Undersized Plywood Woes
I am looking for true 1⁄4 " birch plywood for some flat-panel doors I'm making. My rail bit cuts a slot that's exactly 1⁄4 " wide, and undersize plywood moves around in the slot. Can anyone direct me to dealers who supply true 1⁄4 " plywood?
—Tony Leone, Wesley Chapel, Fla.
Part of your difficulty is that your bit was meant to cut dadoes for solid wood panels sized to 1⁄4 " thick, Tony, not for plywood. If you work with plywood frequently, consider supplementing your two-bit stile-and-rail set with a bit that cuts just the rail and stile profiles, and a set of straight bits sized to common plywood thicknesses for cutting panel slots. The profiling bits require added setup time, but allow you to control the distance from the profile to the slot and the width of the panel slot.
You're unlikely to find true 1⁄4 " birch plywood because commonly available imports come in metric sizes. A 6mm thickness comes close to 1⁄4 " at .2362". However, some suppliers also market 5mm plywood, or .1969", as 1⁄4 " plywood. In our shop, 1⁄2 " Baltic birch measures about 12mm, or .4724".
For construction-grade plywood, the following sizes are common: 3⁄8 , 7⁄16 , 15⁄32 , 19⁄32 , and 23⁄32 ". For these sizes, straight bits like the one shown above can cut dadoes for plywood in such sizes as 7⁄32 or 15⁄64 (for 1⁄4 " plywood), 11⁄32 (for 3⁄8 "), 15⁄32 or 31⁄64 (for 1⁄2 "), and 23/32 (for 3⁄4 ").