Rings or tubes
 

How do you cope with simple geometry to make a tube, ie two circles traced consecutively and then extruded. Ive tried a circle then the offset curve tool but I get two different circles that are not linked, In Viz there is a command for the second circle to be part of the first circle geometry and afterwards one extrudes (l'ensemble), but in Maya I havent found such a command. I enclose sketch to illustrate. It would be good if the answer could be applied to a square as well .:beer:

The easiest way to do this would be using poly primitives. Create two cylinders or two cubes, one inside the other, and do a boolean function to hollow it out.

If you want to use NURBS circles, it will be trickier as they wont be one object after you finish. Even trickier if it's a square because each side of the square is a separate segment. Anyway, one way of doing this with a circle would be to create your two concentric circles, then duplicate and translate them for the other end of the tube. Now, perform the four lofts to create the surfaces (loft inner circle to outer circle at each end an inner circle to inner circle, outer circle to outer circle end to end). Delete your curves, delete your history, and group the lofts. You have to select the entire group when you want to use it as one object....kind of a drag, huh?

Maybe someone else has a more efficient way.

the easiest way to do that, I think, is to take 2 cylinders and boolean. Other than that, extruding the caps of a cylinder in is another way.

If you have to use curves, take those first two circles, duplicate and move them up, loft the outer and inner surfaces with polygon outputs, combine them together, and then use Append to poly tool to fill in the top and bottom.

See? I always take the longway around...heheheh.

Thanks a lot, that works a treat, as both know well you do.

revolve a linear 4point closed curve perhaps
rendering right now but im gonna try it soon:bgreen:

yip....just like i said,makes a very clean ring i might add also

Nurbs
 

First of all...one thing is not true...there's also a possibility to create a nurbs surface, which is only one object....I created a small animated gif for you...I created the circles...duplicated them, and moved them up...afterwards i created a loft with the outer circles and after that a loft with the inner circles...Now create a loft between the outer and the inner ring. In my case I added some isoparms, to create a round edge afterwards. not attach the surfaces, using the blend option. Connect all surfaces and at least Nurbs->open/close surface, with selected "V". Now you delete history, delete all curves..and you have one, clean nurbs-object, without having to convert it to Polys.

hope that helps...

b u l l e t

BulletProof, yes you are right, there is a possibility to create one NURBS surface for tube. I'm taking another approach. This is the same trick that I use for poly tube.

1. create a torus (8 section, 6 span) cubic type.

2. rebuild the surface (using keep CVs, U linear and V cubic.

3. delete isoparms u[1], u[4] and u[7].

You will then get a NURBS tube.

In polygon you have ability to twist the ring 45, so you can use only 4 spans and result directly as polygonal tube.