Latest step in making this as Requested and 2nd update.
I had completed a couple of tasks which now gave me time and space to continue. I used Colejaws to first hold the 10"/250mm platter blank to form the first tenon and rough the surface (those photos are on the mobile have yet to down load). Then forming a second tenon as I am trying to obtain two platters out of the one blank.
The tenons size matters as does shape of the same as centre stands must fit, all will be revealed as the work progresses.
I used a 3 mill parting tool to the depth of approx 2"/50mm then a pull saw at low revs to complete the parting. I achieved a fine pair from the parting, not totally matced in thickness after turning a thickness of approx 8mm for one and about 6mm for the second platter.
I sanded the first platter down to 400 and have used 2 coats of Organ Danish Oil to this stage sealing and stabilising during this lousey weather. Having rained for 3 weeks with only a few days or part days of sunshine for the last days of summer and first days of autumn.