I learned this great trick from another calculus teacher, she suggested buying those paper wedding bells that are made of tissue paper. If you think about it they are made of two cardboard pieces and a *honeycomb* of paper, which when is spun about and the two cardboard pieces joined they make a bell. If you buy bells which are large enough you can cut them into more helpful shapes. I have cut a rectangle form, which generates a cylinder, a 1/4 circle, which generates a hemisphere, and a few other ones. Usually, after seeing a few of these the kids begin to understand what is going on, and they begin visualizing them without the crutch. Hope this helps. If you have any questions about what I mean email me.
Lari Garrison mathematics teacher Warren Township High School