Drill point depth calculator
A drawing gives the hole depth to the end of the full diameter, but the drill ends in a cone. The calculator shows the Z to send the point to so the full diameter reaches the depth — or how far to break through in a through hole.
Quick answer
Drill point length h = (D/2) / tan(angle/2), blind hole Z = L + h. Example: 1/2″ drill, 118° → h ≈ 0.150″; Ø10 mm, 118° → h ≈ 3.00 mm, so a 20 mm full-diameter depth needs Z = 23.0 mm.
Result
- Drill point height
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- Z in the program
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- Full-diameter depth
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Program line (zero at the face, length set to the point)
Z is the depth of the drill point if the drill length in the tool table was set by touching the point to the part face.
Who needs it and why
Program Z to exactly the drawing depth and the full diameter comes out short by the point height — 0.11″ for a 3/8″ drill at 118°. It shows up too late: the screw won't go all the way, the tap bottoms out, the dowel sticks out.
- Blind tapped holes — so the full thread reaches its depth and the tap doesn't hit the cone.
- Through holes — how far to break through so the full diameter goes all the way and no burr ring is left.
- Changing drills — from a 118° HSS drill to a 140° carbide one: the point is shorter, Z should be less.
- Checking a program — what full-diameter depth a given Z will give you.
The formula
h = (D / 2) / tan(angle / 2) — the point height. That is about 0.300·D at 118°, 0.207·D at 135°, 0.182·D at 140° and 0.5·D at 90°. Blind hole: Z = L + h. Through hole: Z = thickness + h + breakthrough.
The Turn G-code Drilling cycle drills on the axis to the set depth, with peck drilling for chip clearing, and shows the pass in the 2D simulator.