I need a 32 tooth spur gear to mesh with the 7/8" X 8TPI leadscrew on my la
the. Gear is for the thread dial. Can any of you point me to a source for t
his gear? I do not have gear hobbing equipment. Can anyone tell me what the
pressure angle would be for this application? Never messed with gears so I
am un-educated. Because of the amount of off topic political stuff here I
seldom come here any more. I'd appreciate if any ideas/info were emailed to
firstname.lastname@example.org Thanks in advance for any help
On 20/02/16 16:22, Gerry wrote:
IIRC the pressure angle will depend on the included angle of your
leadscrew. If my memory is correct your 8TPI will be about 25.1 DP so
not off the shelf but as it's only for a threading dial you should be
able to mark up and file a suitable gear by hand as it doesn't need to
be very accurate or very thick as it transmitting no torque and only an
indicator, you may be able to use 1 module for the application as quite
close. 32 teeth should be fairly easy to mark up with a bit or care and
file by hand. Some years back a mate filed a rack for his Boxford lathe
out of brass angle as he was that tight and it worked fine until he sold
it on. If you don't like the sound of filing one yourself then there are
some online gear generators which will produce the DXF file information
and you could then have it laser or water jet cut.
The gear shape that mates with an Acme screw, for a perfect,
perpendicular relationship, is a conventional involute helical gear.
But an ordinary involute spur gear is close enough for a thread dial.
The pinion on the thread dial of my South Bend 10L is an involute spur
gear, but it's the enveloping type, like the pinion made for a worm
gear. That, after all, is what this is -- a worm-gear set.
But that's really overkill. As has been said, there is no load on this
pinion, so there is no need for it to be an enveloping type. And even
on my SB, the teeth are straight across, not helical.
The one I found that fits my 10L does have slightly helical teeth to
match the lead screw thread angle. The teeth aren't curved. It's
probably South Bend but maybe not from a 10L. The gear is stamped
I'd have to take mine off to see if there is a slight helix to it. If
there is, it's so slight that it's almost invisible, and of no
consequence to either the congurence or to the effectiveness of the
But the teeth definitely are the single-enveloping type. That is,
they're curved in a hollow from one face to the other, like a good
worm pinion. (Double-enveloping only applies to actual worm gear
BTW, my 10L was built in 1945, and it has a War Board plate on it. It
was built for navy shipboard use, with both DC and AC motors. It was
unused and still packed in Cosmoline when my uncle (a former Seabee)
https://www.youtube.com/watch?v=J0o3W4_LRBw This struck me as being possi
ble but I'd need to find a 10TPI acme tap or at least make something suitab
le. I guess one of the issues would be figuring out the OD of the blank. I
am assuming that the circumference would be 4"(4 X 8TPI). Am I on the right
path? Use circumference to figure radius/diameter? Do I really need to be
using something other than this? Something dealing with the major/minor OD
of the teeth instead? Gear designs are all new to me. Thanks for the help s
Since there is no power transmitted by this gear, you could make it out
of Delrin, or something similar. In which case, the hob could be made
out of mild steel by threading a rod 10 tpi Acme and grinding grooves in
it to make cutting edges. The trickiest part would be getting the Acme
profile in the hob. Even that would not have to be very precise.
Just to point out the OP needed a gear to fit to an 8 TPI lathe leadscrew.
Maybe you could actually hob the gear with a 10 TPI tap, but I'd expect an 8
TPI tap would make a much better fit. But, an 8 TPI tap might be harder to
find. A hob could probably be made on the lathe, as this doesn't need high
A 1" - 8 NC tap fits nicely into the leadscrew of my lathe. The gear
could be cut from aluminum since there's little load on it and the
user controls the depth of engagement. I can't say 'no' load because
the threading gear I mentioned yesterday is visibly worn where it
contacted its previous lathe's leadscrew.
The original gear that came with the lathe when new was brass and had a sli
ght helix. The kicker is that the original gear was 15 tooth! I've had the
lathe since new for 9 years. I've never been able to thread with the lathe
and I guess the 15 tooth gear explains why. I always figured that I was doi
ng something wrong and found other ways to work. I am retired now and am tr
ying to get things right. BTW, my previous lathe was a Sheldon 11X56 and ne
ver had problems of any kind except wear
The original gear that came with the lathe when new was brass and had
a slight helix. The kicker is that the original gear was 15 tooth!
I've had the lathe since new for 9 years. I've never been able to
thread with the lathe and I guess the 15 tooth gear explains why. I
always figured that I was doing something wrong and found other ways
to work. I am retired now and am trying to get things right. BTW, my
previous lathe was a Sheldon 11X56 and never had problems of any kind
If you can index the blank on a mill you could probably make an
adequate 'gear' by slitting it with a saw.
I just realized why the gear on my threading dial looks unusual. The
teeth are barely longer than the pitch diameter, and leave a gap to
the leadscrew thread root. I suppose that allows a straight-edged gear
cutting tool, perhaps a slitting saw raised above center height to cut
at the Acme thread flank angle.
I tried to understand what you're saying there but I don't get it. I'd
have to look at the threading-dial gear on my lathe with a magnifying
glass to be sure, but it's almost certainly a hobbed gear with
involute flanks. Whether the tooth is short or long, the flanks come
out as an involute when you hob them with a straight-toothed gear hob
-- which probably is 99% of the hobs used in industry. That applies
whether the gear being made has simple, straight-across teeth, or
whether it's an enveloping type.
(You can see the shape of an enveloping gear if you click on the
animation on this page, which enlarges it:)
I hope it's understood that the tooth geometry here is the same as
that for a rack and pinion, or for a worm drive. A rack is an involute
"gear" of infinite diameter. When you make the diameter infinite (in
other words, a straight rack) the teeth wind up being angular but
straight-sided, like an Acme thread. The same applies to a worm drive,
which is what we're talking about here. For a perfect, conjugate mesh,
the teeth on the pinion are therefore involute.
Again, though, all this complication is moot for the OP's application.
A threading dial drive does not have to be conjugate and it doesn't
transmit power. It's a timing drive. Old clocks had timing drives, and
those gears often were just straight-sided teeth, not involutes or
other conjugate shapes. That's all you need here. The teeth could be
any shape that meshes roughly with the leadscrew. The indicator will
work the same way no matter what. And, as others have said, plastic
should work perfectly well, for a very long time.
On Sunday, February 21, 2016 at 7:49:43 PM UTC-6, John B. wrote:
slight helix. The kicker is that the original gear was 15 tooth! I've had t
he lathe since new for 9 years. I've never been able to thread with the lat
he and I guess the 15 tooth gear explains why. I always figured that I was
doing something wrong and found other ways to work. I am retired now and am
trying to get things right. BTW, my previous lathe was a Sheldon 11X56 and
never had problems of any kind except wear
One reason is that I bought a lathe with a thread dial and expect the threa
d dial to work as it should. The other reason is that threading to a should
er without being able to disengage the halfnut is a pain. Doable, but still
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