Pot shaft extension mod

[Geaney]

Hi Guys,
On my mystery PYE restoration (the one with no on/off switch) I bought a long shaft volume pot from Radio Daze (couldn't find an RS distributor over here). The Radio Daze pot comes as a kit where you manually add the on/off part. Alas the shaft was about half an inch too short and I had not ordered their shaft extension kit. So, I found some aluminium tubing that was a nice press fit for the shaft. I cut the shaft, got the baby gas torch out, heated the tubing, pressed on to the shaft allowing an extra half inch and it worked a treat. Looks a bit neater than having a bulky collar and grub screw affair as the way to extend the shaft.

Cheers, John.

[AlanBeckett]

John,
Very neat.
I think I might have tried adding a couple of pins just to make sure the shafts didn't rotate inside the collar, but that might have been over-egging it.
Alan

[Joe]

Very neat indeed.

- Joe

[AlanBeckett]

If I can bang the (same old) drum again this would be where a little lathe would come in. You could then make your own collars. If you were feeling really heroic you could drill and tap the shaft say M3 and add a piece on with an 'invisible' joint. A bit of Locktite would be helpful.
I'll convince you all in the end
Alan

[Joe]

I AM convinced!

- Joe

[Aerodyne]

I'm convinced too - I just can't find the money for a lathe nor the space to accommodate one. I'd love one, though, having used engineering lathes for years in the school environment I am well aware of the usefulness of them.
-Tony

[AlanBeckett]

See eBay Item number: 180713642162.
I'm not interested myself, and I don't know who made it, but the thing that caught my eye is how small it it.
The ones I know of, from Machinemart, Chester etc are a lot bigger.
Certainly is you only wanted to make small stuff, and had limited space, it could be ideal.
Alan

[Yorkie]

See eBay Item number: 180713642162.
I'm not interested myself, and I don't know who made it, but the thing that caught my eye is how small it it.
The ones I know of, from Machinemart, Chester etc are a lot bigger.
Certainly is you only wanted to make small stuff, and had limited space, it could be ideal.
Alan

That looks a seriously nice bit of kit, unused, with all the change-wheels for screwcutting. A small footprint too. Be interesting to see what it fetches in due course, assuming the reserve is met.

The bijou Macihne Mart lathes look fairly good, and not too pricy on a VAT free day.

I haven't used my little 'Lorch' Schmidt' jobby yet as I've been so busy with other things, but I do have some radio related tasks for it in due course - making some hex spacers from brass stock for example.

Neat job of the spindle extension by the way John! (Is the final instalment of the 'Mystery Pye' cabinet restoration about to hit youtube any time soon?).

David

[Skywave]

I really like that idea: it's cheap, neat, easily done and should be very secure - because the shrinkage of the ali tube, when cold, will make a very tight fit on the pot shaft. I wouldn't have thought any further securing of tube to shaft would be necessary - after all, there's not a lot of torque being developed in rotating a pot shaft, even if an on/off switch action is required, is there? Obviously, the longer the tube, the greater the grip. I suppose that a squirt of freezer aerosol could also be applied to the pot shaft as well, just prior to ass'y., if one wanted that extra bit of security.

I've now added that technique to my list of 'fixes'; thank you for telling us about it.

Al.

[AlanBeckett]

Yes, shrink fitting is a good method. One thou (0.001") interference at room temperature is usually enough, although there are tables that can be consulted if you want to be really accurate. I usually put the inner in the freezer in a plastic bag and the outer in the oven at around 250. The tricky bit is to get them together in the right place before there's sufficient heat transfer to the inner to expand it. Sometimes it doesn't work
Attached is a part made cutter block for a small Bench Plane. Unfortunately the main casting suffered a catastrophic failure for other reasons and I abandoned it. The block is about 75mm Diameter and the shaft is 16mm. As you can see machining it out of the solid would be very wasteful, and this way the shaft is an accurate piece of silver steel. By the way, it isn't trapezoidal, it just the camera angle. It will come in for something one of these days.
Alan

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