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

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.

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

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

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

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