"Ernest Christley" wrote in message
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My biggest concern is the inside tube not being strong enough and taking a
slight bend over time. Then it will no longer slide. Hence my question.
If it were a straight beam, I think I could run the calculations, but how
do you analyze it when the cantilevered beam isn't straight?

Divide the load in to two componants - the load normal to the beam (bending
force) and the load parallel to the beam (tension). The compression load on
the bottom face of the beam will be somewhat reduced by the tension and the
tension load on the top face will be somewhat increased and the sides of
your box will carry shear plus tension.

If your beam is 40 degrees from vertical, the bending force would be the
load (I think you mentioned 300 pounds) times the sine of the angle and the
tension force would be 30 times the cosine of the angle (I'll let you do the
math). (assuming, of course, that I am drawing the picture correctly in my
head) It would be reasonable to assume that the tension force is carried by
the entire cross section of the square tube so divide the force by the cross
section ((width + height) * thickness) and add that stress to whatever
stresses you come up with from the bending.

Or, you could clamp the bar in a vice and jump up and down on it.

--
Geoff
The Sea Hawk at Wow Way d0t Com
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