[David G4EBT]

Yet more pics!

First pic: I cast four knobs in the mould before discarding it. (The knobs were for a Unitra Figaro).

To machine the hole for the brass ferrule it must be completely concentric with the knob and some means of holding the knob in the lathe to machine the rear of the knob flat, then to use a 12mm end mill to mill the hole needs to be devised. 'Jam chucks' which are simply wooden chucks made for the job in hand are widely used in woodturning. I made a simply jam chuck and turned a hole in it to the same profile as the knob, then used some hand-wipe tissue to protect the knob when I pushed it into the chuck. I then 'faced off' the rear of the rough casting, and using a 12mm end mill in the tailstock, I rotated the chuck by hand while advancing the tailstock to the required depth for the brass ferrule.

The second pic is a sketch of the jam chuck.

Third pic is drilling the jam chuck with a Forstner bit before using a turning tool to create the internal profile to suit the sloping side of the knob.

Fourth pic shows the jam chuck with the casting in it, being rotated by hand while advancing the 12mm end mill.

The last pic shows a 12mm ferrule turned on my metalworking lathe with a 1/4" hole and the outside roughened up on the lathe to provide a good key for the epoxy cement used to glue the brass ferrule into the knob.