pic: 2791's Brand New Arm

[Ian Curtis]

Originally Posted by James Tonthat

Flanges and more material, not more thickness.

Flanges are where you'll get the most bang for your buck. Once it starts bending with no flange, there's not much keeping it from continuing to bend. With a flange there is more material that needs to fail before that bending can continue.

Mathematically, bending depends on the moment of inertia, all other things being held equal. The moment of inertia of a rectangular section varies linearly with the length of the edge of rectangle parallel to the direction of the moment, and with the *cube* of the length of the edge of the rectangle perpendicular to the moment. That probably doesn't make a lot of sense*, but it gives you a *huge* increase in strength for a small flange that runs along the edge of you aluminum arm.

*Because I can't explain it well, not because it isn't true.