Update
Geeze it's hard teaching yourself some of this stuff, youtube only goes so far The little motor had some "give" and "play" so any wobble in the discs could be "pushed" out with a little bit of pressure, not so with the "beast" everything is so straight and tight, any wobble shows up like the proverbial dogs balls. Tried ordinary 1/2" nuts,but they aren't square enough, so I had a couple of 50mm threaded flanges made up, bit better, but still not great. Another hit to the c/c and bought a master lap from Gemcuts, locked that down against a 50mm flange, dropped a disc onto that, locked it down with the other 50mm flange and it runs very straight and true, probably not true enough for facetting, but ok for cabbing