Thank you jazz I did try a test piece on an off cut of profile but the rails are just too wide for the 40 mm side of the profile and do not line up on the 80mm side anywhere I could get a good fastening on both sides of the rail.
I will think about how I can do it.
Also what about the ideal hight for z axis from waste board to the bottom of the gantry. As I am looking for fine detail first and rigidity and height second.
Albert