Fixtra

Drill Point & Countersink Calculator

Two things drawings forget to tell you: how far a drill's conical tip sticks past the full diameter, and how deep to plunge a countersink to get the diameter you want. Both, here.

Drill point (tip length)

Tip length (past full Ø)
Total depth for full Ø at 20mm

Tip length = (D / 2) ÷ tan(angle / 2). To get full diameter at a given depth, drill that much deeper by the tip length — or use a flat-bottom/clearance approach.

Countersink (plunge depth)

Plunge depth (Z)
Tool-tip travel below face

Depth Z = (C − d) / 2 ÷ tan(angle / 2). Sink to the head diameter from the chart, then set the stop here. Always confirm on a scrap part first.