[Tristan Lall]

If you haven't already sent it off to be machined, there are a couple things you might want to change.

Firstly, are those recesses in the outer extremities of the frame for the bumpers? (The frame looks like a tall-section C-channel.) If so, that's a bad idea. The bumpers need to be on the frame perimeter, per <R07K>. (As usual, there's some ambiguity as to the precise meaning of that requirement at a formal level, but to err on the safe side, your design probably wouldn't satisfy the rule. That configuration has been allowed in some past years, and disallowed in others—but that's because the rules have been subtly different. Using last year's interpretations as a guide, your design is probably not legal on that count.)

Also, if those recesses are for bumpers, they appear to be a little bit too high. (The bumper zone is between 1 in an 7 in from the floor; since your bumpers are approximately 5 in tall, you need be careful about the top being too high off of the floor.)

As for the lightening triangles, good thinking—but put a big radius (R0.25 in is pretty good, and bigger radii are better in this case) in the corners, for stress relief. This can prevent cracking if the area is subjected to repeated or large stresses. (Also, if it's being machined on a milling machine, there won't really be any simple way to approximate a sharp corner anyway.)

The numerals are cute, but they'll also be invisible behind your bumpers. Lose them—at that size, they're just diminishing the rigidity of your frame members unnecessarily. If you're using them for lightening, try a more conservative pattern of holes or triangles instead.

If you're using a plasma or laser cutter to make the shapes in the aluminum, beware the heat affected zone. (Material properties will diminish in the area of the cuts; the metal will become weaker.) CNC mills, routers and waterjet cutters tend to be nicer for this kind of work.

Are those big pieces of angle (the dark grey ones in the centre) supposed to be steel? If so, why?