My first try at a reproducing the missing tool rest knob. I goofed and made the diameter a bit too small but otherwise it looks pretty good. I'll make another but this was good for getting for the dimensions and general shape. We'll call it proof of concept.
I started by gluing up scraps of maple and beech. Beech is on the outside right.
I always forget to take pictures but I measured the original with calipers, transferred that measurement to the wood blank using the same calipers and a parting tool, then blended the curves.
Before cutting to final size, I drilled a 3/8" hole through the center and installed a 1/4-20 threaded insert. I also marked off 12 equal divisions around the perimeter using the indexing wheel of my lathe then ground 12 grooves using a Dremel. I didn't bother sanding out the burn marks because this will be painted black eventually.
After friction polish (shellac/oil). Not shown here but I also seated the threaded insert a little deeper.
Comparison with original: