Why a screw worm gear ring interference fit to cast iron core wheel side bias
If a good joint center screw hole machining thread, unequal impedance force on both sides of the drill bit
The drill can tilt to the side of the crown, in order to reduce or avoid this happening so the hole center bias cast iron wheel core side.
General assembly of worm wheel core steel or cast iron, bronze and crown, the hardness is much higher than the latter.
