What thread form is a lathe spindle?

[Walney Col]

I've got a Jet mini lathe that takes the same chuck as my old Axminster lathe.
It's got a 1" x 8tpi thread. The question is what thread form will it be?
Both whitworth and UNC taps are available in 1" x 8tpi and they have different thread angles one being 55 and the other 60.

Col.

 

[WoodMangler]

I've got a Jet mini lathe that takes the same chuck as my old Axminster lathe.
It's got a 1" x 8tpi thread. The question is what thread form will it be?
Both whitworth and UNC taps are available in 1" x 8tpi and they have different thread angles one being 55 and the other 60.

This might or might not help - I just offered-up a Whitworth thread gauge to my APTC M330 (which I'm fairly sure is a rebadged Jet) spindle, and it's a really good fit. Unfortunately I don't have an 8TPI UNC gauge to compare it with, so not proof-positive

eta: BEWARE ! If it's an older lathe google "Jet lathe spindle thread-form" and you'll see that the same model might have been produced in more than one thread-form, and even Jet don't know which is which. Might do better to ask Axminster what the thread was on your old Axi lathe. Also, be aware that a 1"UNC male thread will loosely fit a 1"WW female (or vice-versa, can't remember which way round it is), so how good is the old chuck's fit on the new lathe ?

 

[J-G]

I've got a Jet mini lathe that takes the same chuck as my old Axminster lathe.
It's got a 1" x 8tpi thread. The question is what thread form will it be?
Both whitworth and UNC taps are available in 1" x 8tpi and they have different thread angles one being 55 and the other 60.

In an ideal world it ought to be easy to tell the difference - a correct Whitworth 55 degree form should have a radius top and bottom whereas a Unified (or Metric) 60 degree form should have a flat at top and bottom.

In reality, Unified and metric forms are also produced with a radius at the root and Whitworth forms were/are often produced with a flat at the top. It is also common practice to make internal threads only 5/8 deep - ie. the core diameter is enlarged to make tapping or screw-cutting easier.

I've created a comparison of both forms so that you can see the potential interference/clearance - in an ideal 'full-form' thread.

 

[Walney Col]

Thanks for the info. I should be able to identify the thread form easily now.

 

[chipmunk]

Hi Col,
It's definitely UNC thread form.
Jon

 

[Walney Col]

Hi Col,
It's definitely UNC thread form.
Jon

Great. That was the conclusion I just came to myself but it's nice to have it confirmed.