When cutting through an object do you need to make "room" for the cutting tool diameter?

Where the cutter will be placed in relation to the path is a function of two things:

  • the diameter of the cutter — this will determine how much the offset (if any) will be — note that you may want to do a test cut in a scrap of material and measure that first: Shapeoko CNC Router, Rigid, Accurate, Reliable, and Affordable

  • the toolpath selected, which will determine whether there is:

  • Contour | Pocket or Inside / Left — the toolpath will come no closer than 1/2 endmill diameter to the geometry from the inside

  • Contour | Outside / Right — the toolpath will come no closer than 1/2 endmill diameter to the geometry from the outside

  • Contour | No Offset — the toolpath will follow the geometry as precisely as machine motion allows

Play around with assigning toolpaths — you’ll get a preview image of the toolpath after assigning it which will help to show that.

There’s some discussion of this in: