BIZOMAT MAKEOS · Manufacturing
Ball-Nose Scallop Height and Stepover
What scallop height does this stepover leave, or what stepover gives the target height?
Theoretical scallop (cusp) height left by a ball-nose or radiused cutter on a flat surface for a given stepover, or the stepover for a target scallop height.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Calculate | choice | Choose what you want to find. |
| Ball (tool) diameter | mm | Diameter of the ball nose (twice the corner radius for a bull-nose cutter on a flat). |
| Stepover | mm | Distance between adjacent passes (scallop-height mode). |
| Target scallop height | mm | Largest acceptable cusp height (stepover mode). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Calculate
- What it is
- Whether to work out the cusp height left by a stepover you already use, or the largest stepover that keeps the cusp under a target height.
- Units and format
- Choose one of 2 options from the list: Scallop height from stepover; Stepover for a target scallop height.
- Example
- The form opens with “Scallop height from stepover” selected as a worked example. Choose the option that matches your case.
- Get it right
- Only the input for the chosen mode is used: stepover for scallop height, target height for stepover.
What this means: Ball (tool) diameter
- What it is
- The diameter of the ball at the end of the cutter, or twice the corner radius of a bull-nose cutter cutting a flat surface.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger ball leaves a smaller cusp at the same stepover, or allows a larger stepover.
- Get it right
- For a bull-nose cutter use twice the corner radius, not the shank diameter.
What this means: Stepover
- What it is
- The sideways distance between the centres of neighbouring tool passes, as set in the CAM toolpath. Used only when calculating scallop height.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Scallop height rises roughly with the square of the stepover, so small increases matter.
- Get it right
- This is distance, not percentage of tool diameter; convert a percentage stepover to millimetres first.
What this means: Target scallop height
- What it is
- The tallest cusp you will accept between passes, usually set from the surface finish needed. Used only when calculating stepover.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.005 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger allowed height permits a larger stepover and fewer passes.
- Get it right
- Enter millimetres: a few micrometres is a small fraction of a millimetre.
Method and formulas
- h = R − √(R² − (s ÷ 2)²), with R the ball radius and s the stepover.
- s = 2√(2Rh − h²).
- Example: a 10 mm ball with 0.5 mm stepover leaves 6.2539 µm scallops.
Limitations
- Flat surfaces normal to the tool axis; on slopes and curved surfaces the effective radius and scallop change.
- Tool deflection, runout and wear add to the theoretical value.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set stepover for 3D finishing passes
- Trade cycle time against surface finish
- Check a CAM finishing strategy
Who it is for
- Machinists
- CNC programmers
- Manufacturing engineers
What you get
- Scallop height
- Stepover
- Stepover as a share of diameter
Interpreting the result
- Halving the stepover roughly quarters the scallop height but doubles the passes.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1039–1058, 1279–1300. Topic reference; no source tables or recommended settings are reproduced.
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