Forced to live adjust Z between every print... or Reset the printer
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Forced to live adjust Z between every print... or Reset the printer  

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Forced to live adjust Z between every print... or Reset the printer

I have a strange one that I want some help with.  Our Prusa Mini is not behaving like any other Prusa I have worked with.  We can get the perfect Z offset setting using either the built in "Live adjust Z" wizard or by printing our own test files and adjusting the Z while the first layer prints.  Once we get it set it works for one print job.  Mostly.  Usually one corner is off more than the others resulting in the Z being too close in one front corner and too far in the opposite rear corner. (always the same corners)  But in any case we can usually get that one print job to complete.  However, using the same z setting for the next print job fails every single time.  So I find that I am using the Live adjust Z on the first layer of EVERY single print job.  Combine that with the fact that the mesh bed leveling doesn't seem to be helping as much as I have seen on other Prusa printers and I conclude that there is a problem with this particular printer.  Most likely hardware related.  Could be a sensor, a wire or just that the bed is so far out of level that the mesh can't compensate enough.  Those are my theories.  Please correct me.

One last strange part. If I use live adjust Z to get a print to work.  I can usually get the next print job to work correctly simply by powering the printer off for three seconds then back on.  four out of five times that makes it so I don't have to re-adjust the Z.  So that is confusing.

I have been keeping the firmware up to date as new versions are released.  So I am currently running 4.1.0.  

What Have I done?  I have replaced the Extruder gears with the BondTech upgrade for the mini.  I have adjusted the heater block to be about .2 mm higher to shorten the distance of the throat between the heater and the cooling block.  This fixed the issues I had with Heat Creap related filament jams.  I have tried adjusting the sensor (what is it called?  MINDA) both up and down as much as 2 mm in each direction.  

Nothing seems to help.  This problem has plagued this printer since day 1 for us.  The last month or two we have stopped using it and just curse at it.  I would like to get it fixed and restore some faith in Prusa.  The rest of these guys are turning to Creality and I don't like it.

Posted : 20/07/2020 10:37 pm
Active Member
RE: Forced to live adjust Z between every print... or Reset the printer

I use this in Prusa Slicer as the Start G-code in the profiles for my Mini printers and I believe it helps mostly by getting the MINDA to a similar temperature before each print so it can report consistent values. It doesn't sound like you're seeing exactly what I was, but it might be worth a shot.

; start of Start gcode
M221 S100 ; reset flow
M220 S100 ; feed rate
G90 ; use absolute coordinates
M83 ; extruder relative mode

; start MINDA warm up routine
M140 S[first_layer_bed_temperature] ; set bed temp
M104 S170 ; set extruder temp for bed leveling
G28 ; home all
G1 Z1 F50 ; set the Z fairly low
G1 X110 Y90 F4000 ; center the MINDA
M190 S[first_layer_bed_temperature] ; wait for bed temp
M109 R170 ; wait for extruder temp (in case the bed was already warm)
; end MINDA warm up routine

G28 ; home all without mesh bed level
G29 ; mesh bed leveling
M104 S[first_layer_temperature] ; set extruder temp
G92 E0.0
G1 Y-2.0 X179 F2400
G1 Z3 F720
M109 S[first_layer_temperature] ; wait for extruder temp

; intro line
G1 X170 F1000
G1 Z0.6 F720
G1 X120.0 E50.0 F200
G1 X117 Z0.2 F6000 ; move away quick
G92 E0.0
; end of Start gcode

This may or may not work for you, but I thought I'd share what works for me. I use a simple bed level test pattern to set the Live Z rather than using the built-in routine (which doesn't do the warm up this code does).

Oh, and I also have to run both of my Minis about 10C hotter than my MK3 and my CR-10 machines to get the same results from the same filament.

Posted : 21/07/2020 2:12 am