Zprobe offset help

printerdad

Hey guys, im trying to setup my printer after taking a few months off of....trying to setup my printer.
I need to find and set the zprobe offset, but I cant command the printer to lower the nozzles because it isnt homed, but I cant home it until I know the zprobe offset. Using G92 Z, I can raise the tools and lower them back to the position it was at but I cant go lower. Is there a command to unlock the printer so I can lower it without it needing to be homed? Or is there a good way to find the zprobe offset knowing I cant home my z axis? Thanks

Dad

sinned6915

@printerdad you can fake the machine out by giving it a fake number or even by tripping the probe manually so it has a bogus 0 point. then with judiscious commands you can work through it.

you can use M564 to over ride the axis motion limits, but tread carefully.
https://duet3d.dozuki.com/Wiki/Gcode#Section_M564_Limit_axes

try setting G31 with a a large offset, like 10mm and then home Z. no matter what the height is. just fake the machine out to get a starting point. then use a feeler gauge or piece of 20# copy paper and jog to where you just drag the clean, COLD nozzle on the paper.

then use G92 Z0.0 to set the height of 0 or whaever your feeler gauge size was.

then jog up to a point where the probe is NOT triggered. use M119 if you have to verify.

then do a G30 S-1 command to probe that point and simply report the height it stopped at
https://duet3d.dozuki.com/Wiki/Gcode#Section_G30_Single_Z_Probe

use that height as a starting point for setting the probe height with G31. you can use the other options as well, but i never can remember them.
https://duet3d.dozuki.com/Wiki/Gcode#Section_G31_Set_or_Report_Current_Probe_status

if you have feeler gauges, then use one of known size and do a G1 Z(whatever size that is)

the nice thing about RRF is you can tweak the value for G31 Zx.x on the fly and repeat as needed ithout rebooting the machine. dont be afraid to vary it and then move to a know height to check.

no feeler gauges? use an object of known size and move Z to that. obviosly flats are better than rounds, but if you had to, use a drill bit of known size: 1/2" =12.7mm. see how it fits under the nozzle after G1 Z12.7. or use calipers to measure something non-deformable to use as a feeler gauge. metal ruler, washer, anyhting you can use a flat test object under the nozzle.

then print some test object of a SINGLE layer. use baby stepping to get good layer adhesion, and keep track of it.
then measure the resulting object- if you tried for a 0.2mm hi layer, compare to your actual results ad adjusta ccordingly.

larger Z offsets in G31 move the nozzle CLOSR to the bed.

sinned6915

@printerdad i found the reference i was looking for but couldn't before I replied-

https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe#Section_Calibrate_the_Z_probe_trigger_height

printerdad

@sinned6915 thanks very much this is helpful