thread cutting

[ptjw7uk]

Hi All,
I think i'm having a senior moment - if I get a set of dies for a coventry die head can I use it to cut other threads with the same pitch than the size it was designed for.
Its just that I think if the tpi is correct then you should be able to cut any size at the same tpi but then I think weel it says only one size on the die!!
Any thoughts
Peter

[SGW]

Changing the diameter changes the helix angle of the thread....so I don't think it will work.

[ptjw7uk]

I thought from the design of the cutters they cut on the diameter and have a rake to the cutting edge so I thought the rake would not make much of a difference.
Anyone know!!
Peter

[John Stevenson]

Sorry no.

The dies for a Coventry die head are 'sized' according from the distance from the face to the engagement notch.
so 1/4" x 20 dies will be longer than 1/2" x 20 to reach further in.

There is some + and - adjustment on these heads but not enough to get to the next range.

There is nothing to stop you taking one orphan die segment and using it in a holder to screwcut any diameter of that pitch.

Example on left.




.

[ptjw7uk]

Thanks Sir John that is what I was thinking about it means I will have spare dies but I would only need the common metric pitches and only those for the finer threads. Perhaps I should have said chasers.

Peter