Not cutting Z depth correctly

CNC Machines Shapeoko
1

I am cutting an 8" trivet that is 2 sided with opposing diagonal slots. The piece is 3/4" thick, and 8"x8". I am using the Shapeoko Touch Probe to zero the X, Y & Z axis at the lower left corner using the Probe function in Carbide Motion.

The slots are 3/8" deep on both sides and I am insuring that the thickness id “exactly” 3/4". What is happening is that the cutter is not going the full depth of 3/8". The actual full depth is something less, like short about a 1/32" or so on each side.

My spoil board has been surfaced so it’s definitively flat. In the project I have the start depth set to 0.0" and the depth of cut set to 3/8", which is half the thickness of the piece.

Anyone have any idea why this is occurring?

Square_Trivet
Square_Trivet1387×943 532 KB

2

How are you doing this? If you use “3/4” in the software, but the real material thickness is thicker, then you will leave a band of material uncut in the center of the material.

It is very important that your toolpath matches the exact real world thickness of the material.

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If the CAD and CAM geometry checks out, then it’s something physical:

  • wasteboard trammed to be parallel to X and Y axis motion?
  • stock actual thickness? When I did a similar cutting board I used rough cut lumber, so faced/planed off one side, then flipped and registered off the surface of the wasteboard

If all that checks out, then it’s probably mechanical, please see: https://wiki.shapeoko.com/index.php/FAQ#Mechanical

EDIT: or, as @fenrus noted, operator error — placing the Probe as for probing a corner, but probing only for Z has a 3mm discrepancy,

4

One thing to try is to first set zero with the probe, and then use the paper method to see if you end up at the same zero for z

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5

I am running it through the planer then, verifying the thickness with a digital caliper.

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6

If your material is flat and the right thickness but have the workpiece held on the sides, it is possible that the middle bows up.

Check that you have the same zero in the middle of your workpiece.

7

Have your checked your calibration. The belts can stretch and cause slight deviation to the depth cut. Are they cuts all the same depth, if not, you may be getting some slippage of the belt on the gear or on the shaft.

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