Rectengular duct elbow with different size Width and Height

[liviu_culica]

Hey everyone,

I'm currently working on creating a Revit family for a rectangular duct elbow, and I'm encountering some challenges. Here's the situation:

I need the elbow to have different widths and heights on the two connections. The inner and outer radii of the bend should be manually input by the user, and the elbow should adjust accordingly.

I'm only creating solid geometry, without using voids, and I want to ensure the geometry respects the inner and outer radii.

The problem I'm facing is getting the sweep blend to correctly transition between the two profiles (Width1 x Height1 to Width2 x Height2) along the arc of the elbow while maintaining the correct inner and outer radii.

I'm struggling with how to define the arc path and constrain the sweep blend to ensure the elbow adjusts as needed. Any advice or step-by-step guidance would be greatly appreciated!

Thanks in advance!

[colegrovej]

Are these on center or is there allowed to be a height offset? Drop cheek elbow isn't easy, but they are really 3 sectional blocks when you have a height offset.

They are flat from the connectors on each end, with the final third piece in the middle where the offset is built into the drop cheek. That would be how I would define the family. define the 2 ends and then let that geometry control the middle block. Whether this works or not in Revit I do not know.

[liviu_culica]

Thank you for your suggestion! At the moment, I'm not working with a height offset. My main focus is to correctly shape a sweep blend that respects both the inner and outer radii, which will be set up by the user.

The challenge I'm facing is how to define the arc for the sweep path. I need the path to adapt to the radii, and then ensure that the profiles (Width1 x Height1 at the first connection and Width2 x Height2 at the second connection) adjust accordingly.

Additionally, I have straight sections on both ends, with their lengths controlled by parameters (Length1 and Length2). I'm trying to figure out how to define the arc sketch for the sweep blend path, where it should start, and how to manage the transition between the two different profiles along the arc.

Any insights on how to better control the sweep blend in this context would be really helpful!

P.S. If there is another solid geometry solution, I'm open to it.

[liviu_culica]

Please see my reply above, i replied wrong sorry

[colegrovej]

Why don't you just do centerline radius? The straight on the end should not be part of your transition. 

[colegrovej]

Like this? changes two directions

Uses a centerline input value and swept bend with sketched ends. Just define and offset for the center of the sketches and you can change how the fitting is constructed.

 

 Now the inside radi is parallel to the center line radi.

[iainsavage]

This other post might(?) help:

https://forums.autodesk.com/t5/revit-mep-forum/rectengular-duct-elbow-with-different-size/m-p/105958...

[liviu_culica]

I know how to do this on width, but it doesn't help me with height.

[liviu_culica]

Yes, but the inner and outer radii are not respected. I will attach some pictures to show where the Sweep Blend [Red Geometry] does not correctly make the Inner Radius or Outer Radius, unlike the extrusion [green geometry].

[liviu_culica]

And also this

[iainsavage]

Do the radii really need to be modelled so accurately? What is the benefit other than visually?

Per the other post that I attached the link to, to vary the height you have, as far as I know, options of:-

1. Use a swept blend or
2. Use an extrusion and then have other void forms which cut the extrusion.

Or maybe Dynamo can be used to plot points from formulas and join them with NURBS curves? I wouldn't know how to do that though.

[colegrovej]

I do not understand why you need two radii? The size of the openings is what dictates the radii. You change this with an offset.

I also do not understand why your green is is not parallel to your connector. Straight should just be that, straight. You have created a pie wedge

[colegrovej]

the duct should be defined just like you would do it in real life. the inner and outer radii are started from a different center, the center of the arc is offset the distance in the width change. Then you simply add straight to the end which is the offset in the width change again.

From my layout book. 

 

[liviu_culica]

Because the inner and outer should be customizable, I can input any value based on the straight length and main lengths of the elbow.

[liviu_culica]

Yes, with voids I can create the cut-out, but when using 2 voids parametrically, I concluded that the family is overloaded with profiles and geometries, and the loading process in autorouting in projects became very slow.

[liviu_culica]

I completely agree with you. On this principle, I have designed the elbow with cut-out voids. However, the voids add weight during the loading process, so I wanted to recreate the elbow without the voids, using only solids. But I encountered an issue - I couldn't control the middle part, where the inner and outer radius is, when using a sweep blend to achieve the curved shape from small to big.

[colegrovej]

They are customizable. But at the end of the day they can’t be so different the elbow dimensionally won’t work.

[iainsavage · Accepted solution]

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@liviu_culica wrote:
I completely agree with you. On this principle, I have designed the elbow with cut-out voids. However, the voids add weight during the loading process, so I wanted to recreate the elbow without the voids, using only solids. But I encountered an issue - I couldn't control the middle part, where the inner and outer radius is, when using a sweep blend to achieve the curved shape from small to big.

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I think you are focussing too much on what the elbow looks like rather than how it performs in the systems.

If there is a slight kink in the radius when you use a swept blend does it actually make any practical difference to your project or do you just not like its appearance?