Rigid Square-Tube All-Metal Frame for DIY Projects (3D Printer, Metal Frame Furniture, etc)

Update 30/03/2016: I have added this design to Sketchfab for easier 3D viewing: https://skfb.ly/MB6I

Because I can't find aluminum profiles suitable for such projects in my area and, because i know that if here in Western Europe there are still many places which the T-slot/V-slot ALU extrusions are no where to be found, I thought about using the next best thing and that is ALU/Steel square tubes that anyone can find in a hardware store.

I have looked online only to find that all connectors are being plastic, 3d printed or simply bought from the same hardware store supplying the tubes (which is still some sort of plastic -ABS maybe) and I didn't like that.

I wanted an all-metal sturdy frame capable of holding tools or vibrations (3d printer) or just its own weight (furniture: cabinets, etc).

I also wanted a solution that can be easily scaled up without changing the layout of the existing patterns, whatever partition one would like to create.

My solution to this dilemma involves two types of tubes (two patterns of holes that is):

1. Tubes that have 4 holes at each end, two+two for receiving the two threaded legs of U-bolts;
2. Tubes that only have one hole at each end, hole that will receive the bolt that the U-Bolt will lock to when fastened.

The hardware involved is as follows:

• steel/alu tubes, two lengths (L1,L2);
• Long U-Bolts that can fit inside the tube, flush with its face and length that would allow it to span the square dimension and the distance from the hole to the edge of the profile. I used in my design an U-bolt that had M4 threads and a curvature diameter where I could fit almost perfectly an M5 bolt's threaded cylinder;
• Nuts for the U-Bolts (M4 in my design)
• M5 bolt + Nut for the U-bolt's stopper;
• M5 Hex Coupler of a length that would clamp the U-Bolt to the tube's face. This can be either a cut-to-length Hex Coupler or a similar length stack of Washers and/or Nuts.

Note: the need for the hex coupler is dictated by the fact that without it the tube is free to move on the bolt's direction. This might not be a practical issue once the U-Bolts are fastened with locknuts but just to be on the safe side and to accommodate the higher precision needed by machinery like a 3D printer for example. This setup doesn't allow any tube to rotate around its axis or translate along any of his edges. It should be like a single piece of metal carved out from a block.

I have uploaded bot an STL to exemplify (with a nice exploded view of one of the planes) and the RSDOC file I used to build the CAD of the design - you can download and use for free the DesignSpark Mechanical to visualize that one or modify or play with it as you please).

Please let me know if you know of or have an even simpler solution that can be scaled to as many partitions as one needs, keeping the number of individual parts as low as possible.