# Machining A Female Half-moon Shaft?



## Riaan (Oct 26, 2015)

Think "eighties hi-fi knobs".





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!


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## commando57 (Oct 26, 2015)

Drill it and put in a setscrew?


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## RJSakowski (Oct 26, 2015)

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


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## Riaan (Oct 26, 2015)

I've seen the grub screw solution. What if it wasnt acceptable for aesthetic reasons or whatever?


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## kd4gij (Oct 26, 2015)

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,


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## RJSakowski (Oct 26, 2015)

Here is an example:


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## Riaan (Oct 26, 2015)

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 .



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.


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## kd4gij (Oct 26, 2015)

RJSakowski said:


> Here is an example:
> 
> 
> 
> ...


 

  Now why would we buy a $3.00 knob when we can make one for $30.00 and several hours of labor.


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## RJSakowski (Oct 26, 2015)

randyc did the post on the rotary broach. http://www.hobby-machinist.com/threads/a-simple-compact-rotary-broach.33032/

Re:  buy vs. build, I had the impression that the OP was asking how it would be made, not stating that he wanted to make one.


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## Paul in OKC (Oct 26, 2015)

(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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## joshua43214 (Oct 26, 2015)

I have seen them with a small flat spring that presses on the flats.
It might take a bit of trial and error, but should not be too hard to make.
Just plunge mill two slots (more like grooves) on the edge of the hole, bend a piece of steel packing strap into an arc, and fit it into the slots.
I remember pulling the knobs off a stereo amp when I was a teenager and losing a spring 
The spring also had a bit of a tab bent back on the opening end of the knob to aide getting it over the shaft.


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## Riaan (Oct 27, 2015)

RJSakowski said:


> randyc did the post on the rotary broach. http://www.hobby-machinist.com/threads/a-simple-compact-rotary-broach.33032/
> 
> Re:  buy vs. build, I had the impression that the OP was asking how it would be made, not stating that he wanted to make one.



I'm busy restomodding a 280ZX (Fairlady Z), the interior will be getting the 80's hi-fi treatment in this vein, with brushed aluminium facia and toggle switches:




Suffice to say that none of the stuff I've seen online delivers the same look and I'll rot before I butcher a vintage amplifier to repurpose the knobs.


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## RJSakowski (Oct 27, 2015)

Restoring a vintage amplifier does present its problems.  I would expect that Pioneer had their knobs and switches custom made.  I have a Scott receiver of similar vintage with machined aluminum knobs.  The knobs have plastic inserts which are pressed into the aluminum shell.  Perhaps you could use a similar process by purchasing off-the-shelf knobs and turning them down to fit a milled pocket in your machined shells.


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## Fabrickator (Oct 27, 2015)

Sleeve it, did one last week for my Power Feed Lever converting it to a knob.  Find another old knob with the same half-moon, slip-fit style mount.  Machine it down to about 3/8" (for a 1/4" shaft).  Drill out the hole in your good (new) knob to accept it with a slight press fit and a drop of red locktite.  No set screw needed, looks original. True restoration.  There should be almost zero torque on a stereo knob.


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## chips&more (Oct 27, 2015)

A +1 on the insert idea. And would also entertain the rotary broach method, but have concerns on not enough clearance and or too much metal removal…Dave


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## Riaan (Oct 27, 2015)

Some truly excellent ideas bubbling up in this thread. Thank you, gentlemen!


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## TC0853 (Mar 18, 2016)

kd4gij said:


> Now why would we buy a $3.00 knob when we can make one for $30.00 and several hours of labor.


Good point


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## higgite (Mar 18, 2016)

kd4gij said:


> Now why would we buy a $3.00 knob when we can make one for $30.00 and several hours of labor.


For the same reason that I bought a $1500 mill so I can make a carriage stop for my $1800 lathe that I bought so I could make one of these. 




It’s science.

Tom


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## TOOLMASTER (Mar 18, 2016)

LOTS OF KNOBS ON EBAY


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## Tony Wells (Mar 18, 2016)

How many do you need? I have quite a few I can look through.


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## Cadillac STS (Mar 21, 2016)

Could find metal knobs that fit the shaft that already have the half moon or the spring clip inside.  Put that on the lathe and turn it down close to the diameter of the hole.  Then on the knob you make use that slug with the half moon in it as an insert you epoxy into the new knob.


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## Andre (Mar 21, 2016)

Riaan said:


> I'm busy restomodding a 280ZX (Fairlady Z), the interior will be getting the 80's hi-fi treatment in this vein, with brushed aluminium facia and toggle switches:



Pics, please 

I thought the "Fairlady Z" name was dropped after the 240? Did it live on on some models?


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