Are you putting a roundover on them or just leaving them square and smoothing out the corners? We have a DVD that shows how to put an edge detail and a polish on granite. Try this:
http://www.defusco.com/howto-dvds-tool-packages-c-654.html?osCsid=4e0e4ac7c5f406a8a79f51c8a0d530d5The first DVD covers your question. The tools you will need are in the first tool package, unless you also want a router bit :
http://www.defusco.com/diamond-products-grinder-shaping-bits-c-25_621.htmlLet me know if you have any specific questions.
Mark