How about chemical etching?
How about chemical etching?
If you look carefully , you will see that in most cases it's cut with a thin circular cutter. The groove inside is curved. The curvature depends on the dia of the blade . Looks like a static cut . You could do it off the lathe if you can't lock the spindle.
You'll have to make a jig to hold the knobs the right way around. That way there will be no alignment error. However the whole machine assembly will have to be set up to cut the grove in the knob and depth of cut can be fixed like in a vertical drill press. This would also mean that you will need to make a fair quantity of knobs for each setup.
If you can't do it, a plain round dot is better than nothing !![]()
There appears to be two grooves near the front edge. Was this requested for by someone ? Can you post a pic of a single knob from an angle so that we can figure out how it looks. The present picture of a bunch of knobs doesn't do justice to the appearance.
Cheers.
What is the outer diameter of these knobs?