A gear hobbing machine cuts gear teeth by rotating a hob, a cutter shaped like a worm with gashes, in step with the gear blank. It makes spur and helical gears, splined shafts, worm wheels and sprockets quickly and accurately.
Quick facts
- Makes
- Spur and helical gears, splines, sprockets, worm wheels
- Size given as
- Max gear diameter and max module (e.g. 400 mm (15.75 inch), module 6)
- Types
- Mechanical and CNC
- Typical quality
- Around DIN 8–9 as hobbed; ground later for higher grades
- Cannot do
- Internal gears and gears next to a shoulder (use gear shaping)
- Tool
- Hob, chosen by module and pressure angle
Hobbing or shaping?
- Hobbing: faster, the usual method for external spur and helical gears and splines
- Shaping: needed for internal gears and gears close to a shoulder or flange
- Grinding or shaving after heat treatment for high-accuracy gears
What to send for gear cutting
- Number of teeth, module (or DP), pressure angle and helix angle
- Gear quality grade and any profile modification
- Material and heat treatment, with grinding allowance if ground later
- Blank drawing with bore, face width and outside diameter
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Questions
- What is a hob?
- A cutting tool shaped like a worm thread with gashes that form cutting teeth. It rotates in step with the gear blank, generating the tooth shape.
- Can a hobbing machine cut internal gears?
- No. Internal gears are cut by gear shaping or broaching.
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 9 October 2026.