It looks like I'm going to be replacing a potentiometer with a long shaft (6cm), and I can't find a new one. Seems more practical to extend the shaft on a readily-available one with a shorter shaft.

What methods have people here used? The heavy-duty machined brass connectors seem to be a bit of overkill.

Maven

I machine my own from brass rod, I guess you need a lathe which probably not many radio people have. I have two lathes and a mill.
Peter

Shaft extenders are available in the USA, such as here:

http://www.radiodaze.com/category/62.aspx.

And there are some DIY tricks, such as this one:

http://electronics-diy.com/schematics/1108/pot_shaft_extension_close-up_2.jpg.

Hmm - that DIY job looks like it also adapts to a different shaft diameter, but it might result in a wobbly knob where the knob, as in my case, is just suspended at the end of the shaft, no second bush.

Jaycar have machined shaft joints, but they are $6+ and may not be long enough to bind firmly on a shaft with the 25% flattened side for the knob mount.

I might try a few reversible solutions. Maybe a short sleeve of 1/4" copper plumbing tube.

The join ought to be fairly rigid, but it doesn't have to carry any significant torque.

Maven

Does not really matter what is used sometimes. I have made them from Brass, Aluminium & Nylon.

Like another I have a lathe & the flat is easily cut with a die grinder with the lathe stopped.

I normally make a one piece unit where one of two (grub) screws will be long enough to clamp onto the flat (if it has one).

Depending on the situation you can recycle the shaft of another pot & use a socket, which is easy to make if one has the equipment.

I have seen these things at ridiculous prices.

I have a set on the bench that has one if you need a photo?

Marc

There are shaft extension kits here on eBay:

Shaft Extension Kit

Also Jaycar part number CAT. NO. YG2790

Peter

Jaycar part number CAT. NO. YG2790

I didn't mention Jaycar because that coupler was priced at a ridiculous $12.95.

I see that they have reduced the price to $6.95 to run it out of their catalogue. If it were priced at $1.95 I'd pick up a few myself.

After trying a couple of DIY coupling tecniques, I gave up and bought a Jaycar "shaft coupler" for $6.95.

A word of caution on this. The coupler is metric 6mm bore, while the standard pot shaft is Imperial 1/4" and thus slightly larger. It took a bit of filing down to get a reasonable fit for the shaft, and also for the short length of 1/4" round mild steel bar I am using for the extension. If you have a good drill press it would be easier to ream out the brass coupler.

I also hand-filed down the required flat end section to take the knob, and then hacksawed the flattened end lengthwise so there is a bit of flexibility in the part that is pushed into the knob. Those old knobs are quite brittle so I needed a firm fit without too much pressure on the knob housing.

Maven

OK on trying to make one for $6.95.
Alright if you have plenty of brass rod stock, lathe, mill and drill like I have, but for the average radio guy $6.95 is fine, or is it ??. Seeing these are mass produced I think $12.95 is a bit much. If they were $1.95 I would buy 20.
Peter

Yes, you'd be hard-pressed to make one for $6.95 if you were charging for your time.

It's not an item that I have a regular need for. However if I found them in the Jaycar $2 dump bin I'd grab a few for the spares cupboard.

I do not consider filing down the pot shaft good. That is not without risk to the pot. Even that it is done outside of the radio.

I actually keep a 1/4" drill with no point, as it is handy for jobs on the odd occasion, like sockets, where you can get a slightly deeper hole, without the point of the drill creating a weak spot.

Marc

Slip heatshrink onto the longer of the shafts, align the shafts, run a small amount of supaglue over the surfaces, slide the heatshrink over the join. When the glue has dried, apply heat. This is cheap, only a bit nasty & works well.

‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
6A8G.

Heatshrink tecnique sounds good - if you are confident you can get a good straight alignment before gluing. How do you align a flattened end to a round end?

The standard fllattened end is machined/filed down by 25% of the shaft diameter. If both ends at the join were filed down by 50%, you could get a very strong "carpenter's" splint join with a lot of glue surface.

Maven

Whoops! Forgot to mention, make a hacksaw cut 90 degrees to the flattened bit. Then file a tongue into the extension. I cheated, took it to work & did this bit on the bench grinder. Then glue/heatshrink. If you ever need to dissassemble, I reckon a bend in line with the tongue zas opposed to across it would work. As I said, no particularly elegant but it does work

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6A8G.

I can see why I have no stress with extension shafts. Rarely does one find the right length.

Often Aluminium rod is cheaper than brass. Having a lathe makes life so much easier.

If the knob is a bit dodgy and the hole is oversize shrink tube works, if you need to make an extension shaft, for the set with it you have the option of turning it oversize.

You can sometimes recycle the shaft of a dead pot & use a socket. I will make the extension shaft a one piece job and I have made them to fit those spline shaft pots.

Often its hang the cost & time. If you know you are not going to find the thing, the time that would be wasted looking: is better spent making.

Do check RS components & way the costs, they have some long shaft pots.

Marc