I started off making it with a jigsaw, but that didn’t work so well. It was far from perfect. Then I tried using a jig-like compass for the saw that would keep it in alignment but it would bend the blade and go off course.
I was stressed and frustrated and then I posted some question on Reddit and someone recommended a scorp. Something like an awl for scratching but I didn’t take it serious but then he said there’s a video and I saw it and thought I would give it a try.
I had some scrap pieces of aluminum lying around and put something together using that, a draw handle and self-tapping screws. It’s kinda like a compass.
The first circle took me about 3 hours (if I remember right) of going round and round. But I ended up with a perfect circle. You can see the metal dust on my gloves.
The 2nd one took maybe around an hour. What I did was sharpen the end of the scratching screw. I made it real sharp. The first one I left as is. It was much faster and I was excited I got two perfect circles. I thought for sure my round windows would be all crooked!
There is one screw near the wood handle that cuts and a longer screw that goes through 3 layers of aluminum.
They do have hole saws but you are going to pay for a big one. Maybe $50+. The advantage of doing it this way is you can choose the size. You can choose many sizes if you want.