Wrong Z height when infill moves

Hi!

Sorry for the unclear subject, but I'm not quite sure how to explain my issue in a short sentence.

So, I have a Prusa i3 Mk3S clone that was printing beautifully when I decided to build a Mk2.5S from scrap parts I had laying around. Since I had to order some new parts as well, I gave the new parts to my Mk3S. The new parts it got were linear rods, bearings, leadscrews, motors, hotend, 24V power supply, TMC2130's and a SKR Pro v1.1 because I accidentally burned the Rumba I had before. Since I went for a 32 bit board I had to upgrade to Marlin 2.0 (currently 2.0.1) from 1.1.9.
I initially had some issues with print quality, but I found that was due to the nozzle not being screwed on tight enough. I have designed a case for the SKR which I have been trying to print for a couple of weeks now, but I'm having problems.
Now, I'm not a beginner when it comes to 3D printers. I don't know everything, but I'm not a newbie that don't understand the concept of having the right nozzle height and probe offset. In the attached picture you can see the first layer of the SKR case. It has a lot of venting holes, and because of this the infill being laid down isn't one continuous move, but many separate moves. For some reason the distance between nozzle and the bed is different at different infill locations. Sometimes it's too close to the bed and sometimes it's too far from the bed. If i print the SKR case without the venting holes the infill is being laid down in one continuous move and looks just like it should.
I do not know what could be causing this. I have disabled Lift Z in PrusaSlicer, but it made no difference. I'm not sure if it's mechanical or firmware related, but I am sure that I did not have this problem before replacing parts and upgrading to Marlin 2.0, because I printed a almost identical case for the Rumba board I had before. I have attached my config files from Marlin.

Any and all help is much appreciated!

Regards,
Christian

Edited 1 time(s). Last edit at 01/06/2020 07:46AM by chrstrvs.

Since you have moved to a new board, the standard "clear the EEPROM" will avail you not. Also, I kind of doubt that this has anything to do with firmware, first layer issues are almost always hardware.
Therefore, you probably have a mechanical issue. Look for belts binding, bent rods, hiccups in your lead-screw motions or the two sides of the z-axis mounts not being exactly even with each other (pretty easy to do with two steppers to move the z-axis.

good luck,
DLC

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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.

Thank you for your reply, dlc60!

The EEPROM has been cleared several times, so it's definitely not that =)
I failed to mention what I have tried to fix this, which is taking apart the axes one at a time to see if it made any difference and also swapping back to the old parts, but there were no difference in how the first layer looked. After reading your answer I decided to take apart all axes at once and carefully mounting them again. I also changed to the stock y belt idler from a tensioner I found on Thingiverse. After mounting everything back and tightening the belts the first layer does look a lot better, but still far from perfect. At least this confirms your belief that it is a mechanical issue.
I guess there's nothing else to do than to keep looking for what could be mounted incorrectly or broken.

I think I might have found something. It appears that the spring steel sheet is lifting in some places when laying down the first layer and the bed is hot. When the bed is at room temperature the steel sheet doesn't lift. A while ago I noticed that the thermistor had come loose from the bed and was hanging a few mm below so the actual temperature of the bed was higher than what the thermistor was reading. The only theory I can think of is that the magnets have become weaker due to the high temperature and that they are now weaker when hot than when cold. I can't feel any difference when touching a metal part to the magnets when they are hot and when they are cold, but that's not really a scientific test.
Has anyone else experienced something similar?

Quote
chrstrvs
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Has anyone else experienced something similar?

Yes with cheap frying pan made of stamped thin steel sheet on a vitroceram cooktop

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)