Coventry die head mount to Super 7

[Roger King 1Participant @rogerking1]

I have bought a ½” 12DX Coventry die head to (hopefully) enable me to cut some small BSF threads onto the ends of Girling brake rods (1/4″ diameter EN16T steel round bar).

Is there a straightforward way of mounting this device to a Super 7 tailstock?  Mine has the stock MT2 (I think) taper.  Not sure quite what the die head has, but it’s a female fitting, possibly a taper.  Are there standard parts for this sort of thing?  I’ve not done anything like this before.

[Gary YeadonParticipant @garyyeadon51936]

hi Roger its a lot of years since I used one of these die heads on production runs. I am no sure what a super 7 is but I used the die head on a capstan lathe  and set a stop to allow the die head run out and click open after the thread was cut.

Type  this into your browser – ½” 12DX Coventry die head – Search (bing.com)

 

[noel shelleyParticipant @noelshelley55608]

Hi Roger, As gary has said, Normally you would use it on a capstan where the capstan would work to a stop ! Using the tailstock you have to feed the die head onto the work and then stop it at a pre determined point and there will be a pull that causes the die head to open. You should be able to make a 2MT fitting to take the die head, and depending on thread lenghth it may have to be hollow, or buy a blank 2MT arbor and adapt.  I have never used one on the S7 though I have several but I would hope that there will be someone who has ! Good luck Noel.

[peak4Participant @peak4]

My ½” one has a Morse taper. and my ¼” ones have a stub which mounts in a drill chuck in the tailstock.
I don’t use mine for production runs, more for just making sure the threads are square and well formed.
If the thread is fairly long, then you could lock the tailstock barrel, start the cut by sliding the tailstock along the bed, and having it stop against either a bed stop, or the carriage.
That will then allow the diehead to extend and disengage.

Bill

[Roger King 1Participant @rogerking1]

Thanks all, good tips!  Yes, i plan to use it for threading the brake rods because although only ¼” diameter, the threads need to be somewhere between 2-3″ long at least.  I have done some by hand, but unless the die is absolutely square the thread will wander off centre, and once that happens there’s no coming back.

My question is how to attach the die box to the tailstock, and if there’s some sort of adapter available.  I’m a car restorer, panels and mechanicals, and whilst enthusiastic about machining I’ve not done much.  Apologies for the basic questions, but what’s a blank 2MT arbor?

I’m wondering if a taper’s a good idea for this.  I suspect the resistance from thread cutting will result in the box spinning on the taper, but I don’t suppose there’s any alternative.

[bernard towersParticipant @bernardtowers37738]

I fit my 5/16 heads to an adaptor either a no 2 mt or a straight shank for drill chuck use. Both heads are plain shank (for capstan use) and I have drilled a location pin hole to stop rotation but have also fitted an auto stop to allow repeat ops, its only a piece of 30 x 6 mm Bms with a hole bored in one end to be a very close fit on the DH shank and hangs down low enough to just miss the crosslide. There is a stop bolt fitted into the crosslide to act on the piece of Bms stopping the die head moving further onto the workpiece therefore tripping it. On my heads I find that after stopping the head it moves a further 3/32″ before finally disengaging so that has to be allowed for when setting the stop.

[noel shelleyParticipant @noelshelley55608]

Hi Roger a blank arbor is in this case a 2MT shank with a solid lump at the front which you can do as you wish with, drill, thread or what ever. So looking at a couple of small die heads The shaft on the die head is 5/8″ so you would drill your arbor and put a locking screw through the side to fix the DH ! for 3″long you may have to drill down the centre of the arbor to allow the rod to pass. I think you will find blank arbors at Arc Euro Trade amonst others. Always found them very helpful and good prices/quality. Noel.

[Chris GunnParticipant @chrisgunn36534]

Roger, there was a series of articles in the ME magazine by David Earnshaw, the article started on the 2nd March 2018, on how to mount one to a Colchester Bantam. The principle could be applied to the ML7 I would think

Chris Gunn

[JohnFParticipant @johnf59703]

Hi Roger, I have a 1/2″ die head and use it regularly on my Super 7, I made a Morse taper adaptor to mount it int the tailstock, indeed I/we use these in industry on centre lathes and cut many hundreds of threads without any issues of the taper coming loose.

Here is a photo of mine, I did not drill through, never had the need up to now but there’s no problem in doing so within limits of course.   Many of the stub arbors on offer are too small in diameter and length, the nearest I found was here they have one 40 x 40mm better if it was larger but you could of course make your own.

[Roger King 1Participant @rogerking1]

Lots of really good help here, thanks all.

Thanks JohnF, I’ve ordered one of those, at £12 including postage you can’t go far wrong.  Just need to turn it down to suit and make up a sleeve to join them and I should be good to go.

[Roger King 1Participant @rogerking1]

…actually, as the head has a hollow shaft with, I think, an internal taper, I might be able to turn the arbor to fit and then fix it with a tapered pin.  I’ve had to do a few of those lately to fix clutch pedals etc. to their shafts, so I’ve got a few different sized pins and the taper reamers to suit.

[bernard towersParticipant @bernardtowers37738]

If you are making multiple short screws making the auto stop is a worthwhile exercise.

[noel shelley]

On noel shelley Said:

…stop it at a pre determined point and there will be a pull that causes the die head to open.

It would be useful for him to read up on the specific model he has, the 12DX. It has the additional ability to be used in a slightly different manner, operating by means of an external (push) trip.

Wiseman have a digestable summary on their technical pages.

General Tech Info – Coventry Die Heads

A copy of the ‘Book of the Coventry diehead’ is available on vintagemachinery.org (under Alfred Herbert). It does not cover this newer model, but has useful information nonetheless.

I would think that for the 2-3″ of thread he says he wants, it might be necessary to disconnect the tailstock nut or to make the tailstock bed clamp slightly more sophisticated than its current ‘on’ or ‘off’.

[noel shelleyParticipant @noelshelley55608]

The book to which DC31 refers has MANY editions, No 25 possibly being the last. Very interesting ! Mine is on the bookshelves – somewhere ! In the context of the dies they can be sharpened, there were 2 different types of jig the latter one very neat, and done in 3 sizes to suit your die size. I have the 2 smaller sizes. Noel.

[Roger King 1]

On Roger King 1 Said:

Lots of really good help here, thanks all.

Thanks JohnF, I’ve ordered one of those, at £12 including postage you can’t go far wrong.  Just need to turn it down to suit and make up a sleeve to join them and I should be good to go.

Roger, not sure what you mean by “making a sleeve to join them”  you only need to mount the adaptor directly in the headstock, MT2, and bore to 1.000″ dia for a suitable depth then add grub screws.  I’m assuming your die head is the same as mine and all others I have come across where the routing shaft/spigot is 1″ dia for mounting on capstan’s the hole through is to the best of my knowledge parallel for the passage of longer threads.

I did make a couple of flats on the spigot for the grub screws – your choice but it does ensure it will not spin in the adaptor.

John

 

[noel shelleyParticipant @noelshelley55608]

The 2 I got out last night had a 5/8″ spigot, though the 1/2″ DH may well have a 1″ ! One had a flat machined on it to be retained by a grubscrew or setscrew. For a 1/4″ thread one might use a smaller DH. The method of mounting is clearly shown in John Fs picture of a bored out stub arbor with grub screws. Remember that the Myfords have a 2MT spindle so boring out is easy ! Take chuck off, bang the stub arbor down the spindle, making sure its clear of swarf first and you have a concentric hold to be able to bore out, EASY ! Noel.

[Roger King 1]

On Roger King 1 Said:

T

I’m wondering if a taper’s a good idea for this.  I suspect the resistance from thread cutting will result in the box spinning on the taper, but I don’t suppose there’s any alternative.

You don’t have much faith in track rod ends then? :O)

[Phil PParticipant @philp]

This is my set up.

[Phil P]

On Phil P Said:

This is my set up.

The original poster asked “Is there a straightforward way of mounting this device to a Super 7 tailstock?”

Would it be correct to say that your photo does not show a Super 7 tailstock?

To me, it looks like an ML7 tailstock with the quite rare Cowells rack-operated attachment. If the OP does not have these parts, what might be an alternative?

[noel shelleyParticipant @noelshelley55608]

Myfords lever operated tailstock attachment ? OR make a copy of it ! That’s my answer ! Noel.

[Phil PParticipant @philp]

I have used a large 3/4″ diehead fastened to the cross slide.

Then another version where the work says still and the die head is rotated, still mounted on the cross slide.

Whilst that version works well, it still means faffing around removing the top slide each time, so I finally ended up with this attachment that can be fitted and removed in less than a minute.

It can be used with normal die holders and tap holders.

[Roger King 1Participant @rogerking1]

Sorry, been in London all day for the V&A Chanel exhibition – don’t ask…

All good suggestions, and when the arbor arrives I will investigate further.

As to track rod end tapers, no, I would have no faith in them whatsoever if it weren’t for the flipping great nut on the end holding them in tight!

[Alan Wilkinson 1Participant @alanwilkinson1]

Hi I use my die box in the tool post  I made a block with a hole to take the shank of the box its parallel then a flat on the side to hold in tool post this then allows you to do longer threads has the bar will pass through the die box, you can even then set your gears to the right pitch and drive it from the lead screw ensuring it stays in pitch for very long threads, I could post a picture if needed.

ATB Alan

[Howard LewisParticipant @howardlewis46836]

Track Rod End tapers are usualy such tight fits that a screw powered separator has to be use, instead of the usual two hammer method.

I’ve known of a vehicle running quite happily with the taper gripping, despite the nut having fallen off, because the threaded portion has broken off!

Morse tapers, which are “slower” (barely 3 degrees  2MT is 2 degrees 52′)  than the Track Rod End (Often 1 in 6), are described as self gripping tapers. Sometimes they grip so well as to be virtually imposible to remove.

Not too long ago, there was a thread on here, by someone who had INCREDIBLE difficulty in “breaking” a Morse Taper.

If internal and external tapers are a good match, it won’t take a lot of end load to provide a really good grip. Quite often, just slamming into place by hand will result in quite sufficient grip for drilling or even milling with a larger than an inch cutter. Tapping home with a soft mallet, or pulling in with a drawbar will give a good grip.

 

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