How do you calculate ball-nose scallop height?

The exact geometric cusp on a flat surface is R - sqrt(R^2 - (stepover/2)^2). This tool uses a faster planning ratio of step-over divided by tool radius times a finishing factor; with a 0.01 in step-over and a 0.25 in radius the index is 0.04.

What is a good scallop height for a finished surface?

For a smooth, paint-ready or near-polish surface most shops target 0.0005 to 0.002 in of cusp height. Cosmetic Class-A mold surfaces often go below 0.0002 in, while structural parts tolerate 0.003 in or more.

How do I reduce scallop height without killing cycle time?

Use a larger ball radius, tighten step-over only on the visible or critical zones, or switch to constant-cusp/5-axis toolpaths so the effective step-over stays even across slopes instead of bunching up on shallow walls.

Does a bigger ball-nose tool reduce scallops?

Yes. For the same step-over a larger radius leaves a shorter cusp, which is why the radius sits in the denominator here. Going from a 0.25 in to a 0.375 in radius at the same 0.01 in step-over roughly cuts the index by a third.

Step-over vs scallop height - which do I set first?

Set the target scallop height from your finish spec, then back-solve the step-over for your ball radius. Programmers think in scallop because it maps to surface quality; the CAM system converts it to a step-over distance.

Why is my real surface rougher than the calculated scallop?

Tool deflection, runout, worn flutes, surface slope, and feed-per-tooth marks all add roughness on top of geometric scallop. The calculation is the floor, not the finished result.

CNC Machining calculator

Ball Nose Scallop Height Calculator

Scallop height (also called cusp height) is the small ridge of uncovered material left between adjacent passes when a ball-nose end mill finishes a contoured or 3D surface. CNC programmers and mold/die machinists watch it because it directly drives the surface finish that comes off the machine and how much hand polishing or secondary work a part needs. A tighter step-over crushes scallop height but multiplies cycle time, so finding the right balance is one of the most cost-sensitive decisions in 3-axis and 5-axis finishing. This calculator gives you a fast scallop-height index from your step-over and ball radius so you can compare strategies before you cut chips.

What this calculator does

Estimate ball-nose scallop height from step-over, tool radius, and a finishing factor for surfacing operations.
screening finish-machining step-over for molds, dies, contoured parts, and 3D surfacing work
It computes a scallop-height index from the ratio of radial step-over to ball-nose tool radius, scaled by an optional finishing factor.

Formula used

Ball Nose Scallop Height = step-over basis ÷ ball-nose tool radius basis × finishing factor
Keep numerator and denominator on the same job, setup, tool, or production basis.

Inputs explained

Radial step-over between passes:
Ball-nose tool radius:
Surface-finish scaling factor:

How to use the result

Use it when planning finishing passes on contoured, molded, or freeform surfaces to choose a step-over that hits your target finish without over-machining.
This is a planning ratio, not the exact geometric cusp height; true scallop height on a flat surface follows R - sqrt(R^2 - (stepover/2)^2), and real finish is also affected by surface slope, runout, and deflection.

Current U.S. benchmarks

The producer price index for steel mill products stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. Quotes priced off last quarter's material cost miss this move.
The U.S. has 17,154 machine shops establishments employing about 223,303 workers (Census County Business Patterns, 2023).

Common questions

How do you calculate ball-nose scallop height? The exact geometric cusp on a flat surface is R - sqrt(R^2 - (stepover/2)^2). This tool uses a faster planning ratio of step-over divided by tool radius times a finishing factor; with a 0.01 in step-over and a 0.25 in radius the index is 0.04.
What is a good scallop height for a finished surface? For a smooth, paint-ready or near-polish surface most shops target 0.0005 to 0.002 in of cusp height. Cosmetic Class-A mold surfaces often go below 0.0002 in, while structural parts tolerate 0.003 in or more.
How do I reduce scallop height without killing cycle time? Use a larger ball radius, tighten step-over only on the visible or critical zones, or switch to constant-cusp/5-axis toolpaths so the effective step-over stays even across slopes instead of bunching up on shallow walls.
Does a bigger ball-nose tool reduce scallops? Yes. For the same step-over a larger radius leaves a shorter cusp, which is why the radius sits in the denominator here. Going from a 0.25 in to a 0.375 in radius at the same 0.01 in step-over roughly cuts the index by a third.
Step-over vs scallop height - which do I set first? Set the target scallop height from your finish spec, then back-solve the step-over for your ball radius. Programmers think in scallop because it maps to surface quality; the CAM system converts it to a step-over distance.

Last reviewed 2026-05-12.