Is this book of any use?

Thor

I n a nutshell, without having to read a whole book (which is very good BTW thanks Thor) the Coventry die head is like your ordinary die and holder, but the die is in effect split into four pieces, each with a set of teeth on it to cut the thread. The holder holds all four in teh correct position. This means that once you have cut your thread, instead of having to reverse the lathe and wind your one-piece die and holder back off again, you simply yank that handle on the Coventry head and the four toothed cutting sections snap outwards, clearing the job and allowing the carriage to be wound back toward the tailstock with the lathe still running. Saves heaps of time on production work but not that essential for home use.

There is the added advantage that as the cutting teeth wear and the thread they cut becomes a bit oversized, the Coventry head allows you to minutely adjust their depth of cut to bring the thread back into spec, like squeezing down a split die with the clamp screws but much quicker and easier.

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+1 on the thanks to Thor

Nice summary, Hopper.

Further to Rik's observation … The individual inserts can be useful to the amateur, as thread chasers.

MichaelG.

Hi all, the days of cutting threads with Coventry Die heads are far from over, for example the Simba Plough Company of Sleaford Lincolnshire had a requirement for some rather large "studs" threaded 2" Whitworth, the longest of which was 12 feet long with 2 feet of said thread at one end, we had to cut a hole in the wall of the wooden shed that was our workplace, feed the bar through, and the turret of the Herbert No 7B, headstock & finally a well greased wooden plummer block! Then one may take 1 rough & 1 finish pass, job done, proven technology etc etc. Compare this with Cnc, right hand end of machine often blocked with swarf conveyer, left hand end of spindle blocked by obscenely expensive magazine bar feed for delivering bars little over 3 feet long, oops run out of space. Rolled thread? I don't fink so, Thread milling? your having a larff, have you any idea how much such technologies cost? for a thread to be fitted with 2 (very large) nuts & washers, go with the tried & tested.

Bob H

I have a set of single inserts and a holder from Tracy Tool for use as a hand chasers.

In practice I hold one in a QC tool holder.

Neil

Yes, it was a sort of dance. You might have another operation step between the diehead and part-off, like a drill and ream or tap, or just possibly a roller-box – though that would be more likely before the diehead.