How to cut through hard plastic sheets with out cracking.?

Most harder plastics can be cut just like one would cut glass. Score it with your Stanley knife then snap off the plastic along the scored edge.

If you are not comfortable using this method, then you can cut the plastic with a circular saw with a hollow ground blade on it. Using a regular wood cutting blade will melt the plastic as it cuts it making a sloppy edge. A hollow ground blade will cut through the plastic cleanly.

I put a grinding blade on my circular saw, works great, like a chop saw blade, available at any home store or hardware. 7 !/4 " works good for plastic, vinyl, metal...etc.

a straight edge and a plexiglas or lexan scoring tool--these are sold at any diy box store or hardware store

a fine cutting blade on a circular saw or a jig saw .. a box cutter will not do it ...