Great thanks Michael. That was it. It wasn't solid. All good now.

Michael

Hi Michael, I'm glad that solved it.

It can be easier in some ways to work on solids, because then you can cut a solid object up with Boolean commands and the various pieces of the cutting objects will stick around in the result keeping it a solid.

So for example if you have that revolved type shape, before you cut a hole in it it can be nice to seal off the end of it to make it a solid - there is a Construct > Planar command that will seal off planar openings like that.

Here's an illustration where I have a solid cylinder base object, and then I use the Boolean Difference command to cut a hole in it with the rectangle curve - note that the result in this case leaves the side walls that were formed from the rectangle extending out without needing to fill in those areas as a separate step:





- Michael

Here's another example - say you want to carve off the end of a cylinder.

To do that you might draw a curve in a side view that is positioned to intersect it visually, like this:



If your cylinder is an open surface, it might look like this:




You can use Boolean Difference to cut that cylinder surface up using the curve as the cutting object, which will cut it into pieces like this:



Then if you delete the end piece you'll see that you still have an open surface:




However, if you have a solid cylinder that has the ends capped off, it would look like this:







When it's a solid the booleans know how to combine the pieces together to keep the result a solid, which can help to avoid trying to manually build the side wall pieces.

- Michael