Unexplained Plunge Depth

Hey Everyone, I’m having an issue with the Z Depth. I have a Chinese 6040 gantry router from eBay, and Im using the EMC Post Processing output from Fusion360.

When I first power the machine up I zero all three Axis since I "park" the machine at zeros when I shut it down. Whenever I start a new program, I move the machine into position and I touch off all three axis to match the program coordinates for Zero and start the program. After the Z retracts it moves into position and begins to plunge, except it plunges about .400 more than the Z touch off point. After this happens, I jog the machine back to what is supposed to be the top and re touch off, I can rerun the program and the Z is now correct. What is going on?

Are you using tool length compensation from the tool table?

I would guess that your initial touch-off is with no tool loaded, then the G-code chooses a tool (which has a Z offset in the tool table) and then the second time you touch off this is compensated for.

andypugh wrote: Are you using tool length compensation from the tool table?

I would guess that your initial touch-off is with no tool loaded, then the G-code chooses a tool (which has a Z offset in the tool table) and then the second time you touch off this is compensated for.

That is exactly what was happening. I looked at the G-Code and noticed that there was a G43 Z0.6. Thats when I realized exactly what you said. The touch off is done when the machine thinks theres no tool loaded. When I touch off after I run the program, the machine is using the tool that the controller says it has which is correct. I looked at my tool table and saw that there were some values in there that I did not not put in. I'm not sure if these are defaults?

G10 can put values in the tool table, and so can the "tool touch off" button (which actually does a G10 behind the scenes).

It is also possible to edit the tool table, either with a text editor or with the built-in tooledit application (file menu in Axis)

andypugh wrote: G10 can put values in the tool table, and so can the "tool touch off" button (which actually does a G10 behind the scenes).

It is also possible to edit the tool table, either with a text editor or with the built-in tooledit application (file menu in Axis)

Hmm ok, I've basically been trying to figure out LinuxCNC on my own so my work flow may be incorrect, obviously because of this post. Let me ask this. Since my machine is ER11 collet based spindle, my tool lengths are never the same. Since Im now realizing that my initial touch off is not doing what I need it do, that needs to be changed. What if it did this, do everything that I have been doing, except before I touch off the z axis, run an M06 T2 (or whatever the tool is) in MDI, and then do the z touch off. That should tell the control what tool is currently in the spindle correct?

It might be simpler to set the tool length to zero in the tool table.
(and them make sure it stays zero, the bottom line in the Axis window tells you tool number and length)