Best wood for long shelves

[Murray Peterson]

I am building a 6 foot long shelf that is going to be supported at the ends (no option of support in the middle). The shelf needs to support about 50-

70 pounds of weight (stereo equipment), so the "sag" (or deflection) in the center is going to be a problem. I plan on building the shelf as a hollow box, and using steel angle iron on the inside as a stiffener.

Just out of curiosity -- what commonly available wood product is best for resisting deflection under a continuous load (i.e. shelving)? The easily available ones at my local lumber store are: laminated pine, mdf, playwood and particle board, I am assuming that the laminated pine would be best, since all the grain is running longitudinally. Is my assumption correct?

[stoutman]

Check out the sagulator shelf deflection calculator. Might be useful.

[Joe Barta]

You could make the shelves a torsion box. Think hollow core door. Lightweight and very strong. 1/4" ply top and bottom, hardwood edging and pine innards. No steel needed.

Joe Barta

[todd]

For the sheet goods, on average, plywood would be the best, then particle board, then MDF for initial sag.

I'm a bit unclear on how you're going to build the shelf as a hollow box. If you're going to go to that much trouble, and then include a steel angle, I'd suggest just doubling up on the wood for the shelf. Two of the 3/4" glued-up pine boards would deflect only about 3/32 at the middle under a distributed 70 pound load (assuming a shelf depth of 12").

You can get an estimate of sag using the Sagulator at

[Lew Hodgett]

If you are interested, can tell you how to build this shelf using foam, knitted fiber glass and epoxy along with the basic wooden shelf that is say 3/4" thick.

It would probably support at leat 200 lbs, weigh maybe 10 lbs max.

Contact me off list if interested.

Lew

[Murray Peterson]

"todd" wrote in news:wpydnY53iqgCWFzenZ2dnUVZ [e-mail]:

deflection? My experience with purchased bookshelves has been poor -- shelves that progressively sag more as the years go by.

BTW, the loading is not distributed -- almost all of the weight is pretty close to centered.

[Murray Peterson]

Joe Barta wrote in news:Xns9745D6430F2CAjbartaapknet@

207.115.17.102:

That's pretty much what I had in mind, but with some 1/2 inch steel angle- iron screwed to the inside of the front and back edges for increased stiffness. Sounds like my design may be overkill for the application.

[stoutman]

From the sagulator: "The Sagulator computes initial sag only. As an engineering rule of thumb, wood beams/shelves will sag an additional 50% over time beyond the initial deflection induced by the load."

[Joe Barta]

Over 6 feet, 1/2" steel angle ain't gonna do squat. You'd get far more bang for your buck increasing the thickness of the torsion box.

[Joe Barta]

I'm no engineer... more of a shoot from the hip from experience type. I think a torsion box with 1/4" glued on ply top and bottom with a total thickness of 1-3/4" should be strong enough for even the heaviest stereo equipment.

I think the "sagulator" is just a guide and it has no use in calculating the strength of engineered assemblies... which is what a torsion box would be.

Joe Barta

[Tom Woodman]

You can add an enormous amount of support strength to your shelving by adding a cleat underneath the front edge of a shelf. This is usually a 3/4 x 1" plywood strip, glued (and preferebly screwed as well) about 1/2" back from the front edge of the shelf and running the width of the shelf... also gives a classy look to the shelf.

[todd]

We're in luck. I'm a mechanical engineer who specialized in materials engineering. I wasn't attempting to calculate the strength of a torsion box. I'm sure it would work. But for the original poster, I'm just imagining that a couple of 3/4" thick boards that he can buy off the shelf and laminate together would be easier to deal with and would also be very effective.

Of course the sagulator is just a guide. For one, it doesn't take into account end conditions, which can have an effect on deflection. It also makes assumptions regarding the bulk properties of the material that may or may not be true. And it can't do stuff like figure the deflection if a thicker piece is applied to the front of the shelf to add rigidity.

todd

[Joe Barta]

I have a couple questions for you then. Something I always wondered.

Imagine a torsion box, well made with 1/4" ply top and bottom and 1-

1/2" thick. Let's say it's for a shelf 6ft long and 11-1/4" wide. Now imagine a solid plank, 2x12 construction lumber (not fir). Would you think the torsion box would be stiffer or would the solid plank be stiffer?

I would imagine that if one used oak instead of spf, the oak plank would be stronger than both.

Also, would I be correct in thinking that 2 pieces of 1x12 laminated together would be stiffer than a solid 2x12? If so, why? (other than minimizing and spreading out defects, which is pretty obvious)

I know I could probably do some homework and look this stuff up... but you're here, right?

[mogura]

Depends on what sort of plywood it is. Likely to be close. But make the box 2" thick and it will win. 3" and the plank has no chance.

No, it would be the same unless you had trouble finding 2x without splits and things.

j

[Phisherman]

Ply or solid wood deflects the least. You might consider a 2" lip on front and in the back or a torsion box to help. Six feet is a lot.

[todd]

Tell me about the construction of the insides of the torsion box. The makeup of the longitudinal pieces will have the greatest effect on stiffness. I imagine it will be 3/4x1 SPF of some kind.

todd

[Mike Marlow]

Serious overkill Murray. The 1/2 inch would weigh a ton and you won't need the strength that it will bring.

[Joe Barta]

I can't imagine 1/2" angle iron bringing much strength at all over 6 ft... and not that much weight either. Or maybe we're thinking different things. I'm thinking about 1/8" thick steel angle with each leg being 1/2" wide. Am I missing something??

Joe Barta

[dadiOH]

Yep :)

-- dadiOH ____________________________

dadiOH's dandies v3.06... ...a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at

[dadiOH]

Turn 'em over once in a while.

*That* makes a difference.

-- dadiOH ____________________________

dadiOH's dandies v3.06... ...a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at