Thanks Mike, the collet is and was tight, always use spanners and make sure I give it an extra tweak just to make sure, but I will put a mark on it on the next run,
Motor clamp is tight, two alan bolts, but again I will mark it, although if that was loose with the weight of the motor I would expect that to fall or at least for the milling bit to be on the wood.
Z axis ball mount nut, and mount look okay.
I have the step motor off now, the drive coupling are tight on the shafts
The last three items on your list I have no idea what you mean or how to check.
The step motor is very easy to turn and I did wonder if the speed had something to do with it, i.e. as the motor lifts to clear the wood the force pushes the motor a couple of clicks more than it should, which is why it does not happen if I slow the feed rate down, I did think that the motors were braked when the power was on to the machine, well that seems to be the case.
This is a dam nuisance as I am having a cabinet built from alloy and perplex so once its running and the suction is on I could leave it to run, especially as I have all the saftey switches on.