PRS lampshades & CTS pots

Solteroblues

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Oct 14, 2014
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Hi all, I bought some PRS lampshade knobs off of ebay - I assume they are used, but they came in the original (opened) packaging. I am putting in new CTS pots, but the knobs don't fit correctly. The splines appear to be perfectly spaced, but the knob just slips on and off. Am I missing something here? Could the knobs be damaged to the point that they won't fit snugly anymore (they don't appear to be damaged or stripped or anything)? Aren't they supposed to fit CTS pots without problems?

I think I could spread the split shaft apart so that they would fit tighter, but I'm afraid it may just crack. What else could there be wrong?
 
you will need to spread the split shaft out some. once you put the knobs back on they will adjust the splits opening back, but giving a tighter fit in the process. Take your time widening the split. should not need to widen to much to achieve a proper fit.
 
you will need to spread the split shaft out some. once you put the knobs back on they will adjust the splits opening back, but giving a tighter fit in the process. Take your time widening the split. should not need to widen to much to achieve a proper fit.

Are the splines slightly larger on PRS USA pots? Do you know which brand PRS use? Is it their own? I plan to fit CTS pots on my SE and use Lampshade knobs, so I assume I will have the same problem. I'm thinking of trying the Emerson low friction pots, because they should feel like the PRS USA pots.
 
PRS pots are similar to CTS pots. Most of the time the knobs will go on and have a good fit. ( on must brand of pots) Every once and awhile you my have to widen split opening to get a good fit with any knob, not just PRS ones.
 
It seems PRS uses some sort of proprietary pots for their USA stuff.

I have been looking for some speed knobs to replace the lampshade knobs and according to PRS, they use "1/4” split-shaft (6.35MM) CTS style pots" on their USA models. The vast majority of speed knobs I can find are for general USA split-shaft CTS pots, but they’re all 6MM.

I'm left with either ditching the idea entirely, crimping the pots, or drilling out the knobs. Ugh!
 
I'm pretty certain the PRS pots are made by CTS. Either way, you just need to spread the tangs of the shaft a bit with a screwdriver, as the others have mentioned. I had to do it when I replaced the pot on my Mira - knob is on there solid as rock now.
 
I'm pretty certain the PRS pots are made by CTS. Either way, you just need to spread the tangs of the shaft a bit with a screwdriver, as the others have mentioned. I had to do it when I replaced the pot on my Mira - knob is on there solid as rock now.

^^This^^

Piece of cake to widen the tangs a little bit with a flathead screwdriver. Did this on some regular brass shaft CTS pots a few months ago.
 
Morphine's issue is the opposite problem: he is using the PRS-stock pot, but replacement knobs have too small a hole to fit over the shaft. <Insert peurile joke here.>

Crimping the shaft may not work for the smaller bore hole.
 
Morphine's issue is the opposite problem: he is using the PRS-stock pot, but replacement knobs have too small a hole to fit over the shaft. <Insert peurile joke here.>

Crimping the shaft may not work for the smaller bore hole.

Any suggestions on how to fix this (other than using a different knob)? Wondering if it would be possible to drill out the knobs to make it work.
 
Any suggestions on how to fix this (other than using a different knob)? Wondering if it would be possible to drill out the knobs to make it work.

Drilling them out will remove the spline-shaft mating material, and the knob will want to spin on the pot.

I dunno, has anyone actually tried to fit a "6mm" knob on a "6.35 mm" shaft? Maybe tolerances are loose enough that it can be made to work with the shaft crimped a bit?
 
Morphine's issue is the opposite problem: he is using the PRS-stock pot, but replacement knobs have too small a hole to fit over the shaft. <Insert peurile joke here.>

Crimping the shaft may not work for the smaller bore hole.

You have to make sure to buy USA-spec knobs. Gibson brand would be a good go-to. Tons and tons of the knobs out there are import spec. Imports are usually "coarse spline" and USA are usually "fine spline".
 
You have to make sure to buy USA-spec knobs. Gibson brand would be a good go-to. Tons and tons of the knobs out there are import spec. Imports are usually "coarse spline" and USA are usually "fine spline".

Unforunately, Gibsons are also 6mm. So they won't fit without some modding either.

Drilling the knobs seems to be the best bet if you don't want to run the risk of jacking up your pots.
 
Drilling them out will remove the spline-shaft mating material, and the knob will want to spin on the pot.

I dunno, has anyone actually tried to fit a "6mm" knob on a "6.35 mm" shaft? Maybe tolerances are loose enough that it can be made to work with the shaft crimped a bit?

My friend had his done by Gary Brawer in SF. He drillled them out just enough so they would fit snuggly without slipping off or crimping the shaft.
 
I did spread the tangs with a screwdriver and got the knobs to fit better, but I really had to widen them up. If you look at them, they are no longer vertical and parallel, but more like 15 degrees apart now - I actually thought they would crack... But it works now...

Thanks!
 
I did spread the tangs with a screwdriver and got the knobs to fit better, but I really had to widen them up. If you look at them, they are no longer vertical and parallel, but more like 15 degrees apart now - I actually thought they would crack... But it works now...

Thanks!

Yes, it seems like you either have to open the slots in the pot shaft, or use something to fill the gap so that the control knobs stay on.

It's strange, everything about PRS is precision, with the exception of the control knobs, which appear to have been made with the wrong size shaft hole. I have just bought USA PRS Lampshade control knobs to replace the speed knobs on my USA Mc Carty. The original speed knobs were pushed on at the factory with black tape inside to take up the slack.

Does anyone know why PRS don't make their control knobs to fit the shafts of the pots? I find this very odd.
 
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