Dome Knobs With Set-Screw

[Timmsie95]

So I have multiple guitars that have set-screw dome knobs, but I've never had to take them off.
I noticed on the stewmac site, they say to line up the set screw with the split in the shaft, for split shaft pots. But this seems like it wouldn't grab the pot enough (especially for push/pull's), or is the screw wide enough to catch both sides, without squeezing the shaft? Because I can see the screw squeezing the shaft if you had it lined up along one side of the split.

 

[Verne Bunsen]

If you line the set screw up with the split in the shaft, then it will force the two halves of the shaft out ever so slightly within the knob, making for a very secure fit. Lining the set screw up with the "meat" of the shaft will have the tendency to collapse the shaft somewhat, making for a less reliable fit.

Here's a pic showing the split shaft relative to the business end of the knob set screw, may help you to better visualize how things are interacting in there:

 

[Cagey]

The idea isn't to squeeze the shaft in that case, it's to drive the set screw between the two halve of the split shaft so they spread outward and bear on the inner diameter of the knob's mounting hole. It spreads the load more evenly, and tends to center the knob so it rotates without an eccentric wobble. If you tighten the set screw against just one of the tongues of the split shaft, at best you will bend it and the knob will rotate funny, and at worst the tongue will snap off and the pot will be essentially ruined. Happens a lot more than you might think.

 

[Timmsie95]

Okay, that makes sense. Thanks, all!

 

[Hbom]

If you've never taken them off, how can you be sure you have split shafts? You may have solid shafts which IMHO are the correct pots to use with set screw type knobs.
:rock-on:

 

[Timmsie95]

I know because my luthier did it (before I knew what I was doing), and told me what pots he used  :laughing7: