I turned my classroom into a camera obscura one year. I used a piece of copper flashing for the hole, drilled it between two pieces of scrap boards as has been mentions then ran a debur tool around the inside. I did not have the right size hole but it was close enough. We sat in the dark for a while and as the kids' eyes got accustomed to the lack of light they got more and more excited as they watched cars drive past upside down and backwards.

Have fun