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an odd question about lathe TPI

WAUGS

Plastic
Joined
Feb 20, 2023
I have a job that requires placing a wire into a tube that has a groove in it.
the groove is 2 TPI. I have never seen a lathe with less than 4 TPI.
It has to be a manual lathe as it will need to have labor interacting.
it is also up to 48 inches long so no small machine.
Anyone know of a 2 TPI machine?
Any suggestions?
 
I've got an old 14" Whitcomb Blaisdell and a 16" Hendey that can, and I'm sure there are others too. I'm inclined to think larger/slower lathes would have it standard. I think with the right gear train, you could temporally modify about any tool room lathe to do it. For a 4tpi selection, essentially take whatever gear ratio you get between the headstock and the gear box and double the reduction.
 
Actually ,2 tpi is a common leadscrew pitch for bigger lathes .......simple solution is a small milling head that fits the saddle,so only one pass is needed per threaded item,and loads are minimized.
 
As to machines with 2tpi leadscrews,last year I scrapped a Lang 22x84 ,and still have my old Swift 24x72 .....both 2tpi screws...............4 tpi is a finer pitch ,my little Colchester Bantam has a 4 tpi leadscrew,and its only a 10 " lathe
 
I dont have much experience with larger lathes, I'll have to look at a few to see if I can make that work.
 
With most lathes (all?) you'll be overdriving the leadscrew, putting tremendous loads on the gear train. Gears get broken that way, thus the advice to use an active cutting head. Don't know the diameter, but can a Swiss turn do it?
 
don't need to cut anything just need to lay a "wire" into existing groove.
So no load to speak of, just need to follow the 2 TPI.
 
You must have a lot of these if you are thinking of a lathe just to do it.

If the groove is deep enough it can drive a nut with a tangential hole for the wire. The nut can be mounted on the carriage with the tube between centers. The nut will pull the carriage along as the wire is wound around the tube, kinda like winding a spring. Unless the wire is super soft there will be a lot of sprig back when the tensiom is removed.
 
That simplifies it. As long as you are not taking a heavy cut, you can use the appropriate gears on a manual change gear lathe to speed up the lead screw to the proper rate. The lathe does not need to be all that big.

I have a "complete" chart of the screw pitches that I can achieve with my SB-9. I choose to start it at 2 TPI which would require 64 (stud) and 16 (screw) tooth gears with the 8 TPI lead screw. A slow speed or at least a soft start on the motor would be advisable. But 2 TPI is certainly doable. If you are doing it all day, I would lubricate the gears and screw frequently.



don't need to cut anything just need to lay a "wire" into existing groove.
So no load to speak of, just need to follow the 2 TPI.
 
The usual method is to mount a small milling head on the saddle ,and drive the spindle via the leadscrew .....milling the thread needs no excessive loads on the lathe ,and needs only one pass .............I have seen a 20ft long acme thread milled on a 3" heavy wall pipe ,completed in one pass.
 
Our Taiwanese Sharp 3080V lathe has a 2 TPI lead screw. It's a bigger lathe with a 30" swing, 80" centers, a 4" spindle bore and a D1-11 spindle nose.

Here is the same one for sale to give you an idea:

 
My most common parts are 2 tpi in a PK thread. the lathe is a 1989 Promaster 2160, which is the same (methinks) as a Summit.
 
He's not cutting a thread. Just winding some wire in an already cut groove. Unless it is some unusely heavy wire or some other circumstance I would fab a simple motor driven arbor unless I found a really cheap old lathe.A gear box and an Acme screw coupled to the arbor with the wire feed head attached to the screw. I could see maybe 4-5 grand for parts. He still has to make a feed head for the wire with a lathe.
 
He's not cutting a thread. Just winding some wire in an already cut groove. ... I could see maybe 4-5 grand for parts. He still has to make a feed head for the wire with a lathe.

Thread mills operate at a slow spindle speed with the cutter head speed independent of the workhead speed. You can run the cutterhead at any tpi you want, so if you had one, easy to feed the wire from the cutterhead and set the workpiece speed however you want and the feed however you want. But prices on those have gone way up, I bet you can't find one for $2500 anymore :(

Could probably mod a thread grinder to do the same thing, they work similar.

I bet you could make something that would be more compact than a big ol' lathe too - just a hollow spindle and a set of linear ways with a carrier. Two motors to drive, a pair of encoders and a cheap plc for control ...
 
You could just use a VFD to run the lathe at half the speed.

Now, before anyone starts hating on my suggestion, make careful note of the fact that I used the word 'just'. Then, as the coupe de grass, I included the answer to every issue that faced anyone - the VFD. Boom!
 








 
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