Chamfer and radius calculator
A chamfer from a drawing callout like 1×45° or 2×30° — get the radial leg, the hypotenuse and the start and end points. For an edge radius — the points and a ready G2/G3 arc.
Quick answer
Chamfer c × α: radial leg a = c × tan α, face length c / cos α. Example: 2×30° → radial leg 1.155 mm, face 2.309 mm; 1×45° → 1 mm and 1.414 mm. On a diameter X changes by 2a.
Result
- Radial leg
- —
- Diameter change
- —
- Hypotenuse length
- —
- Start on the face
- —
- End on the diameter
- —
Contour (G7, zero at the face)
Points follow the part contour. A tool with a nose radius and no G41/G42 compensation leaves chamfers and radii slightly undersize — keep it in mind for the finishing pass.
Who needs it and why
A drawing calls out a chamfer in short — "1×45°" or "2×30°" — and a radius as "R2". The machine needs coordinates: which diameter to start at on the face, where to end, and for an arc — G2 or G3. The calculator turns the drawing callout into those points.
- If you write G-code by hand — in LinuxCNC, Mach3 or on a control without a chamfer cycle. A 45° chamfer is easy in your head, 30° or 15° needs a tangent, and an error of a few hundredths shows on the part.
- Thread chamfers — the lead-in on a bolt or in a nut, 30° or 45°, at least as deep as the thread. The exact diameter at the face matters here.
- Edge radii — the most common hand-coding mistake is mixing up G2 and G3, so the tool arcs the other way, into the part. The calculator picks the right one.
- Checking — when the code came from CAM or another generator and you want to verify the points against the drawing quickly.
- On a manual lathe — the hypotenuse and the legs tell you how far to feed when you cut a chamfer with the compound slide.
The formulas
- radial leg
a = c · tg α; the diameter at the face is 2a smaller (larger for a bore) - hypotenuse
√(c² + a²) = c / cos α - radius: an arc from
X(D − 2R) Z0toX(D) Z−R
G2 or G3
In G18 the arc direction follows the machine axes, so it is the same for front and rear tool posts: a convex OD edge radius from the face to the diameter is G3, a bore edge radius is G2. Check the program in a simulator before cutting.
The Turn G-code Chamfer/Radius cycle does external and internal, front and back chamfers and radii — all four combinations — with a 2D toolpath preview before you get the code.