Z axis error woes

[Jonathan]

If the rails are not parallel then

If the rails are not parallel then it wouldn't be able to move, assuming you mean rails parallel to each other. If not, rails parallel to what?

[Swarfing]

It will cost nothing to check the bearing holders placed on a rail supported across two supports of a known height surely. The exercise here is to eliminate what it is not so that what ever is left must be the issue?

[JAZZCNC]

Ok first Jonathan is correct.! We are talking about the planes the rails are on rather than being parallel to each other.

Think about it more and you'll see that after surfacing the bed theres no way the bed plane can differ from the rails plane.!!

Would we agree If the rails are level and correct and on equal planes along there entire length then the bed will be surfaced level and the distance from spindle to bed will be the same any where on the table.? . . . Well the same apply's if the rails are not on equal planes after surfacing.! The cutter as machined the bed into the same plane as the rails so therefore the distance from spindle to bed must be the same. . . . .Cant be anything but.!!

That said I'm not saying it's ok and everythings ok having it like this, it's bad because you can't machine anything truely flat and parallel but in this case it's correct or I'm(WE) are right that the distance will be the same.