PETG Layer shift and ruined steel sheet
I just had a most disheartening experience printing PETG on a brand new steel sheet. The PETG is Prusament PETG left over from the MK4 upgrade and I had just successfully printer the same set of parts on a nearly dead steel sheet. I replaced the sheet and started the new print, forgetting to do any calibration first (this may have been the problem). When I came back to retrieve the finished print, I found the layers had shifted twice, the nozzle had contacted the sheet during the initial leveling process, and the parts were stuck to the sheet so firmly that when I finally got one off it peeled the green surface off the steel sheet with it.
I've noticed there is a fair amount of PETG on the nozzle and wonder if I ought to clean it up (probably yes) - would that affect it's ability to find the surface of the platter?
What else did I do wrong that would cause one perfect print followed by an utter disaster?
Thanks
Bill Lugg
RE:
You didn't say, so I can only assume that you printed on the smooth steel sheet. PETG probably sticks a little too well to the smooth sheet. You definitely have to let it cool down completely before you remove the print. I would suggest the satin sheet instead. You shouldn't have any issues with PETG or PLA with the satin sheet.
That being said, you don't have to do any calibration on the MK4 after changing the steel sheet, or the nozzle for that matter. If you have a clean nozzle the loadcell is able to determine the correct z-offset. That was not the case with the MK3S. On that printer you needed to do a first layer calibration after changing the sheet. On the MK4 it's necessary for the nozzle to contact the steel sheet during bed leveling. You want to make sure your nozzle is clean before you start a print.
In terms of the layer shifting you are seeing, that tends to be due to a loose belt, and-or pulley.
RE: PETG Layer shift and ruined steel sheet
You didn't say, so I can only assume that you printed on the smooth steel sheet. PETG probably sticks a little too well to the smooth sheet. You definitely have to let it cool down completely before you remove the print. I would suggest the satin sheet instead. You shouldn't have any issues with PETG or PLA with the satin sheet.
That being said, you don't have to do any calibration on the MK4 after changing the steel sheet, or the nozzle for that matter. If you have a clean nozzle the loadcell is able to determine the correct z-offset. That was not the case with the MK3S. On that printer you needed to do a first layer calibration after changing the sheet. On the MK4 it's necessary for the nozzle to contact the steel sheet during bed leveling. You want to make sure your nozzle is clean before you start a print.
In terms of the layer shifting you are seeing, that tends to be due to a loose belt, and-or pulley.
Thanks for the info. I've got a PEI sheet I've never used, so I guess I'll give it a try after I clean the nozzle. The steel sheet was stone cold before I tried to get the parts off of it, FWIW. I understand the nozzle needs to touch the plate during leveling, but in this case it was dragging the plate between test points, which I suspect was a result of the dirty nozzle.
I'll check the belt too just to make sure there's not a problem. It's curious I'd get one perfect print and the next one would be so bad.
Thanks
Bill Lugg
RE: PETG Layer shift and ruined steel sheet
If the nozzle is dragging, then it's likely that the 2 thumbscrews aren't tight enough and the nozzle is being pushed up when contacting the plate, then dropping again when the nozzle is moved between probes. Check that the thumbscrews are tight. Also, don't print PETG on the PEI sheet - it sticks waaaay too well. I've had PETG peel off the PEI covering. Use the satin or textured sheets with PETG. If you only have the PEI sheet, use a glue stick so that the adhesion isn't too high.
Prusa MK4 since Jan 2024, Printables: @MikeB_1505898
RE: PETG Layer shift and ruined steel sheet
If the nozzle is dragging, then it's likely that the 2 thumbscrews aren't tight enough and the nozzle is being pushed up when contacting the plate, then dropping again when the nozzle is moved between probes. Check that the thumbscrews are tight. Also, don't print PETG on the PEI sheet - it sticks waaaay too well. I've had PETG peel off the PEI covering. Use the satin or textured sheets with PETG. If you only have the PEI sheet, use a glue stick so that the adhesion isn't too high.
Thanks for the tip., I'll check those thumbscrews. Perhaps I spoke incorrectly re the PEI sheet. The sheet I had trouble with is the plain steel sheet with the smooth coating on it. I assume the satin sheet is the one with the "bumpy" coating on it, right? I incorrectly thought that was the PEI sheet. If I'm thinking correctly, I'll try the sheet with the "bumpy"coating, and see if things go better. Also, what are the optimal print temperatures for PETG? I've just been using the defaults in Prusaslicer.
Thanks for the help.
Bill Lugg
RE: PETG Layer shift and ruined steel sheet
Here are the links to the three commonly used steel sheets (smooth, satin, and textured):
https://www.prusa3d.com/product/smooth-pei-steel-sheet/
https://www.prusa3d.com/product/satin-powder-coated-steel-sheet/
https://www.prusa3d.com/product/textured-powder-coated-steel-sheet/
I use the satin sheet for PETG and PLA (which is all I print with). I used to use the textured sheet with my MK3S because it gives you a very nice textured finish on the bottom of your prints. Some people have had issues getting PETG to adhere properly to the textured sheet with the MK4, but you may not.
I always use the standard slicer temperatures.
RE: PETG Layer shift and ruined steel sheet
And here is a guide that includes details of recommended sheets per material: https://help.prusa3d.com/materials