Helical interpolation lets an end mill bore a hole larger than itself. Enter hole diameter, tool diameter, pitch and feed rate to get the helical path radius and the feed the control needs.
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Request a Proposal →Helical interpolation (helical boring) combines circular interpolation with a simultaneous Z-axis feed to create or enlarge bores with a single tool. The tool follows a helical path — a circle with a vertical pitch per revolution.
Helical interpolation is faster for roughing bores and works with standard end mills. Use it for bores that don't require boring-head precision, or to rough out a bore before finishing. For tolerances under IT7, finish with a boring head or reamer.
The bore must be at least 1.05× the tool diameter to allow the tool to enter. For practical cutting, bore should be at least 1.2× tool diameter. Below that, the tool rubs on the bore wall and chip evacuation is poor.
G02/G03 with X, Y, Z, I, J (or R) on the same line. Example: G03 X0 Y0 Z-2.0 I10 J0 F500 — makes one full helix of 2 mm depth with 10 mm radius. Use multiple lines to stack helices for deeper bores.
Enter the bore diameter, tool diameter, depth per revolution, and ramp angle. The calculator shows the helical path radius and the compensated feed rate to maintain the correct chip load at the tool centre.
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Use the calculator freely. If the result points to a tooling or process problem, we can source the exact carbide tooling you need from vetted factories in China. Compare factory-direct pricing.
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MILLING A BORE BY INTERPOLATION? An interpolated bore depends on the cutter's true diameter, not the nominal one — worth confirming with the supplier. See what to confirm before a milling cutter order.
Helical interpolation keeps the cutter in continuous contact, so runout and corner geometry decide whether you hold the bore tolerance. Send the bore diameter, tool diameter and material.