Handwork in Wood Part 20

_No. 18. A dovetail halving or lap-dovetail_, Fig. 265, is a middle-lap joint with the pin made dovetail in shape, and is thus better able to resist tension. It is used for strong tee joints.

_No. 19. A beveled halving_, Fig. 265, is made like a middle-lap joint except that the inner end of the upper member is thinner so that the adjoining cheeks are beveled. It is very strong when loaded above. It was formerly used in house framing.

MODIFIED HALVING JOINTS

_No. 20. A notched joint_, Fig. 265, is made by cutting out a portion of one timber. It is used where it is desired to reduce the height occupied by the upper timber. Joists are notched on to wall plates.

_No. 21. A checked joint or double notch_, Fig. 265, is made by cutting out notches from both the timbers so as to engage each other.

It is used where a single notch would weaken one member too much.

_No. 22. A cogged or corked or caulked joint_, Fig. 265, is made by cutting out only parts of the notch on the lower piece, leaving a "cog" uncut. From the upper piece a notch is cut only wide enough to receive the cog. A cogged joint is stronger than a notched because the upper beam is not weakened at its point of support. It is used in heavy framing.

_No. 23. A forked tenon joint_, Fig. 265, is made by cutting a fork in the end of one member, and notching the other member to fit into the fork, so that neither piece can slip. It is used in knock-down furniture and in connecting a muntin to a rail, where it is desired that the muntin should run thru and also that the rail be continuous.

_No. 24. A rabbet or rebate or ledge joint_, Fig. 266, is made by cutting out a portion of the side or end of a board or timber X to receive the end or side of another, Y. It may then be nailed from either the side or end or from both. The neatest way in small boxes is from the end, or better still it may be only glued.

_No. 25. A dado or grooved joint_, Fig. 266, is made by cutting in one member a groove into which the end or edge of the other member fits.

Properly speaking a groove runs with the grain, a dado across it, so that the bottom of a drawer is inserted in a groove while the back of the drawer is inserted in a dado. Where the whole of the end of one member is let into the other, such a dado is also called a housed dado. Treads of stairs are housed into string boards.

To lay out a dado joint: After carefully dressing up both pieces to be joined, locate accurately with a knife point, on the member to be dadoed, called X, one side of the dado, and square across the piece with a try-square and knife. Then locate the other side of the dado by placing, if possible, the proper part of the other member, called Y, close to the line drawn. If this method of superposition is not possible, locate by measurement. Mark, with a knife point, on X, the thickness thus obtained. Square both these lines as far across the edges of X as Y is to be inserted. Gage to the required depth on both edges with the marking-gage.

To cut the joint: First make with the knife a triangular groove on the waste side of each line, as indicated in Fig. 91, p. 66, and starting in the grooves thus made, saw with the back-saw to the gaged lines on both edges. The waste may now be taken out either with a chisel or with a router, Fig. 122, p. 83. The second member, Y, should just fit into a dado thus made, but if the joint is too tight, the cheeks of the dado may be pared with a chisel. In delicate work it is often wise not to saw at all, but to use only the knife and chisel.

_No. 26. A dado and rabbet_, Fig. 266, is made by cutting a dado in one member, X, and a rabbet on the other, Y, in such a way that the projecting parts of both members will fit tight in the returns of the other member. It is used in boxes and gives plenty of surface for gluing.

_No. 27. A dado, tongue and rabbet_, Fig. 266, is a compound joint, made by cutting a rabbet on one member, Y, and then a dado in this rabbet, into which fits a tongue of the other member, X. It is used in machine-made drawers.

_No. 28. A dovetail dado or gain_, Fig. 266, is made by cutting one or both of the sides of the infitting member, Y, on an angle so that it has to be slid into place and cannot be pulled out sidewise. It is used in book-cases and similar work, in which the shelves are fixed.

To make this joint, first lay out the dovetail on the member to be inserted, called Y, thus: Across one end square a line (A B, No.

28), at the depth to which this member is to be dadoed in. Set the bevel-square at the proper angle for a dovetail, Fig. 250. Score this angle on the edges of the member, as at C D. Cut a groove with a knife on the waste side of A B. Saw to the depth A C, and chisel out the interior angle A C D.

Then lay out the other member, X, thus: mark with the knife the proper place for the flat side of Y, square this line across the face and on the edges as for a simple dado. Lay out the thickness of Y on the face of X by superposition or otherwise and square the face and edges, not with a knife but with a sharp pencil point. Gage the required depth on the edges. Now with the bevel-square as already set, lay out the angle A C D on the edges of X, and across the face at C score a line with knife and try-square. Cut out grooves in the waste for the saw as in a simple dado, and saw to the proper depth and at the proper angle.

Chisel or rout out the waste and when complete, fit the pieces together.

[Ill.u.s.tration: Fig. 250. Laying Out a Dovetail Joint.]

_No. 29. A gain joint_, Fig. 266, is a dado which runs only partly across one member, X. In order to make the edges of both members flush and to conceal the blind end of the gain, the corner of the other member, Y, is correspondingly notched out. In book shelves a gain gives a better appearance than a dado.

A gain joint is laid out in the same way as the dado, except that the lines are not carried clear across the face of X, and only one edge is squared and gaged to the required depth. Knife grooves are made in the waste for starting the saw as in the dado. Before sawing, the blind end of the gain is to be chiseled out for a little s.p.a.ce so as to give play for the back-saw in cutting down to the required depth. To avoid sawing too deep at the blind end, the sawing and chiseling out of waste may be carried on alternately, a little at a time, till the required depth is reached. It is easy to measure the depth of the cut by means of a small nail projecting the proper amount from a trial stick, Fig. 251. The use of the router, Fig. 122, p. 83, facilitates the cutting, and insures an even depth.

[Ill.u.s.tration: Fig. 251. Depth-gage for Dado.]

MORTISE-AND-TENON JOINTS

The tenon in its simplest form is made by dividing the end of a piece of wood into three parts and cutting out rectangular pieces on both sides of the part left in the middle. The mortise is the rectangular hole cut to receive the tenon and is made slightly deeper than the tenon is long. The sides of the tenon and of the mortise are called "cheeks" and the "shoulders" of the tenon are the parts ab.u.t.ting against the mortised piece.

_No. 30. A stub mortise-and-tenon_, Fig. 266, is made by cutting only two sides of the tenon beam. It was formerly used for lower ends of studding or other upright pieces to prevent lateral motion.

_No. 31. A thru mortise-and-tenon_, Fig. 266, is made by cutting the mortise clear thru one member and by cutting the depth of the tenon equal to or more than the thickness of the mortised member. The cheeks of the tenon may be cut on two or four sides. It is used in window sashes.

A thru mortise-and-tenon joint is made in the same way as a blind mortise-and-tenon (see below), except that the mortise is laid out on the two opposite surfaces, and the boring and cutting are done from both, cutting first from one side and then from the other.

_No. 32. A blind mortise-and-tenon_, Fig. 266, is similar to the simple mortise-and-tenon described in 30. The tenon does not extend thru the mortised member and the cheeks of the tenon may be cut on two or four sides.

To make a blind mortise-and-tenon, first make the tenon thus: Locate accurately with a knife point the shoulders of the tenon and square entirely around the piece. On the working edge near the end mark the thickness of the tenon. Set the marking-gage at the proper distance from the working face to one cheek of the tenon and gage the end and the two edges between the end and the knife-lines. Reset the gage to mark the thickness of the tenon and gage that in the same way from the working face. Then mark and gage the width of the tenon in the same way. Whenever there are several tenons of the same size to be cut, they should all be laid out together, that is the marking-gage set once to mark all face cheeks and once to mark all back cheeks. If a mortise-gage is available, use that. Always mark from the working face or working edge. Cut out a triangular groove on the waste side of the knife lines (at the shoulders) as in cutting a dado, Fig. 91, p. 66.

In cutting the tenon, first rip-saw just outside the gaged lines, then crosscut at the shoulder lines. Do all the rip-sawing before the crosscutting. If the pieces are small the back-saw may be used for all cuts. It is well to chamfer the arrises at the end of the tenon to insure its starting easily into the mortise.

Locate the ends of the mortise and square lines across with a sharp pencil in order to avoid leaving knife marks on the finished piece.

Then locate the sides of the mortise from the thickness of the tenon, already determined, and gage between the cross lines. As in the case of like tenons, if there are a number of mortises all alike, set the gage only twice for them all.

In _cutting the mortice_, first fasten the piece so that it will rest solid on the bench. This may be done either in a tail vise or by a handscrew, or by clamping the bench-hook firmly in the vise in such a way that the cleat of the bench-hook overhangs the piece. Then tap the bench-hook with a mallet and the piece will be found to be held tightly down on the bench. See Fig. 76, p. 58.

It is common to loosen up the wood by first boring a series of adjoining holes whose centers follow the center-line of the mortise and whose diameter is slightly less than the width of the mortise.

Take care to bore perpendicularly to the surface, see Fig. 137, p. 86, and no deeper than necessary. Dig out the portions of wood between the auger holes and chisel off thin slices, back to the gage-lines and to the knife-lines, taking care all the time to keep the sides of the mortise perpendicular to the face. This may be tested by placing the chisel against the side of the mortise and standing alongside it a try-square with its head resting on the surface.

Finally test the tenon in the mortise noting carefully where it pinches, if anywhere, and trim carefully. The tighter it fits without danger of splitting the mortised member, the stronger will be the joint.

Many prefer to dig mortises without first boring holes. For this purpose a mortise-chisel, Fig. 68, p. 54, is desirable. The method is to begin at the middle of the mortise, placing the chisel--which should be as wide as the mortise--at right angles to the grain of the wood. Chisel out a V shaped opening about as deep as the mortise, and then from this hole work back to each end, occasionally prying out the chips. Work with the flat side of the chisel toward the middle except the last cut or two at the ends of the mortise.

_No. 33._ In a _mortise-and-tenon joint on rabbeted pieces_, Fig. 266, the tenon is as much shorter on one side than the other as the rabbet is wide. In Fig. 33, ab=cd.

_No. 34. A wedged mortise-and-tenon joint_, Fig. 266, is a thru joint in which after the tenon is driven home, wedges are driven in between the tenon and the sides of the mortise. The wedges are dipped in glue or white lead before being inserted. The sides of the mortise may be slightly dovetailed. It is used to keep a tenon tightly fixed as in wheel spokes.

_No. 35. A wedged mortise-and-tenon joint_, Fig. 266, may also be made by driving the wedges into saw kerfs in the tenon instead of along its sides as in No. 34. It is used in ornamental joints as well as in carpentry.

_No. 36. A fox-tail tenon_, Fig. 266, is a blind mortise-and-tenon in which the mortise is made slightly wider at the bottom than the width of the tenon. Wedges are driven into saw kerfs in the tenon before inserting into the mortise; then when it is driven home the wedges spread out the tenon and make it fill out the mortise. It is used in strong doors and also where the mortised member is already in place so that a wedged mortise-and-tenon is impossible.

_No. 37. A dovetail mortise-and-tenon_, Fig. 266, is a thru mortise-and-tenon beveled on one side so as to form half a dovetail.

The corresponding side of the mortise is also beveled and made wide enough so that when the tenon is pressed well up against its beveled side a wedge may be driven into the s.p.a.ce left on the straight side.

It is used to tenon a beam into a post especially where the post is fixed against a wall. It is also used in machinery frames which are made of wood.

_No. 38. A pinned mortise-and-tenon_, Fig. 267, is one in which a pin is driven thru holes bored thru the mortised beam and thru the tenon to keep them from drawing apart. It is used in heavy framing as in bridges, in wagon-making, in window-sash, etc.

_No. 39. A keyed mortise-and-tenon_, Fig. 267, is one in which the tenon protrudes thru the mortise far enough to receive a removable key and thus be drawn up tight to the mortised member. It is used in work-benches and in ornamental joints like knock-down bookcases and in other mission furniture.

The keyed mortise-and-tenon is made as in a thru mortise-and-tenon, except that before cutting the tenons the holes for wedges should be laid out thus: measuring from the shoulder of the tenon, locate by superposition or measurement the outside of the mortised member.

Deduct from this 1/16" and square a fine pencil-line across the face and opposite side. This line will be the inside of the hole for the wedge, and the 1/16" is deducted to make sure that the key wedges against the mortised member. On the upper surface of the tenon, lay off toward the end the width of the wedge at this point, A B, Fig.

252, and square across. On the under surface, lay off the width of the wedge at this point, C D, and square across.

[Ill.u.s.tration: Fig. 252. Keyed Mortise-and-Tenon Joint.]

Gage the sides of the wedge hole on both upper and lower surfaces of the tenon. After cutting the mortise and tenon, bore and chisel out the hole for the wedge, taking care to cut the side toward the end on a bevel to fit the wedge.

_No. 40. A tusk tenon or shoulder tenon_, Fig. 267, is one in which the tenon proper is quite thin but is reinforced by a thicker shoulder called a "tusk." The upper shoulder is beveled. The object of this form is to weaken the mortised member as little as possible but at the same time to increase the strength of the tenon. It is used in joining tail beams to headers in floor framing.