Step 3: Cutting the dovetail grooves
To reduce strain on the router and dovetail bit, I like to hog out the bulk of the material on a table saw with a dado blade and then finish the dovetails with a dovetail bit on a router table.
Just in case the groove isn't perfectly centered on the block — and it never is — designate the edge of the block that was up against the router table fence as the top of the rail. Make sure that the grooves on both sides use the same edge as the top. This procedure will ensure that all the blocks are matched with each other.
Finally, repeat the process with the remaining four blocks, but only put the grooves on one side. These will be the front and back rails.
When making the dovetails on the front and back rails, adjust the fence on your router table just a tiny bit away from the router bit -- perhaps 1/32 of an inch. This will have the effect of giving the rails a tiny bit of clearance under the table top. Again, designate the edge against the router table fence as the top.