Bore
At a glance
- Circular hole contours only—four or more equal-bulge arcs forming one circle
- Helical entry from clearance; ramp angle or pitch linked in the Passes section
- Finished hole ID from drawing minus tool radius, with optional finish pass and tabs around the bore
Bore mills round holes with a helix — the way to put an accurate 1" hole in a part with a 1/4" endmill. It works only on circular hole contours: closed hole geometry built from equal-bulge arcs that resolve to one circle. The drawing circle is treated as the finished hole ID, so the generated tool-center radius is hole radius minus tool radius; non-circular geometry on a Bore layer is skipped.
Helical entry
Bore always enters with a helix, so there's no Leads tab — the tool's Ramp Angle drives the initial helix down from clearance. In the Passes tab, Ramp Angle and Ramp Pitch are linked: edit either and the other recalculates from the bore radius on the layer. The Passes stepper repeats the same full-depth helix at the same dimensions — useful as a spring pass to clean up tool deflection on deep or hard material.
Sizing and finish
Stock to Leave takes signed radial and axial values, and negative stock is deliberate: when a press-fit needs the hole a thou or two over the drawing, dial in negative radial stock instead of redrawing. Take Finish Cut returns to the nominal bore after the roughing helix, matching Contour behavior.
Tabs
Bore supports the same automatic and manual tab controls as Contour, placed around the bore circumference. The cutting path stays helical — tabbed angular intervals simply lift to tab height on each rough and finish pass, so a large bored slug can't drop or shift before you're ready.