Working alone on carpentry projects has its challenges, especially when it involves 16′ treated lumber (1) I was building a double beam from two 2″ x 8″ x 16′ treated boards that needed to span 13 feet. I set clamps in place to retain the boards as I set each one in place one at a time, one end at a time. When it came time to screw the two boards together for increased strength to support the carport roof, I wanted the tops of the two boards to be flush. One had a crown (arch along the board) of over 1/2″. The other one had no crown, being amazingly straight. They were far too stiff to force flush by hand while I screwed them together. I decided to let gravity do the work for me. I extended an 8′ 2 x 4 about 7′ over one side and clamped it in place. It did the trick (See the set-up at “Leverage“.)
Later, I was curious how much force the 2 x 4 was exerting on the boards to straighten them to flush. Given that 1′ of the 7′ was canceled out by the 1′ hanging over the other side, I had 6′ of board torquing on the 2 x 8’s. Torque = force x lever arm. The center of gravity of the 6′ or torquing board was at 4′. That is the lever arm. The weight of 6′ of 2 x 4 (really 1 1/2 x 3 1/2) varies with exact species and water content. This board was kiln dried but laid in the rain the other day. There are online calculators for board weight (2). Mine was somewhere in the neighborhood of 6 lbs. Therefore, the torque = (6 lbs) x (4 feet) = 24 foot-pounds. That would be the same as hanging my 150 lb person on a board extending about 2 inches from the board. I was actually surprised that it took no more effort than that. I would have only had to exert a little over 20 pounds at the base of my fingers at 14 inches on a lever arm (3). However, that is more challenging than it appears since I am standing on a ladder and needing to force the screw into the board and hold this pose, which involves some core strength, while I use my driver to install at least 1/2 dozen screws. I was not able to get into a position to merely lean on the board. Gravity assist was much easier.
- My wife and some of my friends say that I should ask my friends for help, but they would stand around most of the time while they waited for me to prep for the heavy lifting. My wife and a few of my friends also think that I have too much time on my hands, since I have time to write blog entries like this one.
- https://www.builderscalculator.com/lumber-weight-calculator
- My forearm is a standard 18″ cubit (elbow to middle fingertip). The pads at the base of my fingers are one handbreadth (4″) less.
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