If its a good grade of ally it should be ok. I cant imagine anything in an ER32 creating untenable flex through a lump like that. In industry you wouldn't, due to considerations of durability and resistance to dinging etc but in the home workshop with it's typically low use rates and careful owner care should be fine I reckon.

Although I have an ER32 collet chuck I usually use a Stevenson's square ER32 Collet Block in my 4-jaw chuck. Or, if not requiring the greatest accuracy, a hex block in my 3-jaw.

The aluminium will make perfectly good backplates for smaller lathes. You can try a test cut in the metal to ensure it is nice to work with or not. I doubt if the aluminium would be a nasty soft type to machine grade seeing where it came from.

Take the jaws out of your chuck, assuming that you have some external ones and place one at the radius required by the workpiece. You can assess the number of teeth on the jaws which would be engaged by the scroll, it may be enough for safety. I would not be happy with less than 3 teeth engaged. You need not tighten the jaws much to allow facing cuts and maybe reduce the diameter carefully and then turn the work around. Three flats would certainly be a safe way although the work would probably run eccentrically at first.

Go for the three milled flats then, they only have to be as deep as the ends of the jaws and will not matter with a small er32 plate. Shame about the thickness, though. I would stick a parting blade in about 1/4" and use the groove for a hacksaw guide. I bought some Starret blades for plastic and aluminium with 14tpi, but even with those it would take a long time to cut. If you go for partial parting, then use the tailstock to steady the work, it will be safer.

I would be inclined to buy a backplate from Warco ready to go. You then just have to machine it to fit your collet chuck. Did the same for my WM250 some time ago. Details here *** Fitting Collet Chuck ***

John

Hi Derek, you could cut as deep as you dare with a parting blade and drill and bore a hole in the centre as big as you need to the depth of the thickness you need, that way you would have less hacksawing to do.

Regards Nick.

Edited By Nicholas Farr on 03/06/2022 21:12:33

Ideally, the backplate should start by being machined to fit onto the spindle of the lathe.

If a flange fitting, first machine a register that is a tight fit on the flange. (If it can't be fitted into a chuck, mount on the faceplate, and centre as well as possible ).

Having fitted it to the spindle flange via the new register, you can then machine a register to take the collet chuck backplate.

It will be worth boring the middle of the backplate to at least the same maximum bore of the spindle, so that you can pass long work through the spindle bore..

Hopefully, when you clock the internal taper to check concentyricity, there will be almost no fluctuatioinnofnmthe needle.

Howard