Just as Trussmatic brought back hydraulic plate pressing, House of Design has resurrected pre-plating. Both practices proved themselves in the early days of our industry, but both required disciplined shop floor management, and each had limitations. [For all images, See PDF or View in Full Issue.]
Pre-plating was first deployed in the 1960s with Gang-Nail beam-type presses and involved laying the “next” top and bottom chords just outside the jigging, parallel to the corresponding member and setting the plate – which would become the bottom plate on the following iteration. This method, used extensively in the 1970s by industry leaders Trussway and Shoffner Industries, had the advantage of lessening the pressing force by 50%, and resulted in much improved embedment. As truss runs became shorter and less repetitive, and beam-type presses were replaced by roller gantries in the 1990s, the practice of pre-plating was largely neglected in the U.S.
However, early in the 1990s, a Civil Engineering Professor in Finland, Tuomo Poutanen, applied for International Patent recognition of a production process that took pre-plating to the next level. In addition to plating the underside of the chords, he suggested plating the topside of the webs, and that all plating be done prior to members being placed on the jigging surface. In his patent, he proposes a methodology and posits its advantages, which I have summarized and added to as follows:
- Improved plating accuracy – if a linear saw can measure and cut a board accurately, then it may be handed off to the plating station “controlled by the same automation, i.e., by a single central automatic control unit, which simplifies the process and reduces risk of error.” While this may have seemed farfetched 30 years ago, today’s PLCs and motion-control technologies are up to the task. However, this would require very tight mechanical and computer linkage between the cutting and the pre-plating processes.
- Less assembly time – with current auto-jigging and laser technology, plating is the most time-consuming part of assembly. Without the time spent fetching, positioning, and setting plates, assembly time would be dramatically decreased.
- Shorter setup time – because chords are pre-spliced, the perimeter of the truss is more easily established, especially if there are only three chord members. Note the minimal jigging shown in the image. In 2009, Jim Urmson independently employed this principle with his TCT robotic assembly. Chords members were fed through the TCT linear saw in proper sequence, then spliced immediately after exiting the saw, and then conveyed to the assembly station (https://youtu.be/o9tJeCCGAKI).
- Use of a linear saw (and nesting of cuts) results in considerable savings in material, “on the order of 5%.” In his patent, which was granted in 1995, Professor Poutanen presaged the value of a linear saw over the conventional component cutter, and introduced the term “negative waste,” five years before Jim Urmson sparked the linear saw revolution in the U.S. and Dave McAdoo of Alpine began using identical terminology.
An additional benefit outlined in the patent is prescreening boards for knots or wane that may fall within the plate areas. This would involve projecting plate areas onto boards prior to cutting and culling or reorienting boards that contain unacceptable defects in these areas. Undoubtedly this would yield impressive improvements in quality control, but extending this technology upstream from the saw to its infeed conveyor would take considerable effort.
Professor Poutanen’s ambitious thesis seemed to lie dormant for over 10 years, until he indicated that he sold it to Alpine, who subsequently shared it with House of Design (HoD). In HoD’s floor truss implementation at one of BFS’s Atlanta plants (for more on that story, see my August article, The Last Word on the Promise of Robotics), they pre-plate the underside of chords, the topsides of webs, and pre-splice chords. Even so, the process is not tightly integrated with their linear saw.
High commendations are due Professor Poutanen for his ability to foresee and describe such a quantum leap in truss technology, and for the demonstration, albeit belatedly, of its promising future. His deep knowledge of the truss industry, combined with his advanced engineering expertise, will continue to enrich us.