Chuck Adaptor for Rotary Table

Possibly start by looking back at the thread entitled "3 jaw chuck for rotary table" started 10/08/08 (10th August 2008), or maybe 08/10/08 for those in the US.

You're not likely to find "plans" for this
If I needed an adapter plate, I would measure my existing rotary table, measure the chuck to be used, and sketch the adapter using those dimensions.
Proceed to shop. Get dirty. Make mistakes. Learn from said mistakes. Rinse. Repeat as necessary.

When I needed one, I just used one of the dummy spindle end replicas I'd made of my 9" South Bend's spindle nose when I was making chuck backplates. Made up a locking bar to fit the table's T-slots, cut a slot in the end of the replica for the bar, turned it down to fit the table's recess, bored a hole lengthwise for a big Allen bolt in the thing and tapped another in the bar and I was done. Took all of an afternoon, most of it on the shaper cutting the slot for the locking bar. Locking bar was just a chunk of hot-rolled construction scrap my dad had dragged home. If you've got a cam-lock mount on the lathe, it's gonna get a lot more involved!
Stan

I needed one of these and made one up by trial and error from an old brake disc I had lying around.
Clean up disc faces in lathe, remove backplate from chuck, Machine disk bore (where it fitted on hub) to fit a register I found on chuck. Drill disc to suit tapped fixing holes in rear of chuck and bolt up. Drill holes in friction area of disc to match T-slots in table - oversize to permit some movement for centring. Oviously doesn't self-centre but I centre it with a dial gauge - on the work-piece, to overcome chuck errors
Crude, but it's served me well for a long time.
EK