sbwertz
Member
We don't have metric bits at the Center for the Blind. Can I use an "X" size bit instead? It will be a bit larger...or a 25/64 which is a bit smaller?
I would try the 25/64, then wait a day to let the internal pressures of the wood adjust to the drilling and the heat of the drilling. Some woods will do all kinds of things when the wood is let to sit overnight. You have heated the wood when drilling, exposed the inside of the wood to air, and released the internal pressure of the solid piece of wood when you drilled that hole.
As John T said. There isn't any hard or fast rule to drill bit size. When I start on a new style, I start with a drill bit that is too small and sneak up on the correct size. I then write down that size on the instructions. About half the time my size and the printed size are not the same.
The size on the instructions is the most COMMONLY available drill bit size, NOT the closest / best size.
Many moons ago I got both a 115 piece set and a metric set of drill bits. I sometimes find that an odd size bit (say 13.3mm) will fit best.
When drilling acrylics the hole will be larger than when drilling wood. Go figure!