What is the mitre angle for the first gore of a 4 piece 90-degree elbow?

In the context of HVAC sheet metal fabrication, determining the mitre angle for the first gore of a 4-piece 90-degree elbow requires an understanding of how the pieces will fit together to create the desired angle.

For a 90-degree elbow made up of four sections, each section needs to contribute to the overall angle of 90 degrees. When you divide this angle for four pieces, you find that each gore is generally designed at an angle that helps to smooth the transition and maintain efficient airflow.

In this case, the first gore is typically set at 15 degrees. This allows for a gradual bend rather than a sharp transition, which helps in reducing turbulence and improving the overall performance of the duct system. By breaking up the angle into smaller increments, it also makes the assembly easier and more precise.

Using a 15-degree angle for the first gore provides an effective way to ensure that when all four pieces are assembled, they collectively create a seamless 90-degree elbow, aiding in both functionality and airflow dynamics. It is a common standard used in sheet metal fabrication for this type of fitting.