You may well be right George.
I'm struggling with how the Sorby plate guarantees you will be at 90 deg to the sanding disc.
If I'm right the Sorby plate fits in the tool post ?
If that's the case then I can move my tool post to any angle I like (within reason) so how am I going to be sure I'm 90 deg to the sanding disc ?
Am I over thinking it ?
If I'm being dense here just tell me, I'm from Yorkshire and have a thick hide 