Some of the reproduction floor boards have the reliefs in the back put in by use of a router. The original boards that were in my brother's '32 appear to have been cut by a very large "dado" blade. I was able to approximate that look by using a common hand held circular saw. I set the saw to the depth of the recess and measure the distance from the blade to the four edges of the saw's shoe. Next, I drew an outline of the recess and then built a small fence on the four sides, each side away from the outline by the various blade to shoe dimensions. Next, I positioned the saw at each of the sides of the fence and made a full depth cut from the rear fence to the front fence. Next, I set the blade about 1/16" deep and was able to move the saw back and forth and side to side until I had made a cut that covered the entire outline. I then set the cut deeper, made another cut and repeated until the I had the entire recess cut out. This is a not quite the use for which the saw was intended, so I'd recommend that the utmost in eye, face and other body part protection be employed.