Fitting knobs properly on pot shafts. Going INSANE.

[vikingred]

I guess I've gotten lucky with my builds so far.  I'm running into a problem that is literally driving me insane.  I've adjusted the pot height (500k CTS longshaft) multiple times, tried 3 different knobs (dometop knurled, flattop knurled, other custom knobs with abalone) and when I go to tighten the screw (lightly, softly, on the splines, on the split, no matter where) I get a wobble that scrapes or just looks and feels horrible.  What am I doing wrong?  I've raised the height to where the tip of the pot shaft goes all the way up in the knob, and I've tried it where it only goes in midway or so.  I've tried wrapping the shaft with plumbers tape, electrical tape.  I've tried widening the split in the shaft, I've tried narrowing the split in the shaft.  I just can't for the LIFE of me get any knobs to fit on snugly and rotate evenly.  There is always a wobble.  I've worked on it for hours.  :dontknow:  :help:

EDIT: Just to be clear these are 6mm fine-spline split-shaft pots (long), and all knobs are 6mm holes as well.  I've seen where people are able to use these with dome knobs/tele-type knobs and just position the set screw on the split itself.  Well, it's not working for me.  I just did a search for 500k solid shaft (long) and I can't find any.  WTF.

 

[line6man]

Buy some brass sleeves to convert your split shafts to solid shafts.

 

[vikingred]

Buy some brass sleeves to convert your split shafts to solid shafts.

Really?  Wow.  I'm a dumbass.

 

[Verne Bunsen]

When you say wobble, do you mean that the knob is loose and wobbles on the shaft or that the rotation is "off-center"? Two things come to mind.

The first thing is to make sure that your set screw is aligned with the split in the shaft, as that will give you the most secure fit.

The second is that there are two standard pot shaft sizes: 6mm and 1/4". Generally speaking, split-shaft pots are 6mm and sold shaft pots are 1/4". Set-screw style knobs can be found in both sizes. If you've got a 1/4" knob on a 6mm shaft, it will indeed be slightly off-center. If you don't want to source new knobs, then brass adapter bushings can be used to up the OD of a 6mm shaft to better accomodate a 1/4" knob.

6mm set screw knobs:
http://www.stewmac.com/Hardware_and_Parts/Knobs/Dome_Knob.html
http://www.stewmac.com/Hardware_and_Parts/Knobs/Flat-top_Knob.html

Shaft adapters: http://www.wdmusic.com/brass_pot_sleeves_5_pieces.html

 

[vikingred]

When you say wobble, do you mean that the knob is loose and wobbles on the shaft or that the rotation is "off-center"? Two things come to mind.

The first thing is to make sure that your set screw is aligned with the split in the shaft, as that will give you the most secure fit.

The second is that there are two standard pot shaft sizes: 6mm and 1/4". Generally speaking, split-shaft pots are 6mm and sold shaft pots are 1/4". Set-screw style knobs can be found in both sizes. If you've got a 1/4" knob on a 6mm shaft, it will indeed be slightly off-center. If you don't want to source new knobs, then brass adapter bushings can be used to up the OD of a 6mm shaft to better accomodate a 1/4" knob.

6mm set screw knobs:
http://www.stewmac.com/Hardware_and_Parts/Knobs/Dome_Knob.html
http://www.stewmac.com/Hardware_and_Parts/Knobs/Flat-top_Knob.html

Shaft adapters: http://www.wdmusic.com/brass_pot_sleeves_5_pieces.html

No, it's the rotation being off center.  These are not 1/4" knobs they are 6mm.  Went ahead and order some brass adapters off ebay (12 for $6.95).  Was so trying to get this build done this weekend.  It's been the bane of my existence, such a beautiful machine, but every step of the way a monster.  It's just 2 pots, a master volume and master tone, I may look around the house find something I can cut with a dremel wheel, if not it'll just have to wait.  Thanks ya'll.

 

[vikingred]

HEATSHRINK TUBING!  Check it out.  Gonna try it.

 

[Verne Bunsen]

These are not 1/4" knobs they are 6mm.

6mm is the smaller size, 1/4" is larger. The adapters have 6mm ID and 1/4" OD to make the smaller 6mm shaft properly fill a 1/4" hole; If your knobs are 6mm then the bushings won't do anything for you. Your knobs wouldn't fit over them. But if your knobs are 6mm you shouldn't be having issues with a sloppy fit on a split shaft pot, either.

 

[vikingred]

These are not 1/4" knobs they are 6mm.

6mm is the smaller size, 1/4" is larger. The adapters have 6mm ID and 1/4" OD to make the smaller 6mm shaft properly fill a 1/4" hole; If your knobs are 6mm then the bushings won't do anything for you. Your knobs wouldn't fit over them. But if your knobs are 6mm you shouldn't be having issues with a sloppy fit on a split shaft pot, either.

Well, but I am.  6mm shaft, 6mm knob hole.  And nothing is fixing it.  And I just accidentally broke off one of the split sides of one shaft, so I've got to unsolder all the work and install another pot.  Man o man.

 

[Verne Bunsen]

That is really strange.  When you put the knob on the shaft, are you aligning the set screw with the split? That will allow the set screw to get a better/deeper bite and will spread the two halves just a bit to create a nice snug fit. Aligning the set screw with the meat of one of the sides could possibly collapse it and cause the knob to sit crooked? Maybe? I'm intrigued to know the circumstances of how the shaft got broken, as that could be a clue. I've never seen that. I have 6mm set-screw style knobs on 6mm split shaft pots on 3 Teles and I've never encountered what you're describing. If you're certain on the knob size and you've tried different knobs and it's happening on both pots, then the only variable left is how the knob is going on, right?

 

[stratamania]

Why not just get some solid shaft pots in this instance.

 

[Vallhagen]

HEATSHRINK TUBING!  Check it out.  Gonna try it.

I was actually on my way to deliver that hint when i read your first post. It has worked fine to me.

 

[mayfly]

You probably need to have something in the split to keep the split from collapsing when you tighten the screw on the knob.  I find a little piece of tie wrap works fine for this, but anything that's the same width/depth as the slot will do.  Based on your assertion that you broke off a tab, this is probably your problem.

Or as others suggest, you could just use a solid shaft pot.  You're putting a new one in anyway.

 

[BigSteve22]

You probably need to have something in the split to keep the split from collapsing when you tighten the screw on the knob.

I broke a split shaft on an Epiphone one time. It bent all the way in when the knob shifted as I was tightening the set screw and I didn't notice until it was too late. I carefully bent it back up, but it broke off anyway. I cut a small piece of maple to fit the slot, put the wood and the broken piece on the shaft, and slipped the knob over it. Tightened the set screw against the broken piece, and it worked like a charm.

 

[vikingred]

Why not just get some solid shaft pots in this instance.

I have been unable to find 500k long+solid 6mm shafts ANYWHERE.  Maybe my google skills suck. 

 

[vikingred]

You probably need to have something in the split to keep the split from collapsing when you tighten the screw on the knob.  I find a little piece of tie wrap works fine for this, but anything that's the same width/depth as the slot will do.  Based on your assertion that you broke off a tab, this is probably your problem.

Or as others suggest, you could just use a solid shaft pot.  You're putting a new one in anyway.

Yeah I botched it.  I'm about to start redoing the electronics right now and give it another shot.

 

[Punxsutawney]

You probably need to have something in the split to keep the split from collapsing when you tighten the screw on the knob.  I find a little piece of tie wrap works fine for this, but anything that's the same width/depth as the slot will do.  Based on your assertion that you broke off a tab, this is probably your problem.

Or as others suggest, you could just use a solid shaft pot.  You're putting a new one in anyway.

Yeah I botched it.  I'm about to start redoing the electronics right now and give it another shot.

It's almost 2 years since you last posted in this thread, but I'm keen to know how you went.  I'm curious about this topic and googling this issue I stumbled onto your problem here.

Just for defining terms, so there's no confusion, I'll refer to the "bushing shaft" as the initial part of the potentiometer column, that the bushing nut is screwed onto, so that the pot can be secured to the guitar body – it is NOT the actual section that the knobs are attached to.  I will call the "knob shaft" that smaller end section after the bushing shaft on the potentiometer column, where the knob is actually inserted and fitted onto, which maybe either "knurled" (i.e. split shaft) or "solid".  God, that was horrible and I'm glad definitions are over!

I'm very keen on Schaller Dome knobs, which have a 6mm diameter knob shaft hole in them – I'm yet to find out if there are any spline shapes inside though.  I'm looking at Bourns Premium 95 pots, which are available in a "long" bushing shaft (3/4" length) and a shorter "standard" length bushing shaft (unsure of length as yet) – both are available in 6mm knob shaft diameters.  Unfortunately, only the "standard" length bushing shaft has an optional solid "knob shaft".  I am not sure if the "standard" bushing length pot, is long enough to fit in the rear control cavity of my telecaster guitar body (too close to call, but I bet on "NO!").  Like you have found in general, the "long" bushing shaft pot does not have the option for a solid knob shaft, which is really annoying!


It sounds like knob shafts, that are knurled, are a piece of junk, but I don't know and I would like to.  I have read from others, but not here, who have stated they cannot be secured without movement (i.e. like you've reported).  Maybe this is a spline issue on the knob shaft with the hole it's inserted into, but I don't know much about this as of yet.  In any event, I keep hearing knurled knob shafts are very easy to break when bent and that happened to you too!  I'm inclined to think they are terrible, because the split knob shaft has no strength and gives way at it's very centre?  I did notice that the Bourns knurled knob shafts, have splines on them; maybe there are also splines inside the knob hole and they are incompatible?  Is it possible the shape of the knob shaft and the shape of the knob hole are incompatible?  If they are the same shape, then it appears knurled shafts suck and the only option to strengthen it, is to chock the split.

I'm not interested in anything but the Bourns pots and if it has to be the longer 3/4" bushing shaft option (with no alternative but a knurled knob shaft), then I wonder what would be the best way to fill/chock the split in the knob shaft.

There is also another factor to consider, apart from knurled knob shafts and/or splines and that is the shape of the top of the knob shaft compared to the bottom of the shaft hole in the knob (where they both meet).  If they are different shapes, it would be a problem, particularly if you have a collapsing knurled knob shaft!

 

[Fat Pete]

My 2 cents:

You're probably right, the short shaft isn't a good option for a rear routed guitar.

I've never seen a knob with a set screw - like the Schaller - that is also splined.

So, if you're set on Bourns, you're set on splined, split shaft pots.

You can either, line up the set screw with the split so if there is any bending it will be outwards and contained by the knob, or pack/chock the split - with anything reasonably incompressible. If there's wiggle with these methods, maybe try a few wraps of PTFE (plumber's) tape.

The bushing adaptor sleeves you can get probably won't fit the Schaller knobs, but are a good option for knobs drilled to 1/4" (6.35mm) when using 6mm pots.

The shape of the end of the shaft is unlikely to be an issue as the knobs won't go all the way down the short 'knob shaft' anyway.

Good luck!