OK here is a thought, Take a Zservo drive setup that allows slaving the servo to an outside encoder as a follower( electronic geared). Then when you need to follow switch over from Mach inputs to slaved inputs and then the z will follow the surface encoder up and down.

I have seen that part work Saved to an encoder and use electronic gearing to drive the servomotor. From Mach you could diasble the Zdrive outputs and enable the Slave drive just before a cutting move .

Just a thought, A weird one but one just the same(;-)TP

OK here is a thought, Take a Zservo drive setup that allows slaving the servo to an outside encoder as a follower( electronic geared). Then when you need to follow switch over from Mach inputs to slaved inputs and then the z will follow the surface encoder up and down.

I have seen that part work Saved to an encoder and use electronic gearing to drive the servomotor. From Mach you could diasble the Zdrive outputs and enable the Slave drive just before a cutting move .

Just a thought, A weird one but one just the same(;-)TP

Not so weird.  If I can't get satisfactory results from attempting this directly with THC Up/Down, I'll basically attempt to do what you described.  In reality, I believe this works out to being a separate THC since all processing is done in the AVR.  The only difference from a completely separate THC, is that I'll use the same mechanics and driver between both Mach & my controller.  This eliminates any extra hardware since I'll just share the same control signals.

Brett

So, I've had some time to think about this while I was waiting for a better ADC chip to arrive.  I believe I can do closed loop control with the THC commands and a slaved axis.  Here's what I'm thinking:

Slave Z Axis in Mach to C Axis.  Use C Axis output as input to AVR.  Steps/direction becomes position(encoder) info back to AVR.

Touch Probe for tool height goes through AVR to Mach.  Recorded height sensor touch position can be sent for G28.1 initial height sensing (When it reaches the previous Z touch position it sends the output).

Since Mach waits for Arc Good signal, I should be able to function along these lines:
   1) Mach Probes initial height - we send recorded sensor location as touch output and wait for Z to stop.
   2) Mach moves to pierce height (router depth?), Z Stops
   3) We see Mach Z stop, we record the position, send an ARC Good to Mach and start controlling the height.
   4) Monitor for Mach Z motion.  When Z retracts past initial height, stop height control.

In plasma, the torch touches off and then rises to pierce height.  Can this be reversed in Mach so that, after a touch off, Mach lowers to cutting depth?

I think it could work fairly well.  Does this appear potentially functional?  Am I missing something?

Thanks
Brett