Adding geometry to cut as a pocket with a finishing pass

One technique which is often suggested to avoid slotting is to add geometry around a part which one wishes to cut out and cut as a pocket down to tab depth — here’s one technique for that.

In this case, the project is a bevel gauge which will be cut out of 0.0625" (~1.5mm) thick aluminum:


Due to the narrowness of the angles, an 0.03125" endmill has to be used, so after importing and scaling the file (we will be cutting out one which is 3") we select the perimeter and offset it twice, once by the desired chipload (0.01") and again by half again the endmill diameter:

(control click on the profile, then delete the extraneous bits of path left in the centers of the divots)

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Select the offset paths and assign a pocket operation:

Note the Depth Per Pass and set the depth of the pocket to leave the desired tab thickness, in this case, twice the 0.098mm depth per pass.

Select the original path and assign a cut from stock top down to stock bottom, adding tabs as desired:


Add toolpaths for the text and holes, then preview to verify, then make G-Code and cut.

Cutting in aluminum w/ a #122 we’ll need feeds and speeds. There is an example of this at:

These settings are:

  • Depth per Pass: 0.102mm
  • Stepover: 0.356mm
  • Spindle speed: 9200RPM
  • Feedrate: 190.068mm
  • Plungerate: 25.4mm

Managed to get it cut, but had to use Grbl’s feedrate override to finish the cut:

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Some Questions…

You said a technique to avoid “slotting.” What is slotting?

You added two offsets. Why two and what was the rational for the offset distances?



Slotting is cutting a slot just as wide as the endmill will cut — a follow path / Contour | No offset cut into the material — the tool is engaged along the entire leading edge of the cut (a half-circle).

The two offsets allowed one to cut a pocket which would leave a “roughing clearance” adjacent to the material. Then one can make a finishing pass to take off that last thickness of material to get to the final dimension.

Available at:

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