I had to replace the volume/pwr switch pot on my Philco Hippo. I need to extend the shaft on this pot. I removed the brass shaft from the original bad pot and am hoping to use it to extend the shaft on the new one. The shaft needs to end up at the height shown in the photo below. Any ideas on how to securely attach the extension ? I will use my Dremel to cut the brass extension to the required length-- once I know how I'm going to proceed..

The easiest solution is a 1/4" shaft coupler. These maybe expensive, but you can get them cheaper from radio parts suppliers, I think.

https://www.amazon.com/uxcell-Coupling-L25xD14-Coupler-Connector/dp/B07PBZP78C

Shops that sell hobby robotics parts will also have them.

I used to make my own, but no longer have a lathe.

Rich

I did one many years ago fr a member.

I ground the pot shaft with a flat section made to be an opposite to the extension, meshed the two and held them together with a brass tubing that I heated to expand and then pressed on over the joint and let cool to shrink.

As far as I know it worked.

cheers

John

Purchase a 12 inch length of thinwall brass tubing, ID=0.250 inch, from a local brick-and-mortar hobby store. or an internet hobby store. K&S Metal Shapes is a commonly-seen brand. Also purchase an inexpensive razor saw with which to cut the tubing.

Slice off a length of tubing about an inch and a half long, and debur the cut end with sandpaper. It should fit perfectly over both the original shaft and the extender.

Now you have an option: you can either abrade the shaft ends with a file or sandpaper so that they will have "tooth" for the epoxy that you will use to join the shafts; or you can file a half-round for a half inch or so in each shaft end such that they will interlock with each other. The abraded approach is fine for low-torque applications like volume controls, but for extending bandswitches I prefer the "stepped ends" idea.

When you have the shafts cut and prepped, slather the abraded ends with J-B Weld epoxy and fit the two shafts inside the tubing. Use denatured alcohol to clean off excess epoxy that oozes out before it cures.

Immobilize the joined shafts while the epoxy cures, ensuring that the assembly is perfectly straight. Once you get it straight, don't touch it for 24 hours.

If you mess up (possible to do but not very likely) and you need to remove the extension shaft, clamp a vise-grip near the chassis end of the original shaft to serve as a heatsink, then heat the coupling with a small butane torch. When the epoxy gets hot enough it will turn to goo and the shaft and coupling tube can be pulled apart. The spent epoxy residue can be wiped of with an acetone-wetted paper towel.

Half lap them with a second cut file, and add two hose clamps.

Double layer of heatshrink tubing instead of the clunky clamps!

The possibilities are (almost) endless.

I've used a section of a telescoping antenna as a sleeve, length cut to fit, and secured with crazy glue if necessary.

Yes indeed… including heavy duty (thick wall) heat shrink tubing, though I've never had call to use it… yet. lol


Large: https://i.ebayimg.com/images/g/xJEAAOxy ... -l1600.jpg

I found a 1/4" ID coupler at Lowe's for a dollar. fits the shaft diameter perfectly on my rca 813k.

I bought the shaft couplers on Amazon awhile back for a radio but they were so thick and clunky I had problems with where they passed through the cabinet.

Then I bought the 1/4" ID thinwall tubing mentioned above and JBWelded the shafts and thinwall tubing together. That works much better.

The K&S thinwall tubing has 1/64th inch wall thickness. So the total increase in OD is only 1/32 inch, not likely to cause a mechanical interference problem. The Amazon shaft couplers were probably intended to solve heavy-duty problems. But, whatever works is a good solution.

It amazes me what folks will do rather than just buy the right parts!

Shrink tubing works in very low torque applications.

Filing flats on a shaft is a lot work and hard to get really flat parallel surfaces.

Heating brass tubing is about the best, but don't crush the tubing by using too much torque on the knob setscrew.

Yes, I have tried all of these with varying degrees of success. So when I see shaft couplings, shaft sections, and panel bearings at ham swap meets, I buy them for a "rainy" day.

https://mgs4u.com/product/14-to-14-shaft-coupling/


https://www.rfparts.com/capacitors/capacitors-shaftcoupler.html



Rich

PS: We forgot one other idea: drill and tap the existing shaft for a 6-32 screw (cut off the head). Drill and tap a 1/4 brass or aluminum shaft for 6-32. Screw the pieces together with a drop of thread locker or super glue on the screw.

Obviously you've never been shipwrecked and stranded on a desert island.
I'm done here.

Some of us have shops with tools ....

Grinding a flat accurately on a shaft is a couple of minutes work.
Joining the two with the flats together and held by brass tubing is very tight and straight

Not every situation will accommodate those bulky shaft couplers.

cheers

John

True, but I don't have a bench grinder; I only have a file.

Rich

Sorry, if I was a bit dismissive.

I used to have a shop full of tools but everyone of them and 50 years of radio and test equipment collecting went to ashes in the 2017 Tubbs Fire. I have to buy rather than make most of the time.

Rich

Please don't use a bench grinder for aluminum or brass.

With a Basketball named Wilson as a companion?

I take the control apart and replace the shaft with one of sufficient length. There is a 'C' clip to be installed: cutting the ring it sits in is easy with a drill and hacksaw blade. Keep it simple. Craig