Mounting a chuck on a Rotary table

[black5f]

A drawing (of sorts) of the other idea. Make the plates, drill tap etc and put a hole in the middle of each. If your not confident of the accuracy of the plate, make a mandrel, bit of bar faced off, drill and tap centre and bolt (counter sunk) on each plate in turn and very gently face off all 4 surfaces so chuck will be dead parallel to face of table?? Apologies for the crude scribble! I have no idea of your skill on the lathe or your.. if you're like me, incredible scrounging skills and alergic to buying things when you can spend 6 months making one! But just to add, 120 deg holes are very easy. Again, 3 jaw chuck and mandrel you just made with a plate bolted to it through the centre in lathe, get a bit of scrap bar (or a snapped off pencil) that just fits between a flat conveinient surface like the bench and the chuck (lathe) jaw. Turn the lathe off! Hold the jaw down on the scrap so its wedged between jaw and bench and using the crossslide and a sharp turning tool, scribe a line with the lathe tool. Turn the chuck till the next jaw rests on the scrap, hold and scibe again, then do again with the final jaw = 3 x very accurate lines at 120 degress apart. Decide where the bolt centres will be, set the lathe tool to the right diameter (PCD) and rotate the chuck by hand marking the hole centres?
Hope this is of some help.