I just bought some aluminum to make my own cookie cutters but was wondering how you join the ends? Also, should you sand down the "top" so you don't cut yourself when you're pushing down it? Use a towel? Tape?

I'm not sure how you attach the ends ...some kind of soldering or rivets?. Try folding over the top edge of the metal (before you bend for your design). This will give a blunt edge for your hand.

I would fold the left side in and the right side out-sort of like a hook & Eye theory-to make them attach after you cut out your cutter-the maybe try to pinch the ends down with a pair of pliers to keep them together-just an idea.

The best way is a rivet. they have a hand-held rivet that sort of looks like a staple gun for about $20 at the big hardware stores.

The edges may be very sharp, so either fold the tiny edge over and flatten or sand them. Otherwise, you will need lots of bandaids.