Boring 40-Foot Long Utility Poles for Conduit Passage

A machine was designed, constructed and tested which will bore 2-1/2 inch diameter holes lengthwise through 40 foot long wood poles at a rate of 12 feet per minute. A special boring hit was designed to accomplish the high speed boring and to permit the wood particles to be scavenged to the rear through the rotating boring tube. The machine is 96 feet long. It consists of three air operated centering clamps and a movable boring tool assembly at each end. Poles shorter than 40 feet can be bored by moving the clamps. Each boring tool assembly bores approximately half-way through the length of the pole. A peripheral miss distance of 3/8 inch was permitted where the holes meet, but miss distance averaged less than 1/8 inch. One inch electrical conduit is readily pushed through the pole. The bored poles were found to dry faster and absorb more preservative. Strength reduction on a 30 foot long pole 8 inches at the ground line is calculated to be about 1.0 percent in bending and 9.8 percent in shear.

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