Ive done loads of big prints on it no problem. In fact id say the print quality is downright spectacular.

Recently i got involved with MasksForDocs, and printed a bunch of face shields for hospitals. I was printing 8 Prusa RC3 shields on my printer at a time no problem. No adhesion problems, never had to do any prep for the bed besides the occasional wipe with isopropyl. But the recommended material for doing these prints is PETG. I went to my local store that sells filament and picked up 2 spools.

First problem i noticed was that the prints were nearly fusing themselves to the bed. Unfortunately i didnt read up on PETG before i started printing, i see on Prusa's website they recommend wiping down the bed with windex before printing. The print i did took a chunk out of my bed, that was my bad. But i did a few more prints with the windex, i even used the Live Z Adjust setting to raise my Z axis height like somebody suggested. Now i have more chunks missing out of my bed, it helped but not enough. Yes im waiting for the bed to cool before removing. And the print quality... sucks. I was using the settings for Prusament PETG, i believe 240 for first layer and 250 for the rest, which matched the box of filament i have. I get a ton of stringing, and in some of the earlier prints random chunks would be missing from the final piece. 

All in all, i gave up after a few days and switched back to PLA. however, the first print i did crashed on the X axis. So i tried a different print which crashed too. I finally moved the X axis slowly by hand and noticed it gets hung up in some spots. The metal guide rails were dry so i greased them. That seemed to have stopped it crashing but now i swear im hearing an occasional squeal i never heard before. Also after the X axis moved back and forth mopping up the grase into the bearing, theres some leftover gunk and its black. Could this be bearing material? I dont think the bearings were tightened down too hard to begin with, the screws already seemed loose when i checked them just now. 

If i could get help on my PETG problems that would be nice but right now im most focused on the health of my machine. I dont want to have to worry about prints failing because of bearings. Should i replace them? Thanks in advance.

This topic was modified 1 year ago 2 times by Kate
Posted : 09/04/2020 3:57 am
delirium8413
(@delirium8413)
New Member

I cannot say much on the print bed, my own situation with PETG has been with the textured sheet From Prusa. One observation I have had though is if I try to remove the print as soon as the print is completes it is stuck to the base pretty well but will pop off when it is flexed. If I wait until the print bed has cooled to room temperature the print will left off with little to now force needed.

As for the bearings, I to had an issue with my X-axis crashing two days ago in the middle of a print. after disassembling the the thing to remove the bearings it was specifically the lower bearing that was binding to the rail. Lubing the rail did seem to to resolve the crashes for now, but I also had the extra grease build up being black in color. What I ended up doing was wiping down the rail then applying a little bit more lube then running a (~3hr) print and then wiping the rail down again and applied lube again if there was still some black residue. After two runs things are looking better. I have not noticed any squeaks at all during this process though.

One thing i would like to also point out because I was to frustrated at the time to think to do this, if you do disassemble the X-Axis to inspect the bearings apply some lube to the inside of the bearing before you put them back on the rail. Additionally, during the disassembly I did notice the boot of the sticking bearing appearing to be slightly damaged, I am guessing it is a manufacturing defect, and I did order a replacement set of bearing just to have on hand just in case.

I can relate to the stress I suspect you are having and hope this information is helpful.

Posted : 09/04/2020 1:32 pm
Peter M
(@peter-m)
Noble Member

Use glue stick if it still holds on to hard, for petg.

Posted : 09/04/2020 5:07 pm
Kate
 Kate
(@kate-4)
Active Member

@delirium8413

Thanks for the advice! Umfortunately your PETG experience has not matched mine, i did mention this in the post but i always waited until everything cooled before i tried removing the print. 

Regarding the axis. Ive had time to break down the printer some and began checking a few things out. Strangely once i took the motor off i did not notice any binding on the gantry. Perhaps my X stepper was overtightened, and over time caused extra wear on the bearings?

Below you can see the bearings removed from the axis. As you can see the bottom center one has a badly torn boot. This must be my issue, right?[caption id="attachment_24277" align="alignnone" width="600"] Worn X bearings?[/caption]

Posted : 10/04/2020 1:25 am
JoanTabb
(@joantabb)
Moderator

what are the rails like?
were you using a smooth build plate or a textured one? 
If you find PETG hard to remove, dribble some IPA on the build plare around the model and let it sit a while, and try again, if it's sill stuck well, try dribbling IPA around the bottom of the model on the build plate, again letting it soak until the ipa evaporates and then try flexing the build plate gently, again...  if the model starts to release but is still solid towards the middle, try some more IPA and flex again... 

Please  lube the linear bearings before using them again  

 

Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 10/04/2020 2:39 am
Kate
 Kate
(@kate-4)
Active Member

@joantabb

Rails are good as far as i can tell. Ive rolled them on the table, they are straight.

Unfortunately some balls fell out of the bearings, now i need new bearings for sure.

Im using the textured bed, does the smooth bed work any better?

Posted : 10/04/2020 7:45 pm
Kate
 Kate
(@kate-4)
Active Member

Oh wait! I thought i had been using the textured sheet. Turns out i have the smooth sheet. Ive ordered the textured sheet. Maybe thats been my problem all along!

Posted : 10/04/2020 8:16 pm
JoanTabb
(@joantabb)
Moderator

PETG can damage Smooth sheets easily... 

I hope the  textured sheet treats you well. 

Do you have suitable lube for the new bearings? 

I would lube when I fit the new bearings

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 10/04/2020 11:20 pm
Kate
 Kate
(@kate-4)
Active Member

@joantabb

Is the lube that ships with the printer not sufficient?

Posted : 11/04/2020 4:09 am
JoanTabb
(@joantabb)
Moderator

The bearings are apparently shipped with rust protection fluid installed,  a number of the people who rely upon this as a lubricant, have problems some time aft building the printer, when the bearings start jamming.  

I have always lubed my bearings and so far I have not had problems. 

My last mk3 came with a small tube of Prusa branded, white lithium grease, so I used that on the build... 

previously I have used Yellow LM2 Lithium grease on two printers, 'Slug Slime' Machine oil on one printer and white Lithium bicycle grease on the other printer, simply because they were handy at that stage in the build process. 

there doesn't seem to be any difference in performance between them

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 11/04/2020 7:01 pm
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