Best wood for long shelves

[Robert Bonomi]

Yeah. other folks thought you meant 1/2" _thick_ steel -- a continuous piece running the length of the shelf.

[Joe Barta]

1/2" thick angle iron... in a shelf? I can't visualize that. What are the length of the legs and how would it be oriented?

[Mike Marlow]

D'OH!!!! Color me the same color as a brain fart! I'm thinking 1/2" thick steel - and wondering why anyone would want to do such a thing. Some days are just really bad...

[Chris Friesen]

The angle iron has a modulus of elasticity that is about 15 times that of wood.

That 1/2" angle iron gives about as much strength as a 1/2"x2" lip of oak under the shelf.

Of course, if you put the 2" dimention vertically under the shelf, the lip is about 16x stronger.

For those who care about the math, the deflection of a beam is inversely proportional to the width of the rectangular cross section. However, it is inversely proportional to the *cube* of the height of the cross section.

Chris

[Murray Peterson]

Chris Friesen wrote in news:11s62ile2t3sqb2 @corp.supernews.com:

Thanks -- those numbers help me a lot. I wanted to create a shelf with quite a thin cross-section (1.2 inches at most), but then ran into problems with deflection.

Sounds like the interior piece of iron could be enough to get me what I need.

I'll put the thing together sometime in the next week (if work permits). I'll post back and let everyone know how it worked (or didn't).

Thanks to all for their helpful responses. Learning new things is always fun, especially if I can see the results hanging on my wall :-)

[todd]

Unfortunately, it has a moment of inertia (even assuming there are 2 of them as the poster suggested) about 350 times less than the shelf. In the end, unless 1/2" angle iron is a lot thicker than I think, it doesn't end up contributing much to the combined moment of inertia, which means it doesn't reduce deflection in a significant way.

i.e. not very much.

Of course, if the lip is made of tungsten carbide, it would be 30x stronger.

It's also directly proportional to the cube of the length. If the OP could reduce the width just 6", the deflection would drop about 25%.

todd

[Chris Friesen]

Oh, certainly. I should have maybe qualified that statement.

Yep.

True. But I think my suggestion is more practical.

Yep.

It was kind of fun digging up my old statics references--I trained as an engineer, but I've been doing software for the past 6 years.

Chris