chuck back plate adapters

[petertha]

Looking for some input. I purchased a dividing head with 1.5–8external/male threaded spindle. I’ve been eyeing a 5”chuck to use with it. A semi-finishedcast iron back plate was included with the DH & they are also commerciallyavailable. It’s already threaded 1.5-8 but the rest of the surfaces are notfinished. From what I can tell, if I selected a plain back chuck, I would have tomachine the back plate on all surfaces including a ledge on the front face thatmatches/engages a recess in the chuck back, plus drill/tap the chuck mountingbolt holes.

I’m only guessing here, but maybe these semi-machined platesare more intended to be finished for end use on lathes with 1.5-8 threaded headstock? Ie. screw the rough plate on, machine the OD, face & ledge. Then it’salready axial & ready to mate to the chuck flush?
But my lathe is D1-4 so not really an option that way. Howwould I mount the rough plate properly in my lathe chuck to ensure the ID threadsare perfectly axial before carrying on with the rest of the machining? I canvisualize gripping it, but could I expect to accurately dial in on the skinny,winding ID threads? I thought about making an adapter stub with 1.5-8 threads& similarly screw the plate onto that? But for that effort, maybe better tojust start with a slab of material & machine the ID threads + OD + face stepall in one turning operation? I don’t see fully finished 1.5-8 backplatesavailable. You can get a ready to mount 1.5-8 threaded chuck, but I think theyare kind of integral/permanent?

Which brings me to issue #2. Ideally, I’d like to alsoutilize the same chuck body for a rotary table or even on the mill table. Itwould be nice if the 1.5-8 backplate could detach, leaving me a flat datumsurface on the chuck backside to mount directly or a separate (non-threaded)plate. Hope this makes sense.

 

[chipenter]

You didn't say what mounting your lathe headstock has , I cut a mounting for my dividing head on a Morse taper blank arbor , that can go in the head or tail stock of the lathe and the mill .

 

[petertha]

You didn't say what mounting your lathe headstock has , I cut a mounting for my dividing head on a Morse taper blank arbor , that can go in the head or tail stock of the lathe and the mill .

My headstock is MT5 spindle, D1-4 mount. Can you show a picture or sketch of what you mean?

 

[deverett]

The most positive way involves making a dummy spindle with the 1-1/2" x 8 thread on one end. Hold the stock in the 4 jaw chuck and dialled in to zero. Cut the thread and then you can use your new dummy spindle for all your backplate projects. Don't forget to incorporate the chuck register behind the thread.

Dave
The Emerald Isle

 

[chipenter]

Sorry your lathe is bigger than I thought , having looked at the arbors http://www.arceurotrade.co.uk/Catalogue/Blank-End-Arbors mT3 is just to small at 1 1\2 inch , mine is 1 inch by 12 tpi a lot smaller than yours .

 

[pkastagehand]

As Dave said, make a dummy arbor. I did the internal threading and back seat on my backing plate, testing the fit on the dividing head till I got that right. Then I used that as my thread gage for a stub arbor. Put a slug-o-steel in the chuck of the lathe and left it there through the entire remaining process. I turned diameter, shoulder and thread of the stub till my plate fit properly. Then I put the backing plate on and left it there and turned the all the features needed on front and edge to fit the little chuck I was mounting.

Paul