It's been a while so heres a little update.. been working on the Z axis and also repairing my mill in the meantime as I stripped the plastic gear on my Chester champion.
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But it's not moving very freely, I have clocked the rails up within 0,01 and put it all together including the ballnut and tried to push it up the rails, I could just about move it but it didn't feel very nice, I took the plate off and greased the carriages, and tried the rails on there own. one felt lovely and smooth but the other felt notchy on one of the carriages. So I carefully removed the rail and it appears as though I have a ball bearing missing!
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Would this cause a notchy/stiff feel in the carriage or have I got other problems? I measured one of the ball bearings and it was 3.98mm so am I right in assuming 4mm. This is the first time the rail has been off so it must of been missing when I got the rails and if it hadn't been for the notchy feel I wouldn't of taken it off so please no telling me off for removing it :-P

Cheers, Charlie