DoveTail Joints

Re-printed from The Manufacturer and Builder, Volume one, 1869

        The strongest and most permanent joint made in carpentry and cabinet-making, where pieces of wood are fastened together at right angles, is the dove-tail. When made in some of its most approved and perfected forms, it is equal, in neatness and artistic finish to the mitre joint; The mitre is a comparatively neater method of joining wood at an angle, but the dove-tail possesses the greatest possible strength. It is generally employed in articles made of thin materials, such, for instance, as drawers, boxes, chests, etc. If we examine a dove-tailed box, we observe that it consists of six pieces, or sides, four of which are interlaced, or dove-tailed together at the corners, forming a rigid frame-work. This is shown in Fig. 1. When properly put together, the joint formed by the two pieces A and B is strengthened and braced by those of C and D. The rigidity of the box is of course still further increased by attaching the bottom, which may be done by means of screws, or glue and screws may be both employed. There is an advantage in the employment of the latter, for if the dove-tails should be somewhat loosely fitted, or the glue lose its adhesive power, the screws will prevent any disposition of the four sides “to rack.” When we wish to have the lid of considerable depth, and fastened together by dove-tails, the box is made sufficiently deep to form both box and cover. The top and bottom pieces are then added. The six pieces so joined have the appearance of a rectangular block or cube. A saw is employed to separate the cover, or lid, from the bottom portion. This method has the advantage of saving some labor in dove-tailing. It insures the exact agreement in size and form of box and cover. It would be somewhat difficult to effect this were they separately made. This would especially be the case in making such articles as desks and writing-cases. In all boxes where the bottom and lid are made together, the line of division is marked on the four exterior sides. One of the dove-tail pins is placed on that line. This pin should be about twice as wide as the others. When divided in forming the cover, either part is then of the size of the others. In order to have the cover and box show a mitre joint, the dove-tail and joint pin are made to a mitre; whereas, if the pin were left square, or made as usual, the box when cut open would show the rectangular lines of the pin and dove-tail.  The top and bottom of the box may be fitted in various ways. They may be glued, or otherwise fastened, on the square edges of its sides. They may be rebated; or, to cause a more finished appearance, they may be both rebated and mitred.  

        In Fig. 2, the common dove-tail joint is shown, in which the dove-tails and pins are seen upon both sides; When the grain of the wood of the parts joined together runs in the same direction, such parts will expand and contract equally, should they be equally moist and dry. This expansion or contraction can then take place without injury to the work. In order to effect this, it is advisable to make the work from the same board, or from pieces of boards of the same quality of timber, and having come as near as may be from the same relative position in the logs from which they were sawn. This can be very readily ascertained by an examination of the ends of the pieces, the curvature or configuration of the grain furnishing the desired information. If the pieces of work have the grain running in contrary directions, as seen in Fig. 3, it is evident that the portion D would entirely prevent the expansion of C, and the ‘restraint would cause injury to the joint. This would be the inevitable result in case of much expansion or shrinkage. In order to explain this more fully, let Fig. 4 represent the surface of a board, its edge being indicated by a b, and the end by c d. It is evident that no contraction can occur in the direction of the line a b, which is that of the grain of the wood. Along this line the wood-fibres remain quite rigid, the shrinkage taking place in the direction of the line c d. The flexible fibres are in this direction, and more or less disposed to become curved from exposure to the atmosphere. The four marginal lines of the board are not likely to change very materially in respect to each other, and if made parallel and square at first will remain so.  

         Fig. 5 represents the ordinary dove-tail joint. Fig. 6 shows the parts before they are put together. The pins are shown at P, and the dove-tails at C. The pins and dove-tails are commonly made of about the same size, as this gives the strongest kind of attachment; but in many forms of cabinet-work the dove-tails are made on the front, or more exposed portion, and the pins are cut about one fourth less in size than the dove-tails, in order that as little as possible of the end wood may be seen. In laying out dove-tails, the sides and ends of the boards are first marked across with a gauge or square, to indicate the inside measure of the box or drawer, and also the bottom of the pins and dove-tails. The portions beyond the lines are left a little longer than ultimately required. In laying out the pins very little care is required. It is a common practice to mark them off at random. Care must be taken to leave the outside pins nearly twice as large as the inside ones. The dove-tails are then marked from the pins; they thus become exact counterparts of each other. The piece upon which the pins are made is laid upon the work-bench, and that upon which the dove-tails are to be made is held vertically upon it in the exact position that the two pieces are to occupy. A fine point or pencil is then used to mark the outline of each pin. This being done, a fine saw may be used for both pin and dove-tail, taking care that it follows the outlines and does not cut below the gauge mark that limits the interior of the work. By not cutting into the outline marks, both pins and dove-tails will be a trifle too large, and in driving them together they will compress each other a little, and produce a close and accurate joint. After cutting with a saw to the depth required for the pins and dove-tails, a sharp chisel is used to remove the wood that remains between the portions that are to be retained. A ready method of doing this is to lay the several pieces one upon another, similar to a flight of stairs, and cut half way through them successively, and then turn them over, arrange them as before, and cut the other side, which operation removes the pieces. This method enables a mechanic to work with celerity, and also permits him to see what he is doing. The chisel should be held so that the cut will extend inward at the base of the pins and dove-tails, meeting at the centre of the board. This will insure a tight-fitting joint when the work is put together.

        It is advisable not to make the pins and dove-tails with any considerable degree of bevel, or the connection will be deficient in strength. When pine or soft, brittle wood is employed, the parts should be slightly beveled; but more bevel should be allowed to hard wood, such as oak or mahogany. In making the out-lines of the work upon some hard woods—mahogany, for instance—it is difficult to observe the lines; but if the surface of the wood be rubbed with chalk before marking, the lines will be rendered conspicuous.

        In gluing the dove-tails of a box, as seen in Fig. 1, it is best that the pins on the side A be first sparingly glued, and held by some sort of fixture in a vertical position, with the glued end uppermost. The end B, which is to be attached, is held horizontally, and forced down upon A. This is conveniently done by blows of a mallet or hammer, which, to prevent injury to the work, are received upon a piece of waste wood placed directly over the pins. When the pins come flush with the upper face of the board B, the piece of waste wood is placed beside them, so as to allow the pins to rise above the surface. It is essential that the pins and dove-tails should exceed the thickness of the board, so that when the superfluous length is planed off, a good, clear joint is apparent. The second side, C, is then glued, similar to A, and held in the same manner, and B is forced down upon it. The three sides of the box are thus united. The pins upon the other ends of A and C are then glued; the end B is placed face downward upon the bench or floor, resting upon two smooth strips of wood, placed close beside the projecting pins. Care should be taken to have it rest firmly. The remaining side, D, is then driven down upon it, and the four sides of the box united. The superfluous glue, forced out by the crowding together of the parts, is then scraped off, while yet soft, with a chisel; but, where moisture will not affect the work, the remaining portions of the glue may be washed off with a sponge, wet with hot water from the glue kettle. Where it can be safely applied, this is the best method, as every vestige of the glue is removed from the surface of the work.

        To ascertain if the box has become rhomboidal, or, as it is technically termed, “out of square,” it can be tested with the fitting square, and it should be immediately corrected before the glue becomes “set,” or dry. This correction can be made by pressure applied to the longer diagonal. A ready means of ascertaining any deviation from a square is to find the exact distance that should exist between diagonals, and then to cut a thin strip of wood of just this length, and so sharpen the ends that they will be more acute than the angles of the box. It will exactly fill the space between the diagonal lines if the angles are correct—that is, if they are exactly ninety degrees.  

        In some kinds of dove-tails the pins are more or less concealed. Fig. 7 shows a form called the lap dove-tail, which is generally employed for the fronts of drawers. Fig. 8 shows the manner of attachment. The pins are on the front of the drawer, and are first made. Gauge lines are marked to denote how far the pins shall extend inward. It. will be observed that neither pins nor dove-tails extend quite through the wood in which they are respectively formed; hence the concealment of their end grain. It is, however, immaterial in which piece the pins or dove-tails are made. The depth of the latter is generally about one eighth of an inch less than the thickness of the piece containing them, and the pins are of a corresponding length. If the ends of the pins were made even with the end of the wood, they would reach the bottom of the dove-tails, and an open corner would be the result. The pins are generally cut back one eighth of an inch from the front end; otherwise the amount of the dove-tails would be shallower than the thickness of the piece in which they are made. In drawers, the sides are about half the thickness of the front; the dove-tails are, therefore, cut quite through them, the same as in the ordinary dove-tail, shown in Fig. 5. If the front part of the drawer is to be covered with veneer, the pins are cut quite through with a saw, the kerfs being entirely concealed when the veneer is applied.  

        Fig. 9 shows the mitre dove-tail joint, and Fig. 10 represents its construction. This is the neatest and the most difficult to make. The pieces must be cut to the external dimensions of the work, and then rebated out square at each end; and after the pins and dove-tails have been formed, the square rebates are cut into a mitre joint, a rebate plane being used for the purpose. When properly finished, neither the pins nor their mode of concealment can be seen, and the work has the appearance of a plain mitre joint. As in the mitre, this rebate should have an angle of forty-five degrees.  

        In Fig. 11 is seen another form of finish sometimes given to the lap dove-tail, shown in Fig. 7. When the two pieces are put together, they resemble the form seen in Fig. 12, and the final finish is given by simply rounding the corner, removing the angular projections, until it assumes the appearance seen in Fig. 11. Boxes are often made by rebating one side or piece, the end of the other being received into this rebate, and then glued and nailed. The successive operations present the appearances shown in the cuts. It is quite a quick and cheap method of joining, and, when nailed from both angles, is, next in strength to the dove-tail.  

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