This was the final design we ended up using on the MSE Printer. It's pretty elegant, actually... The pieces that hold the frame also act as bar mounts and motor mounts. The glaring issue with this:
It's hard to put together!
Because the mounting features of this frame are composed mainly of blind holes, the only way to have everything fit is by assembling everything all at once. For example, if we push all the aluminum angles into their respective holes, there's no way to insert the linear rods.
This lead to an awkward dance of sandwiching the printer together, and brought about what is most likely the biggest failure of this printer.
Everything. Is. Glued. Together.
We had always planned on gluing things in place -- it's a cheap, easy way to secure things! The problem is that now the frame and rods are permanently affixed... and if one of our axes needs to be replaced, the printer will likely have to be broken apart.
Unfortunately, we were late. This was a school project, and we had deadlines to hit. So, we did what any student would do:
We said "Fuck it", and glued it anyway.