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 snipped-for-privacy@lsu.edu Thanks in advance for any help
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 THD-100R.
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 gear set.
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 sets.)
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) got it.
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 o far!
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 precision.
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
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:)
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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.
I've suggested a 32 tooth 1 module gear which I work out has a pitch error of about 0.0013" per tooth so I think would work fine and it a standard offering from many sources.
Yeah. The only things that matter are that you have the right NUMBER of teeth, to get the timing right; and that the teeth engage the leadscrew well enough that it doesn't jump or slip.
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 a pain
Could be, Martin, but the metric versions of my lathe use a different style thread dial, one with three gears and three mounting holes. BTW the seller , Matt at Quality Machine Tools is going to send me the proper gear this we ek. Lathe is a Precision Mathews 1340. I thank all of you for your input
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