todays finds
 

Just picked up a Stromberg-Carlson 501A and another silvertone tombstone.
The SC has busted potmetal gears...going to try matching something up in plastic or metal. Maybe some of these clock repair parts places got some large diameter gears? The tuners are not tied together, so that makes things a bit easier:D The guy threw in a bunch of 78 records also.

Congrats!
A couple of nice radios awaiting some TLC.
Geez-potmetal-I wish I knew who the engineer was on THAT project!

Pot metal was used in most late 20's radios. It wasn't a problem until they became 40 or more years old which the designers never intended.

Removed the chassis and found evidence that some critter lived in there one time. Fliped it over and found no damage to wiring or anything. 3 larger 1uf tar cans underneath. Replaced the tar cans. Hooked it up and got a few stations:banana: Just have to figure out something about the turner gears, have not found anything yet.

That's pretty neat, the old gal sings again after 85 years (the Radio Museum dates it 1926.) Are the tar caps restuffable? Would be neat to have them there looking original. Can you post some pix of the gear problem? Someone might have an idea looking at them. Thanks!

Edit: I found this picture on the web. Is the gear you're talking about the gray one that the arrow points to here? I would imagine the fine tuning knob has a gear that meshes with this. What you may be able to do is substitute an o- ring on the fine tuning gear to bear against this large one, or vice versa, and superglue it in place. Or if not an o-ring, a strip of rubber such as is used on VCR belts, etc. This presupposes that the gears in question are still in some kind of shape but have just "lost their teeth" and have not otherwise crumbled into dust.

Sorry, having trouble with posting this picture.

There is only a 2 inch strip of gear left, the rest totally gone. I measured (estimated) the gear to be 4 1/2" or 116 mm with 10 teeth per inch ( counted the remaining piece)
I really have not found anything close, so now I'm looking at small size chain and sprockets.

Finally got around to this one again. This is the solution I came up with.
I found these plastic roller chain and sprockets on a site in England, seems like they have alot of stuff for robotics. Their site is www.motionco.co.uk
I had to drill them out to the correct size. The knob assembly was spring loaded, but the wrong direction, so I found a spring to pull the two together for the correct direction. Works real nice. The radio itself is a good performer.
Below is what was left of the potmetal gears and the new plastic ones installed.

That's a pretty good fix. I have an AK with potmetal parts crumbled away like a cookie like that hub you show. I'm going to bookmark motionco for when I get around to that. There may be similar parts available this side of the drink. Congrats on a neat solution!

Since I got this electrically finished, my attention turned to the cabinet. I removed all the trim pieces from the front panel. The finish underneath the trim pieces are real nice, and shows the original color. But the rest of it is blistered and flaking off.....guess it's strip time:scratch2:
Also discolored are the trim pieces themselves. The wood finish is dark, and the trim pieces are also dark, makes the radio look like a dungeon radio....too dark for my taste. So I experimented with some super fine steel wool.

Great idea, if I understand correctly, it looks like you are able to remove patina on the high spots without stripping the entire piece, so the markings and lettering stand out better but it still looks 'old'. Very nice.

On the gear detail...
I have a buddy with a desktop laser cutter. He can cut wood, phenolic, and non-PVC plastic (I think), but no metal. Runs of a CAD/CAM file. It's in a community/membership-based shop in Columbus. If the teeth are not too fine, I believe he could cut one of those in pretty short order.

I realize you've engineered a good solution, so you're no longer needing a replacement gear. But is this a common need out is resto-land? And do you think phenolic would hold up to the tuning duties?

(There are many of these community shops out there, too.)

Chip

From what I read most of these potmetal gears just crumble. I have no idea how many of these are still in the "wild" or the demand for such pieces. The small gear on the other end of the knob shaft was not pot metal, but some kind of fiber. I Have a 3d printer and I was going to try to print one, but it would have had to be made in 4 pieces and then bonded together.

That sprocket and gear idea looks good. I have an old '27 Victrola Automatic Orthophonic phonograph that has the first commercial record changer, and it had a lot of pot metal parts that are critical for the changer to work. All were damaged or totally disintegrated. I was able to get reproductions for everything but the record size selector gear set and was thinking of doing something like this sprocket thing, or just a lever pulling on a couple of wires or chains to replace the 'action' of the gears. Thanks for the tip and I'll look into using this kind of system!