Got back to my X1 mill and tried JohnS suggestion to reduce the acceleration. Tried a search on the web, not a lot of help so just winged it. Also tried JohnS suggestion about the spaced under the z-axis and it definately showed it losing steps on the up direction.
Thought some more and have now tried a dial gauge, and old one I have had for some time and never found a use for in that it works by pulling up the plunger. So I fixed the plunger rod to a chuck in the z-axis and proceeded to raise and lower the head, could not detect that much change but it did alter over 10 cycles, ie gets lower.
I then thought about the gibs and tried to adjust them, this has made it worse.
I also noticed another strange thing in that if I jog up or down using the slowest jog rate the dial gauge shows the head to move in the same direction for a few steps after I have changed direction?
I have read on the web that some have had problems with the head gibs saying that are difficult to set due the weight of it. I may now have to consider a counter weight system as for what I want the mill for a poor z-axis is next to useless.
Peter