Coventry die head - make tailstock adaptor for the lathe

I got a rather nice example of the 3/4" sized Coventry die head from ebay last year. I've also acquired several sets of die for it - mostly metric which are actually pretty popular and thus less commonplace. 

Not much use having a die head if you can't use it but it won't just fit my machine out of the box. It has a (hollow) 1-1/2" parallel shank, while my lathe has a MT3 taper in the tailstock. As that's where I expect to make most use of it, I need to make up some form of adaptor.

Quick scan in the cupboard and I found some spare MT3 arbors. Pretty sure the JT6 arbor came as an extra with the auto reversing tapping headI bought in Canada. Either way, it's not needed for anything else, so I'll use it for this job.

Also have an MT3-MT4 adaptor that allows me to fit MT3 tooling in the spindle of the lathe. So I can mount the MT3 arbor in the spindle directly and machine the JT6 taper off, leaving a simple parallel stub. Looks dramatic but with hardened parts, you need to run the machine at its fastest speed.

  

The cunning plan is shown in the pencilCAD sketch:

• Make a simple parallel extension and glue it onto the modified arbor using Loctite. The hollow shank will be a sliding fit on this part. Might as well drill it out hollow, to allow work to extend into it if necessary.
• To prevent the die head body from spinning, I need to make a drive dog that will also allow the head to slide as the thread is made. I will weld a simple bracket onto the extension, with a shaft sticking out, parallel to the tailstock axis. Note that the MT3 arbor has a tang to prevent rotation.
• The drive dog will pick up on this shaft. It needs to have a pinch bolt arrangement to clamp onto the shank of the die head.

Here's the current state of play:

Next:

• Machine the extension piece. Drill and bore out the end to fit over the arbor. Drill throughto allow work piece to pass through.
• Make up and weld the drive dog arm and shaft.
• Make up the clamp dog.
• Job done.