Knobs Too Loose or Too Tight on Pots

[natron_mn]

One of the things I've had the most difficulty with on my builds is attaching the knobs to my potentiometers. They are either too loose, and continue to turn even as the pot is at its min or max position, or they are too tight and the pot turns slowly. On professional pedals, turning the knob is usually a smooth process, but I just can't seem to nail that 100% of the time on my builds.

Wondering if anyone else has this issue, or what you do to get the knobs to turn smoothly?

If it helps, I usually use the smooth shaft pots from Tayda Electronics. So first, are pots from Tayda crappy or are they equivalent to Small Bear, Mammoth, etc? Second, should I be getting the spline shaft pots so the screw in the knob has something to stick to?

[blackieNYC]

Ab - if the knob turns slowly, your pot needs to be raised up a hair. It's scraping against the immobile part of the shaft.
And if this makes the pot too high, you have to add washers to the shaft, inside the enclosure.
The only risk of screwing the pots on too tight is stripping the set screw or threads.

[EBK]

I assume by "too tight", you mean that the base of the knob is making contact with either the threaded bushing of the pot or the surface of the enclosure.  Is that correct?  If so, use something as a spacer inside the knob to lift it up a bit.  I've used small pieces of bamboo chopsticks for that purpose.

[rutabaga bob]

Regarding the tight/slow turn, one thing I had happen was the knob sat too low and was fouling up on the nut.  Never had set-screw issues the other way on these types of pots...just make sure you can get the screw really tightened down.  Using a too-narrow/small blade might not allow you to torque the screw properly.  The threads in the knob itself haven't been over-tightened and stripped, have they?  Shoot, it's just plastic...

[natron_mn]

Ab - if the knob turns slowly, your pot needs to be raised up a hair. It's scraping against the immobile part of the shaft.
And if this makes the pot too high, you have to add washers to the shaft, inside the enclosure.
The only risk of screwing the pots on too tight is stripping the set screw or threads.

What do you mean the pot needs to be raised up? Or do you mean the knob needs to be raised up?

As far as the knob making contact with the threaded bushing... you could be right! I've never really paid attention to how low I have my knob set.

[EBK]

Depending on the knob, you may alternatively be able to use a drill bit to widen the part of the knob's opening that is rubbing on the bushing.

[anotherjim]

Some pots are very stiff from new. I think they have a sticky grease on the shafts. A squirt of Servisol can loosen them up by an amazing degree - sometimes too much.
Shaft diameter - a tenth of a millimeter is enough for it to be too tight or too loose. We have 6mm, 6.3mm and 1/4" out there. Try to find knobs that match.
Heat shrink on the shaft might help?

[blackieNYC]

I meant knob not pot. 
The part that sticks up thru the hole is the rotating shaft, and the non-rotating threaded cylinder. If the knob sits too low, the base of the knob or even the set screw itself will rub against the threads, or maybe the nut on the top of the whole.  If you put two washers under the box's surface, on the threaded shaft, those threads will sit lower in the hole when seen from above. Then It will be less likely to interfere with the base of the knob.
The alternative is to raise the knob up away from the surface of the box, and tighten the set screw there. Usually this is ok, sometimes the knob looks silly, raised up too high. 

[EBK]

If you put two washers under the box's surface, on the threaded shaft, those threads will sit lower in the hole when seen from above. Then It will be less likely to interfere with the base of the knob.

The knob would sit at the same height as before wrt the threaded bushing if you let it slide down.  I'd combine this technique with a spacer inside the knob.

sometimes the knob looks silly, raised up too high.

I fully agree with you there.

[stallik]

Occasionally, I've wanted to stiffen up the pot rotation to make it a little harder to accidentally adjust a setting but still leave the pot adjustable for when you do. My technique is to pop an O ring under the knob so that it touches both the bottom of the knob and the enclosure. Friction can be adjusted by applying more pressure when mounting the knob.
Effective, cheap and may even help prevent crap getting into the pot. Opposite of what you're trying to achieve but thought I'd mention it.

[duck_arse]

put something between the knob skirt and the front panel to space the knob before you tighten the screw. then remove the spacer (but leave the knob). I like to glue felt to the knob skirt under, then trim round the edge, just because.

don't tighten the screw in tayda knobs too much, they can't take much torque to start with. and if you use set-screw knobs on splined shafts, the knob will tilt or nose to one side. I've not yet seen an explanation of the mechanics of this, nor found an effective repeatable solution.

[davepedals]

if the knob is loose on a metal shaft,  seat knob properly - remove set screw, drill small indentation in shaft through screw hole then remove knob and drill a bit larger, not deep however.  Now set screw has something to sorta lock into.  Who knows?

[Kipper4]

Amazing.
Not a single knob gag yet.

[blackieNYC]

I guess to put it more simply, two things can interfere: 
1. the threads on the pot shaft.  they won't touch the knob, but they can touch the set screw. Get the threads down lower into the enclosure. By some means.
2. the nut, sitting just above the surface of the enclosure. It can scrape the bottom of the knob.  You can raise the knob. Conceivably you leave out the top-side washer (careful!) or find a thinner nut.

I have some pots that are threaded much further up the shaft.  For a thicker enclosure I suppose.  From Tayda I think - my ordering mistake.  I would have to stack a lot of hardware on the inside to get those threads inside the box. Stupid.

No knob gag at all? That's talent.

[Tony Forestiere]

... and if you use set-screw knobs on splined shafts, the knob will tilt or nose to one side. I've not yet seen an explanation of the mechanics of this, nor found an effective repeatable solution.

If using splined shaft pots with set screw knobs, most guys around here will place the snapped off pot locating tang into the shaft slot. Keeps the gap in the shaft from compressing when the set screw is tightened. Also using a couple of pieces of cereal box thick cardboard shims between the knob and encosure surface will help with interference issues.

[davent]

Splined shafts are a thinner diameter then the holes in set screw knobs. Even filling the shaft gap the set screw knob won't sit properly, tilted and looking like crap to us OCD types. You can buy a bushing to slip over the splined shaft to give you a 1/4" shaft but it's still not perfect. Plus the for the cost of the bushing and cheap splined pot you could easily get the proper pots for the knobs you want to use.

Pick your knobs first then get the proper pots to go with them. The selection of set screw knobs swamps whats available for splined knobs.

dave

[duck_arse]

I thought

.... most guys around here ....

were

.... us OCD types ....

I know I'm banging-on about splines and sets all the time. and, if I jamb the snapped-off tab up the splined, and then set the knob so the screw aligns to the split in the shaft, exactly what stops my pot from rotating? [and the knob still noses, by the way.]

[antonis]

Be aware of the existence of 6mm and 6.35mm (1/4") shaft pots..