I'm seeing this in just about every 60's era Zenith I work on as of late - the little white plastic gear in the tuner for the fine tuning is split and loose on the shaft - or occasionally in pieces, having fallen off the shaft entirely.

For reference, here's an example (https://i.imgur.com/F5AcCPc.jpg), from a 1965 21" B&W 60 pound metal "portable".

You can see how the plastic gear has split - the plastic is now very brittle. I have attempted to epoxy these back together with no real success, the plastic does not take to the glue very well, and it doesn't really stay stuck together. And, like the most recent one of these I worked on - sometimes the gear is broken into multiple pieces.

Now, as much as I dislike the practice of using a 3D printer to solve any and all problems, this is one of those problems that a 3D printer is about the best solution I can think of. Of course, the gear is too tiny and has too much fine detail for a common home printer, but I know that commercial machines can handle this.

Now, I'm prepared to spend the time to carefully measure one of these things with calipers and figure out the dimensions and pitch and get an STL file created for this part. But before I go reinventing the wheel, er, gear - has anyone already done this or is there an available replacement? And does anyone know how many different gears Zenith used - or was it all the same in this period? The three sets I've had apart recently all used the same one, but they were also similar mid 60's designs.

-Ian

If you can find an intact gear I'd probably just make a silicone mold like those used to reproduce NLA radio knobs and cast a new plastic or lead* gear....how much is a commercial grade 3D printer print going to cost VS the casting?

* There are some silicone mold compounds available that can take molten solder or pewter as the new casting material....I'm planning to do this on some damaged pot metal parts on my capeheart turn over changer (glue the pot metal together, make a mold, cast a new solder metal part).

But before I go reinventing the wheel, er, gear - has anyone already done this or is there an available replacement?
I've done similar gears by superglue-ing them back together while being held in a vice-grip pliers, and then drilled out the center hole to make it a bit larger.
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If you can find an intact gear I'd probably just make a silicone mold like those used to reproduce NLA radio knobs and cast a new plastic or lead* gear....how much is a commercial grade 3D printer print going to cost VS the casting?

An incredibly common failure in old Apple II and Macintosh 800K 3 1/2" floppy drives is the tiny little gear in the eject mechanism. This is somewhat thinner, but roughly the same size, and those cost something like four bucks apiece. I can't imagine these Zenith gears would cost much more than that to have produced.

The complexity and number of variables and materials involved in creating a mold for, and casting - such a tiny part... I can't imagine I could ever do it cheaper.

Not to mention, this is a part that just about anyone working on a Zenith from this era is going to need. Ideally, if I can get this 3D modeled, then anyone that needed one could easily get one.

-Ian

Yes - this gear, like many gears from that era turn brittle and break. I have the old fine tuning gear from my 1966 Zenith that is cracked but still in one piece if you want to use that as a master. I can send it to you.

Dave

I'm pretty sure that I still have an original NOS replacement for that gear somewhere. If anyone wants it for re-engineering I'll look for it.

John

That was a common problem, even when the sets were relatively new. I remember fixing one with epoxy, and it held up well.