The Technique of FURNITURE MAKING

HAND-CUT DOVETAILS

Three types are used: (a) through dovetails which show on both sides of a corner joint (154:1); (b) lapped dovetails which show on one face but are concealed on the other by a lap or lip (154:2), and (c) secret dovetails in which the joint is entirely hidden (155:2). For an understanding of the principles involved— which are intrinsically the same for both hand and machine dovetails with only the procedure

differing—it is necessary to describe the laying out and cutting of all three types in some detail.

Through dovetails

These show as end-grain wedge-shaped pins on one surface and square or oblong end-grain tails on the other (154:1). The true shape of both tail and pin resemble a dove's tail (after which they are named), and in through dovetailing by hand it is usual to make the tails at their widest part about twice that of the pins, but for extra strong work they can be equal and are colloquially known as 'cistern dovetails'. There are, there­fore, no hard and fast rules regarding their width, and as with all other types a compromise is usually effected between strength and appearance.

Setting/laying out

The two sides to be joined need not be of equal thickness, but the thickness of each must be constant across the width and the long-grain edges must be parallel. It is advisable to cut the ends truly square and to the overall length, as this facilitates the setting out which must be accurately done, but a fractional fullness in the length can be left for subsequent cleaning off. Assuming that the ends have been cut square and to the true length then either a sharp marking-gauge or a cutting-gauge is set to the exact thickness of one piece (154:lA) and gauged all round the end of the other piece (B); the thickness of (B) is then similarly gauged round (A). The spacing of the separate dovetails must now be determined, and while an experi­enced worker might trust his eye alone the beginner should adopt the following procedure. Determine first the width of the end-grain pins (B) and, assuming that each pin is to be approximately 1/2 in (12.5 mm) in width, gauge a 1/4 in (6 mm) from each parallel edge of 154:6A to accommodate half a pin, and divide the space between into as many divisions as there will be whole pins. If these are, say, four then five divisions are required, and 5 in (127 mm) (or any number of inches [millimetres] easily divisible by five) is measured off on the rule and measured obliquely across the board as shown; the divisions can then be drawn in to give the exact centre of four equally spaced pins.

Dovetail rakes or bevels

The actual rake of the dovetail must now be decided. For carcass-work where strength is necessary and appearance of little consequence the slope can correspond to a slope of 1 in 5 or 1 in 6; while for show-work, drawer sides, etc., 1 in 7, and for very fine decorative dovetailing 1 in 8, can be used, always bearing in mind that the rake must not be too coarse, i. e. much below 1 in 5, or the short grain will be too weak, while too fine a pin, i. e. over 1 in 8, will have no real holding power. To set out these rakes it is only necessary to square a line across the bench-top and measure off the distances as in 154:3, setting an adjustable bevel to the rake or making up a simple wooden template (154:7). With proficiency neither bevel nor template will be required, and the eye alone will soon grow accustomed to the required slopes.

Cutting the dovetails

In practice it hardly matters whether the actual pins or the tails are treated first (although in some instances—tall carcass sides and in secret dovetails—the pins must be worked first and the tails from them), but as a rule the tail side is marked out and the pin side from it. After marking out the tail side in pencil (154:6, 7) the pin sockets or cores are sawn in with the fine dovetail saw, with the tail piece held in the vice and tilted over to bring the markings vertical (156). This sawing should be on the pencil-line, square across the edge and down to the gauge - lines, but the pin sockets should not be chiselled out at this stage—a mistake beginners often make—for the actual pins must be marked out before any chiselling away can be done. The pin piece (B) is then held in the vice (154:10), and the tail piece packed up and placed on it truly square with the edges flush (the drawing shows the positioning for a lap dovetail in which the tail piece is set back for the lap). The point of the saw is then drawn through the cuts, transferring them to the end grain of the pin piece, and once this is done then the pin sockets on the tail piece can be chiselled out, working from either side in a series of bevel cuts (154:11), so that the waste is fully supported with the last cuts vertical and exactly on the gauge-line; the end shoulders can then be sawn

in with the fine dovetail-saw. Sawing in of the pins in the pin piece can now be done, again held in the vice and sawing-in as in 154:8 but down to the gauge-line on either side for through dovetails, with a centre cut in each tail socket to clear the waste. It is a useful pre­caution to mark this waste 'O' as in 154:9, and the sawing must always be on the waste side and alongside, but never on the gauge-marks or the pins will be too small. Alternatively, instead of sawing out small wedged-shaped pieces along­side the pins as for lap dovetails (154:8), the pins are sawn in and the waste partially sawn away with a scroll-saw. It hardly matters which, but here again a fast worker will not bother to set up another tool.

Chiselling the sockets will be done as for the tail piece, and it is customary to incline the vertical cuts through the thickness fractionally inwards towards the centre so that the bed of the sockets is undercut; but the cuts must not go over the gauge-lines on the faces. When all the cutting has been finished the dovetails can be tried together, but they should never be knocked fully home until they are glued up, for it is axiomatic that a good dovetail only fits once. Application of through dovetails is in box sides, etc. and in all right-angled framings where it does not matter if the joint shows.