BIZOMAT MAKEOS · Manufacturing
Ball-Nose Finishing Plan (Stepover, Speed, Feed and Time)
What stepover gives my target cusp height with this ball-nose cutter, what speed suits its effective diameter, and how long will finishing the area take?
Plan of ball-nose finish milling on a flat or gently curved area: stepover for the target scallop height, or the scallop for a stepover you set (as the scallop height tool), effective cutting diameter at the axial engagement and the spindle speed for the cutting speed there (as the ball nose diameter tool), held to the machine maximum, the feed rate, number of passes and finishing time for the area.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Ball-nose diameter | mm | Diameter of the ball-nose cutter. |
| Flutes | Number of flutes. | |
| Axial engagement | mm | Depth of the ball in the material (sets the effective diameter). |
| Scallop height wanted | µm | Largest scallop (cusp) height the surface may have. |
| Stepover chosen (0 = from the scallop) | mm | Stepover you intend to program; 0 uses the stepover for the scallop target. |
| Cutting speed at the effective diameter | m/min | Cutting speed wanted at the effective diameter. |
| Feed per tooth | mm | Feed per tooth. |
| Largest spindle speed | rpm | Highest spindle speed. |
| Area length (pass direction) | mm | Length of each finishing pass. |
| Area width (stepover direction) | mm | Width of the area across the passes. |
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: Ball-nose diameter
- What it is
- The diameter of the ball-nose cutter, twice the radius of its spherical tip.
- 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 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 allows a wider stepover for the same scallop.
- Get it right
- Use the diameter, not the ball radius.
What this means: Flutes
- What it is
- The number of cutting flutes on the ball-nose cutter.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 12. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Feed rate rises in proportion, so finishing time falls.
What this means: Axial engagement
- What it is
- How deep the ball tip sits in the material, measured along the tool axis. It sets the effective cutting diameter at the contact point.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It must not exceed the ball radius; shallow engagement cuts with a much smaller effective diameter.
What this means: Scallop height wanted
- What it is
- The largest scallop (cusp) height left between neighbouring passes that the finished surface may have.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts 0.1 µm to 1000 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 µm 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 scallop permits a wider stepover and fewer passes.
- Get it right
- Enter micrometres; 1 mm = 1000 µm.
What this means: Stepover chosen (0 = from the scallop)
- What it is
- The sideways distance between neighbouring finishing passes that you intend to program.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A wider stepover means fewer passes but a taller scallop.
- Get it right
- Enter 0 to use the stepover that just meets the scallop target.
What this means: Cutting speed at the effective diameter
- What it is
- The cutting speed you want at the effective diameter, the point where the ball actually cuts, from the cutter maker’s data.
- Units and format
- Enter a number in m/min: metres per minute. The form accepts 0.000001 m/min to 2000 m/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 m/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Spindle speed and feed rate rise in proportion until the machine limit.
- Get it right
- Not the speed at the full ball diameter; the tool works out the effective diameter.
What this means: Feed per tooth
- What it is
- The feed per tooth for the ball-nose cutter, from the cutter maker’s data.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.05 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Feed rate rises in proportion and finishing time falls.
- Get it right
- Per tooth, not per revolution.
What this means: Largest spindle speed
- What it is
- The highest spindle speed the machine can run. If the cutting speed needs more, the spindle is held at this limit.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 100000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15000 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Area length (pass direction)
- What it is
- The length of each finishing pass across the area, in the direction the cutter feeds.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Finishing time is proportional to it.
What this means: Area width (stepover direction)
- What it is
- The width of the area measured across the passes, in the stepover direction. It sets the number of passes.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Method and formulas
- Stepover for scallop h: s = 2√(2Rh − h²); scallop for stepover s: h = R − √(R² − s² ÷ 4) (as the scallop height tool).
- Effective diameter D_e = 2√[a_p (D − a_p)]; n = min(1000 v_c ÷ π D_e, n_max) (as the ball nose diameter tool).
- Feed = n z f_z; passes = width ÷ stepover (rounded up); time = passes × length ÷ feed.
- Example: a 0.28281 mm stepover leaves 2 µm; at 15,000 rpm and 1,500 mm/min the 100 × 80 mm area takes 18.867 min.
Limitations
- Flat surface normal to the tool; slopes change the scallop and effective diameter.
- Stepover moves and lead-in time are not included.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Program a finishing pass for a mould or die surface
- Trade surface finish against machining time
- Set spindle speed for a small effective diameter
Who it is for
- CNC programmers
- Mould makers
- Manufacturing engineers
What you get
- Stepover and scallop height
- Effective diameter, spindle speed and feed
- Passes and finishing time
Interpreting the result
- Halving the scallop height only shortens the stepover by about 30%, but the time rises in the same proportion.
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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Open the Ball-Nose Finishing Plan (Stepover, Speed, Feed and Time) calculator