There was only one problem: the cutoff wheel itself. After reading the comments lots of folks posted (some helpful, some not), it was made clear that using the cutoff wheel was not a good idea, since it can't take pressure on the top and could break and send pieces flying! Way too dangerous! One guy said he used acrylic, but couldn't cut it into a perfect circle. I knew I wasn't going to go out and buy acrylic just to cut a sloppy circle so I set about looking around the house for something else.
Step 1: Find an Appropriate Size Bottle Cap!
Step 2: Drill a Hole!
Step 3: Screw Onto Your Mandrel
Hope this was helpful!