metal lathe thread dial

[bert4255]

I would like to make a thread dial for my lathe. it is a large lathe has a 49" swing, nt that that matters. How do i determine how many teeth the thread dial needs in relation to the lead screw. Is there a ratio? I want to do imperial threads.

[RussellT]

I think we need more information.  Is the lead screw metric or imperial.  What's the thread pitch?

Russell

[bert4255]

I think the lead screw is imperial. I'm not sure on pitch. I'll try and find out. thanks

[John Stevenson]

The gear has to be a multiple of the threads per inch.
Just guessing from the size but your lathe probably has a 4 tpi thread so the gear needs to be a minimum of 8 or better 16 teeth

[bert4255]

Thanks John, I will check and see what the thread count is

[bert4255]

John, I'm getting about 2 1/2 threads per inch, not even 2 1/2. how do i determine if it is metric screw or imperial
thanks

[shipto]

Some pictures of the screw with a ruler lined up might help.

[bert4255]

ok, it is a metric leadscrew with a 2.5" TPI

[Pete.]

That would be a 10mm pitch screw. It's a big boy alright.

A large lathe like that might well have a single tooth dog clutch which would remove the need for a dial. What make is it?

[bert4255]

Peter, I figured it out thanks

[mattinker]

Thread dials get more complicated on metric lathes. Inch dial gauges are easier than metric ones because they work using parts of an inch as the base. You can need several thread dial gears to make a metric lead screw work.

I would make a ten tooth gear (four times the aprox  TPI, even though it is metric!) I would then use the technique that Tom Lipton describes here https://www.youtube.com/watch?v=HXt4TWa382Q i am sure the a mathematicians who could work it al out , I suffer from what the Americans call "Matth anxiety" S o I do things to avoid calculating!

Regards, Matthew