Peter, the disc should just peel off, I used to have to peel them off and glue the new one one when I was a kid.
The grinder come with two large balanced cast iron (37cm diameter) discs, ans a
Clamp plate to make sure to remove all air bubbles from under the disc when glueing disc on grinding wheel.
They used 40 grit to sharpen combs and used 80 grit to sharpen cutters.