Duct takeoff/elbow problem

[breimler]

I am having a problem with ABS 2007.1 trying to insert a fitting where one is not needed. Please see the attached drawing. ABS is trying to insert a mitered elbow between the takeoff and the 90 degree elbow. If I make the distance between the upper and lower ducts greater it doesn't do this, but why would there be a minimum space required if there is adequate space between the 90 and the takeoff?

Any help is greatly appreciated.

Thanks,

Brad

[Anonymous]

Hi Brad,

I have tried to reproduce your problem using ABS 2007.1 but don't get the
strange elbow that are in the attached drawing. But I'm having difficulties
to get the branch to connect at the top of the main at all. I have found
three alternative solutions to draw the branch though:
Alternative A:
1. Draw a square duct 30"x30" on the correct elevation.
2. Pick two points for the branch duct before connecting to the main
trunk.You will get several suggestions to connect.
3. Press N for Next to select the solution where the duct is connected to
top if the main. End Duct Add
4. Modify the branch to the correct size

Alternative B:
1. Start Add Duct and pick a point on the main trunk.
2. Lock the elevation and enter the elevation you want, Note that the take
off is inserted on top of the main
3. Pick a point to draw the horizontal branch

Alternative C:
1. Start Add Duct and pick a point on the main trunk. You will get an
message box telling you that the size is to big. Answer No.
2. Enter P for Plane to change plane to draw the duct in z-direction. Pick a
point above the main
3. Pick third point to the right to draw a horizontal duct. End Duct Add
4. Select the horizontal duct and use the elevation grip to set the correct
elevation

You mention that it works better if the elevation difference is greater. I
think your problem is related to a defect we have found regarding connecting
a branch using an off-center take-off. If the elevation difference between
the ducts are small we try to connect without using elbows and place the
take-off off-center. When the calculation is made we some times mix up the
dimensions and that causes some problem on rectangular duct work with big
differences in height and width.

/Bosse

wrote in message news:5412533@discussion.autodesk.com...
I am having a problem with ABS 2007.1 trying to insert a fitting where one
is not needed. Please see the attached drawing. ABS is trying to insert a
mitered elbow between the takeoff and the 90 degree elbow. If I make the
distance between the upper and lower ducts greater it doesn't do this, but
why would there be a minimum space required if there is adequate space
between the 90 and the takeoff?

Any help is greatly appreciated.

Thanks,

Brad