I'm not sure this will be the final, but it's modular and easy enough to change. Faced a piece of 3/4" round aluminum rod for the adapter.
This will hold the shoulder piece to the rod.
Cut a flat.
Don't try this at home. This is poor practice and stupid. The workpiece could fly out of the chuck. Angled the piece in the jaws and cut a flat. This will angle the shoulder plate on the rod.
Also angled the adapter for the mounting hole. Spotted, and progressively through drilled...
to 3/8" to fit the main rod on the buttplate.
The pinch clamp hole needs to be offset on the rod. Spotted and through drilled with a 4.2mm bit --the tapping size for M5 x 0.8mm.
Used an endmill to cut a pocket for the head of the clamping bolt.
With an arbor, I set up a slitting saw in the Taig lathe. As the lathe is completely modular, it's possible to mount the milling vise to the crosslide
The crosslide allows for easy control over slot width.
Cut a piece of 3/4" aluminum plate--this will be the actual shoulder piece --and faced both ends to get 90 degree corners.
Found the mounting hole location and through drilled. Note the bolt in the drill press table--ideally it would be a taller brass stud(--non marring). It keeps the work from becoming a helicopter on the drill bit.
Through drilled with the 4.2mm bit. Trying to standardize the threads on the buttplate. With just a couple exceptions, most all the fasteners being used are M5.
Tapped. The upper shoulder piece will bolt to this adapter.
Still in the rough. Man, the finishing is gonna just about kill me.
A hasty assembly.
The plan is to contour the ends of the lower blocks to fit the shoulder and add some side taper to reduce their width--then put a satin finish on all the aluminum.
Before that happens, I need to make the baseplate to attach this whole mess to the stock.
Check back in a couple days.