The Technique of FURNITURE MAKING

Corner lock joint

Also known as box lock or finger joint it has considerable decorative possibilities if cleanly cut in good wood. It is usually regarded as a machine joint but can be cut easily, though somewhat laboriously, by hand, for the pins must be fine (about 3/16 in [5 mm] or 1/4 in [6 mm] wide) as there are no bevelled shoulders to hold the joint, which relies entirely on the glue to hold it. Setting or laying out and cutting is the same as for dovetails, but the board width must be equally divided and very accurately set out. Cutting can be simplified by placing the two ends together in the vice (162:2), and offsetting one by the thickness of the saw-blade, cutting one side of each pin into the waste (w), and then reversing the offset as shown by the arrows. The pins which remain after the sockets have been cut are shaded in the drawing.

MACHINE-CUT DOVETAILS

Machine dovetails are easily recognizable in finished work, for both pins and sockets are equal in width and the rake is fairly coarse (20 per cent). As has already been mentioned, the hand-cut terms are transposed, and the tail (drawer side) becomes the pin or male piece entering a socket in the female piece (drawer front). In machining lap dovetails both pieces are cut together, the male vertically and the lapped female horizontally, and therefore the movement of the finger plates and the rotation of the cutters, one for each pin and correspond­ing socket, give a rounded base to both pin and socket. In theory this could detract from the strength of the dovetails, but with a machine of the Brookman type (163), the cutting is so exact that in all probability the total strength is as good as the average hand-cut dovetails. Dis­advantages are coarseness of appearance in show dovetails, and the difficulty of fitting an arbitrary grouping of whole pins into an odd width. In handwork and with, for example, a drawer side 43/8 in (111 mm) wide the dovetails would be spaced accordingly, but in machine - work a pitch must be chosen which will best fit without sacrificing part of the shoulder adjoining a pin, a fault often seen in cheap mass- production work. The normal practice is to use 1 in (25 mm) pitch furniture-style pins, and to limit the drawer width accordingly, with other pitches for special work or where it is necessary to reduce the width and therefore the spacing of the individual pins. The actual length of the pin can be varied plus or minus 25 per cent over the

normal, and thus the thickness of the female piece (drawer front) and the width of the lap are immaterial.

Figure 164 shows the various types of dovetail possible with the Brookman dovetailing machines (163 and 165), with the 25 spindle automatic version with pneumatic clamps capable of cutting two drawer sides and two fronts simultaneously. These machines can also be used for dovetailing curved drawer fronts and thus their versatility is very great.