Radial slot cutting

[easymike29]

Unless I am not understanding the question I would clamp the knob in a Spindex mounted horizontally on a horizontal Rotary table. The Spindex would of course need to be mounted at the correct distance from the center of the Rotab.
Rotate the Rotab through the appropriate 90 degree arc, index. repeat.

Gene

 

[Maplehead]

I made a jig for my rotary grooved knobs. Here's the first to come out of it. It's not perfect as I have yet to at the groove end stops to the jig, so I just eyeballed how long they should be.

 

[Maplehead]

Here's the jig.

 

[Silverbullet]

Looks like you've done a good job ,why mess with success .