Well, I've had the wood cut at B&Q, and found that the operator has used the wrong side of the blade to make measurements. The upshot of this is that all the dimensions are 2mm less than my requirements!

I didn't think much of this until I tried making up a Y slide, and found that the base is too narrow - by about 2mm!

Anyway, apart from this, I am having a problem I was dreading when fitting the second guide rod/support to the slide. I used epoxy glue to give the guides an even bed to sit in, and the upshot is that the supports have warped (just a little). I have glued one rod/support to the base and am now trying to fit the second.

However hard I try, I cannot get the 8 bearing runners to stay tight against the guides across the full travel of the slide. How difficult can it be?

I know I need to check squareness, but is there anything else I should do? I have heard about having to "shim" the runners?

Unless this is solved neatly, I think I may have chosen the wrong design based on my abilities. I hope not as I have £70 worth of 12mm guide rods...