Circular Ductwork pattern development for Sheet Metal Work (on the Bench)
Circular Ductwork pattern development for Sheet Metal Work (on the Bench)
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Illustrating below methods of parallel line pattern development.
Starting at the basics, showing the division of both the Diameter and Circumference of any Circular duct. The divisional number of 12 is considered the most favoured, considering layout time and accuracy. Before CNC and computer programming, HVAC Ductwork was always manufactured with the minimum length of seam required, welded, Riveted or Grooved, depending on the section of duct.
First example:
45 degree angle spigot on flat plate showing orifice.
Although showing above the pattern development (parallel line) method, Using a Square, Scriber and Dividers will suffice. All pattern development will commence in the actual replicating the Duct section full size. In time the Apprentice will learn that material wastage will be minimal on the full layout. Knowing the Diameter, Angle and Height, cut the material Circumference + lap (if required) X Height + lap (if required). It is a good idea to scribe a line parallel to the bottom circumference edge equal to the lap allowance or if no lap the distance to be of a distance for the dividers to accurately use as an arc centre.
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