Cutting the Dado in the Rails...

The dado's in the rails are cut to an approximate depth of 3/4", which would leave about an inch of solid wood for nailing the subfloor to.

To cut the dado, one could use a router set up with an 7/16" dado bit, but the bit was not available. Another option is to use dado blades on the table saw, but my set will only cut to a depth of 1/2" due to their diameter. The dado's seen here we cut using multiple passes on a single blade on the table saw.

The first cut was set to leave 1/2" on the side at a depth of 3/4". Next, the rail was flipped and ran through again to make the initial cut on the opposite side. All the boards were ran through this process of establishing the outside cuts.

The process of removing the middle "meat" of the wood from the dado involved moving the rip fence out in small increments, making a pass, flipping the rail around and making the next cut, and finally moving through all the remaining boards. It only took three adjustments to the fence to dado the 7/16" from the rails.

In the initial set-up for the outside dado cuts, use scrap 2 X 4 pieces and keep the measurements tight; you really want a snug fit here!

Be very careful in this phase of cutting the dado on the table saw. The guard cannot be used in this step and after many passes, it is very easy to get lazy with safety. A SUCCESSFUL PROJECT WILL INCLUDE HAVING ALL TEN FINGERS WHEN THE DAY IS DONE!