Don't even trust the % that allakhazam posts here. It usually works out. I've tested it with fletching, and it's impeccably accurate. (if thats even remotely close to how its spelled).
But these bow cams, I had someone do these for me today... they had a 252 skill with mod. so theoretically, a 92% chance of success.
Out of 12 planar steel combines, 3 e'cian ice combines, and 4 molten metal combines... i got 5 planar steel and one molten metal cam. and we were grouped, so i saw all the failures happen.
Thats a total of six successes out of ninteen combines. take that as you like, i know there was some bad luck in there, but if its consistant, i don't call it luck. The percentage for success is nowhere near 90 or 92% if your skill is maxed or pushed over to 252. I don't see how it could possibly be more than 60%.