Coventry die head

I want to buy a coventry die head for use when I have a lot of threading to do

whats a good size to buy?

What do the sizes mean 1/4, 1/2, 3/4, 1",

Is this the maximum size it will do as i'm sure i've seen 1 1/4" dies for use in a 1" holder

I cant imagine I will want to cut bigger than 14mm or so mainly 6 and 8 mm

Ian

In which case you need a 1/2" die head, they will go up to 14mm

The size relates to the nominal maximum thread diameter that can be cut with a given diehead. It is possible to cut slightly larger fine pitch short threads than the specified head size; but I suspect that dies for this are pretty rare. The choice of diehead will also depend upon the smallest thread you want to cut. It is uneconomic to manufacture chasers for a large head but for small threads. Also, a large diehead will probably strip a small thread rather than disengage.

You also need to consider the lathe, and drive system, to be used. For the 3/4" and 1" dieheads you will need a lot of torque at low speeds to cut a coarse thread. That implies a belt or geared head; using a VFD to simply reduce the speed probably won't cut it.

Avoid the 3/8" dieheads; they don't seem to have been very popular and there are limited chasers available.

Regards,

Andrew

Thanks for that I guess I'll look out for a 1/2" one then

Ian

Well I bought a 1/2 " one off ebay yesterday afternoon it came today and it easily mounted into my toolpost in a boring bar holder which was 1" dia hole the die head was 1" too so no problems there.

Moved it to centre position by eye

A piece of 3/8ths in the lathe speed at 200 rpm lube and advanced the saddle at a speed to suit the advance and then stopped when I thought enough and the die head snapped open ....result a lovely thread 3/8 UNC

why had I not bought one of these years ago..now just to aquire lots more dies

Edited By Ian Parkin on 15/04/2015 14:07:50

Make sure to check size of thread produced.