_No. 41. A double mortise-and-tenon_, Fig. 267, consists of two tenons side by side in one piece fitting into two corresponding mortises. It is used in joinery, as in door-frames, but not in carpentry.
_No. 42. A haunched mortise-and-tenon_, Fig. 267, is made by cutting away part of the tenon so that that part of it will be much shorter than the rest. The haunch gives the tenon great lateral strength and saves cutting so large a mortise hole. It is used in panel construction, as where the rails are joined to the stiles of doors.
First plow the groove in all the members. This should be of the same width as the thickness of the tenons, which is ordinarily one-third of the thickness of the frame. The groove is approximately as deep as it is wide. Lay out and cut the tenon the width of the entire piece, minus, of course, the depth of the groove. The mortise should not come too near the end, or the portion of wood outside it will shear out.
Hence the tenon is narrowed on the outside enough to insure strength in the mortised piece. The rule is that the tenon should be one-half the width of the rail, minus the groove. But enough of the tenon is left full width to fill up the groove at the outer end of the mortised piece. This is called the _haunch_. The width of the mortise is equal to the width of the groove, its length to the width of the tenon.
Before a.s.sembling the panel frame, put soap or tallow on the corners of the panel to prevent its being glued to the frame.
_No. 43. Table or taper haunching_, Fig. 267. Sometimes, as in table construction, for the sake of stiffening the rail, or in places where it is desirable that the haunch does not show, the haunch is beveled from the tenon to the edge of the rail.
_No. 44. A bare-faced tenon_, Fig. 267, is one in which a cheek is cut from only one side. It is used where the rail is thinner than the stile and it is desirable to keep the mortise near the middle of the stile.
_No. 45. A housed mortise-and-tenon_, Fig. 267, is one in which the whole of the end of one member is let in for a short distance or "housed" into the other. It is common in grill work and in railings.
_No. 46. A slip-joint or end or open mortise-and-tenon_, Fig. 267, is what would remain if a mortised member were sawn off along one side of the tenoned member. Window screens and other light frames such as those for slates and for printing photographs have this joint. This joint multiplied is used for small machine-made boxes, and is then called _corner locking_.
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 s.p.a.ces between both tails and tenons are called mortises or sockets.
_No. 47. A thru single dovetail_, Fig. 267, is similar to a slip-joint except that instead of a tenon there is a dovetail. It is used in window-sashes.
_No. 48. A thru-multiple dovetail_, Fig. 267, 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 s.p.a.ces as there are to be tails (dovetails). From the division points of these s.p.a.ces, 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 s.p.a.ces between them, as in No. 48, p. 267. For the sake of appearance they may be as much as four times as wide as the s.p.a.ces, but ordinarily should not be wider than 1-3/4".
Set the bevel-square so that it will fit the angle A B C, Fig. 250, p.
159, in a right angle triangle, the long side of which is 3" and the short side 5/8". 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, p. 66, 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_, Fig. 267, 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, p. 190, and Fig. 287, p. 191. 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_, Fig. 267, 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_, Fig. 267, 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.
[Ill.u.s.tration: Fig. 253. Gluing Together a Picture-Frame (See also Fig. 254.)]
_No. 52. A plain miter_, Fig. 268, 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.
[Ill.u.s.tration: Fig. 254. Picture-Frame-Clamp.]
For gluing mitered frames, the most convenient way is with the aid of the picture-frame-vise, Fig. 172, p. 101. 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 1/8" 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.
[Ill.u.s.tration: Fig. 255. Picture-Frame-Clamp. (See also Fig. 254.)]
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 ill.u.s.tration. 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.
[Ill.u.s.tration: Fig. 256. Gluing up a Column Joint. (Pinch-Dogs at Top of Joints.)]
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.
[Ill.u.s.tration: Fig. 257. One Method of Gluing up a Six-Sided Taboret.]
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, p.
103, may be driven into the end grain, and corrugated fasteners, Fig.
228, p. 125, also driven into the ends, make the joint quite secure.
_No. 53. A doweled miter_, Fig. 268, 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_, Fig. 268, 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_, Fig. 268, 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_, Fig. 268, 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_, Fig. 268, 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.
[Ill.u.s.tration: Fig. 258. Devices for Gluing Beveled Edges.]