Jogging question

In Mach 4, is it possible to type in coordinates and command the machine to move to that spot? I can’t figure out how.

Also, how do folks calibrate the z axis (measuring off the spoil board) after a tool change on a 4x8 machine with a full sheet of plywood on the bed?

Many thanks!


  1. You can type a G0 command into the MDI tab. It will use the active work offset.

  2. You could offset by the material thickness manually, or put your origin at the stock top instead, or use bit collars in conjunction with G43 tool length offsets.

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Here is a good video reference. starts at 2:20

Credit JN Woodworks who I see is active on this forum. He has some really good vids when a picture is worth a 1,000 words.

Thank you. I knew there must be a way. Thankful for this forum and to YouTube. I can’t imagine the disasters that would unfolded if these resources and people didn’t exists!


@Johnkay another quick 'n dirty way to set new Z zero after tool change, would be with the auto z touch plate…or use manual incremental button jogging to get the new bit just above the work surface, put a piece of paper between, and move it down down down ever so slowly a thousanth click at a time when close, until the paper catches between surface and bit. This is arguably the least accurate and highest possibility of idiot error (been there) but it is pretty quick. If this is a highly discouraged practice, anyone please correct me and I’ll delete this, but I’ve had good luck with it, taking ordinary precautions.

I put the tool in the collet without tightening it, then lowering Z until the tool touches the work piece surface/gets pushed in slightly. Then I tighten the collet nut, raise Z and start program.
In the absence of a touch plate, this works well for me and prevents crashing into the material by accident (within certain bounds).

@Johnkay can clarify, but I think the question was about how to set the Z height at the spoil board when the spoil board is completely blocked by a sheet of plywood.

Ah, yes. My bad. I reference off of top of material to avoid that challenge.

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I’ve got the avid touch plate and it does a fine job. I get much better results if I zero off the spoil board in that it doesn’t mess up the spoil board. Was just curious if there are ways around it. Would love to have a bit setter or an ATC but I can barely run the machine as is! Thanks to all who have answered.


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