The faceted surface left by hobbing: generating flats along the profile from the finite number of hob gashes, and feed marks along the face from the axial feed per revolution. Their size depends on the number of gashes, the number of starts and the feed rate, and they are visible in profile and lead traces as small regular waves. Finer feeds or a finishing process such as shaving or grinding remove them.
Scallops on the flank are too coarse, drop the feed for the finish pass or the lead trace will look like a saw blade.
Also heard as
- feed marks
- generating flats
- hob marks
Related terms
Hobbing
Generating gear teeth with a rotating worm-shaped cutter that turns in step with the blank.
Hob
A gear cutter shaped like a worm with gashes across its threads, used on a hobbing machine.
Trace
The printed plot of a tooth's measured profile or helix from a gear checker, read against tolerance bands.