Newbie worn gear questions
Paul Hovnanian P.E.
making a worm and mating gear.
I've seen it done either way: The worm is made of a hard substance (steel)
and the gear of brass or plastic. Or the worm is made of brass and the
gear of steel. Which sort of answers my question, since I can't recall ever
seeing a plastic worm.
What are the arguments for either approach?
Another thing I'm considering is an anti backlash mechanism for this setup.
The two ways I can think of doing this are: The Worm axis can be adjusted
towards the gear to take up slack. Or a split gear, like two gears
sandwitched together, where one can be rotated w.r.t the other to take up
the slack between the pitches of the worm. I've seen this kind of thing
done in some auto transmissions.
--
Paul Hovnanian pa...@hovnanian.com
----------------------------------------------------------------------
Have gnu, will travel.
whit3rd
> I'm considering making a telescope mount with clock drive. It will involve
> making a worm and mating gear.
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.
Dave B
<pa...@hovnanian.com> wrote:
>I'm considering making a telescope mount with clock drive. It will involve
>making a worm and mating gear.
>
>I've seen it done either way: The worm is made of a hard substance (steel)
>and the gear of brass or plastic. Or the worm is made of brass and the
>gear of steel. Which sort of answers my question, since I can't recall ever
>seeing a plastic worm.
>
>What are the arguments for either approach?
>
>Another thing I'm considering is an anti backlash mechanism for this setup.
>The two ways I can think of doing this are: The Worm axis can be adjusted
>towards the gear to take up slack. Or a split gear, like two gears
>sandwitched together, where one can be rotated w.r.t the other to take up
>the slack between the pitches of the worm. I've seen this kind of thing
>done in some auto transmissions.
http://www.sdp-si.com/eStore/CoverPg/Gears.htm
db
Jim Stewart
> I'm considering making a telescope mount with clock drive. It will involve
> making a worm and mating gear.
>
> I've seen it done either way: The worm is made of a hard substance (steel)
> and the gear of brass or plastic. Or the worm is made of brass and the
> gear of steel. Which sort of answers my question, since I can't recall ever
> seeing a plastic worm.
>
> What are the arguments for either approach?
>
> Another thing I'm considering is an anti backlash mechanism for this setup.
> The two ways I can think of doing this are: The Worm axis can be adjusted
> towards the gear to take up slack. Or a split gear, like two gears
> sandwitched together, where one can be rotated w.r.t the other to take up
> the slack between the pitches of the worm. I've seen this kind of thing
> done in some auto transmissions.
>
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.
axolotl
Chris Heapy had a writeup on his site under "projects", which can now be
accessed only through Archive:
Kevin Gallimore
Mark Rand
>
>
>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.
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:-
http://kansai.anesth.or.jp/gijutu/kousaku/easyweb.easynet.co.uk/chrish/homepge2.htm
The relevant page is:-
http://kansai.anesth.or.jp/gijutu/kousaku/easyweb.easynet.co.uk/chrish/worms.htm
Mark Rand
RTFM
Ned Simmons
<pa...@hovnanian.com> wrote:
>I'm considering making a telescope mount with clock drive. It will involve
>making a worm and mating gear.
>
>I've seen it done either way: The worm is made of a hard substance (steel)
>and the gear of brass or plastic. Or the worm is made of brass and the
>gear of steel. Which sort of answers my question, since I can't recall ever
>seeing a plastic worm.
>
>What are the arguments for either approach?
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.
>
>Another thing I'm considering is an anti backlash mechanism for this setup.
>The two ways I can think of doing this are: The Worm axis can be adjusted
>towards the gear to take up slack. Or a split gear, like two gears
>sandwitched together, where one can be rotated w.r.t the other to take up
>the slack between the pitches of the worm. I've seen this kind of thing
>done in some auto transmissions.
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?
--
Ned Simmons
Lewis Hartswick
> sandwitched together, where one can be rotated w.r.t the other to take up
> the slack between the pitches of the worm. I've seen this kind of thing
> done in some auto transmissions.
>
in WWII so it must work. I have used and torn apart
some of them back in the 50's.
...Lew...
Paul Hovnanian P.E.
your sanity.").
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
"Nothing Important Happened Today"
-- King George III, diary entry July 4, 1776
sta...@prolynx.com
> I'm considering making a telescope mount with clock drive. It will involve
> making a worm and mating gear.
>
> I've seen it done either way: The worm is made of a hard substance (steel)
> and the gear of brass or plastic. Or the worm is made of brass and the
> gear of steel. Which sort of answers my question, since I can't recall ever
> seeing a plastic worm.
>
> What are the arguments for either approach?
>
> Another thing I'm considering is an anti backlash mechanism for this setup.
> The two ways I can think of doing this are: The Worm axis can be adjusted
> towards the gear to take up slack. Or a split gear, like two gears
> sandwitched together, where one can be rotated w.r.t the other to take up
> the slack between the pitches of the worm. I've seen this kind of thing
> done in some auto transmissions.
>
> --
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
Wes
>Here's a how-to book, "Gears & Gear Cutting" by Ivan Law. Covers
>small shop techniques.
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
sta...@prolynx.com
Amazon, $8-9
Stan
Wes
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
Wes
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