Diehead threading question

There is a lead on the start of the dies and the last cut doesn't take a lot off. It works in exactly the same way that a split die works by hand when you do a second pass.

-- Regards,

John Stevenson Nottingham, England.

I have messed up threads a couple of times because it hasn't picked up correctly on the finishing cut. I think that's a drawback with using dieheads for odd one's & two's of threading jobs. In a production situation you'll quickly get a feel for the feed pressure & speed needed for a good thread, & spoiling one or two often doesn't matter too much. If, as I have done, you're cutting a thread on the end of a stainless propellor shaft that you've spent half a day machining, there'll be a bit of swearing & cursing if it's not right first time! You don't always need to use two cuts - one is often fine for free cutting material.

Cheers Tim

Tim Leech Dutton Dry-Dock

Traditional & Modern canal craft repairs

So it's not just me then :-))

I still can't see how volume production was achieved if it was so hit and miss, and the book doesn't give any help at all, it just goes through the motions of first and second cut etc.

Free-cutting material aside, the book goes into great detail about tougher materials, so it would need to be a little bit more regular than just luck IMO.

-- Peter A Forbes Prepair Ltd, Luton, UK snipped-for-privacy@easynet.co.uk

Probably due to the tapered lead on the chasers allowing correct engagement with the roughed thread prior to the fine pass.

As a topical aside, I have often used the Coventry diehead to cut VERY undersize threads as a means of obtaining hard-to-find threaded items, for instance the last job involved threading a M8x 1.00 capscrew, then adjusting the cut to resulting in a M7 x 1.00 capscrew, with no turning of the OD required prior to threading - so long as a full thread is required!

No problems were encountered in picking up the thread for the second cut despite the large difference.

I think there is about 1/16" adjustment each way on a 1/2" diehead, which allows a great deal of versatility, and saves buying chasers for that one-off job.

Festina Lente

MARK

One reason I started using die heads was that I needed to cut a number of 3" long 10mm x 26 tpi threads, no problem with 3/8 x 26 chasers in a 1/2" head.

Cheers Tim

Tim Leech Dutton Dry-Dock

Traditional & Modern canal craft repairs

I don't see it as hit and miss, but there is a bit of human input needed. If you're a bit too timid or agressive with the feed it'll screw up If you're making 1000 widgets on a capstan, it probably won't matter too much if you spoil the threads on a couple of the early ones, after that you should have the feel for it. Doing on-offs on a centre lathe with a heavy carriage isn't quite as straightforward. If you're having a lot of trouble, it's worth checking that everything is working freely in the die head, especially the sprung axial movement, and that the chasers are correctly ground.

Cheers Tim

Tim Leech Dutton Dry-Dock

Traditional & Modern canal craft repairs

When you have had to make 12,000 sump studs [ 1/4" BSF on both ends ] for Rolls Royce Meteors for being a naughty boy as an apprentice you soon get the 'feel' :)

One Ward was set to do nothing but studs. It was know as the punishment machine. I seemed to live on it. One reason I have always detested production work from that day on.

-- Regards,

John Stevenson Nottingham, England.

OK, take it a stage further, what happens on an automatic? does the motor reverse out and retain the position with reference to the thread start? (Coventry Dies were supplied for automatics as well as manual use) or is there another way? I am excluding external threads cut with single toolpost-held chasers here, only referencing Dieheads, and I suppose the other makes can be included, not just Coventry (Herbert)

-- Peter A Forbes Prepair Ltd, Luton, UK snipped-for-privacy@easynet.co.uk

I only ever used this type of diehead once (on a CVA auto screw m/c) and the tool room called it a floating diehead and it really seemed to be superfluous for the job it was called for.

Another BIG advantage is the fact that the diehead can be set to self-open once the requisite length of thread has been cut, allowing quick and easy retraction of the diehead, allowing another operation to take place.

If, like a lot of my work, no further op is required, then the spindle can be declutched, a new blank mounted on its driver (or in the chuck) and the cycle begins again without stopping or reversing the motor. This not only saves time, but wear and tear on the motor and Dewhurst switch.

I keep a few scrap pieces handy to test the cut after setting up the chasers; invariably some adjustment is necessary depending on how much the chasers have been reground, and also to get the "feel" of the job and verify the ergonomics of it all before committing to thread up a batch. Handy to know if you've put in the chasers in the wrong sequence!

Having the diehead mounted on a capstan saves more time and even more bed wear.

Couldn't face doing 12,000 of the bloody things though!

Festina lente

MARK