Help Understanding M671 Z-Manual Adjustment
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Thank you David! I am running 1.19, but it turns out I had a space in the M671 string which broke it. It's fixed now it looks.
For those of you wondering what "correct," looks like, if you have M671 configured properly, you'll get something that looks about like this in your G-code console after running G32. It may help for sanity sake to run M671 without parameters to remember what screw is what when looking at the G32 correction results.
G32
Manual corrections required: 0.07 turn up (-0.04mm) 0.63 turn down (0.31mm) 0.65 turn down (0.32mm) 0.10 turn up (-0.05mm) -
One question, and this may be a browser thing…after I successfully run the G32 with M671 properly working now, it won't pull up the height map like it used to, and the option to show probed points remains grayed out.
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Adding on to this-I run G32, and get the direct corrections. I apply them (or as close to as I can by hand…sort of hard to dial precisely 0.41 of a turn). Rerun G32, and the results say to apply basically the same correction again. I know 4-point math is wonky, and I'm not discounting I'm doing something wrong.
As an example:
8:48:18 PMManual corrections required: 0.44 turn up (-0.22mm) 0.36 turn up (-0.18mm) 0.41 turn up (-0.20mm) 0.53 turn up (-0.27mm)
8:46:47 PMManual corrections required: 0.46 turn up (-0.23mm) 0.40 turn up (-0.20mm) 0.45 turn up (-0.22mm) 0.55 turn up (-0.28mm) -
One question, and this may be a browser thing…after I successfully run the G32 with M671 properly working now, it won't pull up the height map like it used to, and the option to show probed points remains grayed out.
To get the height map I suggest you use mesh bed compensation (G29).
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Adding on to this-I run G32, and get the direct corrections. I apply them (or as close to as I can by hand…sort of hard to dial precisely 0.41 of a turn). Rerun G32, and the results say to apply basically the same correction again. I know 4-point math is wonky, and I'm not discounting I'm doing something wrong.
As an example:
8:48:18 PMManual corrections required: 0.44 turn up (-0.22mm) 0.36 turn up (-0.18mm) 0.41 turn up (-0.20mm) 0.53 turn up (-0.27mm)
8:46:47 PMManual corrections required: 0.46 turn up (-0.23mm) 0.40 turn up (-0.20mm) 0.45 turn up (-0.22mm) 0.55 turn up (-0.28mm)Overall, what you have is a height error of about 0.45mm between this set of bed probing and Z homing. This probably means that you are Z homing in the centre of the bed, but either the bed is dome-shaped or (more likely) the X carriage is sagging in the middle of its travel. If we subtract the first value (which is closest to the average) in each correction from the other 3 we get:
1st run: 0 +0.03mm +0.01mm -0.05mm
2nd run: 0 +0.04mm +0.02mm -0.05mmMaybe I should change the code to leave one of the screws alone.
It's possible that the calculation could be wrong because I haven't had any feedback on the 4-screw case before, just my own simulation of it. Try duplicating the block of G30 commands in bed.g, but in the first block change S4 on the final G30 command to S-1. That will print out the probe height errors the first time, then the manual corrections the second time. From that we should be able to check that the corrections look sensible.
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I think altering the calculation code to leave one screw alone may be well advised, if for nothing more than to have one less point for an end user to over/undershoot and further skew things.
I'll rerun this all here in a bit when I go home for lunch, and post up my homeall.g, bed.g (with your suggested tweak), and M671 line.
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[bed.g] G30 P0 X15 Y75 H0 Z-99999 G30 P1 X15 Y225 H0 Z-99999 G30 P2 X290 Y225 H0 Z-99999 G30 P3 X290 Y75 H0 Z-99999 G30 P4 X150 Y150 H0 Z-99999 S-1 ; done to check calculations at DC42's request. G30 P0 X15 Y75 H0 Z-99999 G30 P1 X15 Y225 H0 Z-99999 G30 P2 X290 Y225 H0 Z-99999 G30 P3 X290 Y75 H0 Z-99999 G30 P4 X150 Y150 H0 Z-99999 S4[homeall.g] ; Relative positioning G91 ; Lift Z G1 Z5 F6000 ; Move quickly to X axis endstop and stop there (first pass) G1 X305 F1800 S1 ; Go back a few mm G91 G1 X-5 F6000 G90 ; Move slowly to X axis endstop once more (second pass) G1 X305 F360 S1 ; Move quickly to Y axis endstop and stop there (first pass) G1 Y305 F1800 S1 ; Go back a few mm G91 G1 Y-5 F6000 G90 ; Move slowly to X axis endstop once more (second pass) G1 Y305 F360 S1 ; Absolute positioning G90 ; Go to near front and home Z G1 X30 Y30 F6000; (150,180.5 for probe at dead center) G30[c]M671 X10:10:295:295 Y75:225:225:75 S1.0 P0.5[/c]
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[G32 Results] 11:47:48AM Bed probe heights: -0.213 -0.219 0.461 1.087 0.323, mean 0.288, deviation from mean 0.485 Manual corrections required: 0.51 turn up (-0.25mm) 0.43 turn up (-0.21mm) 0.48 turn up (-0.24mm) 0.61 turn up (-0.30mm) 11:47:24AM G32 Bed probe heights: -0.213 -0.219 0.461 1.087 0.323, mean 0.288, deviation from mean 0.485 -
Playing with this more, I really do think that the computation for manual adjustment needs to be three screws only.
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It's already on my list to change for the next release.
