Give you a gander on how to find center of any size coin, using any size punch hole. When you decide to upgrade to silver, more expensive coin rings, a digital caliper is a cheap, effective, accurate way to find dead center of your coin.
Digital Caliper – http://www.amazon.com/Inch-Digital-Caliper-Extra-Battery/dp/B0002JFMIO/ref=sr_1_2?ie=UTF8&qid=1410720188&sr=8-2&keywords=digital+caliper
Punch and Die set -http://www.harborfreight.com/9-piece-punch-and-die-set-95547.html