Adding scribe height question

[classicdaily]

I am in the process of designing and building a plasma table. I want to plan for other things such as adding a scribe and rotary axis.

I currently have a z slide with floating head for plasma torch built in. I will end up with around 6" of z travel.

My main question is does the scribe air slide need to be on the moving z axis. And thus know the height of the material.

Or does the air slide for the scribe mount on the carriage and just come down until it hits the material. This seems somewhat uncontrolled...

[tcaudle]

An air cylinder is not a proportional linear motion device. It either is fully extended or fully retracted. There is no way for it to "know" where the material is. You control the downforce so the material stops it from going all the way down. Now, if you are going to use an engraving tool with no air then you treat it like a router and control the depth of cut with the Z position. A lot of the control of a pneumatic plate marker is in the CAM and POST.
You can program in offsets (including Z) that resets the XYZ positions to center the plate marker . The Z offset is used to pick up the Z (torch) before you lower the air cylinder. Depending on the weight of the plate marker and cylinder mounting, it may tax your Z motor to drag all that mass around while cutting with the plasma. Its pretty easy to mount it to the Z plate (that does not move) and work out the extension to the metal and the downforce needed to produce good marks.

[classicdaily]

So are you having that with the proper air pressure on the slide it will just bottom out to the material ? And doesn't need to know where the height the if material is?

So if I have 8.5" from the bottom of my z and the smallest material I could use a air slide with say 9" of travel?

[plasmartist]

The answer to your question is yes.