On 2/12/2013 7:00 PM, Darro wrote:
On Tue, 12 Feb 2013 16:36:04 -0800, wrote:
wrote in message
...
....
... beam ... spruce or hemlock ... to make up a beam
that is 2-1/2 inches in the vertical dimension and 3" in the
horizontal.

The total load on the beam would be about 30lbs. and would be
distributed evenly along the full length of the beam.

....

... Any other information that would help me construct a strong and
sag-resistant assemble/disassemble beam of 2x3 lengths would be
welcome as well.

....


Change your plans to steel if you need that small a cross section. Or
increase the size if you are going to use wood.

Since I hadn't considered the sagging that will inevitably occur as
the wood fibres stretch over time, I'll go back to the drawing board
and take a close look at steel alternatives.

....

Since softwoods are generally about 35 lb/cu-ft, your 3x3 (roughly) will
weigh about 25 lb or so while you're talking of only 30 lb load uniform
total load which is only 2.5 lb/ft.

An unsupported 12-ft 2x4 will sag some w/ time on edge and definitely
will laid flat--as somebody else said, you want the long edge down.

Your best plan would be to buy two 2x6 14-s and cut to fit for simplicity.

If you really want the smaller cross section use 2 tubafors and stiffen
'em w/ a 1/2" plywood gusset between them--nail and construction
adhesive or use one of the waterproof glues.

Alternatively, use 1x material and make it a box beam--cut the beam
weight by roughly a third.

But, w/o knowing what it is you're actually trying to do, my initial
response is still to just go get a couple 2x6's, nail 'em together and
cut 'em to length and be done w/ it.

--