Die head and chasers... got a bunch, no idea! swap for knowledge?

Hi all.

here's me reaching out again for a little help.
Recently, a local machine / metal fabricator shop closed down after 50 years in business.
I went over and although I wanted to take a lot of the machines I don't have space, did get a N2 fly press and a bunch of stuff.

As everything little was likely to get to the scrap I managed to save a bunch of reamers, taps and dies.
And also 2 small die heads and a box full of chasers.
All UNF and UNC as that's what I use, there was a bunch of BSW and BSF but left that behind.

Now, I have seen these being used on youtube, but to be honest I don't have a clue, but always fancied having one for threading now and again. Never bought because they were kind of pricey, but as this was free... I want to learn now.

Could anyone explain what I have? It seems like 2 small die heads, the one that looks like it might work is missing the top plate though?
Also, only have a couple of chasers that will fit, all the others are bigger....
Although it does seems like I have a lot of sets of the same size, which I think they are 3/4... so I'd need a 3/4 die head? - I'm still sorting through the loose chasers in the big box.

Now... I have a bunch of this stuff, some of the big chasers I have no use, so I wonder if someone local to Andover, Hampshire would be interested in swapping for knowledge? show me on their lathe the use of a die head? maybe they have a die head spare that would fit most of my chasers and willing to swap for some of the bigger chasers? or some of the big taps I have?

thanks!

Edited By JP Santos on 05/03/2023 13:01:30

They are Coventry dieheads.

There is a manufacturer's publication, imaginatively titled "The book of the Coventry Diehead". Free pdf copies are available online.

Study it well.

This picture should give you some guidance as to the size of the dies for a given size of head:

There are four dies per set, labelled 1 to 4. Not only do the thread type and die type have to match for all dies in a set there is also an arbitrary number on the dies which needs to be same for all dies in a set. The arbitrary number is related to the numbers on a tapered rule used when sharpening the dies, 51 in this case:

Andrew

The book of the coventry die head comes in many editions, running to ed 27 I think. How they work is clever and interesting. DO NOT try to sharpen them unless you have the special jigs ! depending on size they can need considerable torque to operate. Good luck Noel.

Hi Andrew,

Thanks for those photos, it helps!

While I was sorting all the bits out I had a dig about on the internet and ended up finding some more info.

So the dies heads I have are 1/2"...unfortunately only have 2 complete sets of thread chasers!

However... I have about 16 complete sets of 3/4" ! meaning I'll have to get a die head for the 3/4"

I did find a nice table with all the details on the chasers.
and also learned about how they are numbered (that's how I've put all the loose set together).

Guess next step now is to sell some of the big sets I have no use, some of the bigs taps and fund a second hand 3/4 die head.

One thing that I'm quite not sure yet is how to the attach them on the lathe. the one with the MT end, easy enough, straight on the tail stock, but the other one....? I seen some videos on youtube where people have held them on just a chuck, but somehow to me that doesnt look correct?
 

Edited By JP Santos on 05/03/2023 17:45:04

What a shame you didn’t pick up the Whitworth chasers. If you decide to sell one of the heads sit would make it so much more saleable.

regards Martin

Are they desirable? I can go back Monday evening for another look, i'm sure they'll still be there.
you mean one of the heads I have with whitworth would make it desirable?
I'll probably end up selling these 2 heads so I can buy a 3/4 head as that's the most of the chasers I have.

Didn't think they would be desirable, I have a bunch of Whitworth spanners, even tried to given them away, some good old english brands, tried everywhere, lathe groups, steam engines, etc... no one wanted. so I use them to when I need to modify a spanner, cut them, grind them, etc... it breaks my heart doing so, but was that was chucking in the skip after no one was interested.

The die heads are worth good money, especially with complete (4) dies.

All the ones I have sold have gone overseas.

Jim

Odd chaser dies can be used on their own with a suitable holder as chasers. They can easily be sharpened at home and provide excellent formed threads on their own (without the die box).

Bob

I suppose I am making the assumption you are in the UK. Larger scale traction engine builders I believe tend to use Whitworth form. UNF UNC not so much. Andrew Johnston is more knowledgeable than me re die heads. Anyway if the dies are up for grabs for free it gives people choice.

regards Martin

If the Whitworth dies are for free I'd definitely acquire them. Assuming they are in sets they have a value in the Uk.

Andrew

Have a look at Wiseman Threading Tools Ltd . Redditch . You will find all details of available parts and combined with the handbook mentioned in a post above , I am sure clear up any question you may have , as they have in the past for me ! .

If you can clamp one chaser in your lathe's toolpost, it makes a nice screwcutting tool.

The special jig for sharpening these dies also needs a special grinder: a tool-&-cutter grinder or (I think) a surface-grinder.

I'm unconvinced as to the general suitability of MT taper for mounting a Coventry Die Head. By their very nature there is significant lengthways pulling force on the head as it cuts the thread which will tend to pull it out of the MT socket.

When using one with an MT taper in a tailstock the tailstock has to be fed hard enough to keep it properly seated in the taper but not so hard as to interfere with the thread profile. When reaching the end of the thread the taper seating grip has to be sufficient to resist the spring forces as the head pulls forward to trigger the opening process. If the taper grip is inadequate the head will go round with the job rather than continue cutting the thread. A bit fraught methinks.

If the tapers are less than perfect it would seem that the only safe way is to eschew the self opening feature and use it like a simple fixed tailstock die carrier keeping continuous feed force applied and stopping the lathe when you get to the end of the thread. The head can then be opened manually. Perfectly practical unless the tapers are distressed almost to the point of being unusable but it does loose most of the benefits. Frankly an ordinary sliding die holder is may then be easier, although they too will spin if the tapers are poor.

My die head has a parallel shank so I made a simple holder to mount it in a Dickson QC tool holder by welding a split tube to a solid bar. I feed up to a bed stop using the saddle hand wheel whereupon the thread pulls the head forward to trigger the disengagement. The disengagement pull forward distance is significant. Power feed by setting up the appropriate pitch and driving as per screw cutting works well but the half nuts need to be dropped promptly and final feed to the stop done by hand.

I trimmed the bar to match the tube radius on the lathe with it mounted in the toolpost to ensure all was aligned. Did the same to finish the bore. The portion behind the die head shank is bored little larger so I can easily set it on centre using a short cylinder gauge mounted in the tailstock taper.

It lives permanently in that toolholder, carefully selected as being the grottiest one which I didn't mind loosing from general stock.

Clive

A basic surface grinder is all that is needed. The required angles and placement of the dies is taken care of by fixtures:

Andrew

Posted by Clive foster

I'm unconvinced as to the general suitability of MT taper for mounting a Coventry Die Head. By their very nature there is significant lengthways pulling force on the head as it cuts the thread which will tend to pull it out of the MT socket.

There is no problem with using die heads with a morse taper, I have cut probably thousands of threads mainly with 1/2" or 1/4" units and never a problem.

Those with a parallel spigot are generally use on capstan lathes, the one I have and use is a 1/2" unit and to facilitate its use on my lathes made a No2 Morse taper holder with a 1" hole for the die box -- never a problem.

John

John

I'm impressed that a Morse Taper works so well at holding a die head.

Like most folk using older machines I've had too many issues with drills pulling out of, presumably, less than perfect tapers to be totally confident in their holding power against pull out forces.

Not quite the same but even after recutting the socket the MT 3 on my big Pollard drill isn't totally reliable when holding Pollard tapping heads. Which admittedly are quite large and quite heavy. Lifting the drill down-feed handle to engage auto reverse occasionally drops the taper either immediately or part way back.

Hence my skepticism as to whether the mutual grip of an old shank in an old socket will suffice. My first encounters with a brand new shank in brand new taper were somewhat educational. The difference between old, albeit still adequately functional when used with care, and new being profound.

Clive

If you want to see one in action have a look at Mr Crispin's channel on Youtube.

He does not use the MT in the tailstock barrel but has made a sleeve to clamp the diehead and tailstock barrel together thus eliminating the risk of the DH pulling out of the tailstock socket.

HTH

Dave

My die-head came with a similar sleeve, made for the tailstock of a heftier lathe than my Harrison L5; but that would be the best approach on a reasonably large machine.

I'd suggest a clamp rather than grub-screw fitting so you don't risk indenting the tailstock barrel.

For a small lathe I think a tool-post fitting (as Clive Foster's) or saddle mounting may be better.