The Three Cross Pieces. Key Piece.
The pieces required are as follows:—
.—Six pieces, 31⁄2 ins. long, with a half slot cut in the centre as shown. This slot must be exactly the width of the wood's thickness, and cut exactly half way through, so that, if two pieces are placed across by means of the halved joint, their surfaces will be flush. The slot must also be exactly in the centre.
.—Six pieces, size 21⁄2 ins. long, with a half-cut centre slot similar to that of .
.—Six required, these being 11⁄2 ins. in length, and with slots in the middle as before.
.—One of these last six requires special treatment, as it forms the key block of the puzzle. After its slot has been cut, one half of the narrow part must be sawn away, as shown in . The inner edge must also be gently rounded. The special use of this vital piece, which we will call the "key," will be fully explained presently.
.—Then, in addition to these, there are three central bars to make. Like the other parts they are 1⁄2 in. by 1⁄2 in., but are each 41⁄2 ins. long, and are cut as shown in . The end projections a are 1⁄2 in. long, and the cut-away part is exactly half the depth of the wood. Two of the three pieces (X and Y in ) are similar, but the slot b of the third one (Z) is only 1⁄4 in. wide instead of 1⁄2 in. As will be noticed, this 1⁄4-in. slot is not in the centre, but corresponds with the right-hand half of the larger slots of X and Y.
In making these twenty-one pieces, what should be borne in mind is that the different parts fit closely into each other. Consequently the slots, in width, must be cut so as to grip the thickness of the wood; in depth they must be exactly half this thickness.