1/2" coventry die head on a myford super7

Assuming you use belts/backgear to get the slow speeds needed by Coventry dieheads, and not a VFD, then you should have plenty of torque to cut (presumably) M8 in stainless steel. However, I'd be more concerned about a tailstock chuck being able to grip the diehead sufficiently. I'd also wonder about the keyway on the tailstock barrel, I don't know if Myford lathes have a protruding screw or proper keyway to take the torque. It may help to visualise how much torque you'd need to apply to cut the thread by hand with a conventional die and stock.

I've cut threads in stainless steel using a Coventry diehead on a manual lathe, but I used a bed mounted capstan attachment rather than the tailstock.

Andrew

Ian when I purchased my super 7 it came with a couple of die heads which I have since given to a friend to use on his capstan lathe, basically the die head was fitted into a piece of round bar the end of which was turned down to fit into 1/2 chuck I recall having a play the die head was fitted with 5/16 UNC dies I used the tail stock chuck and I used the saddle to 'arrest' the tail stock thus opening the die head the resulting thread seemed fine to me !

H

Agree that the Myford should have more than enough power when run at the appropriate speed. Use plenty of coolant / cutting oil or at least a generous coat of a good threading compound. I find Trefolex good.

Better to mount the die head off the cross or top slide I think as a die head intrinsically try to pull forward so an MT taper won't be as bulletproof secure as a clamp. Means bit more trouble to line up. I made setting bar to align the clamp before fitting the die head. Using mine mounted in this manner on my Smart & Brown 1024 and consider that feeding the die via the saddle hand wheel gives much better feel and control than feeding form the tailstock would. Also puts your eye-line level with the die head so its easier to judge where you are in the float range before it auto pulls off. Working form the tailstock you are either at arms length with the feed or observing form behind which seems not to be as good.

That said I've not tried feeding form the tailstock so my fears may be exaggerated.

Clive.

Not tried on my Super 7 but I have a very clean unmolested 1/2" die head with instruction book for sale. See Classified. Robert Butler

Ian, absolutely no problem using a 1/2 die head on a Super 7 I have bee using one for many years, I used a No2 morse blank end and bored it to the spigot dia of the die head mounted directly in the tailstock. Using a slow speed and the die head auto release is simple.

PM me you email if you want a photo. John

I use mine in a MT2 ER40 collet chuck in the tailstock on the Super 7, no problems cutting 1/2" UNF in 304.

I am in the process of sorting out a MT2 holder for my rear QCTP though as I believe it will be more convenient for larger tooling and will give me longer travel for drilling and reaming.

- Nick

thanks for all the advice i think i will try the mt2 to er32 or er40 for holding the die head in place .Not sure of the size of the shaft yet just hoping the 3 jaw chuck will hold the 8mm stainless ok

Ian

Ian, PM sent.

I got my die head and could not believe my luck it was fitted with m8 x 1.25mm chasers the size i need also bought a grinder jig looks like fun to have a go at

Starting in ME 4567, ME 4569, and continuing in ME 4571, David Earnshaw has an article on using Coventry Dieheads, including a fixture for using it in the tailstock of a Myford lathe.

Ian S C

i got it working but the 2mt is not really secure enough it kept turning but managed to cut a good thread on 316 stainless , the chasers i got were slightly rusty and not the correct cutting angles for stainless thik there grade s20 for normal steel so not sure if it would cut much easier with the correct sharp chasers installed but on the plus side its very fast

ian

Ah the posh version! There are at least two variants for different ranges of chasers. Did you also get the tapered 'rules' used to check the height of the newly ground teeth? Old style jigs on the left, then the newer style and on the right the tapered measurement jigs:

Although the chasers came in a variety of throat and rake angles S20 seems to be far and away the most common, especially if buying new. In my experience S20 works fine on steel, stainless steel, brass and bronze. The most important parameter is cutting speed. Too fast and the threads are torn rather than cut.

Andrew

HI Andrew,

How many Jigs do I need to sharpen a Coventry Die? Do I need Jig A+B+C? What are these jigs called?

Chas L

The basic answer is A and C.

Coventry dies need grinding on the taper at the front to provide a clean throat angle. They also need grinding on the flat face to create a new cutting face that is on the centre line of the work.

The fixtures A are grinding fixtures that allow grinding of both faces for a standard throat angle of 20° and a top rake on the cutting face of 12°. All four dies in a set need grinding together. The grinding fixtures come in a variety of options. The smaller ones may only cover one diehead size with two fixtures required for RH and LH. Whereas the larger ones may cover a range of diehead sizes and both LH and RH.

The fixtures B are baseplates that allow the grinding fixtures to be set at different angles for different throat and cutting face angles. It is unlikely you will need these, unless you have dies specifically for brass.

The fixtures C are height gauges and are used to determine the height of the new cutting face so that it is on the centreline of the work. The numbers on these gauges are arbitrary and get larger as the diehead size increases. The exact number is specific to a particular set of dies, and should be marked on each die in a set. If these numbers are different then you don't have a complete set! The height gauges have an overhung rule. All you need to do is grind the cutting face until the die stops at the number engraved on the die when slid along the overhang on the gauge.

If that's not clear i can take some pictures to give a better illustration.

Andrew

Purely curiosity, what speed should the die heads be used at?

Bert

Hi Andrew,

Thanks very much for this info, I now have the situation in perspective. Also I know 2 things. Firstly that I have a grinding fixture and a baseplate for 3/8 - 1/2 inch dies but no height gauge( both early pattern). Secondly that I have never missed out on buying a height gauge at autojumbles because I did not recognise what it was

I don't know what my chances are of buying a height guage on its own but the search is on!

Best wishes, Chas