Knob for Colvern potentiometer with short shaft

[Jolly 7]

Can anyone please help me with finding a suitable knob for Colvern multi turn potentiometer. I tried around six different knobs, but the shaft is too short for the k grub screws to attach to. Are there special knobs designed for this type of potentiometer ?

[pmmunro]

A collet knob might suit your needs. If the shaft is at least as long as its diameter, this type of knob will be suitable. You will need to know the shaft diameter, probably either 6mm or 1/4".

PMM

[CambridgeWorks]

Post crossed!

Collet fixing would probably suit. Loads of different styles available.
Need to know the shaft diameter and diameter/ height of knob you require for anyone to be able to assist you.
Rob

[Jolly 7]

Thanks for the replies. I have attached a picture of the pot in its intended housing .The shaft diameter is 6.25 mm and it is only 5 mm long.

[Chrispy57]

Hi Jolly - perhaps that was designed as a posh preset trimmer type of potentiometer, with the screwdriver slot and pitifully short shaft, and never intended to have a knob fitted? I have come across similar, but single-turn pots behind the panels of some old AVO test equipment.

Cheers
Chris

[60 oldjohn]

Originally Posted by Chrispy57

Hi Jolly - perhaps that was designed as a posh preset trimmer type of potentiometer, with the screwdriver slot and pitifully short shaft, and never intended to have a knob fitted?

Cheers
Chris

I agree, there were caps available (Like a valve cap) to finish them off and deter fiddlers.

[Chrispy57]

It's too nice not to use if you have an application requiring a knob, so perhaps some form of "shaft extender" would be a viable option? And a bit of mechanical ingenuity in the mounting arrangement to allow the longer shaft to fit through the necessary panel. Good luck.

Cheers
Chris

[radiomobile]

Two suggestions:

1 Countersink the knob so the potentiometer circlip does not prevent the knob going
on to the shaft quite so far.

2 If you have access to a belt sander/linisher remove some material from the knob so
the grub screw is right at the bottom.

[Jolly 7]

Thanks for the further replies. It's a really nice wire wound pot I bought off the forum and comes in very handy for the test bench.

I have now implemented a temporary solution using a plastic knob from a broken stereo. Using a step drill I carefully got rid of the D-shaped cavity inside the knob till I ensured that the pot shaft was going deep enough inside. I then put some hot glue inside the cavity and pressed the shaft into it, holding it tight for a couple of seconds.

The shaft is now rotating freely along with the knob. I am not sure how durable this solution is, but I can always look at the other suggestions provided if my solution fails. I don't intend to use the pot elsewhere, so a semi-permanently glued knob is fine.

[Diabolical Artificer]

I've dug out four knobs that might fit, all fit a similar Colvern pot to yours. They either have deep skirts or low grub screws. Yours for cost of postage - £3.

Drop me a PM if interested, Andy.

[Radio Wrangler]

If needed, I have some black collet knobs here which should get a very good grip on that length of shaft. FOC.

David

[Jolly 7]

Originally Posted by Diabolical Artificer

I've dug out four knobs that might fit, all fit a similar Colvern pot to yours. They either have deep skirts or low grub screws. Yours for cost of postage - £3.

Drop me a PM if interested, Andy.

PM sent.

[Jolly 7]

Originally Posted by Radio Wrangler

If needed, I have some black collet knobs here which should get a very good grip on that length of shaft. FOC.

David

Thanks very much for the offer David. Hopefully Andy should get me sorted out.