Nowadays a Bastard File is one that disappears into cyberspace just as you've almost finished working on it.
As an apprentice I helped on a couple of projects which involved making spiral and involute flutes on shafts these were done by linking either a rotary table or dividing head to a milling machines feed mechanism so that they rotated as the bed of the mill moved along. Working out the ratio between them to get the correct end result was a complete nightmare but we eventually got the required locus, I think that was the posh word for it. I also learned to chisel keyways in machine shafts.
