Move to Go. Do not pass Go.
OK, so I'm about back to where I was before, when I was racking the machine and trying to bend the ball screw out of true. I've got the machine moving smoothly and I'm setting up homing prior to figuring out the limits and setting the soft limits and I've hit a snag, done some reading to avoid wasting the time of people and I'm not confident yet.

Problem is dual X axis homing, Z homes OK, Y homes OK, when I select X home, (thankfully at 2% speed) the maching starts to rack as one X axis motor is turning, the other isnt. The weird thing is that under jog movement they both move together, so now I'm into the Mach ports/pins and homing screens. Ports and pins I have X and B axis configured correctly I believe, they move on jog so I'm OK with that, Z,Y,X Home I have values and the diagnostics page in Mach confirms they work and Y and Z home OK anyway. I *do not* have a home input signal for the B Axis as I assumed that as its slaved to my X axis that would be OK, clearly its not so I suspect I need to add input signal values for the B Axis and copy the X Axis home port and pin setting to fool mach into seeing the same switch? Is that the answer? as always advice appreciated, thanks.