Dovetail Joints

"Dovetail" refers to the shape of the projections of one member, when looked at broadside. These projections are called dovetails, or merely tails.

The projections on the other member are called tenons or pins, and the spaces between both tails and tenons are called mortises or sockets.

No. 47. A thru single dovetail is similar to a slip-joint except that instead of a tenon there is a dovetail. It is used in win

ow-sashes.

No. 48. A thru-multiple dovetail consists of a series of alternate tails and tenons which fit one another closely. It is used in tool-chests and in other strong as well as fine boxes.

To make a thru multiple dovetail joint, first square lines with a sharp pencil around the ends of both members to locate the inner ends of the dovetails and the pins, d e on X, Fig. 250, and l m on Y. The distance of this line from the ends of each member may, if desired, be slightly (1⁄32") greater than the thickness of the other member. Divide this line, d e, on the member to be dovetailed, X, into as many equal spaces as there are to be tails (dovetails). From the division points of these spaces, a b c, to the right and left lay off one-half of the greatest width of the mortises to be cut out, and also the same distance from d and from e, as at f f f f and g g g g.

The strongest arrangement of dovetails is to make them equal in width to the spaces between them. For the sake of appearance they may be as much as four times as wide as the spaces, but ordinarily should not be wider than 1¾".

Set the bevel-square so that it will fit the angle A B C, Fig. 250, in a right angle triangle, the long side of which is 3" and the short side ⅝". This is approximately an angle of 80° or a little more than one to five. From the points f f f f and g g g g lay off this angle to the end of the piece. Carry these lines across the end at right angles to the surface, h i, Fig. 250, and repeat the dovetail angles on the other surface. Mark plainly the parts to be cut out (the mortises), as on X in Fig. 250. Score with a knife point the inner ends of the mortises, d to f, g to f, etc., and across the edge at d and at e. With a dovetail-saw, Fig. 93, cut on the mortise side of each line down to the cross line, d-e, and also along the cross line from d to f and e to g. Chisel out the mortises taking care to keep the line d-e straight and square. The ends (not the sides) of the mortises may be slightly undercut to insure a tight fit.

Fasten the other member, Y, upright in the vise so that the end to be tenoned will be flush with the top of the bench, and with the working face toward the bench. Place on it the working face of X, (the member already dovetailed,) taking care that the inner ends of the mortises are in line with the working face of Y, and that the edges of the two members are in the same plane, as X on Y in Fig. 250. Scribe with a knife point along the sides of the tails on the end of Y (f'-j' and g'-h'). Remove Y from the vise and square down these lines to the cross line l-m (j'-n and h'-o). Score with the knife point the inner ends of the mortises of Y (n-o). Saw with a dovetail-saw on the mortise sides of these lines, chisel out the mortises and fit the parts together. When glued together, the joints should be dressed off.

Where there are several parts to be made alike, it is necessary to lay out the dovetails on only one X member. This may be used as a templet for laying out the others and they can then be sawn separately. Or all the X members may be clamped carefully together, with one X already laid out, rights and lefts in pairs, and edges and ends flush, the depth mark gaged all around, and then all sawn at once.

The dovetail joint is also made by first laying out and cutting the members having the pins, and then superposing this on the piece to be dovetailed, and scribing around the pins.

No. 49. A lap or half blind dovetail is a dovetail joint in which the tails on one member do not extend entirely thru the thickness of the other member. It is used in joining the sides to the fronts of drawers and other fittings where only one side is seen.

If the joint is to be used for a drawer front, the groove for the drawer bottom should be cut or at least laid out before laying out the joint. See also drawers, and Fig. 287. On the end of the drawer front, gage the depth of the joint. Gage the same distance on both broad surfaces of the drawer sides, marking from the front ends. Lay out and cut the dovetails as in a thru dovetail joint, taking especial care to have the groove for the bottom completely within the lower tail. Take care also to make the sides, one right and one left, not both alike, so that the groove will come inside. Lay out the drawer front by superposing the dovetailed side, X, on the end of the front, Y, as in a thru dovetail. Saw and chisel out the mortises and fit together.

No. 50. A stopped lap dovetail is one in which neither the tails nor the pins extend thru the other members. Hence the joint is concealed. The lap may be rounded. It is used in fine boxes, trays, etc.

No. 51. The blind miter or secret dovetail is a joint in which only part, say one-half, of both boards is dovetailed, the outer portion being mitered. The edges of the boards are also mitered right thru for a short distance so that when finished the dovetails are invisible. It is used in highly finished boxes.

BEVELED JOINTS

A beveled joint is made by beveling the members so that the plane of the joint bisects the angle at which the members meet. This is called the "miter" and may be 45 degrees or any other angle. It is a neat but weak joint unless reinforced by a spline, nails, or in some other way.

No. 52. A plain miter is a joint where the beveled edges or ends abut and are simply glued or nailed together. It is commonly used in picture-frames, inside trim, columns, boxes, and taborets, four or more sided.

For gluing mitered frames, the most convenient way is with the aid of the picture-frame-vise, Fig. 172. Nails are driven or splines inserted as soon as each joint is glued. Where this vise is not available, an ordinary metalworking vise may be used, as follows: Fasten one member, X, face side up, firmly in the vise. Bore holes in the other member, Y, at the proper places for the nails. Insert nails in the holes, apply the glue to both mitered surfaces, place the glued surfaces together, letting Y project about ⅛" beyond X. A convenient way to hold Y in place is in the left hand, palm up, while the left forearm rests upon X. Drive one of the nails home, and continue driving until the parts exactly fit. Then drive home the other nail. Now fasten together in the same way the other two members of the picture-frame, and then, one at a time, the third and fourth joint. This is the method used in picture-frame factories, and when once learned is very simple.

For gluing together at once all the members of a mitered frame, the device shown in Fig. 253 is convenient and is easily made. Out of two pieces of wood somewhat longer than the two end pieces of the frame, gains are cut of the exact length of the ends, as shown in the illustration. By applying two clamps lengthwise on the frame, all four joints may be glued together at once. If the frame does not come up square, it may be squared by means of a temporary brace, A, in Fig. 253.

The device shown in Figs. 254 and 255, is also an easily made and efficient tool. At least the small pieces, which receive the corners of the frame, should be made of hard wood such as maple. It is self-adjusting but care must be taken not to buckle the parts of a narrow frame by over pressure. It is well to soap or oil the corner pieces to prevent their being glued to the frame.

In gluing together long mitered joints, in six or eight sided taborets or columns, in which the members meet edgewise, one method is to wrap a few turns of bale wire around the parts and drive in wedges under the wire to obtain pressure, Fig. 256. Another method is to wrap a stout rope, such as is used for window weights, around all the pieces, properly set up, then to tighten it by twisting it with a stick thru a loop, Fig. 257. A still more effective way is by means of the Noxall Column Clamp, a powerful device, used chiefly for gluing up such pieces as the pillar of a centrally supported table, Fig. 259. Care must be taken with all these devices to protect the corners, unless they are to be rounded off afterward. A good way to protect them is with pieces fastened together in the shape shown in Fig. 258, b, and Fig. 257, the interior angle being equal to the exterior angle of the piece to be glued. In the case of a taboret with slender legs, care must be taken to insert blocks between the separate legs as well, to brace them apart and to keep them from bending under the pressure. These methods have the advantage that they are speedy, since all the pieces go together at once; but unless the pieces fit exactly the joints will not close.

Another method is to glue and clamp the pieces of the taboret together two by two, using blocks as shown in Fig. 258, a. Care should be taken to put the pressure of the handscrews as far out as possible so as to be sure that the outside of the joint closes. This method has the advantage that, as only one joint is glued at a time, the work can be done more deliberately. Moreover, if when three pairs of a six-sided taboret are together, the other three joints do not fit exactly, they can then be refitted.

Another method is to glue pieces of soft wood on the exterior of each pieces as shown in Fig. 258, c. These blocks should be of such shape that the opposite sides of each pair are parallel. When the glue is dry, they are used as corners on which to clamp the handscrews. This method has the disadvantage that the blocks may break loose at a critical moment.

In addition to any of these methods of tightening the joints, to make sure that the ends of the joints close tight, pinch-dogs, Fig. 178, may be driven into the end grain, and corrugated fasteners, Fig. 228, also driven into the ends, make the joint quite secure.

No. 53. A doweled miter is one in which one or more dowels are inserted and glued into holes bored into the beveled edges. It may be used instead of nails, as in large picture frames.

No. 54. A spline or tongue miter is one which has a spline or tongue inserted at right angles to the joint. Since it furnishes more gluing surface, it is stronger than a plain miter.

No. 55. A slip-feather or slip-key miter is one which is strengthened by a slip of hardwood glued into a saw kerf cut across the mitered angle. It is used in picture-frames and in boxes.

No. 56. A slip-dovetail miter is one in which a trapezoidal shaped key is inserted in a dovetail socket cut straight across the miter. When dressed off, it gives the appearance of a dovetail on each face. It is used for the same purpose as a spline miter.

No. 57. A double dovetail keyed miter is one in which a double dovetail key made of hard wood is inlaid across the joint. This is a favorite joint with Oriental joiners.

No. 58. A ledge and miter or lipped miter joint is made by rabbeting and mitering the boards to be joined so that the outer portion of the two boards meet in a miter. It is strong and good looking and may be glued or nailed. It is used for fine boxes.

No. 59. A stopped miter is useful for joining pieces of different widths, when both sides can be seen.

No. 60. A double-tongue miter is made by cutting on the adjoining edges tongues which engage in each other. It is used in high class joinery, on members that join lengthwise of the grain.

No. 61. A stretcher joint is a slip joint in which one or both sides is mitered. It is used in frames for stretching canvass for paintings by driving wedges from the inside. Two forms are shown in 61a and 61b.

No. 62. A strut joint is a form of miter joint used in making trusses.

No. 63 and 64. A thrust joint or tie joint or toe joint is one in which two beams meet at an oblique angle, one receiving the thrust of the other. The toe may be either square as in 63, or oblique as in 64. The pieces are bolted or strapped together with iron. It is used for the batter braces of bridges.

No. 65. A plain brace joint is one in which the brace is simply mitered and nailed into place. It is used for bracket supports.

No. 66. A housed brace joint is a joint in which the brace is housed into the rectangular members except that the outer end of the mortise is cut at right angles and the inner end diagonally to receive the brace which is cut to correspond. It is much stronger than 65.

No. 67. An oblique mortise-and-tenon or bevel-shoulder joint is one in which the shoulders of the tenoned beam are cut obliquely and its end is cut off at right angles. The cheeks of the mortise are correspondingly sunk. By these means the tenon prevents lateral motion while the whole width of the beam presses against the abutment. Thus a much larger bearing surface is obtained. The whole is bolted or strapped together. It is used in heavy truss work.

No. 68. A bridle joint is an oblique joint in which a bridle or "tongue" is left in an oblique notch cut out of one beam. Over this tongue is fitted a grooved socket cut obliquely in the other beam. It is used in truss construction.

No. 69. A bird's mouth joint is an angular notch cut in a timber to allow it to fit snugly over the member on which it rests. It is used in rafters where they fit over the plate.

No. 70. A plain or rubbed or squeezed or glue joint is one in which the edges of two boards are glued and rubbed together tight. It is used in table-tops, drawing-boards, etc.

To make this joint, first the boards are all laid down flat, side by side, and arranged in the proper order. Three considerations determine what this order is to be: (1), if the grain is of prime importance, as in quartered oak, then the boards are arranged so as to give the best appearance of the grain. (2), if possible, the boards should be so arranged that the warping of each board shall counteract that of the adjacent ones. For this purpose the boards are so laid that the annual rings of one shall alternate in direction with the annual rings of the next, Fig. 280, a. (3), if possible, the boards should be so arranged that after being glued together they can all be planed smooth in the same direction. When the above requirements have been met so far as possible, this order should be marked on adjoining edges for later identification. The edges of the boards to be joined should be finished with a jointer.

There are two principal methods of gluing edge-to-edge joints, rubbing and squeezing. In a rubbed joint, the surfaces to be joined should be planed so as to meet thruout exactly. After properly planing one edge of each board, keep one board in the vise, jointed edge up, and place its to-be neighbor in position upon it. Then use these four tests for an exact fit. (1) Sight down the end to see that the faces lie in the same plane. (2) Examine the crack from both sides. Be sure that both ends touch. Test this by pulling down hard on one end of the upper board and noticing if the other end is still in contact. If the other end opens, swing the upper board horizontally on the lower board to see where the high place is and then correct it. (3) See if the upper board stands firmly on the lower board by feeling gently to see if it rocks, or by rapping lightly the lower board. (4) Slide the top board slowly on the lower one to see if it adheres or "sucks."

After the pieces have been warmed, which should be done if possible, the glue is spread on them, Fig. 260, and they are then rubbed slowly back and forth in the direction of the grain, pressure being applied by the hand and care being taken not to open the joint in the least. As the glue sets, the rubbing becomes more difficult. It should be stopped when the boards are in their proper relative positions. In rubbing together the edges of two boards, handscrews may be fastened to one in such a way that their jaws serve as guides for the other board to slide between, Fig. 261. Care must be taken to make the jaws of the handscrew diverge enough not to pinch the upper board.

Another method is to clamp a spare board alongside and projecting above the lower board. This spare board acts as a guide against which the upper board can be pushed as it is rubbed back and forth. The rubbed joint is especially suitable for short boards.

In joining long boards, a squeezed joint is common. In this case, the edges are planed so as to be very slightly concave from end to end. The object of this is to counteract the subsequent shrinkage which is likely to take place at the ends of the boards before it does at the middle. The pressure of the clamps may be depended upon to close up the middle, and, especially if dowels are inserted, the joint will be strong enough to resist the elasticity of the boards.

When the fit is good, warm the wood if possible, prepare the clamps, put a thin film of glue over both edges which are to be together, apply the clamps rapidly, keeping the faces flush, and set away to dry for at least six hours. Then another piece may be added in the same manner. If the boards are thin and wide, and therefore likely to buckle, they may first be handscrewed to cross-strips to prevent their buckling. The cross-strips are, of course, slightly shorter than the combined width of the boards so that the full pressure of the clamps may come on the glued joint.

No. 71. A rebated, rabbeted or fillistered joint. Rebating is the cutting of a rectangular slip out of the side of a piece of wood. The re-entering angle left upon the wood is called the rebate or rabbet. A rebated joint, then, is one in which corresponding rebates are taken off edges so that the joined boards may overlap. It is used in flooring and siding.

A board is rebated and filleted when two adjoining rebates are filled with a fillet.

No. 72. A matched or tongue-and-groove joint is made by making a projection or "tongue" in the center of the edge of one board, and a corresponding groove in the center of the other so that they will match together. When used for flooring, the lower side of the grooved board is slightly rebated so that the upper edges will surely touch. This sort of flooring can be blind-nailed.

No. 73. A beaded joint is similar to a matched joint except that a bead is worked on one edge to disguise the joint for decorative purposes.

No. 74. A spline-joint is made by plowing corresponding grooves in the edges to be joined and inserting a spline or slip-feather. It is used in plank flooring.

No. 75. A doweled joint is made by jointing the two edges carefully, boring holes opposite each other and inserting dowel pins when the two edges are glued together. It is used in table tops, etc.

Where the boards are thick enough to allow it, a squeezed joint is greatly strengthened by the insertion of dowels.

The essential point in inserting dowels is to have the holes for them directly opposite one another and at right angles to the surface. The following is a convenient method where boards are to be joined edge to edge, Fig. 262. Place the two boards back to back in the vise with the edges and ends flush. Determine approximately where the dowels are to be inserted. With the gage, mark short lines at the points of insertion in the center of each edge, gaging from the outside faces. Across these lines score accurately with a try-square and knife. Then bore the holes with a dowel-bit at the intersection of the lines, Fig. 263. If this is carefully done, the holes will be directly opposite one another, and equidistant from the faces of both boards. All the holes should be of equal depth, say 1", in order that the dowel-pins, which should also be cut of equal lengths, may be interchangeable. After boring, the holes may be slightly countersunk in order to insure a tight joint and the easy slipping of the pins into place. The latter result may also be obtained by slightly pointing the pins with a dowel-pointer, Fig. 123. It is also a wise precaution to cut a small groove along the length of the pin to allow superfluous glue to escape from the hole. The dowel should be dipped in glue and inserted when the glue is applied to the joint.