Hi Mark,

> I tried to duplicate what you did, but when I select the two tube
> surfaces and then show points I get a set of points that describe rectangles.

Yup, this "show points" part is just for seeing the size of the underlying surface.



> If I delete those points, then the tubes just go away. What am I doing wrong?

You don't want to delete the points, it's the trimming boundaries (edges) that you want to delete - here's the steps that I wrote above again, pay particular attention to the part in bold:

"I've attached a version of your file here with those tube surfaces untrimmed and with the original full extended tube recovered. I created this version by selecting one edge of each of those surfaces, and then doing a Ctrl+A so that all the edges on each one were selected, and then pushing Delete to remove those trimming boundaries."

So the steps are to make an edge selection, not a control point selection - turning on control points is just the way to visualize the size of the underlying surface that's underneath all the trimming information.


> I wanted to extend the tubes above that flat surface but NOT below the more
> complex ends on the other end of the tubes (if that makes any sense).

After untrimming it gets extended in both directions, and then if you want the other end to stay as it was before you can then use Edit > Trim on the new big surfaces and cut them with the pieces on the other end. Sometimes in preparation for the retrim it can be convenient to do a ctrl+c copy of the edges before you hit delete to remove them, then after they are deleted and the surfaces are untrimmed do a ctrl+v to paste them back in and then those are used as cutting objects for the Trim.

That's what I did to produce the result in the attached version - it now has the bottom trimmed off to how it was before and the top is extended, is this what you needed?

Also if you like you can just keep your old pieces exactly how they were and construct your extended piece as a separate object by duplicating the end edges of the 2 surfaces in the double-end extended piece (to duplicate edges select them and then do Ctrl+C and then Ctrl+V) and then you will have some profile curves that you can extrude however you need to build the extended part and then cut the original with the extended piece. The untrimmed + retrimmed version is kind of cleaner though since it's all one single big surface rather than made up of multiple pieces.

- Michael