I have been creating model rockets with things around the house. (Pringles cans, Paper towel tubes, etc.) However, I've found it to be more cost effective to buy a pack of BT-20 tubes and cut them down to use for my A, B, & C motor mounts. I needed a way to cut a 18" tube into six motor mount tubes.
This jig allows you to cut the right length of tube for A, B, and C sized engines.
I have also included my motor mount spacer template. Simply print the template and glue it to a cereal box or shoe box. When dry, cut out the center ring and, starting from the outside, cut down the rings as needed to fit your tube. This will center the engine in whatever you're using for the body tube.