Display Encoder position with button to zero.

Andy - I tied the button to pin hm2_7i43.0.encoder.01.reset and it works great for the X.

I also did this for the Z but if the zpos-cmd is at 0.500", it will zero the encoder and then walk 0.500 to meet the zpos-cmd. Is there a way to reset both the zpos-cmd and the encoder simultaneously?

I'm sure you are wondering why I want to do this for Z so I will try to Explain:

The Z axis is controlled by a hydraulic cylinder with a moog servo valve. This being the case, there is a small amount of "Stick and Slip" on the Z axis when trying to make very fine movements. It may float back and forth about ±.0004" while trying to land on position. I have a hard stop with an adjustable fine thread screw so when we have to grind up to a shoulder we can approach it slowly and carefully. The operator may have to command the position just beyond the hard stop (using the MPG) to keep some pressure on it while adjusting the screw to its final position. Once the face is ground or touched, I want to set that at zero. As the machine is currently configured, If the commanded position is beyond the stop, it won't zero the axis at the hard stop location (actual encoder position).

Hopefully you can understand what I was trying to say. Let me know if I can clarify better.

Is this a standard cylinder or a hydrostatic one? (the hydraulic servo machines I used to work with used hydrostatic cylinders and managed positioning to microns at huge loads)

I expect that you are right that touch-off works to the commanded rather than measured position. You might be able to get round that by incorporating your own sall offsets within hal (look at the "offset" HAL component.) Mux2 can be used to store and latch a value, if you feed its output to the input.

This is a standard hydraulic cylinder. I added the servovalve to control the table via PID loop. I think it would be better at precise positioning if the ways were linear bearings rather than flat/v-ways. I believe It's the stick/slip on the ways that is the issue. The ways have been flaked and I believe they should not be.

Here is the thread from the original build - www.cnczone.com/forums/linuxcnc-formerly...er-emc2-project.html

I see the offset HAL component has 5 pins but I am a little unclear of their function. Is this correct? (I have a feeling I am way off here)

offset.N.offset - The offset value (I would net this to my zpos-cmd) ?
offset.N.in - This is the input for the value that gets added to the offset ?
offset.N.out - Equal to: (offset.N.offset + offset.N.in) ?
offset.N.fb-in - The feedback input (I would net this to zpos-fb) ?
offset.N.fb-out - Equal to: (offset.N.fb-in - offset.N.offset) ?

So I would use Mux2 to store and latch the offset.N.fb-out value?

Is it possible that there is air in the system, causing problems?

That is a possibility, The main cylinder has "choke coils" at each end that bleed the air out. When the machine starts up after sitting a while I have to run it to each end of the stroke to get the air out of the cylinder. It runs smooth after that. When given a position command, it may stop within 0.0002" of the desired location, then the output will slowly start to climb until it overcomes the friction but it may overshoot by 0.0002" once it moves. This leads me to believe it is the "stick/slip" of the ways. The ways were flaked on this machine which should not have happened and I believe this increases the force required to overcome the static friction. Even if the machine did stop on a dime, I would still want to use a hard stop just to prevent unintended crashes.