2 Radius Throat-Radius Heel Elbow-No Seams
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Study the shop drawing. Remember that the first number for the duct size is always what we “see in the view”. The second number is the depth, or hidden view
- Calculate the blank sizes
- Cheek
- The drawing shows an opening size of 4” wide and a throat radius of 4”. So the horizontal dimension is 8”. Because the fitting is symmetrical, the vertical dimension is the same, 8”. Our blank size is 8”x 8”
- The drawing shows an opening size of 4” wide and a throat radius of 4”. So the horizontal dimension is 8”. Because the fitting is symmetrical, the vertical dimension is the same, 8”. Our blank size is 8”x 8”
- Throat
- The throat is shown as a 4” radius. Using an arc length formula, we can compute as follows: R x 2 x π x 90°/360°. This gives us 6 5/16”. The second dimension comes from the depth of the opening, given at 6”. So our blank size is 6 5/16” x 6”
- The throat is shown as a 4” radius. Using an arc length formula, we can compute as follows: R x 2 x π x 90°/360°. This gives us 6 5/16”. The second dimension comes from the depth of the opening, given at 6”. So our blank size is 6 5/16” x 6”
- Heel
- Because the throat is 4” and the opening is 4”, to get to the outside, where the heel sits, it is a radius of 8”. Again we can use the arc length formula: R x 2 x π x 90°/360° which gives us 12 9/16”. So our blank size is 12 9/16” x 6”
- Because the throat is 4” and the opening is 4”, to get to the outside, where the heel sits, it is a radius of 8”. Again we can use the arc length formula: R x 2 x π x 90°/360° which gives us 12 9/16”. So our blank size is 12 9/16” x 6”
- Cheek
- Draw or shear the blanks. We’ll only draw out the cheek in this case because there is no layout to the heel or throat. If we were in the shop, we would be shearing all of the blank sizes
- Mark the cheek with an arrow for airflow. If you had sheared all the blanks, you would mark them all for airflow
- From the outside, mark the opening at 4”. Notice we always mark the opening, it is the most important feature of the fitting.
- Swing the arcs. Set you compass from the lower right corner (radius point) to the very outside (heel) and swing an arc. Then adjust the compass to the inside of the opening (throat) and swing another arc from the same radius point. In this case we have swung an 8” and a 4” radius
