In order to make a structure "sturdy", you need to identify any "degrees of freedom" it acquires and eliminate them. Often than not, eliminating undesired degrees of freedom (aka wiggle) involves fixing the distance between two identified points in the design.
This could be achieved by connecting these two points with a rod of a solid material (such as metal). Since a metal rod cannot be compressed nor stretched easily, the objective is achieved and the wiggle is eliminated at a trivial additional weight (especially if the rod was hollow, which is the approach advised in this instructable).
In this instructable, I will be teaching you how to turn a light-weight, soft-metal tube such as those out of aluminum or brass into a support beam to support any kind of form you are working on. I have used this method in many cases and it has always given me excellent results. In the main photo above you see a handle that I designed with such beams which allowed me to use it to carry a 40 kilograms apparatus without flexing.
So let's begin!
Step 1: Get What You Need
Light aluminum and brass tubing is common and easily obtainable through hobby and building-material stores. I recommend aluminum tubing from building-material stores as they are very cheap and do the job well. A 3-meter length of tubing costs 10 AED in the UAE, which is equivalent to $3 US.
As for a pressing die, any two cylindrical pieces would do, even if out of wood. In my case, I decided to use a weld-on-type door hinge which I purchased for 5 AED ($1.5 US).
The good thing about door hinges is that they can be used to press and to stamp (more on this later in this instructable).
Once you have your materials ready, make sure you have a vice nearby and let's get started!
Step 2: Cut the Tubes Into Length and Press the Ends
To flatten the ends of the two pipes, just press them tightly on a vice (watch the video).
Step 3: Mark the Center Zone (for a Cross Brace) and Press It Flat With the Die
Once the ends of the tubes has been flattened. It is the time to arrange the pipes in their assembly position and mark the center zone on each tube.
Once marked, use the pressing die and a vice to flatten that center zone on each tube (watch the video).
Step 4: Optionally, Stamp the Ends and the Center
This is an optional step, and mostly an experimental one.
Since I got a door hinge as a pressing die, I thought of using the mating interface as a stamping die. I used this technique on both of the ends and the center zones (watch the video).
This allowed the centers to align themselves once pressed against each other.
Step 5: Center Punch, Drill and Rivet the Center
Riveting is a good way to go about assembling the cross brace if you're making one, it is permanent and really strong. I used 4mm rivets.
Step 6: Drill the Ends and Attach to the Structure
To demonstrate the effectiveness of this approach, I used the fabricated cross brace to enforce a weak frame made out of MDF. Furthermore, and to solidify the point, I abstained from using threaded fasteners but rather used free-rotating "split pins" as the main mean of assembly, hence providing a better proof of the rigidity contributed by the cross brace.
At the end of this instructable, my hope is that you'd see how effective and economic this approach is. If so, the please share photos of what you build with this technique and any modifications/improvements you have in mind. Thank you!