Calculate chamfer diameter or axial depth from base diameter, chamfer size, and included angle for external OD or internal bore chamfers.
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Chamfer Diameter Formula
The calculator uses ideal right-triangle geometry to find face diameter, axial depth or the angle from measured dimensions.
Mode 1: Diameter from chamfer size C
Dchamfer = Dstart ยฑ 2 ร C
Mode 2: Axial Z depth from included angle
Z = radial width / tan(ฮธ/2)
- Dstart: starting diameter before the chamfer is cut
- Dchamfer: diameter measured at the chamfered face
- Dbase: base diameter of the bore or shaft below the chamfer
- C: chamfer size, radial distance per side (the leg length on a 45ยฐ chamfer)
- ฮธ: included angle of the chamfer or countersink
- Z: axial depth relative to the base-diameter intersection
Use Diameter from C when the print calls out a chamfer like 1.5 ร 45ยฐ and you need the diameter at the face. Add 2C for an internal chamfer (bore opens up). Subtract 2C for an external chamfer (OD shrinks).
Use Depth from angle when you know the base diameter and the target chamfer diameter and need the Z depth for a CNC program. The included angle covers standard 90ยฐ chamfers and countersinks at 60ยฐ, 82ยฐ, 100ยฐ, and 120ยฐ, plus 118ยฐ or a custom angle. Angle mode uses twice atan(radial width / axial depth), with the per-side angle measured from the part axis.
Common Chamfer and Countersink Values
Standard chamfer callouts and the diameter change they produce per side:
| Callout | C (radial) | Diameter change (2C) |
|---|---|---|
| 0.5 ร 45ยฐ | 0.5 mm | 1.0 mm |
| 1.0 ร 45ยฐ | 1.0 mm | 2.0 mm |
| 1.5 ร 45ยฐ | 1.5 mm | 3.0 mm |
| 2.0 ร 45ยฐ | 2.0 mm | 4.0 mm |
| 1/32 ร 45ยฐ | 0.03125 in | 0.0625 in |
| 1/16 ร 45ยฐ | 0.0625 in | 0.125 in |
Standard countersink angles and where they are used:
| Included angle | Typical use |
|---|---|
| 60ยฐ | Lathe centers, deburring |
| 82ยฐ | Inch flat head screws (UNC/UNF) |
| 90ยฐ | Metric flat head screws, general chamfers |
| 100ยฐ | Aerospace flat head fasteners |
| 120ยฐ | Sheet metal countersinks, drill point match |
Worked Examples
Example 1: External 45ยฐ chamfer. A shaft is 25 mm OD with a 1.5 ร 45ยฐ chamfer. The diameter at the chamfered face is 25 โ 2(1.5) = 22 mm. The Z depth equals C, so 1.5 mm.
Example 2: 82ยฐ countersink for a #10 flat head screw. The pilot hole is 5.0 mm and the head needs to sit flush at a 9.4 mm face diameter. Depth = (9.4 โ 5.0) / (2 ร tan(41ยฐ)) = 4.4 / 1.738 = 2.53 mm of axial travel.
FAQ
Is C the leg length or the hypotenuse? C is the leg length, measured radially per side. On a 45ยฐ chamfer the axial depth equals C. On other angles they differ.
Why does the diameter grow on an internal chamfer? The chamfer cuts material away from the bore wall, so the opening at the face is wider than the base bore. Add 2C instead of subtracting.
Does the calculator account for tool tip radius or dwell? No. It returns ideal straight-sided geometry. Establish the actual tool geometry, datum, clearance and offsets through your machining setup; the result is not a direct machine Z command.
Can I use inches and millimeters together? Yes. Each input has its own unit selector. The result is converted to the unit you choose and also shown in mm and inches.
