Sixty Years of Machines: Introduction

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Issue #11245 - December 2019 | Page #8
By Joe Kannapell, P.E.

When do CMs go after new technology? Primarily when they’ve had several good years under their belt. But once new equipment has proven to be much better than what it replaces, it continues to sell even in slower economies. This is illustrated by the apparent inflection point midway through the last sixty years (see chart—See PDF or View in Full Issue). From 1984 until 1991, equipment sales had sunk to new lows, but then gained momentum during the 17-year surge that followed. A similar run up is occurring now, 8 years into the current housing expansion. Labor shortages, complex roof designs, and technological advancements accelerate adoption. Manual saws are replaced with computerized versions which basically perform the same task, only much faster. Contrarily, assembly equipment is changing much more radically. Truss plants overwhelmingly are converting to roller gantry systems, with many of these incorporating automated setup. In retrospect, it seems obvious that we would replace manual saws with computerized versions, and vertical presses with roller gantries. But why was our industry so slow on the uptake? Is this the reason we haven’t robot-i-sized by now? Actually, our machinery evolved slowly for reasons that are worth exploring, to better understand what’s ahead.

Assembly Equipment in the 1970s

Though truss equipment had been commercialized for 15 years, my first exposure to the major suppliers was in the boardroom of a St. Louis hotel in 1972. At the head of the table was Carroll Sanford, who invented the Roller Gantry. Also in attendance were Cal Jureit, who introduced the Gang-Nail vertical press, and our founder, Walter Moehlenpah, inventor of the most widely used C-frame press. Among smaller manufacturers seated around the table was Bill McAlpine, who had only recently begun selling truss equipment.

Machinery sales were booming back then, as housing starts had reached a level that has never been equaled. Jureit’s Gang-Nail commanded the largest share of the roof truss equipment sales. Moehlenpah’s Hydro-Air had the widest distribution of lower-priced equipment. And, fortunately for us, Sanford’s winning Roll-a-Master gantry system was not being aggressively marketed, and so far had limited use.

Why did vertical presses dominate truss equipment sales at the onset of our industry, when today they are largely sidelined? The explanation is found in the evolution of the truss connector plate, from long-tooth to short-tooth. Sanford’s design was very close to today’s models (shown in photo at left—See PDF or View in Full Issue) with 5/16” long teeth. Jureit’s and Moehlenpah’s resembled conventional nails, with teeth up to 7/8” long, almost triple the length of Sanford’s. The length of the teeth dictated the type of fabrication equipment required. A roller gantry cannot properly embed longer tooth plates, as the nails bend over, while shorter teeth penetrated the wood fibers effectively. A vertical press can embed any truss plate.

The simplicity of the roller gantry understates its main advantage: the ability to impart much greater force than even powerful vertical presses. Truss plates require a minimum of 1000 lbs of force for full embedment. Consequently, a 10x10 plate requires 10 x 10 x 1000 = 100,000 lbs or 50 tons, which equals the maximum capacity of a Gang-Nail Mark 4 or Mark 5. This limitation is particularly restrictive, given that the 40-foot scissor truss shown contains (5x6=30 + 8x8=64) 94 total square inches of plate to be pressed at mid-span. While the vertical press embeds the entire plate area simultaneously, the circular drum of the roller gantry embeds only a small portion of the truss plate as it rolls across its full extent, requiring dramatically less force.

Despite the obvious mechanical advantage of the roller gantry, why it took 30 years to eclipse the vertical press is worth further explanation…

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