The indexing knob is used to hold work on a lathe stationary while you cut a flute or a reed with a router setup. There are usually 24 or more equally spaced index settings. After one flute or reed is cut, the work on the lathe is rotated to the next desired position. The indexing knob can also lock the lathe spindle while you install or remove a chuck.
Barry
I've done some minor work on a lathe for a year now, and I'm wondering what
> this indexing knob on the headstock can be used for...supposed to be for
> fluting and reeding, but it seems to only lock the lathe preventing it from > turning.
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