We are trying to fabricate gored-elbows. But we have a problem in reducing the diameter of a gored-elbow to fit inside the raw opening of a spiral-duct. Our gored-elbow has bead-&-slip connector in both ends. Shop people told me that the diameter of our gored-elbow should be the same throughout the duct body including the two connector ends. Let say we have a row of 8" round spiral duct, and we need to connect a gored-elbow to the spiral duct. Please see pictures 1.
The diameter of the gored-elbow needs to be slightly reduced in order to fit in the raw opening of the spiral duct. Therefore, a nominal 8" gored-elbow needs to be reduced to 7.8125". We have tried to add a 0.1875 "Diameter Reduction" to our gored-elbow as shown in picture 2. But the problem is that the part size is not correct. We expect the part width to be 25.54" for a nominal 8" diameter with 0.1875" reduction plus 1" for a gore-lap seam. But we find that the part width in the Connector-In remains to be not-reduced (that is 26.13"). Please see picture 3 for the odd part shape. We want to see the part-width in both ends to be 25.54". We have tried all three "Diameter Type" - those are "Nominal", "Outside", and "Inside" - with the same 0.1875" diameter reduction; but none of those makes any difference.
Is there a way to reduce the diameter throughout the whole duct body? By the way, I am using CAMduct 2019 just in case this makes any difference.
We could have kept the gored-elbow to be 8" and then crimped the connector ends to make the air openings slightly smaller than 8". But this is one extra step that we want to eliminate.
We could have changed the nominal diameter of our gored-elbow to 7.8125". But this means we need to manually adjust the diameter when we draw the gored-elbow. This is one problem. The other problem is that when we connect the 7.8125" gored-elbow to an 8" spiral duct, we will get a warning message "Connectors are different sizes" as shown in picture 4. There has to be a better way.
Please let me know how to fix this problem. Thanks.
Jaysom