Kind of an engineering question, really...

[Dave Richards]

Assume two pieces of wood of the same species. One is 3/4" x 5-1/2"; the other, 1-1/2" x 5-1/2". Both pieces are supported on edge with the same span. How much stiffer is the second piece than the first?

[Carl Eyman]

I remember my soldier's manual when I was a combat engineer oh so many years ago that the load carrying capacity of a wooden beam was given as pounds per inch of width. (For a given span and heirht of beam, of course) Later after receiving an engineering degree, I learned one had to consider the thickness to height ratio. That is the thinner the piece the more lateral movement which messes up the load carrying ability. Hence the practice of bridging between floor joists. But overall I think the Corps was right: load carrying is proportional to thickness within certain limits. I am anxiously awaiting rebuttals. Carl, ex 1st Lt. Corps of Engineers Army of U S (1943 to 1951)

[Lee Schierer]

The property of interest is section moduluis which is related to stiffness. You calculate it using I = (B X H ^3)/3. The height (H) is the heigth of the piece. In your case B= either .75 or 1.5, H= 5.5. For the thinner piece I = 41.5 the thicker piece I= 83.2 or just twice as stiff.

Hope this helps.

[Dave Richards]

Thank you gentlemen. I guess I'll have to build that bridge to Hawaii with 2x6s instead of 1x6s. Hmmm...it's gonna cost a bit more than I thought. :(

Actually, I guess I'll use 2x6s for the base for my new bandsaw.

Thanks again.

Dave