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Originally Posted by Kevin Sevcik
While it is, indeed, very rigid and durable, it's not the best strength/weight option out there. A simple hollow square aluminum extrusion with the same weight per linear inch is going to be stronger than an extruded profile like this, because it will have all its mass at the outer extremities of the profile instead of wasted in the middle.
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This is true. However, you need to ask yourself, what is strong enough? I did this year... and I found a result that I like.
The moment of inertia of 80/20 1010, which is 1" x 1", is .04413 in^4
The moment of interia of 1" x 1" x 1/8 thick box is 0.0570 in^4
The weight of 80/20 1010 is 0.495 lbs / ft
The weight of 1" x 1" x 1/8 aluminum box is 0.511 lbs / ft
I would say that these two are comparable. However, after I've done some calculations, I actually think that 1" box
and extrusion is overkill. 461 is going to use 20mm aluminum this year on our frame from Bosch.
20mm Bosch Extrusion
0.269 lbs / ft
Moment of inertia = 0.016 in^4
Quick number crunching calculation...
Let's say the 3' side of your frame has a robot ride up and apply all 130 lbs on one side right in the middle (worst case)
Stress at the ends and at the load point for a fixed end beam with a load F at the center, length L and section modulus Z (I / y) is:
F*L / 8 * Z for ends, -(F*L / 8 * Z) at load point.
20mm Bosch
(130 lbs * 36 in)/ (8*(.016 in^4)/(10mm/25.4mm/in)) =14,395 PSI.
The tensile stress for 6061 aluminum is around 30,000 PSI... I would say that 20mm is safe enough. Factor of Safety around 2ish... before bending would occur in the aluminum. And if it bends... you replace it. It's quick.
Using 1" box with 1/8" walls:
(130 lbs * 36 in)/ (8*(.0570 in^4)/(.5 in)) = 5,131 PSI.
Factor of safety around 6ish... that's a bit much for me.
My two cents.
Good luck everyone!
Matt