Curved & Sloped Wall Cap

[willofmaine]

What's the best way to create a concrete cap for a stone wall that's both curved and the top of which slopes up and down? After finally getting an extrude-along-path (based on a 3d polygon) to work, the profile twists seemingly uncontrollably from start to finish. Thanks!

[Guest]

There's an untwist command to help reduce the twisting ..

"Unrotate 3D objects" under the Modify menu

Edited March 16, 2007 by Katie

[willofmaine]

Thanks Katie; never would have found that command! But, in this case, it didn't seem to do anything...

[Jonathan Pickup]

could you use the Extract Curve tool to extract the surface of the wall? maybe you could then use the protrusion tool to make it the size you want

[islandmon]

The twist is created by the bezier vertices as they fluctuate around the axis in the Z dihedral.

One way to correct this situation is to constrain the bezier dihedral to Z values equal to the top of the wall, only.

In other words, lateral precessional vectors.

[willofmaine]

Thanks for the responses. I didn't have much luck with using the Extract Curve tool; in any case, the cap is wider than the wall, so I'm not sure it would help even if I could get it to work. How does one 'constrain the bezier dihedral to Z values'?........

[islandmon]

The NURBS Path occupies a 12d VectorSpace. Assuming a 90? arc for the curve and 5? Rise of the wall ,

the NURB must use XYZ coordinates of arc curve based on the radius centered at XYZ,

then the NURB requires a Bezier control point opposite the center @ 45? on the outside of the arc.

The angular deflection between these 2 controls is the dihedral of the curve.

For minimal 'twist' of the profile the dihedral angle should be equal to the Rise angle.

Therefore, you will need to add back the angular difference of 5? to the base of the Cap Profile

if you want it to sit flush on top of the wall object.

[willofmaine]

Thanks Islandmon. By changing the angle of rotation of the profile (if that's what you're suggestion) I've been able to 'minimize' the twist in that instead of the start being flat and the end very twisted, both start and end were twisted half as much. I think next time maybe I will try using combinations of sweeps and straight, sloped extrudes...; though in all cases a single path that could be manipulated would be best...