What is the best way to mark out for bearing blocks and linear rails?

[EddyCurrent]

Hiwin type rails have one side ground as a datum side, same with the bearing blocks. So I laid a straight edge along where the rails would sit and clamped it at each end, then the rail was clamped to the straight edge using the datum side. I used a drill the same diameter as the holes in the rail to spot drill the underlying metal giving a dimple the same as you would get from a centre punch, then I drilled the dimpled holes with a tapping size drill right through. Becaue my X rails were mounted on 3mm thick box section I glued a piece of 30x6mm flat bar inside using Gorilla glue, the Y rails were mounted on aluminium that was 6mm thick so was okay on it's own. Bearing blocks were marked out as you say with a printout, I counterbored the aluminium to make the cap head screws flush, you need a bit of adjustment for the bearing blocks so the mounting holes don't need to be a very neat fit. I finally tightened the bearing blocks down once they were mounted on the rail but first made sure the datum faces were on the same side so I could also use a straight edge along them, i.e. 2 blocks per rail.