Is there a way to make G28 not change G53 coordinates? Or an alternative?

I’ve got a z touch plate working but it was a surprise to me that it sets the machine coordinates to z0 when the touch plate is triggered by a G28 command.
Of course it does!
These are the commands recommended for the tiny touch plate:
G28 Z
G92 Z0.5
G0 Z5 F480

I thought G28 positioned the tool tip at the trigger point and you had to issue a command like G92 Z0.5 to set Z in your workspace (I use G54).
What actually happens is G28 Z moves the bit to the z endstop (the touchplate in this case) AND sets the Z in machine coordinate space to 0.
This makes sense if you are using the trigger as an endstop but not if you are using the trigger to set the top of your material.
What I’d like to do is probe the touch plate and do a G92 Z0.5 in G54 space only, not machine space.
Is there a way to probe without changing Z in machine space?

I hope this makes sense!

G38.2 is probably what you want. You might have to configure the probe, but before you go down that path you can at least test with M119 and see if you are getting triggers on z_probe.


Had to:
#define G38_PROBE_TARGET
in Configuration_adv.h


#error “Z_SAFE_HOMING is recommended when homing with a probe. Enable Z_SAFE_HOMING or comment out this line to continue.”
in Warnings.cpp

G38.2 probes down once and stops when it hits the touch plate and DOES NOT SET Z TO 0 AUTOMATICALLY. Perfect!
Is there an advantage to trying to replicate the double touch that G28 does?

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You can enable the same double-touch as G28 by enabling MULTIPLE_PROBING in Configuration.h.

I can’t say how much benefit it would provide, but it’s possible it could help. I don’t know.


Coolness factor is significantly increased with double touch. Z0 is unchanged.

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