The Strength of Maple

No question the hard rock maple I purchased this week from Alamo Hardwoods is harder than any wood products I've ever purchased.  It feels somewhat like marble, and has been milled perfectly, with no slivers or any other indication that it was not cast in some faux stone factory.  (With the exception of the quick rough cut to cut the board in half, which unfortunately left a long point that needs to be filed down and a small split in the end of the wood that will probably not be noticed when the shelf is in position.)

But one can wonder, does this mean greater or lesser strength than, say, a pine shelf?  Hardness does not necessarily translate into strength, particularly if what is hard becomes more rigid.  Rigid objects that do not bend when under stress fail catastrophically when subjected to too much stress.  This fact is fundamental, so well known it is a central proverb of the Tao.

However according to published information, hard rock maple is considerably stronger than Pine.  When subjected to increasing weight, the pine shelf will break first.

http://workshopcompanion.com/KnowHow/Design/Nature_of_Wood/3_Wood_Strength/3_Wood_Strength.htm

Here are the numbers for Hard Maple:

specific gravity, compressive strength psi, bending strength psi, stiffness, hardness

0.63,7830,15800,1.83,1450

Here are the numbers for White Pine

0.35,4800,8600,1.24,380

The compressive strength is 63% greater, and the bending strength is 84% greater.  The stiffness is also somewhat greater, but no where near as much as you would expect based on the hardness, which is almost 4 times greater.  So maple bends proportionately with its ultimate strength as compared with pine, but it's about 75% stronger.

Right now, as Rob left it, strength is very important because there is no center support bracket.  The shelf is supported entirely around its 3 sided perimeter.  That's one reason I didn't want to go with any pre-fabricated shelf made of wire mesh or wood slats.  Big box stores sell closet shelves made of veneered wood slats, probably made in China, for more than half the price I paid for solid hard rock American maple.  Also, those pre-packaged closet shelves are too big for this closet, which somehow comes to exactly 47 inches wide (the standard is 48).  And the pole is only about 11 inches from the back of the closet, making 12 inches a good choice of depth, whereas pre-packaged closet shelves are most frequently 16 inches deep.  I noted that all the existing closet shelves in my home are 12 inches deep also.  When I was measuring the space, it seemed like either 12 or 14 inches deep would work, but 16 inches would make the space above the shelf very hard to get to without using a ladder.  I also noticed that the closet poles project somewhat further from the back wall than the shelf.  I didn't want the shelf to project that much more than the shelf, but an inch seemed OK.

I recall I have Skandia shelves that are 40 inches long.  They are only supported on the two ends (and not along the length of the shelf in the back, as a closet shelf is).  And it is very strong, strong enough to hold hundreds of pounds of equipment.  Skandia used to show a picture with more than a dozen guys putting their weight on a single Skandia shelf.

Just checking now, I'm surprised to see that Skandia shelving is made of pine!  It doesn't seem at all like the pine you get at home centers, it seems much stronger and denser as well as being nicely milled and coated with urethane.

Lundia, the US factory which actually preceded Skandia, makes 48" shelves in various pine grades.

So I think the 47" maple shelf supported on 3 sides is sufficient without any center support, although I might still add one.  I suspect a wimpy support as used in my built-in closets would be weaker than the shelf itself, so the shelf would be protecting the wimpy bracket.