Gary
Active member
The guide does work, you can set it on top of the putty ring. You only need it to get it started. Just do not use the glass bit to drill the plywood, find a hole saw to match!
Even if you chose to make some super large putty ring, you are still using a guide to try to cut a circle, which is going to still try and skip, which will cause stress on the glass. It's not a good choice. The best option is to put as little stress as you can on the tank. Not to mention, you WILL not get a perfect cut making a hole in wood, and if somehow you did, your going to rub the diamond edge on wood. Again, it's a bad idea and IMHO will not work out with favorable results over the other methods mentioned.