My pottery work does involve a lot of slab work. My mugs, cups, boat bowls etc.. are all cut out from slabs of clay.
I have always used sheets of plastic or stiff paper on the clay and cut with my knife. Works great, but when you have to do hundreds of these it can get very tiring.
I made these template cutters similar to tile cutters. I initially got the idea from seeing a video where stacks of denim fabric were being cut into templates for legs, pockets etc... with these hydraulic cutters.
I made these cutters from wood and some out of chopping boards and metal straps. It takes time making one, but it sure speeds up the process. I used them extensively in 2014 and am making similar ones for all the pieces I need to cut.