Drill Point & Countersink Depth
Drill point length from diameter and point angle, the travel to break through a plate or reach a full-diameter blind depth, and countersink depth to a diameter.
Point length and volume, the total travel to program for a through or blind hole with your clearance, and for a countersink the depth to the hole edge and to the virtual apex.
Example: A Ø10 drill with a 118° point has a 3.004 point; through 20 mm plate with 2 clearance it travels 25.004. A 90° countersink to Ø12 over a 6.5 hole is 2.75 deep.
The cone
at the end of the drill.
How the point length is found and how it changes the depth you program.
Point length
A drill point is a cone with the point angle φ at its apex, so its length is p = (D/2) ÷ tan(φ/2): 0.300·D for a 118° point, 0.207·D for 135°. The cone’s volume, π·(D/2)²·p/3, is the material the tip removes before the full diameter cuts.
Through and blind
Through a plate of thickness T the tip breaks out at T but the full diameter only clears the far face after T + p; add your clearance beyond that. A blind hole dimensioned to full diameter needs a travel of depth + p — the tip goes p deeper than the drawing depth — while a drawing dimensioned to the tip means programming the depth as given.
Countersink
For a countersink of angle θ opening to diameter Dcs over a hole d, the depth from the surface to where the cone meets the hole is (Dcs − d) ÷ 2 ÷ tan(θ/2); the depth to the virtual apex, Dcs ÷ 2 ÷ tan(θ/2), is useful when the tool tip is the reference. The angle must match the fastener head from the drawing. Split or web-thinned points are slightly shorter than the pure cone. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- Cone geometry: point p = (D/2) ÷ tan(φ/2); through travel = T + p + clearance; blind travel = full-diameter depth + p; countersink depth = (Dcs − d) ÷ 2 ÷ tan(θ/2)
Last reviewed 20 September 2026. How results are checked: How we verify.