Beams and Tusk Tenons

Tapered pegs passing through the misaligned holes draw the joint tight.

If a beam is unable to support its own weight, you could just make it larger—but that would make it heavier as well. The trick is to make the timber larger in the right direction. The strength of a rectangular beam varies directly as to changes in its width, but as the square of changes in its depth. Make a timber twice as wide and it gets twice as heavy and twice as strong. Make a timber twice as deep, and it gets twice as heavy, but four times as strong.

How might you connect joists to a big summer beam running down the middle of a room without weakening it? The beam has to shoulder its load even after you cut it full of holes. The trick is to cut into the part of the beam that's doing the least work. Any beam is under compression on top, and under tension below. That's how an I-beam saves weight—the top is squeezed, the bottom is stretched, and you leave out the fat in the middle. In good timber design, mortises only cut into the waist of the beam, the neutral area, not into the top or bottom.

The tenon can fail as well. A tusk tenon gains more support from stepped reinforcements above or below the main tenon. Where the construction permits, the shallow shoulders of tusk tenons can gain extra security by having the narrow central tenon pass all the way through the mortised beam. This tongue extends out far enough for a tapered wedge or key to pass through and keep the joint pulled tight. These days, any through tenon secured by a transverse wedge is called a tusk tenon. This gives you more opportunities to make the observation about timber framing in Alabama, where the Tusc-a-loosa, but in the old sense, the tusk was only the strengthening shoulder of a shallow tenon.

Woodworking Tools and Installation Tips

Woodworking Tools and Installation Tips

There are a lot of things that either needs to be repaired, or put together when youre a homeowner. If youre a new homeowner, and have just gotten out of apartment style living, you might want to take this list with you to the hardware store. From remolding jobs to putting together furniture you can use these 5 power tools to get your stuff together. Dont forget too that youll need a few extra tools for other jobs around the house.

Get My Free Ebook


Post a comment