Touch Plate Preference Settings / Z offset issue

[NewAgent45]

I prefer to set jobs up with the XY datum position in center. The exception would be a job where tiling is used. I don’t worry about re-zeroing z with a tool change. You can always reposition the tool and re-zero using the touch plate at another position then move back to (0, 0, 0) before running the toolpath. Most of the time this works fine for me. But I have always had an issue with the tool making a small mark when starting the run.

This morning I did some testing and changed my touch plate preference settings.
Original Settings were as follow:
CNC Shark HD / Black Diamond
Controller version: 2.0
Actual Touch plate thickness: 0.376”
Safe-Height up: 0.250
Touch Plate Setting: 0.375

Testing:
With material in the machine we adjusted the touch plate setting down in 0.001” steps. With each step we used the touch plate to zero the bit, removed the touch plate, and selected move to zero. Then we checked to determine if the bit touched the material. We moved the material over a little bit with each step. When we reached a value that the bit didn’t touch the material we lowered the value one more increment (0.001”). We ran a test engrave program with no issues to complete the test.

The final touch plate preference setting is 0.366” or a difference of 0.375 – 0.366 = 0.009”. This amount of z offset seems like a lot. Can anyone comment on this? What issues might I encounter keeping this preference value as my standard setting?

Thanks in advance for addressing this issue.

.......... Rod

[Mimbler]

On my piranha it is off by .019. It is totally consistent. The only thing you should be careful of is to insure your controller remembers your setting. On the piranha, it forgets everytime it is turned off, so I need to reset the offset whenever I use the touchplate after turning off the machine. NWA says they will fix that in the next firmware upgrade,
Mike

[gmm50]

We have a spoil board and mount 1/2 inch thick plastic sheets to machine on top of the spoil board. We attached a dial indicator over the 9 1/2 x 24 inch plastics sheets and fount a 0.015 inch deviations after leveling everything and running a big fly cutter across the spoil board. That deviation seems to all be in the thickness variation in the plastic we're cutting.

My point is that the touch plate is so large the underlying material might have large variations (in Z) across the length and width of the touch plate. I'm not surprised in the actual numbers reported. We measured the touch plate thickness and used that number. We also keep the TP in a closed box so debree can't accumulate.