Humble Beginnings - For Alu

[D.C.]

Yup that is the one.

If you are mounting a metal frame on top of two bits of what looks like wood... Don't.

Wood swells and expands depending on moisture content, the arrangement you have will warp the frame and throw your rails out of alignment. You also have your linear rails going over a joint. Don't do that either, unless you are going to take your frame to a big engineering shop and have the whole thing surface ground you will have zero chance of fitting the rails properly with that arrangement.