Can Lasers Do It All?

With the introduction of lasers, setting up a truss while accurately controlling its perimeter and profile has never been quicker or easier. But do lasers do the job by themselves? The answer is no. They cannot. Here is why.

Lasers provide excellent and accurate information to truss builders about where the lumber needs to be as the truss is pressed; however, without proper blocking and properly located stops, the truss is at the mercy of the gantry. As the gantry rolls the connectors into place, the lateral force exerted by the roller attempts to push the truss from side to side. Hard, fast stops and blocking or jigging (for photo, See PDF or View in Full Issue) prevent the truss from moving, thus inhibiting the distortion of the truss profile. This is also the reason that automatic jigging must be designed to prevent this lateral motion. Supplemental manual jigging must be used too. No existing system totally prevents some motion, although the closest exception is likely the vertical hydraulic press system. Some machinery requires additional blocking to prevent lateral movement while the truss is being pressed. This also is exacerbated each time another similar truss is pressed. Each roll loosens the jigging until the umpteenth truss is sloppy in the jig. The best way to prevent this migration is to install significant heel stops on all trusses including and especially scissor trusses. Some plants depend on stapling chord transitions, hoping this will resolve the problem; but unless you are building one and one and one, the lack of proper blocking can create variations between trusses. Also keep in mind that, if the gantry is pressed from left to right, then right to left on the next truss, the variations will double from truss to truss. These variations result in waviness which is revealed in the finished product application and resulting finished surfaces.

Here are a few key items to consider.

1. The gantry always pushes the truss members in the direction of the gantry movement.
2. All bottom chord heels must have a solid stop to prevent this movement.
3. Webs or chords that are parallel to the gantry roller are extremely susceptible to lateral movement.
4. Attic room verticals often are pushed out of place, creating member to member gaps or misaligned web members.
5. Studio vault designs with vertical web members are very susceptible.
6. C-press systems or hydraulic press systems do not have this problem and tend to be more accurate.
7. Sometimes you are accused of having this variation and take the heat unfairly. This presumed variation can be created by the erection contractor due to their actions, omissions, or variations to footings, walls, and crooked string lines.
8. Crowning lumber is important with webs when they become part of the surface plane of the building. An example is kneewalls in an attic frame.

How can you tell if this is occurring?

1. Carefully stack like trusses, aligning the bearings one on top of the other. This will reveal movements and variations between trusses.
2. Notice if your first truss is tight in the jig but subsequent trusses are loose.
3. Listen to your customer. Record customer complaints from your end user. Although you often will not be the cause, always address their concerns.
4. Sometimes you are the problem! Get a handle on the issues. Recording and then analyzing the trends will help facilitate corrective action.

In summary, there is no substitute for heel stops. Building better trusses begins with managing important control points. Current framing methods use the heel as the location when setting trusses. In the old days, framers used the peak, but times have changed! Now heels are often the most important location on a truss.

An ANSI/TPI 1 3rd Party Quality Assurance Authorized Agent covering the Southeastern United States, Glenn Traylor is an independent consultant with almost four decades of experience in the structural building components industry. 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.