Zeroing Z and Manual Jogging

I’ve looked through the topics here but I have not found anything that is exactly what I’m doing. I have had issues with repeating patterns - namely cutting stars on a flag union. My initial problem was that the stars did not come out to be the same size. So I figured that the board is slightly warped and that my clamps were not holding the material down well enough. I made new clamps. Then I found out that my hold-down screws were too long and were actually raising the waster board. I have resurfaced the waste board, found the correct length screws, and now use six clamps to hold the piece down.

Here’s the issue finally - I set zero (all) in the lower left per normal. I will manually jog back to the center to check my Z-zero again. If it is off a bit I might reset Z only. This is where I think there is a problem. When I have done this my Z gets messed up (too low) and I have ruined more that a few boards now. Is there a bug that will not allow to zero the Z axis anywhere but where Z and Y are set?

I have a bit setter but I do not have a Zero probe.

No, but your stock or wasteboard is probably not perpendicular to your endmill (tram).

No bug that I’m aware of, I regularly re-zero the Z, when changing bits partway through a job for example.

How / what are you using to do the initial X, Y, Z zero?

How are you then resetting zero in the middle of the workpiece?

How much Z difference are you seeing across the workpiece?

I checked several locations around the waste board using a digital gauge and measuring from the bottom of the tram beam. I found that I had variations of 0.02 +/- inches. So I resurfaced again yesterday.

What I was initially doing was to set my XY and Z, and then jog to the middle of the area to be carved. I’d recheck Z and if it were off I’d reset Z only. This would leave the XY coordinates back at the starting point.

I think I need to buy the probe too.

OK,

I just re-read your original post and saw you have a bitsetter, have you tried unplugging that and using the machine without it to test if that is the trigger?

When you’re setting the XYZ zero are you doing this manually? Just jogging down until you see the bit touch? (I found that a chamfer / V cutter works well when you have to do this)

Is there anything different about the way you’re re-setting the zero in the middle of the piece?

Once you have zeroed in the middle, check out where your zero is really at and test the level less destructively by jogging to a known Z height in Carbide Motion and then jogging around in X and Y and testing the gap under the cutter bit.

Go to 1mm steps and step the Z axis down toward indicated zero in CC, at zero check the cutter is really touching the workpiece in the middle and then jog around and check in other places, that should show if the surface of the workpiece is a long way out of flat.

Another thing that can help make sure your job is going to do what you wanted is to jog up to, say 20mm Z (or whatever your maximum cut depth is) and then manually zero Z, now load and run your file with the router off and watch it cut air, it’s easy to stop when it goes wrong and you can see a “physical simulation” of what your cut gcode is going to do.

Sometimes it’s necessary to surface the workpiece if it’s not flat, that’s better than trying to twist it flat with clamps. You can use the Shapeoko like a jointer, put the non-flat side down on the wasteboard and shim it in place, clamp it down and run a surfacing job across the top, flip the part and surface again. Or, if you have a jointer, planer, thicknesser, use that instead it’s much faster.

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