Why grind a gear after hardening?

Hardening moves the teeth a little. Grinding removes that distortion and the hardening scale, so the gear meets its quality class and runs quietly.

What accuracy does gear grinding give?

Typically DIN or ISO class 4–6, much finer than a hobbed and hardened gear, which is usually around class 8–10.

Can any gear be ground?

Most external spur and helical gears can. The design must leave room for the wheel to run out at the ends of the teeth; gears next to a shoulder may need a groove.

Gear grinding job work: accuracy, methods, when needed

Gear grinding finishes the teeth of a gear with an abrasive wheel after the gear has been hardened. Hardening distorts the teeth slightly; grinding removes that distortion and brings the profile, lead and pitch to tight limits. Ground gears run quieter, carry more load and last longer, so they are used in gearboxes, machine tools and high-speed drives.

Quick facts

Done after: Hobbing or shaping, then hardening (case carburising, induction or through hardening)
Main methods: Generating (threaded wheel) and profile (form wheel)
Typical quality: About DIN 4–6 / ISO 1328 class 4–6
Stock removed: Usually about 0.1–0.3 mm (0.0039–0.0118 inch) per flank
Gear types: Spur and helical, external; internal on special machines
Usually priced: Per gear, by module, teeth and face width

How it is done

The gear is cut (hobbed or shaped) with grinding allowance left on the flanks
It is hardened, which hardens the surface and moves the teeth slightly
The bore or shaft journals are ground first so the gear runs true on the machine
The teeth are ground with a threaded wheel (generating) or a form wheel tooth by tooth (profile)
Profile, lead and pitch are checked on a gear tester and a report is given

Generating or profile grinding?

	Generating (threaded wheel)	Profile (form wheel)
Speed	Fast, good for batches	Slower, tooth by tooth
Best for	Small and medium modules, volume work	Large modules, few pieces, special profiles
Profile changes	Needs wheel dressing for each module	Wheel dressed to any profile, including tip relief

What to send the grinder

Gear drawing with module, teeth, pressure angle, helix angle and face width
Required quality class (DIN, ISO or AGMA) and any profile or lead modifications
Material, hardening method and surface hardness
Datum to grind from (bore, shaft journals or faces)
Grinding allowance left on the teeth
Whether a gear inspection report is needed

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Questions

Why grind a gear after hardening?: Hardening moves the teeth a little. Grinding removes that distortion and the hardening scale, so the gear meets its quality class and runs quietly.
What accuracy does gear grinding give?: Typically DIN or ISO class 4–6, much finer than a hobbed and hardened gear, which is usually around class 8–10.
Can any gear be ground?: Most external spur and helical gears can. The design must leave room for the wheel to run out at the ends of the teeth; gears next to a shoulder may need a groove.

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 22 October 2026.