Plenty of info to answer your question. There really is very little maths, it's a method described by Bill Wilkins in Model Engine Builder mag No 7 and made popular by Randall Cox on his "Hoglett" and "Open Six" engiens engine. You can buy digital back issues.
I did draw it out for someone but will have to see if I still have the image. Works well though, this is a 3 lobe cam done that way




Edited By JasonB on 19/08/2015 13:57:08