Machining
Lathe chamfer and radius calculator for CNC
Compute approach/retract points for chamfers and radius with RE compensation — fewer manual trials at the machine.
Lathe chamfer / radius calculator
Exit chamfer or radius: turning bottom-up (X+, Z−) without G41/G42. Z zero at the part face.
For 45°: k ≈ 0.4142, delta = r·k. Example D=100, C=1, r=0.8.
CNC code result
Theory (nominal)
X98.000 Z0.000 → X100.000 Z-1.000
Tool tip
G1 X97.337 Z0.331
G1 X100.937 Z-1.000
G0 X97.000 Z1.000 (Approach to the face at safe diameter) G1 X97.337 Z0.331 F0.2 (Plunge ahead of the face accounting for nose radius r) G1 X100.937 Z-1.000 F0.1 (Turn chamfer bottom-up on exit, X+, Z-) G1 Z-2.000 (Short pass along the shaft cylinder) G0 X102.000 (Safe retract on diameter)
k=0.414 · kfin=1.172 · delta=r·k
Warning: Calculation is on diameter (X axis). Verify tool offset (T-code) before running. Feeds F0.1 / F0.2 are indicative.
Diagram: external contour (shaft) · chamfer
Frequently asked questions
Why account for tool nose radius RE?
The programmed path differs from the finished edge when RE is non-zero. The calculator adjusts approach points for accurate chamfers and radius.