Quality Control Top 10
Along with helping a plant meet building code and industry standard quality control (QC) requirements, a well-managed QC program gives component manufacturers an objective tool to evaluate quality plant-wide. The more QC becomes part of a plant’s culture, the more benefits a company will reap from its QC program. The following question from a plant manager addresses how to help all staff get engaged in the plant’s QC mission.
Our plant wants to put more of an emphasis on QC. Do you have any suggestions of how to alert workers to common QC errors they should catch?
It helps everyone when QC becomes second nature in the plant. Analyzing QC data and related information gathered from the shop floor to spot trends in your manufacturing are critical steps to strategically improving your quality. Another good way to increase awareness of the importance of QC is to create QC boards or posters strategically located throughout the plant. This can serve as a quick reminder and valuable resource on key QC issues.
The board can be created any number of ways. It can show real examples of good quality and bad quality so workers can clearly see what is expected versus problems that have occurred due to carelessness or working too fast. For instance, you can include sample joints on your board showing rolled teeth, damaged lumber and other conditions. You could also take pictures and put those on your board. Here are our top 10 QC issues to consider when assembling a QC board.
1. Overall Dimensions. Height and span should be within tolerance. Most plants establish ¼" manufacturing tolerances for both height and span.
2. Lumber Type. Confirm that the actual size/species/grade of webs and chords are the same as specified on the truss design drawing.
3. Lumber Condition. Condition of overall board must be acceptable—no web and chord items such as checks, splits, cracks, large knots, lots of wane, etc. in the plate area, and no broken members post plating. (See Photo 1.)
4. Plate Size and Gauge. Actual plate size in the X and Y direction need to be the same size or greater than what is specified on the truss design drawing. High strength plates cannot necessarily be swapped for regular strength plates and vice versa. (See Photo 2.)
5. Plate Placement. For critical joints with Joint QC Details, placement must be within the tolerance polygon and members must be within the defect tolerance. If there is no Joint QC Detail, each member must have enough teeth and be within a ½" tolerance from the specified placement in any direction. (See Photo 3.)
6. Rotation. Rotation should meet the requirements set according to the design software (typically +/-10°). Watch out for plates mistakenly rotated 90°. (See Photo 4.)
7. Embedment. A 1/32" tolerance is allowed around the perimeter of the plate except for areas 1" or closer to where members intersect. (See Photo 5.)
8. Member Gaps. Up to a 1/8" gap tolerance is allowed in the plate area except for floor truss chord splices (for these, up to a 1/32" gap is allowed). (See Photo 6.)
9. Defective Teeth in Plate Area. Check for lumber issues such as excessive wane, pitch, loose knots, or anything that creates a void. (See Photo 7.)
10. Rolled Teeth in Plate Area. Inspect plate for rolled teeth due to over hammering. (See Photo 8.)
Implementing a QC Program
The In-Plant WTCA QC program helps manufacturers monitor the quality of trusses they manufacture and provides the plant with a data management system. The program requires regularly inspecting trusses and entering the data into the software program, allowing staff to store data and create reports to assess in-plant quality. This program also offers an official In-Plant WTCA QC 100% voluntary certification. For more information, visit sbcindustry.com/wtcaqc.php.
Updates to QC Standard
Work is underway by the TPI 1 Project Committee to revise and reaffirm the ANSI/TPI 1 standard and Chapter 3: Quality Criteria for the Manufacture of Metal Plate Connected Wood Trusses. Chapter 3 addresses quality control requirements including:
- Implementing a quality control manual
- Inspection frequency
- Inspecting trusses for quality criteria
- Third-party inspections
The 2012 standard is expected to be finalized next year.