Constant Z height changes during print  

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mark.m30
(@mark-m30)
Eminent Member

I was surprised to see during a print the Z height readout on the screen is changing in height by up to 0.4mm over the print bed. I'm assuming this is due to the bed level compensations being applied after the mesh level readings are made. The first layers of prints that are taking up most of the bed are coming out great, I'm just a little taken aback that the bed would be out by so much in the first place.

Best Answer by stixpjr:

Yes, this is a known "feature" present in the last couple of firmware releases. See:

https://github.com/prusa3d/Prusa-Firmware-Buddy/issues/608

Posted : 19/10/2020 9:57 pm
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 -2
(@-2)
Illustrious Member

You're probably seeing the retractions as well as any compensation going on. If the print looks good, ignore the minutia.

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 19/10/2020 10:05 pm
mark.m30
(@mark-m30)
Eminent Member

@tim-m30

It's not retractions as it's happening while perimeters and infill are being are being extruded; for instance infilling single lines from one corner of the bed to another. I think you mean Z-hop and not retractions. Retractions are what the extruder does and not the z-axis.

And half a millimeter out of flat is not something to be proud of.

Posted : 19/10/2020 10:33 pm
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 -2
(@-2)
Illustrious Member

Yeah - I'm lazy and include Z-lift and z-hop in my definition of retraction: honestly, I'm not sure if layer one bed compensation even shows up in the Z display ... I've watched layer one go down, watching for the threaded rods to turn, yet the display is fixed at 0.2 mm. 

You might try printing a 100 mm diameter 0.2 mm thick circle - see if you can see the numbers changing.

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 19/10/2020 10:57 pm
mark.m30
(@mark-m30)
Eminent Member

@tim-m30

I just updated the firmware this morning, so don't know if it's part of the update as I wasn't looking at the numbers until noticing it today. My Mk3 Z display stays fixed on the layer height it's printing and I assume it's just getting that from the G-code. It's display certainly isn't as responsive as the Mini's LCD.

Posted : 19/10/2020 11:11 pm
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 -2
(@-2)
Illustrious Member

Yeah - I get caught up by responding to MINI questions (I have zero experience with Mini's).  But my Mk3 will change values during printing; and it does report the programmed Z changes during printing. I doubt my bed is perfect, but it was saying 0.20 the full duration of a 100mm diameter circle I was printing to check my Live-Z (layer 1 of recent prints were a bit off).

When printing layers above 1, my Z display is jumping all over the place. I've always considered that normal, and just the gcode doing all the wipes and retractions it is supposed to do.

This post was modified 1 month ago by --
It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 20/10/2020 12:23 am
mark.m30
(@mark-m30)
Eminent Member

@tim-m30

Yes, I see the same behavior from the Mk3, and the display jumping as its Z-hopping from one perimeter or infill operation to the next, but it always settles into current layer Z-height as it's, say, laying a large infill and stays that way all the way across the bed.

Posted : 20/10/2020 1:22 am
Salvinor
(@salvinor)
New Member

I'm experiencing the same thing.

The Z value is constantly changing and oftentimes by a large margin.
Changes of about 0.6mm across the bed are quite common. (estimated because the value changes rapidly)

So at least you can see the bed leveling compensation working and it does a good job since my prints come out fine (although I have the 1st layer calibration issue where the MINDA always measures different values so I have to adjust 1st layer height every time)

I too own an MK3S and like the fixed Z-height display better.

This way you can tell exactly the progress in printing.

Because sometimes when I watch the mesmerizing printing process and stumble across interesting printing patterns I check the exact layer in Prusa Slicer to see what's going on.

I'm sure a simple firmware change could change the display behaviour and give the actual Z height from the gcode.
I think it would even better because beginners could be confused by the ever changing numbers and suspect some kind of defect.

Posted : 20/10/2020 3:50 pm
stixpjr
(@stixpjr)
New Member

Yes, this is a known "feature" present in the last couple of firmware releases. See:

https://github.com/prusa3d/Prusa-Firmware-Buddy/issues/608

Posted : 22/10/2020 8:26 am
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