Gear Lapping

Gear Lapping

Gear Lapping - When dealing with large quantities of fairly small case­hardened steel gears, it is possible to correct the errors due to distortion which takes place during hardening, by lapping, which is a much less expensive process than profile grinding. The lap is a cast iron gear of the same normal pitch and pressure angle as the gear to be lapped, but with a different spiral angle, so that when the two are meshed together their centre lines are not parallel.

This means that when gear and lap are rotated, a sliding action occurs at all points in the area of contact. The lap is coated with grind­ing paste, and when it is rotated in mesh with the gear to be lapped, the sliding action causes the grinding paste to smooth away the high spots on the teeth of the gear.

As always occurs in lapping, the harder member (the gear) is lapped, whilst the softer one (the lap) is only very slightly affected, and may be used many times without serious loss of accuracy. To rover the face width of the gear, it is moved backward and forward parallel to its centre line whilst rotating in mesh with the lap i.e, the cast iron gear.

Spiral bevel gears designed for mounting on rear axles of motor cars are made from case-hardened steel and corrected for any errors due to distortion, by lapping process.