/3/ - 3DCG

>>628709
Here's the way I do it in Blender. it gives much cleaner, faster results than manually extruding and rotating. Of course, I'm sure this is applicable to other software as well.

>Step 1
Make the three extrusions for your tube as shown in the first picture. Notice how each extrusion occupies a 2x2m grid, where the blue hallway transitions to the red hallway via the purple turn.

>Step 2
Add the desired number of loop cuts. Five is usually what I do. I strongly suggest using odd numbers of loop cuts.

>Step 3
Place the 3D cursor exactly where the three grid squares share a vert in the interior of the turn. [Shift +S → Cursor to grid] is great for this. Set your pivot center to the 3D Cursor

>Step 4
Start by selecting all five of the loop cuts you added, and scale (S) on both axis EXCEPT the Z axis. You can lock it by pressing Shift + Z after you press S to scale. Once you scale the five loop cuts, deselect the outer two and scale the remaining. Do this until the last loop cut as shown in the final four pictures.

And that's how it's done.