[Nathan Slingerland]

Thanks Sam! Thanks Tony!

Automatic Tuning Flex Coupling

I've been working on rebuilding the automatic tuning flex coupling.

[Image: https://farm8.staticflickr.com/7839/4584...0bb9_z.jpg]

Here it is removed from the tuner:

[Image: https://farm5.staticflickr.com/4852/4603...0998_z.jpg] [Image: https://farm8.staticflickr.com/7920/3181...59a8_z.jpg] [Image: https://farm5.staticflickr.com/4865/4603...3504_z.jpg]

You can easily see that the old one is stiff and cracked. That makes the tuning mechanism hard to turn unless the RF subchassis and automatic tuning dial are perfectly aligned along their axes. There needs to be some flex in the system in order  for the dial to always tune smoothly.

The first stop was to visit the excellent article in the Philco Library's tech section on exactly this topic. It was a great source of ideas and inspiration - but I ran into a few things that prevented me from just doing things exactly the same.

I disassembled the coupling by drilling out the rivets:

[Image: https://farm5.staticflickr.com/4888/3181...8ddb_z.jpg]

The resulting pieces:

[Image: https://farm8.staticflickr.com/7891/4603...6af8_z.jpg]

Hmmm... a few too many pieces actually! The metal parts are made of a pretty brittle material and I broke the thin center piece while I was trying to push out the rivets.  

[Image: https://farm5.staticflickr.com/4834/4670...5ed3_z.jpg] [Image: https://farm5.staticflickr.com/4822/3184...de1d_z.jpg] [Image: https://farm8.staticflickr.com/7829/4676...a57c_z.jpg]

In the mean time - ordering the cloth impregnated neoprene sheet. I found a sheet with similar specs from zoro.com - actaully eBay.

[Image: https://farm5.staticflickr.com/4894/3288...1bca_z.jpg]

What I didn't think about too carefully ahead of time was the following:

After disassembly the next step was to cut new rubber disks from the sheet of material. This was done with a gasket circle cutter and a punch for the rivet holes.

I don't own either of those tools. Always on the lookout for an excuse to buy a new set of tools I researched it but it looked like nice gasket circle cutter (especially 2" diameter) would set me back some $$$. So I decided instead look around for a similar precut circular gasket. I should've done that first as I found just the thing at my local hardware store!

[Image: https://farm5.staticflickr.com/4816/4586...7743_z.jpg]

While it's not reinforced with cloth like the original it looked robust enough to give it a shot. I went with the 1" ID, 2.25" OD neoprene washer. It's about the same thickness as the original.

I picked up some 5/8" long screw posts (aka Chicago screws) to replaced the long drilled out rivets:

[Image: https://farm8.staticflickr.com/7837/3981...3a3b_z.jpg]

I used one of the old rubber washers as template and drilled holes in the new ones:

[Image: https://farm8.staticflickr.com/7835/3290...544d_z.jpg]

I attached the outer set screws pieces with 3/16" x 3/8" pop rivets:

[Image: https://farm5.staticflickr.com/4901/4678...4a08_z.jpg] [Image: https://farm8.staticflickr.com/7896/3184...51f5_z.jpg]

I used finishing washers as the spacers which keep the two washers apart (part of the original piece that broke).

[Image: https://farm8.staticflickr.com/7862/4586...c89e_z.jpg]

and recreated the middle piece from aluminum stock (~0.060" thick).

[Image: https://farm5.staticflickr.com/4851/4585...0a90_z.jpg]  [Image: https://farm8.staticflickr.com/7854/3183...eecb_z.jpg] [Image: https://farm5.staticflickr.com/4848/4678...a5c7_z.jpg]

And all the pieces put together:

[Image: https://farm8.staticflickr.com/7823/4605...09d6_z.jpg] [Image: https://farm5.staticflickr.com/4873/4673...9d11_z.jpg]

And reinstalled:

[Image: https://farm5.staticflickr.com/4808/4673...0fee_z.jpg] [Image: https://farm8.staticflickr.com/7880/3184...8cd8_z.jpg]

It seems like it works quite a bit more smoothly and the tuning mechanism turns easily. We'll see for sure once the dial is reinstalled.