After dismantled the axis and checked the lead-screw for damage, it was dead straight? I checked the motor and sent a current through to set it spinning, the coupler was wobbling! How can it be off centre? I first thought that this was due to poor manufacturing considering I had already been dealt a bad hand from the Chinese supplier of the supporting bar which had differences in diameter but this was not so. I had a theory, was the worm screws in the coupler holding the lead-screw off centre? You would need to tighten each one an equal amount to hold the lead-screw dead in the middle. My research on the internet confirmed by theory and suggested a different type of coupler called a ‘clamp shaft coupler’ which, as the name suggests, clamps down over the spindle and lead-screw keeping both centred. I put an order in for a couple to be on the next slow boat from china.