What Can We Do About Missing Connector Plates?

Previously, we’ve reviewed the top manufacturers’ defects according to a survey of In-house inspections. (See my April 2020 article, “How Do Your Manufacturing Errors Rank on the List?”, for the top ten items and ways to correct them.) While wane in the plated area topped the list, the second highest defect was missing connector plates. Of all the issues, it seems like that would be the easiest to remedy, but yet it is always on the list. Let’s discuss the problem and then evaluate some of the potential solutions.

The Problem

Connectors are required on both sides of the truss to transfer load. Having only a single connector application will change the load characteristics and create a single shear configuration that was not considered in the engineering. We all know that, but sometimes situations in the manufacturing process will result in missing or ineffectual plates. In a gantry press system, the gantry sometimes doesn’t press the bottom plate adequately to ensure the connector makes it all the way down the line into the finish roller. Likewise, gaps designed in the table for lift-outs or walk-thru can create areas where a gantry cannot press adequately. These problems are not normally an issue with C-press systems, however, truss builders can forget to plate joints in any system.

Potential Solutions

Knowing that we want and need those truss plates, what can we do about it? Listed from very sensible to less effective are steps you can take:

1. Provide special training to stackers on how to visually detect missing connectors. For example, often the top plate dictates the bottom plate as long as the plate extends beyond the web and chord – this can be easy to detect when personnel are instructed to make the effort.
2. Make adjustments to the gantry, or adjust the table to correct low spots. Tables should be releveled every 6–12 months. Jacks exist on most systems to facilitate this maintenance. This should be done with an optical transit.
3. Cover gaps in tables with pads, or shift and reposition trusses to avoid connectors over gaps in tables as the truss is being set up.
4. Stack trusses vertically to help identify missing connectors. Each truss can have a complete visual inspection after it is completed. (The downside for this approach, however, is that vertical stacking can present safety issues which have to be addressed appropriately to prevent injury.)
5. Use an inspection mirror on a pole to inspect trusses as they are coming off the conveyor after pressing, such as the one shown above. (The downside to this approach is that it may slow down stacking, and negotiating through moving trusses can present a danger.)
6. Pre-plate back plates to webs or chords prior to assembly. (The downside is that it occasionally is more difficult to correctly position connectors during pre-plating and it requires critical attention.)
7. Create a check-and-balance system by pre-picking connectors. This will help eliminate the inadvertent missing plates due to omission. Stage with truss parts and pieces.
8. Keep the area around feed rollers clean, so dropped connectors can be quickly identified. This often happens as the truss approaches the finish roller.
9. Install angled mirrors under the finish roller output that will assist the stackers in seeing back plates. This should be suitable for the environment, and stainless polished mirrors, such as the one shown, work better than glass because they are shatter-proof.
10. Install a plate sensing machine to alert you if a plate is missing. (The downside here is that no machinery currently exists on the market that is reasonable in cost and is effective at detecting missing connectors. Optical systems are extremely cost-prohibitive and do not exist for our industry.)

The Bottom Line

Missing plates are a liability that needs to be addressed. Training and vigilance should be employed to make sure your product meets the design requirements. Missing connector plates are a black eye to our industry that can be remedied.

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.