Back Thrust

Unlike the B2 the C3 has a back thrust consisting of a crown casting and a hardened steel mandrel insert. It is adjusted to leave a very slight well oiled gap.  The crown screws on in place of the removeable false mandrel and should be fitted when general turning is being undertaken as it takes the load off the bearings.  The power from the headstock pulley is then transmitted via the spur gear to the  worm on the front mandrel,  then via the worm wheel on the screw cutting spindle which bears against it and down through the reversing gearbox to the leadscrew itself.