No need to break your brain if you use sensible units such as the British standard fat bloke

The standard fat bloke weighs 16 stone which translates conveniently to a downward force of 1000 Newtons.

Direct drive on to a 5mm pitch screw requires 0.8 Nm of torque to lift one fat bloke off the floor.

Look at your cutter in it's collet and ask yourself, how many fat blokes could stand on the sharp end of this before it snaps?

Multiply by 0.8, call it Newton meters and anything above that is superfluous.