I made a back plate for a 6" 4 jaw chuck from a bit of scrap steel 250 mm dia x 80 mm thick, as it had been flame cut from a sheet of hot rolled steel the start of the cut was in my bit of scrap, so I had to mount it off center, and work in low back gear, took a couple of days to end up with a very servicable back plate, thread cut and all, my first internal thread. Think the hardest bit of the job was carrying the lump of scrap around town until I got the bus home, thats a heavy bit of metal. Ian S C