So to make a cutter, I cut the can open, I use regular scissors to do that. If you have only a very nice pair of scissors that are beautifully sharpened, then maybe use some other tool for the cutting since the aluminium might damage or atleast blunt the scissors.
Cut out a strip from the can and bend one edge a bit over to make the edge less sharp, this edge will be the top edge of the cutter, so you don't hurt your hands.
I made a very small cutter so I made it from only a one layer of can aluminium. If you require something more sturdy, cut out a wider piece and then fold and press it in half lenghtwise, that edge will be the cutting side. Then bend the two edges on the other edge over to make the edge where your hands will press the cutter.
Then I form the cutter, the hardest thing is to keep the corners perpendicular to the egde, so the cutter will not get crooked.
I cut off the excess material and glue the flaps together, trying to make sure the edges are again on the same level. I've used two composite epoxy resin, not sure if that is the best glue to use if you are really making cookie cutters. Although I doubt the glue is going to leave any residues on the cookies once it's hardened. I read someplace that you could even staple the flaps together. I haven't tried that but it might work. So once the glue had dried I had myself a very nice roof tile cutter.
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