My wife started to work with clay - and to make 'plates' she is using a Roller Pin. With wooden sticks on the side she tried to get the same thickness over the whole plate! Often the sticks slid away so that was not the ideal solution... Therefore I have created some Rings to increase thicknes by 2mm, (Ring_1) 4mm (Ring_2) and 6mm (Ring_3)

The diameter of the rolling Pin is 9cm, I have also added the 123d Design files if you want to adapt to your needs! Printed on Makerbot 2x, ABS 230 degrees Nozzle, 110 degrees Printbed. 2 shells and 10% infill, no support, no raft! 0,2mm print height