[ger21]

You jog the machine down to the top of the part, and zero the Z axis there. You're control software should allow you to do that, as well as re-zero when doing a tool change.

[pixburghenat]

I think ger21 means the surface will be gone after the first cut.

I use a surface gauge and set my tools from it whenever my parts surface is removed.

You can also use any known highth block, the vice, or the table. Block should be machined.
Set the block next to your part and measure the difference between the top of your part and the block.
Record the difference and adjust the Z offset.

Double check your math and what you type in the control.
Write everything down in case of intruptions.

Scott

[under-dog]

I used to use the touch off to a surface(usually my vise) and recalibret Z

I recently bought an electronic height gage and love it. Red light glares on when the tool makes contact so it eliminates potential discrepencies with the paper method.


I also made a riser block for it so it is dead nuts on to the "0" of the z height of the center of my 4th axis. This way when I flip mill or run a 4 axis program and need to tool change it is easy/ Just change the tool out jog over and touch down and re zero. In the case of a 2D cut part being flip milled I just calculate in the offset to the top of my part when I re-zero the Z on tool changes.