Eccentric Ducts

[Anonymous]

I am trying to alter a transitions eccentricity and it won't let me use (-1) as a value to make it concentric in one plane and eccentric in the other.

???

[CADmonkey_UK_Building_Services]

Have you tried -0.9?

Good old fashioned Mirroring can be useful, too. Then you could use +1

Or try using a different part. My UK library has several types of transition pieces. I've found some work more predictably than others when it comes to offsets and angles.

I think Width and Height get confused easily by the software.

Usually, I copy the 2 unconnected segments off to the side and mess around with the transitions there, because all kinds of wierd and not-so-wonderful things happen if I try to do it in-situ.

[Anonymous]

Hi Brewzer,

Sometimes if I'm getting fed up with trying to modify an eccentric transition, I find the best thing to do is just redraw it using the justifications. So if you wanted a transition that was flat-on-bottom, but centered horizontally, set the Vertical Justification to Bottom and leave the Horizontal Justification at Center when drawing the duct. Similarly, if you wanted a transition that was flat-on-top, and flat-on-right, you can set the Vertical to Top, and Horizontal to Right.

Sorry if you already know about this, but it took me a while before I learned this nifty little trick.

Best of luck,
-Brad

[Anonymous]

I have since found out that I can just use a concentric reducer and alter the eccentricity in there.

BUT

I also have found an issue with double eccentric transitions. When the height of the duct is different as it transitions, the part works correctly but when the height is equal, it squares the transition up to have no eccentricity in the Z.

Does MEP do set downs and set ups in one piece? This could be achieved easily with an duct transition that accepted = heights and allows a throat length adjustment. Would be nice to get one in 2010 .......

....... did a screen capture to show what happens ...........

copied the highlighted duct on the left (to the right) then changed the 800 height to 750 and it auto flattened!! (also does the same when widths are different) Edited by: brewzer on Feb 20, 2009 5:26 AM

[Anonymous]

Hey Brewzer,

It IS possible to do step-ups and step-downs with the OOTB eccentric transition, however, just not when the height of both connections is the same. The formula the eccentric transitions use to modify how far they move up/down is: d = (|h1-h2|/2)*x (where | is the sign for absolute value). In this equation, the x is the Eccentricity Z value you set in the drop down list. For example, if your duct transitions from 20" to 12" tall, then setting x=1 will move the 12" connection up 4". If you wanted to move the connection up 8", you could set x=2, or for 6": x=1.5. However, if h1=h2, then h1-h2=0, and no matter what you set as x, you will always wind up with 0. It uses this same formula to calculate the eccentric offset in the X direction.

I've tried to create an eccentric transition that allows you to make step-ups/downs with the same size duct height, but I don't think I've had much luck. Part of the problem is that AMEP won't let you enter negative values except for in the Eccentric Offset fields that are automatically created when you set the part to be Eccentric. Unfortunately, there's not much control when using these auto fields. Maybe someone else out there has had more luck than I have.

I know this doesn't answer your question very well, but hopefully it at least helps clear things up when using eccentric transitions.
-Brad

[Anonymous]

(accidentally did a double-post, decided to remove this one)

[gregg.stanley]

I think there are 2 problems in this post. 1 is that content builder does not support negative values, but it does create all the eccentric planes for a Ecc. Transition when the Eccentric Flag is set. to be able to utilize this, set the parameter visibility to True so it becomes a selection in fitting add.

A double offset is complicated, the way I have found to overcome this is to build an offset left and an offset right transition so you never need to add a negative value. This is a workaround but does work if you need both options.

Hope this helps

Gregg Stanley
AutoCAD MEP QA