2.5 tpi

[DiscoDan]

I have an old blacksmith vise and the screw is 2.5 tpi. I was hoping to use this as a demonstration piece during the Tuckahoe Steam and Gas Association show July 11th through the 14th. Unfortunately the lathe that we have for demonstrations does 2 tpi or 3 tpi. What would I need to do to cut a 2.5 tpi thread on this lathe? Is it even possible? Is more information needed about the gear train in order to answer the question?

 

[SLK001]

Is more information needed about the gear train in order to answer the question?

Yes.

 

[GrifterGuru]

Ok, well looking at that threading list:

2 TPI requires a 20 screw and a 50 stud
3 TPI requires a 30 screw and a 50 stud.

Question is, can you fit a 25 screw to run with a 50 stud and cut a 2.5TPI thread?

It is just a question, one that Iwould ask myself and then see if it could be done.

 

[SLK001]

The gearing is proportional, so a 25 tooth with a 50 stud should give you 2.5 TPI.

 

[GrifterGuru]

The gearing is proportional, so a 25 tooth with a 50 stud should give you 2.5 TPI.

That was the question I raised as being potentially possible.

 

[benmychree]

I'd make a 25T change gear in place of the 30 T for 2.5 TPI, It would replace the 30 T gear for 3TPI.

 

[epanzella]

There are a few combinations you can use to get 2.5tpi depending on what change gears you have. If you can do 5 tpi double the leadscrew speed. If you have a 10 tpi setting, quadruple the lead screw speed to get 2.5 tpi. You can do the math for other combos that are not as "neat" as the ones I mentioned.

 

[Jake M]

I'm just looking at the chart-

For 2 tpi there is a 20 tooth gear that's "allowed" on the screw.
For 5 tpi it's a 40 tooth stud gear and a 40 tooth screw gear.

40 on the stud gear, and 20 on the screw gear, should oughtta do it. I think...

Take a scratch pass on some scrap before you cut up something nice.....