Usually, stock for the two members of the cross-lap joint can be best planed to width and thickness in one piece. Place two sets of face marks on the piece, so that there shall be one set of marks on each member after they are separated.
Fig. 119. Cross-lap Joint.
(1) Square the two ends, measure from each of these the desired length of each member, square knife lines around, saw-apart, finishing the ends square to the lines. (2) Measure from one end of each member the required distance to the nearer edge of the joint. Since the corresponding faces of the two members must be on the same side of the piece when the parts are put together, it will be necessary to lay off the groove of one member on the face and of the other member on the side opposite the face. If the joints are to be in the middle of each member but one measurement need be made. (3) Square sharp knife lines across at these points. (4) By superposition, locate and knife the second edge of each joint. (5) If the joints are to be in the middle of each member, before proceeding farther, test to see that the lines have been laid out properly. If the members are placed side by side and the ends evened as in laying out in (2) above, the lines will of necessity correspond. Turn one of the members end for end and even the two ends; the lines ought still to correspond. If they do not, points marked midway between the corresponding lines will give the correct position for the new lines, Fig. 120. (6) Extend the knife lines across the two adjoining surfaces of each member. (7) Set the gage for the required depth and gage between the knife lines on the surfaces. Though the groove on one member is laid out on the side opposite the face, do not make the mistake of holding the head of the gage against other than the face. (8) Saw accurately, Section 13, Fig. 32, to the knife lines and to a depth indicated by the gage lines. (9) Chisel out the waste stock, Section 38. (10) Test as shown in Fig. 121. A well-made cross-lap joint is one in which the members can be put together with the pressure of the hands and which will not fall apart of their own weight. Fig. 122 shows the results of "forcing a fit."
Fig. 120. Testing for Like Dimensions.
Fig. 121. Testing Bottom of Joint.
Fig. 122. Effect of Too Tight a Fit.