Fig. 118. Testing Dado for Depth.
A dado, Fig. 118, is made by cutting a rectangular groove entirely across one member into which the end of another member fits. Dadoes are cut across the grain of the wood; when similar openings are cut parallel to the grain, they are called simply grooves. Dadoes are used in the making of shelving, window and door frames, etc.
(1) Locate by means of the rule one side of the dado and mark its position with the point of the knife. (2) At this point, square a sharp line across the piece with knife and try-square. (3) By superposition, locate and mark the second side. (4) Square these lines across the edges of the piece a distance equal to the approximate depth of the dado. (5) Set the gage for the required depth and gage between the knife lines on the two edges. (6) Saw just far enough inside the knife lines that the sides of the dado may be finished to the lines with the chisel. Saw down just to the gage lines, watching both edges that the kerfs be not made too deep. (7) Chisel out the waste until the bottom of the dado is smooth and true. Test the bottom as shown in Fig. 118. Two brads are driven into a block having a straight edge until they project a distance equal to the proposed depth of the dado. (8) Pare the sides of the dado to the knife lines. These sides might be finished in another way, by setting a wide chisel in the knife line and tapping it gently with a mallet. If care is taken the successive settings of the chisel need not show.
Where the dado is to be cut on a piece narrow enough that the saw may be made to follow the line accurately, it is considered better practice to saw accurately to the line.