Well here goes... Aluminium frame router design

[IanS1]

This is what I had in mind, There will be aluminium blocks in each end of the X box section tapped to accept the the two bolts through the legs?

As Jazz as pointed out, the more adjustability you have, the better. Cutting and fixing the ends of the X box section the way you have drawn could make the adjustability more restrictive. Also, bolting through the end uprights may cause the frame to warp as you tighten the bolts.

[EddyCurrent]

Your frame is similar to mine, this is what I did;

http://www.mycncuk.com/threads/6565-...2425#post52425
But I also welded matching 10mm 'pads' onto the underside of the X box section, http://www.mycncuk.com/threads/6565-...4294#post54294
That was a mistake I think ! http://www.mycncuk.com/threads/6565-...4024#post54024
I always intended to use epoxy as well.

Instead of welding to the underside of the X box section, I would glue a piece of flat bar inside it using Gorilla Glue, similar to this ; http://www.mycncuk.com/threads/6565-...4981#post54981
because it increases the wall thickness of the box section allowing a secure fastening through the plates welded to the top of the legs.