Why sweep modifier rotate it's shape when working in 3D spline?

[Waseem_Dabbas]

I have this issue that happen when I'm applying sweep modifier to a 3 dimensional spline that described in an attached image, any idea what is the reason and how can I solve it?
Thank you

[leeminardi · Accepted solution]

The twist vector is ill defined when two vertices are directly above each other. 

Try using LOFT instead.  Draw the centerline of the shape and a square of the cross section then go to Create, Compound Objects and use Loft.  It may not be necessary but loft provides you with the ability to twist segment of the shape.

[Waseem_Dabbas]

That helps, thanks a lot 

[Waseem_Dabbas · Accepted solution]

Also I would like to add (One other guy answered me in another forum) that if you disable an option 'Optimize' under the 'Interpolation' menu inside Spline modifiers with steps at least '1'  it will fix this problem even if you are using sweep modifier.

[Anonymous]

I solved the issue by selecting the vertex on the other end and clicked "MAKE FIRST". 

[Waseem_Dabbas]

I tried your method, it works for the side of the "make first" vertex, but it doesn't for the rest of the line, in short, it flipped the rotate.

[Anonymous]

Please send file here so I can take a look at.

[Anonymous]

Did you you also try to add your Square shape in the middle of the path ?
When I use Loft on a complex path, I always have one shape at the beginning of the path, at the middle and at the end. This will give you a better control.
If it still gives you strange results, use the method I suggested. It works fine here.

[Waseem_Dabbas]

Please find the file in the attachment

[Waseem_Dabbas]

"Loft" is working fine, I was asking about the sweep modifier.

[Anonymous]

Works also here with the sweep modifier.
Can't find your file here 

[Anonymous]

[Waseem_Dabbas]

it doesn't work with the shape i'm doing

[Waseem_Dabbas]

oops! my fault

I re attached

[Anonymous]

Like already said: Turn OFF optimize in the spline interpolation.

[Waseem_Dabbas]

sure, I already mention that in the third comment.

Thanks a lot.

[Anonymous]

Ah, I see. thought you did it with a custom shape.
Build in sections (especially BAR) are sometimes need some  additional tweaking.
See screenshot below:

[Anonymous]

.....and tick "Banking" in the sweep modifier