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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 size. On the drawing, the length is given as 10” and will be one of the blank size dimensions. The second dimension comes from the perimeter of the duct. In our case, the duct is 4” x 6”. So, 4”+6”+4”+6”= 20”. So our blank is 20” x 10”
- Draw the blank size out. In the shop we would be shearing the piece of metal
- Draw an arrow indicating the direction of air flow
- Working from one side, mark off the perimeter at each end
- Connect the points at each end to create the line
