Machining A Female Half-moon Shaft?

Riaan

Riaan

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Think "eighties hi-fi knobs".
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These dials are usually metalized plastic and have the shaft pocket splined or with a half-moon section to mate with the switch shaft. Since they are cast as-is if plastic or forged with a die if metal in production, it's no problem if you have that equipment. But how would you manually machine the pocket from a blank while preserving your tooth enamel?

The splines I can invision should be straightforward with an indexing head or rotary table and a shaping bit, but what about the half-moon?

Thanks!
 
That type of knob was also made from metal. They are usually found on high end electronic test equipment. Those knobs have one or two set screws to index and fix the knob.

Bob
 
I've seen the grub screw solution. What if it wasnt acceptable for aesthetic reasons or whatever?
 
If I was to make one for the object in your photo. Where a set screw won't work. I would drill and ream the hole. And then turn a piece of mild steel doun and grind it to the size needed and epoxy it in the knob .

Or invest in or build a rotary broach. Some one on this forum did a wright up on building one,


 
Last edited:
kd4gij said:
If I was to make one for the object in your photo. Where a set screw won't work. I would drill and ream the hole. And then turn a piece of mild steel doun and grind it to the size needed and epoxy it in the knob .
Click to expand...

That sounds like a good solution. Come to think of it, a fat dollop of epoxy in the hole would probable do the trick all on its own since you have to afix the knob to the shaft somehow anyway so it doesnt fall off.
 
(Now why would we buy a $3.00 knob when we can make one for $30.00 and several hours of labor.)

I've had that disease! Still get it once in a while:)
 
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