MK4 First Layer Problem with PETG  

RE: MK4 First Layer Problem with PETG

I have the same problem with both PLA and PETG. In fact, the auto bed leveling ends up being "too high" about 50% of the time for me.

No matter how much I make sure the nozzle is clean and the bed sheets are clean, the auto bed level still fails 50% of the time.

The loadcell is likely not working as expected. I don't like this loadcell implementation at all. Any hints on how to check whether the loadcell readings are as expected?

RE: MK4 First Layer Problem with PETG

Just a wild-ass guess here, but maybe the thumbscrews that hold the hot end in are not tight enough?
If there’s a little vertical wiggle in the nozzle, I could see it fooling the load cell to some extent.

RE: MK4 First Layer Problem with PETG

Thanks for the input. I've gone through mechanical set up a bunch of times now and the thumb screws are as tight as they're going to get without using wrenches. I've also cleaned the nozzle and the bed sheet to the point that they can be used for heart surgery. But still no joy.

I'm now experimenting with changing the start code with all of the baloney nozzle cleaning crap. Given the length of the nozzle, I'm just setting the nozzle/bed temp to actual printing temp, retracting the filament a good 2cm (i.e. prevent ooze), and then doing the nozzle clean and MBL at full temp. One print seems to be succesful.

Posted by: @jmck

Just a wild-ass guess here, but maybe the thumbscrews that hold the hot end in are not tight enough?
If there’s a little vertical wiggle in the nozzle, I could see it fooling the load cell to some extent.

RE:

The tube of the nozzle assembly has 2 grooves that are supposed to be perfectly aligned with the thumb screws so that the assembly cannot slide even with a bad tightening, and thus avoid also an exessive tightening that will damage the tube.

RE: MK4 First Layer Problem with PETG

I don’t notice the 1st layer issue as a PETG issue, but more as a textured sheet issue- though that is only time I’ve used the PETG.  PETG seems to stick better to the satin sheet, but PLA doesn’t stick as well to the satin, but PLA does well with the smooth sheet.

I think that the more texture, the more ‘free-space’ due to surface roughness.  PETG Filament my MK3S sticks like crazy, but is a lot less on the Mk4.  I think there needs to be a tweak for the sheet being used?  I think the PETG on the textured sheet needs to be about 50 microns lower.  the problem is that there is no option I can tell to tweak the height?

I like being able to switch sheets, but I’m getting pretty good at calibrating the Zero Z.

I’m not a G-code guy, but is there a line that we could put in that changes the height by a set amount???

RE: MK4 First Layer Problem with PETG

I checked the different sheets when I had the problems, but this doesn't seems to be the issue here. Usually on my Prusa Mini I printed PLA on the smooth sheet and PETG on the textured  and they all stick well. Then on the MK4 i tested PLA on all 3 sheets (smooth, satin and textured) and they are all good and have a correct first layer height. PETG has always a to high first layer (tested on textured and satin). So it is not a problem with the different sheets but with the Material.

RE: MK4 First Layer Problem with PETG

I had a heck of a time initially with PETG on my MK4. What seems to have been the problem is that for some reason the default settings for Generic PETG in Prusaslicer has the setting “keep fan always on” under Cooling set to “true”. Changing that made a huge difference for me. I also raised the first layer bed and nozzle temps, which seems to have also helped my bed adhesion for PETG printing.

Your results may vary of course, but it’s worth a shot.

RE: MK4 First Layer Problem with PETG

I just did these things, and while I'm not sure the raising of the temperature helped any, I did all three, raised nozzle temps, bed temps, and disabled "always on" cooling fan.  The next print with everything else the same is sticking to the bed.  I had previously tried just printing on clean powder coated sheet, smooth sheet with glue stick, changed nozzle to a fresh one, cleaned bed, glue stick on powder coated sheet, etc...Everything I could think of.  This is the first thing that got my first layer correct.  To be fair the print I'm attempting has a bunch of intricate lines on 1st layer, so it's pretty much designed to fail with PETG, but it's printing now at least, I appeared to have gotten a pretty much perfect first layer, on layer 6 or 7 now, and printing like a champ.  Time to walk away.

RE: MK4 First Layer Problem with PETG

Check the bottom bearing holder on the X axis for proper orientation.  The is a notch in the bearing holder that leaves room for the hotend and nozzle.  If the bearing holder is in backwards, the hotend and nozzle can't fully seat, and it will seriously screw up the leveling and first layer.  I learned this the hard way.  Prusa doesn't give you a heads up in the assembly manual.

I have printed dozens of PETG prints, and every print has been great.  Just don't print PETG on the smooth sheet because it sticks like crazy and you might never get the PETG off.  I always use the textured sheet (unless I really need a smooth finish on the bottom) to print PETG.

RE: MK4 First Layer Problem with PETG

I had a similar problem where the first layer didn't stick properly on the bed at certain areas (see video). This happened with PETG (and to a lesser degree also with PLA) on the smooth and powder coated sheet.

I contacted Prusa Support and Marcin helped me to resolve the problem with the following steps: 

• trying the same print w/ PLA on the smooth sheet to make sure the powder coated on is not the problem
• checking if the loadcell sensor works (self-test)
• taking off the heatbed and confirming that the Y-carriages have the right orientation and do not have any play
• reassembling the heatbed by tightening the 9 heatbed screws: tighten all 9 heatbed screws with equal force, do not overtighten anything. Use just finger strength, and stop as soon as you feel resistance.

The last step solved the problem: I guess I initially used too much strength and overtightened some of the screws which led to an unequal heat expansion.

RE: MK4 First Layer Problem with PETG

Thanks for this!  I had increased bed and nozzle temperatures with little help but turning off the "Keep fan always on" filament setting made a huge difference.  This is on a Mk4, input shaping with the current beta silcer and firmware but I tried non-IS and it didn't really help either.

Posted by: @build-stuff-with-bob

I had a heck of a time initially with PETG on my MK4. What seems to have been the problem is that for some reason the default settings for Generic PETG in Prusaslicer has the setting “keep fan always on” under Cooling set to “true”. Changing that made a huge difference for me. I also raised the first layer bed and nozzle temps, which seems to have also helped my bed adhesion for PETG printing.

Your results may vary of course, but it’s worth a shot.