Lasers can be exact, but their data can be misinterpreted. Having the equipment is only part of the equation—it also must be used and understood properly.
For example, the connection in the photograph [See PDF or View in Full Issue] was misallocated. The plate should have been dropped to the bottom of the chord covering the splice but, because of the projection of the laser, the builder positioned the plate as shown.
The diagram [See PDF or View in Full Issue] illustrates the problem. As the material height rises from the table top, the system has an adjustment that corrects the parallax which occurs due to the angle of the laser relative to the position the laser is projecting.
Often, the truss builder is aware of this, because they have been trained to understand this relationship. Unfortunately, in some instances, the builder does not have this knowledge or does not understand. This causes the builder to misinterpret the information and place the plate in the wrong location. In fact, the error increases as the distance from the laser increases.
So, knowing this is a problem waiting to happen, the question is—how do we address it in practice?
Shop drawings are the best source of information for truss builders. But, because many plants are now depending solely on the laser to present plate placement information, it is important the builder understands how lifting the truss members changes the projection image. In addition, steps can be developed to reconcile this problem.
- Initially the laser projects to the table. This provides the location to arrange pucks and blocking.
- As lumber is added, the projector is adjusted to project 1 ½ inches up from the table.
- Laser projection will be accurate to place top connectors.
- After top connectors are placed, the truss can be bottom plated using the top plate to translate the proper placement.
- A screen or shop drawing should be available to the builder to help ensure communication of plate placement information.
Lasers are an excellent tool in your plant. But, like with all tools, you have to learn how to use them properly.
Glenn Traylor is an independent consultant with almost four decades of experience in the structural building components industry. While he is a TPI 3rd Party In-Plant Quality Assurance Authorized Agent covering the Southeastern United States and performs 3rd party safety auditor services, these articles represent his personal views, knowledge, and experience. Glenn serves as a trainer-evaluator-auditor covering sales, design, PM, QA, customer service, and production elements of the truss industry. He also provides project management specifically pertaining to structural building components, including on-site inspections and ANSI/TPI 1 compliance assessments. Glenn provides new plant and retrofit designs, equipment evaluations, ROI, capacity analysis, and CPM analysis