Section 59: Four-piece Short Radius Duct 90 Degree Elbow

Formulas and Measurements

• Where they intersect is the Apex Multiply the duct Call Out size times.75 (or 3/4) and mark that measurement from the Apex along the horizontal line Draw a semi-circle at this point using half the O.D.I Then from the Apex, draw arcs from both O.D.I. points on the horizontal line to the vertical line Bisect the large arc then with dividers set at the radius of the large arc draw a trisection point below the bisect line Set dividers at bisect and trisect points on the arc and do one walk-down on the large arc line.

Procedure

1. Step 1

   Draw a 90 degree angle with the vertical line to the left. Where they intersect is the Apex

2. Step 2

   Multiply the duct Call Out size times.75 (or 3/4) and mark that measurement from the Apex along the horizontal line

3. Step 3

   Draw a semi-circle at this point using half the O.D.I

4. Step 4

   Then from the Apex, draw arcs from both O.D.I. points on the horizontal line to the vertical line

5. Step 5

   Bisect the large arc then with dividers set at the radius of the large arc draw a trisection point below the bisect line

6. Step 6

   Set dividers at bisect and trisect points on the arc and do one walk-down on the large arc line. Draw a line from this point to the Apex

7. Step 7

   Trisect the semi-circle into six equal parts. Draw 90 degree vertical lines from the trisected points to the horizontal line. Label these points

8. Step 8

   Draw Stretch-out and add for lap allowance