HOW TO BUILD ANTENNA TRUSS

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Issue # 078 - November/December 1982

One of the components most commonly used in projects out at the Eco-Village is antenna truss . . . a lightweight, sturdy, triangulated material made from electrical metallic tubing (E.M.T.) and 1/4" steel rod. And despite all the articles we've run about things built with the versatile framework, we've never explained just how we go about assembling it . . . at a considerable saving over the cost of buying the commercial variety.

Truss gains its strength by virtue of the fact that its triangulated members are subjected to either compression (pushing) or tension (pulling) rather than bending, as is the case with a simple beam. Since materials generally have more strength under compression and tension than they do when subject to bending, truss sections can be both lighter and stronger than can a comparable single member. Of course, antenna truss was specifically designed to resist flex and twist. That property makes it especially sturdy when sticking up in the air (to hold a windplant, for example), but we've found it to be quite useful in many other applications, as well.

For standing towers, three-tube truss provides the most strength, but simple bar truss (made with two pieces of E.M.T. and an interlace of the 1/4" steel rod) can be quite effective for supporting loads in a horizontal plane. The following explanation will lead you through the process of building the three-tube material . . . but if your application could be handled by simple two-tube truss, then you can just stop part-way through the procedure.

LAYING UP THE SECTIONS

E.M.T. comes in bundles of ten 10'-long pieces, and—fortunately—the lengths are usually uniform enough to allow the tubes to be married without any trimming. We use a wooden frame to hold the conduit in place during truss fabrication. It consists of a 2 X 10 X 12' board with stops placed 10 feet, 1/8 inch apart. Locater strips, made from a 10' piece of one-by stock ripped to 1" widths, are nailed to each edge to keep the tubes from falling of the board, and to the center to hold them apart. This leaves a considerable gap between the locaters . . . so that tubes of different diameters (we've used 3/8", 1/2", and 3/4" material) and truss of varying widths can be handled.