Need a way to turn a 30 tpi screw.

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JackF
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Need a way to turn a 30 tpi screw.

Post by JackF » Sun Feb 25, 2018 11:14 am

My lathe chart for threading jumps from 28 t0 32 tpi. The barrel retaining screw in a 1894 Stevens Favorite I am working on is 30 tpi, I know this from another Favorite I just acquired. I'm pretty sure I could buy another from one of the sites online selling these things but I would prefer to make it myself. :) Besides that, I am a tight wad. :roll: :wink: :lol: So I was thinking maybe there is a metric thread that is very close to 30 tpi. What better place than here at Chaski to ask this queation. :roll: :wink:



Jack.

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GlennW
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Re: Need a way to turn a 30 tpi screw.

Post by GlennW » Sun Feb 25, 2018 1:51 pm

That would be .846mm pitch.

The closest would most likely be .8mm which would be 31.74 tpi.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

Russ Hanscom
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Re: Need a way to turn a 30 tpi screw.

Post by Russ Hanscom » Sun Feb 25, 2018 2:27 pm

Do you have any change gear options? Even if you have a quick change gear box, frequently they are driven by an exposed pair of gears on the left/outer end. Those gears could be swapped/replaced to give alternate pitches.

choprboy
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Re: Need a way to turn a 30 tpi screw.

Post by choprboy » Sun Feb 25, 2018 2:32 pm

Does your lathe have change-able gearing (for metric/different sizes) between the spindle and the threading box? Can you recalculate for a different input ratio?

So, for instance, your threading box is driven by a 30tooth gear on the spindle and a 60tooth gear on the threading input. The threading chart gives you a 20tpi threading option for that gearset. Install a 90tooth gear on the threading input (leaving the 30tooth spindle the same) and your 20tpi thread chart now produces 30tpi.

JackF
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Re: Need a way to turn a 30 tpi screw.

Post by JackF » Sun Feb 25, 2018 8:12 pm

The lathe is a Grizzly 0554 14X40 and id does have a quick change gear box. I will look into swapping gears. It does turn metric to but as Glen points out 31.74 is as close as I can see to 30 tpi. It will have to wait however till I get back from a 3 day Elk hunt. Thanks for the replies.

Jack.

johnfreese
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Re: Need a way to turn a 30 tpi screw.

Post by johnfreese » Tue Feb 27, 2018 9:51 pm

Threading dies are not too expensive. It would be possible to introduce a 30 and 32 tooth gears (on a common shaft) into the change gears but quite expensive.

WJH
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Re: Need a way to turn a 30 tpi screw.

Post by WJH » Wed Feb 28, 2018 11:29 pm

johnfreese wrote:
Tue Feb 27, 2018 9:51 pm
Threading dies are not too expensive. It would be possible to introduce a 30 and 32 tooth gears (on a common shaft) into the change gears but quite expensive.
Very cheap if you print them!

JackF
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Re: Need a way to turn a 30 tpi screw.

Post by JackF » Thu Mar 01, 2018 10:59 am

Thanks for the added replies. Will start looking into what the tooth count is on the existing gears to figure what I need to make a 30 tpi screw. That will have to wait a couple of days however as the Elk hunt was a success. :) :) This was a private land owner hunt to help the land owners (ranchers) protect their winter cattle grazing pastures and hay stacks. A snow storm on the day I got there helped bring the Elk back down again and I got my cow on the second day. We, the rancher and I skinned and quartered the Elk on the spot and packed it back to the truck. Now I need to get the meat to the processor. I am keeping the ribs, neck, back straps and tender loins to process myself and am dropping off just the front and rear quarters for the processor. :) This 75 year old is feeling a little sore today. :roll: :wink: :lol:


Jack.

Cary Stewart
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Re: Need a way to turn a 30 tpi screw.

Post by Cary Stewart » Sun Mar 04, 2018 7:43 pm

For what it is worth. Any Unimat table top lathe with the Thread Cutting attachment and a 30TPI Former and Guide can cut a thread about 1" long on any diameter up to about 1". I checked and both the DB200 (cast iron), SL and SL1000 (die cast) and the Unimat 3/4 had this device as an optional extra. A little fiddly to use but the system does work. There were two other odd TPIs that were available 22TPI (I think) and 50TPI.
Question. What is your application for the odd screw thread? We have often wondered about these. Conjecture is they were used in gun smith work.
Cary

Jaxian
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Re: Need a way to turn a 30 tpi screw.

Post by Jaxian » Mon Mar 05, 2018 4:45 am

Do you know someone with a CNC lathe? They will turn any lead you want.

JackF
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Re: Need a way to turn a 30 tpi screw.

Post by JackF » Mon Mar 05, 2018 10:53 am

Cary,the 30tpi thread I need is for the barrel retaining screw for a 1894 Stevens Favorite single shot 22.

Jaxian, thanks for that. Now to find someone nearby with a CNC lathe. :)


Jack.

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SteveM
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Re: Need a way to turn a 30 tpi screw.

Post by SteveM » Mon Mar 05, 2018 12:37 pm

Do you have 60tpi on the gearbox and can you change some gears to cut the leadscrew speed in half?

Steve

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