ha 720 would get nowhere near 10mm of bite unless it was moving forward at a rediculous speed *waits for smart arsed comment from mouldy*

Tooth engagement is a balance between forward velocity and rotational velocity. I wrote a big post on it a while ago.

Energy in a disc is all about the moment of inertia of the disc. A useful tool to work it out is here, granted it's all in US units but you can do a quick conversion

http://www.teamcosmos.com/ke/ke.shtml

For reference, the original hypnodisc had around 6kJ of kinetic energy, typhoon 2 could store 40kJ, boner's drum when it was doing a few thousand rpm was 0.7kJ, supernova in robot wars was around 30kJ, middleweight typhoon could store around 12kJ.