Loft is fantastic

:D:D pretty basic really but i'm very happy.

I wanted to draw a piece of duct....a transition piece to go from circular duct to rectangular duct, and make it so that the circular is offset from the rectangular.

i didn't need anything too pro so i started with a rectangle and a circle, then started drawing a few interconnecting lines. having no idea where to go from there i tried a few 3D commands, but none of my usual seemed appropriate.

hmm.....wonder what loft does?

quick search on yt......

YES! what an amazing command LOFT is!

click - click - click and it's done! i reckon the whole shape could be done in under a dozen clicks!

gave SHELL a go with it and it's exactly what i was aiming for (never thinking i would get close). i've no idea why it is called 'loft' tho!

i hope the yt link helps others

Rectangular2.dwg

Since you like that tool so much - here is a 6yr old (almost 7 now) tutorial that uses the Loft command.

http://home.pct.edu/~jmather/content/CAD238/AutoCAD%202007%20Tutorial%206.pdf

....a transition piece to go from circular duct to rectangular duct.....

I should also point out that that transition piece is wrong in several respects.

I will post correct solution when I get a chance.

First of all you must have some bends in the corners, even if you could do inside radius approching xero, you would still have outside radius the thickness of the material

And Shell doesn't return the correct geometry as sheet metal is cut in the flat with the edges perpendicular to the flat, so when it is folded it looks like this (I greatly exaggerated the sheet metal thickness so that the difference can be seen, but in your example using Shell these edges were parallel.

another view of the bent thickness

resulting from bending the flat pattern

When we learn Developments in school folding sheets of paper we might ignore real-world things like accounting for Bend Allowance as well.

Bend Allowance - sheet metal stretches on the outside of a bend and compresses on the inside of the bend. Calculation of allowance depends on Material properties, Thickness, Bend Radius and Bend Angle (and perhaps grain in the material).

Modern CAD programs take care of these calculations and developments for us.