And your blade will effectively be a wheel, with the work piece as a brake.
High rpm with low torque won't be terribly effective I don't think.
If I was going to do something like this I might use one bike as a power plant and run chains from the rear cogs to the front cogs of 2 other bikes, assuming 21 speed bike used as the main drive one rear cog would be taken to drive the rest of the cassette and then the gearing for the other 2 could be fairly adjustable using the gearing the bike comes with to drive another chain to the motor, a drive belt around the rim or even direct friction drive from the Tyre.
I would probably just saw off the rear triangles of the driven drive trains and fit the rear gear lever to what was left of the frame.