Newbie worn gear questions

The worm is the easy part; if you want good mechanical coupling, though, the gear has a complex shape. That argues for a gear from something easy to machine, but durable. Bronze?

One approach uses a tap as a cutter, to fully form the gear teeth after rough-cutting. Gears so cut usually DON'T smoothly go the full

360 degrees (you'll actually be needing less than 360 unless your climate includes a midnight sun in summer). Something like an Acme tooth form will let you use a worm that can be supported on rollers and not just at the ends. If you prefer a sharp thread form, a large diameter worm is good. Bowing/push-out of the worm can cause motion glitches.

db

There is or was an excellent webpage describing exactly what you want. As close as I can recall, the author cut two lengths of thread in a piece of drill rod stock. One length was saved to use as the worm, the second was slitted part way through to use as a cutter to make the gear.

The gear was a round piece of AL plate, gashed part way at intervals where the teeth would be. Then the cutter was positioned against the gear and rotated. It dragged the gear around slowly cutting the teeth to mate with it.

The result was a very accurately fitted worm gear assembly. Unfortunately, I can't find the website now.

Chris Heapy had a writeup on his site under "projects", which can now be accessed only through Archive:

Kevin Gallimore

It was on Chris Heapy's marvelous website. Unfortunately Chris just gave up one day for some reason :-(

Luckily, this lot have a mirror of it:-

The relevant page is:-

Mark Rand RTFM

Unlike the rolling contact in involute gears, the sliding contact between the worm and gear places demands on the materials similar to a plain bearing and journal. A common combination for quality worm gear sets is a hardened steel worm and aluminum bronze worm gear. Since the worm normally sees the most wear, it's made from the harder material. Phosphor bronze is another possibility for the worm gear, and some phosphor bronzes machine quite nicely compared to aluminum bronze, which can be a bitch. For a lightly loaded low duty gear set, either may be overkill.

I've also seen split worms, and I think I even purchased a reducer with such a setup, but I can't remember who the manufacturer was. Cone Drive maybe?

Paul Hovnanian P.E. wrote:Or a split gear, like two gears

That is the way it was done in the ARC aircraft radios in WWII so it must work. I have used and torn apart some of them back in the 50's. ...Lew...

Excellent stuff. This is advice I can use (besides "Don't do it. Save your sanity.").

Here's a how-to book, "Gears & Gear Cutting" by Ivan Law. Covers small shop techniques. As far as worm and wheel materials, they need to be different. Usually the worm is hardened steel and the wheel is something else, bronze, Micarta, fiber, whatever. There's a lot of sliding going on and you'll get galling if the materials are the same. Check out what's out there for ready-made availability, I usually don't go in for one-offs if I can buy stuff at a reasonable price. There's enough amateur telescope activity that you should be able to find clock drive parts or even whole clock drives, it's not like the '20s or '30s where everything had to be done from scratch. The main problem with making the worm is that it usually turns out to be very coarse and an odd pitch from a thread-cutting standpoint with a lathe. With what's available today, you could probably turn out a pretty good drive using steppers or servos and microcontroller drivers, leaving in the option of computer control. Some of the lower- priced ready-mades already have that.

Stan

Ivan's book is excellent. Somehow I have misplaced it in the stacks and boxes of books and periodicals I have at home. It is the one book I know I have, that I'd consider purchasing again, just because I can't locate it.

Wes

d boxes of books

Amazon, $8-9

Stan

boxes of books

I'll just buy another copy. Maybe a few other books I can't locate will show up shortly after. ;)

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

boxes of books

I missed the deal. The book was going for about 18 bucks the other night.

However, I did score "Workholding in the Lathe (Workshop Practice Series)" Tubal Cain; Paperback; $8.63 + 3.99 shipping.

Wes