Z Axis Shift, G-Code issue, or....?  

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JaydeMonster
(@jaydemonster)
New Member

Hi! First post here, as I'm new to 3d Printing and had our i3 Mk3s+ for about a month.
Latest firmware is installed.
I've run PLA and PETG and ran into this issue on about 1/2 of my prints, various files. At first I considered it a belt issue on the Z axis as the print shifts on the z axis, sometimes small and sometimes over a 1/4 of an inch. However I have begun noticing a height pattern and my latest print doesn't quite make sense as far as a print shift goes.
 Printing a bed of these light blue figures for my son's friends and we had a couple of shifts. The bottom one is slight but the same height on the print progress as prior print shifts (See the white chair?) Then higher up on the taller figures on the bed there is a very considerable shift. However, the lower shift only appears to be on one set of parts (the feet) and not the head or the taller ghost figures on the print bed. 
We've printed these files, but with different slices, several times with success. Could this be a g-code or software issue? If so how do I prevent/correct it?
I just noticed our biggest print that had a shift at the top is in the background, seems the taller the print, the bigger the shift on the print if it does happen.
Thanks in Advance

Prusa Slicer, printing from SD Card.
Geeetech PLA (brand new roll, I need to adjust settings a bit to get it smoother). 

Posted : 26/02/2021 2:42 pm
Clemens M.
(@clemens-m)
Honorable Member

I would have said too that it is an issue of the belt tension. One idea could be to use a GCode viewer and have a look there if you can see those shifts there. You can use that one which is coming with Prusa Slicer (since 2.3.0) or you can use an online gcode viewer or simulator. Give it a try. But I would say it is a mechanical problem.

Best regards, Clemens

Posted : 26/02/2021 3:09 pm
Clarmrrsn
(@clarmrrsn)
Reputable Member

It looks to me like one if the belts is loose on either your X or Y axis, as the shift is horizontal. (Z axis is lead screws)

I would check belt tension on the bed Y and print carriage X.  And also check your linear bearings run smoothly on the rods on all axis. (Did you lubricate them on installation,  or since?)

Switch off and very slowly move the bed bad and forward to feel if there are any skips or tight spots. Do the same with the X axis (Don't move them too quickly as the motors act as a generator and can pass back current the board.

Clean all the rods with IPA and apply a small amount of grease to the surface of the rods,  just a very fine coating (Superlube grease with PTFE is best) 

Retest and see how it goes

Tank you very much!...
Posted : 26/02/2021 3:20 pm
Clemens M.
(@clemens-m)
Honorable Member

Be careful - it can either be too high or too low belt tension - both can lead to this layer shifting issue.

Best regards, Clemens

Posted : 26/02/2021 3:31 pm
Clarmrrsn
(@clarmrrsn)
Reputable Member

Good to know Clemens.

Every day's a school day 😀

Tank you very much!...
Posted : 26/02/2021 3:34 pm
JaydeMonster
(@jaydemonster)
New Member

Thank you, Clemens and Clarmrrsn!
I was confused because some parts had the shift and some didn't on the lower portion of the prints, though the top one on the ghosts looks like an obvious tooth jump. I will check the belts again. 🙂

Posted : 26/02/2021 3:42 pm
fuchsr
(@fuchsr)
Honorable Member

I wish there were a more objective way to set belt tension properly. But I found this little gadget to be very useful:

https://www.prusaprinters.org/prints/46639-tension-meter-for-the-gt2-belts-of-i3-mk3s-or-prus

Posted : 26/02/2021 9:19 pm
Clarmrrsn liked
Clarmrrsn
(@clarmrrsn)
Reputable Member

@fuchsr

That's a very handy little tool, can see me printing one right after build to double check tension.

I have always used feel to judge, pressing belt and feeling tension amount, 20 years of tensioning belts of this type gives a feel of what is too tight, but I am always up for an extra tool in the arsenal, removes any doubt 😀

This post was modified 2 months ago by Clarmrrsn
Tank you very much!...
Posted : 26/02/2021 9:26 pm
towlerg
(@towlerg)
Prominent Member

I wonder if it is possible to set the tension using it's frequency when "plucked".

Posted : 27/02/2021 11:12 am
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