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

In a four-piece 90-degree elbow, the mitre angle is essential for ensuring that the sections fit together correctly, allowing for smooth airflow and structural integrity. Each of the four pieces of the elbow must be cut at a specific angle to create the correct overall bend without any significant gaps or misalignments.

For a 90-degree elbow made from four separate pieces, dividing the total 90 degrees by the number of pieces results in each piece having a mitre angle of 22.5 degrees. This ensures that when assembled, the pieces form the perfect right angle necessary for the elbow.

Choosing 15 degrees would not accommodate the total 90-degree requirement with four pieces, as it would result in only 60 degrees total when calculated (15 degrees x 4 pieces). Similarly, other values like 30 degrees or 45 degrees also do not yield the correct total angle when multiplied by four. Therefore, for a four-piece 90-degree elbow, the correct mitre angle is indeed 22.5 degrees.