DIY straight edge with Epoxy+ aluminum profile. Will it work?

[mekanik]

Hi Don't see much of a problem here, you say width of rails 1160 so your straight edge will span that distance, to ensure the 1800 rail is straight set the master rail onto the grout leveled frame member and lightly clamp both ends, drill and tap the frame for the hole in the centre of the rail, work your way from the centre of the rail to the ends drilling tapping correcting and fixing the rail as you go, you will have a section of rail that can be verified straight with the straight edge, all you have to do is extend the straight edge 200mm each end to set the remaining portions of rail. the second rail can be set using a fixture with carriages set on the master rail and on the one your trying to bring into spec, most find that using the gantry works OK.
Regarding drilling and tapping you need a couple of jigs that will align in the countersunk holes of your rail, one to align the drill and one to keep the tap vertical.
Regards
Mike