How to Build an Antenna Truss

How to build an antenna truss. Here's an easy-to-assemble item that MOTHER's crew uses for strong, lightweight framing; including laying up the sections, bending the rod, a detailed diagram and instructions.


| November/December 1982



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Diagram: Antenna truss.


ILLUSTRATION: MOTHER EARTH NEWS STAFF

Learn how to build an antenna truss with this diagram and detailed instructions. 

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 inch 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 inch 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.

HOW TO BUILD AN ANTENNA TRUSS: LAYING UP THE SECTIONS

E.M.T. comes in bundles of ten 10 feet-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 by 10 by 12 foot board with stops placed 10 feet, 1/8 inches apart. Locater strips, made from a 10 foot piece of one-by stock ripped to 1 inch 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 inch, 1/2 inch, and 3/4 inch material) and truss of varying widths can be handled.

Once the E.M.T. is placed in the frame, you'll have to decide how wide the truss you're going to build will be. Naturally, there are a number of different considerations involved in this decision . . . including strength and convenience. (If you have any doubt about the ability of the truss to handle the load you're going to put on it, then either calculate the stress, strain, etc. according to engineering procedure, or ask someone else to do it for you . . . using the information in this article.)





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