KEVOS® MAKEOS · Gears
Involute Gear Cutter Number
Which involute gear milling cutter number should cut this spur, helical or bevel gear?
The standard involute gear milling cutter number (1 to 8, and the half-number series) for a spur gear, or for a helical or bevel gear from its formative (equivalent) number of teeth.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Gear type | choice | Kind of gear being milled. |
| Number of teeth | teeth | Actual number of teeth. |
| Helix angle (helical) | ° | Helix angle of a helical gear. |
| Pitch cone angle (bevel) | ° | Pitch cone angle of a bevel gear (see the bevel gear tool). |
Method and formulas
- Helical: formative teeth = N ÷ cos³ψ. Bevel: formative teeth = N ÷ cos δ (back-cone method).
- Regular cutters: No. 1 135–rack; 2 55–134; 3 35–54; 4 26–34; 5 21–25; 6 17–20; 7 14–16; 8 12–13.
- Half numbers: 1½ 80–134; 2½ 42–54; 3½ 30–34; 4½ 23–25; 5½ 19–20; 6½ 15–16; 7½ 13.
- Example: a 30-tooth helical gear at 30° has 46.188 formative teeth: use a No. 3 cutter.
Limitations
- Form cutters give approximately correct profiles; generated teeth (hobbing, shaping) are more accurate.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Pick the right form cutter for milling gear teeth
- Find the equivalent teeth for helical and bevel gears
- Decide when a half-number cutter is worth using
Who it is for
- Machinists
- Toolmakers
What you get
- Formative (equivalent) number of teeth
- Regular cutter number
- Half-number cutter
Interpreting the result
- Use the half-number cutter when the tooth count is near the lower end of a regular cutter’s range and accuracy matters.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2148–2150, 820–829. Topic reference; no source tables or recommended settings are reproduced.
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