Woodwork Joints Part 3

Next take up a marking gauge, and set the marking point to half the thickness of the wood. The distance may be measured, and its exactness tested, by p.r.i.c.king a small hole from each side of the wood with the marking gauge and carefully noting that the p.r.i.c.ked holes coincide. The gauge mark is clearly shown in the various ill.u.s.trations. Now, take a pencil and scribble or mark "waste" on the parts you intend to cut away.

This will save trouble later on, especially if you are making several joints at once. Take your sharp penknife or marking knife blade, and cut fairly deeply into the marked line on the portion you are going to pare away.

[Ill.u.s.tration: Fig. 66.--Chiselling away Wood up to Gauge Line.]

[Ill.u.s.tration: Fig. 67.--How work is held when Sawing Shoulder.]

Fix the wood firmly in your vice, or against your cutting board or bench stop, as may be more convenient to you, and with a sharp chisel cut away the wood up to the marked line, as at Fig. 66. The channel in the sketch is exaggerated, so as to show the method clearly. The object of using a penknife or marking knife to mark your work, instead of using a pencil, will be obvious. Owing to the knife having scored about 1/16 in. deep across the fibres of the wood, the timber will come away cleanly when the chisel is used, as at Fig. 66. The small channel thus made will form a guide in which to start your tenon or dovetail saw; it prevents the saw cutting on the wrong side of the marked line and thus making the halving too wide.

[Ill.u.s.tration: Fig. 68.--Paring away Waste with Chisel.]

[Ill.u.s.tration: Fig. 69.--Showing an Oblique Halved Joint.]

SAWING.--Lay the work on the cutting board as at Fig. 67; or, if you prefer, put the work in the vice. Carefully saw down the work until you _just touch_ the gauge line. Do not press heavily with the saw; use it lightly; the weight of the back iron which is fixed on the saw will ensure the saw feeding into the work quite fast enough. If the saw is newly sharpened it will, in fact, be an advantage to slightly ease the weight of the saw from off the wood, owing to the keenness of its edge.

If the halving is a very wide one, additional cuts may be sawn between the outside marks, and these will greatly facilitate the removal of the waste wood when paring it away. For sawing the joint reference may be made to the chapter on Dovetailing.

[Ill.u.s.tration: Fig. 70.--Sawing the Cheek of a Halving Joint.]

PARING away the waste material with a chisel is the next step, and this is shown at Fig. 68. The work may be chiselled either in a vertical or a horizontal position. The horizontal position is the easiest for the amateur who has a vice or handscrew, because he may hold the work securely with a mechanical device and so avoid the unnecessary risk to his fingers.

Take the chisel and cut away A, Fig. 68; now turn the chisel and cut away B; after which keep the chisel horizontal and cut off "the top of the hill," as it were, C. Repeat the three operations until you gradually pare the wood away exactly to the gauge line. When chiselling, if you find a tendency for the work to chip or crumble at the back edge owing to the forward pressure of the chisel, turn your wood round and begin to cut from the other edge, allowing the chisel to finish paring at the centre.

JOINTS OTHER THAN A RIGHT ANGLE.--If the halving joint is at an angle similar to the sketch shown at Fig. 69, great care will have to be exercised in the use of the chisel, owing to the change in the direction of the grain of the wood. The arrow marks in this sketch distinctly indicate the direction in which the chiselling must be done so as to give a smooth result. This change of direction for cutting also applies to the bottom of the halving joint.

CUTTING JOINT AT END OF TIMBER (Fig. 70).--Should the halving joint be used at the end of a piece of wood, as at Fig. 30, the waste material may be roughly sawn away and the flat surface trimmed up with a chisel.

To saw out this type of halving joint, proceed to work the shoulder line as already described; then place the piece of wood obliquely in the vice as shown (Fig. 70) and proceed to saw down the vertical line, carefully watching the gauge line to see that you saw on the _waste_ side of the lines. Then turn the piece of timber with its opposite edge towards you, and again use the saw as ill.u.s.trated. You will this time only have to watch the gauge mark on the edge of the wood, because the saw will readily follow in the saw kerf already made. Now place the wood vertically in the vice, and keeping the saw in a horizontal position, saw down to the shoulder line.

Halving joints properly made and fitted should knock together with the weight of the clenched fist; the use of a heavy mallet or hammer will deface the work.

[Ill.u.s.tration: Fig. 71.--Joints used in the erection of a Queen Post Roof Truss.]

THE BRIDLE JOINT

A bridle joint is often defined as the reverse of a mortise and tenon, and is chiefly used in the carpentry and joinery trades. The name probably originated from the fact that it bears some resemblance to the manner in which a bit slips into the horse's mouth and is fastened to the bridle. There are fewer varieties of the bridle joint than of the halved or the mortise and tenon; and this being the case we may take the opportunity of giving a few detailed directions, with explanatory ill.u.s.trations, on the setting out and the making.

[Ill.u.s.tration: Fig. 72.--Simple Bridle Joint.]

Fig. 72 shows a bridle joint in what is perhaps its simplest form, the separate pieces being given at the left and the completed joint at the right. A joint of this type may be applied in nearly all cases where a halved or a mortise and tenon joint could be used. Bridle joints have an advantage as regards appearance over the mortise and tenoned variety in cases such as Fig. 73, which shows an occasional table leg fitted to the circular top framing. The bridle joint here allows the grain of the leg to run through to the top, and gives a better and more workmanlike appearance to the completed article.

[Ill.u.s.tration: Fig. 73.--Table Leg Bridle-jointed to Rail.]

Fig. 74 is a "Mitred bridle joint," the part _a_ showing the upright portion separated. This is a most useful joint for positions similar to that shown in the small gla.s.s frame, Fig. 75. The wood framing in this case is only 1-3/8 in. in width, and if a mortise were used it would have to be exceptionally small. The shaped rail at the bottom of this frame again shows the application of the bridle joint.

Fig. 76 shows an "Oblique bridle joint," used in many instances as a brace, or strut, to prevent framing from racking. (See also Figs. 31 and 32.)

Fig. 77 is a "Stopped bridle joint," used in positions where the top or bottom edge of the work meets the eye, and where, if the rail were allowed to run through, the end grain would appear unsightly.

[Ill.u.s.tration: Fig. 74.--Mitre Bridle Joint.]

[Ill.u.s.tration: Fig. 75.--Mirror Frame with Bridle Joints.]

Fig. 78 is a so-called bridle-joint at the corner of a frame. This is also called an "Open slot mortise and tenon joint," a good strong, serviceable joint which can be used instead of the closed mortise and tenon type, its advantage being that less labour is required in the making. (See also Fig. 169.)

Fig. 79 is an "Oblique angle bridle joint," used in similar positions to the above, but when the two pieces meet at an acute angle at the end of a frame.

Fig. 80 shows the application of the bridle joint to a roof truss. Two sketches are shown at the joining of the tie beam and the princ.i.p.al rafter. The joint _a_ is the type generally used. (See also Fig. 71 for the joints in a queen post roof.)

[Ill.u.s.tration: Fig. 76.--Oblique Bridle Joint.]

[Ill.u.s.tration: Fig. 77.--Stopped Bridle Joint.]

[Ill.u.s.tration: Fig. 78.--Bridle Joint at Corner of Frame.]

[Ill.u.s.tration: Fig. 79.--Oblique Angle Bridle Joint.]

[Ill.u.s.tration: Fig. 80.--Application of Bridle Joint to Roof Truss.]

SETTING OUT AND MARKING.--It is a safe rule, when setting out a bridle joint, to divide the thickness of the timber into three equal parts. This will leave the timber on each side of the tongue equal to the thickness of the tongue, thus giving uniform strength to the joint. The bridle joint is chiefly used for connecting the internal parts of wooden frames.

It is stronger than the halving joint, and, owing to its peculiar construction, requires little in the way of pegs, screws or nails to secure it in position. Fig. 81 ill.u.s.trates the joint, both open and closed.

To understand the method of setting out and marking, glance at the sketch, Fig. 81. It is not necessary that the bridle piece A be the same width as the cross piece B; but it must be remembered when setting out the joint with the marking knife or pencil that the width marked W on piece B must be equal to the width W on the piece A. The timber should be fairly accurately sawn or planed to the same thickness, and all edges should be square and true.

The wood is placed upon the bench, and the joint marked out by using a marking knife or penknife blade and the try square. A knife blade is much better than a pencil, as the sharp edge severs the fibres of the wood and gives a finer line than the pencil. It is not always necessary to exactly square and trim the end of piece A; it may with advantage in many cases be left at least 1/4 in. longer than necessary and levelled off with the saw, plane and chisel after the joint is put together. (See Method of Cutting in Fig. 92, page 47.)

When the piece A has to have a bridle joint fitted at each end, it is customary to cut the timber about 3/8 in. longer than necessary, and mark the shoulder lines C to the exact length, after which the joints are cut.

This leaves the ends standing over the horizontal rails, and, after fixing the complete frame together, the small projecting ends are levelled off flush with the cross rails.

GAUGING.--After squaring all the shoulder lines round the timber with the knife and try square, the mortise gauge should be set so as to strike the two gauge lines marked G, Figs. 83 and 84, at one operation. If the worker does not possess a mortise gauge the lines may be marked at two distinct operations with the aid of the marking gauge (Fig. 82). The gauge should be adjusted so as to mark the wood into thirds, and the stock of the gauge (the portion of the gauge containing the thumb screw in Fig. 82) must be used from the face side of the timber when gauging up the whole of the pieces forming a frame. The face mark on the work is indicated by a glorified comma, and the edge mark is shown by X, as in the various ill.u.s.trations. Fig. 82 shows the method of holding the gauge in the right hand whilst gauging the lines on the work.

[Ill.u.s.tration: Fig. 81.--Bridle Joint, open and closed.]

[Ill.u.s.tration: Fig. 82.--Gauging the Timber.]

The joint, when marked out, will appear as at Figs. 83 and 84, and the portions which are to be cut away may be shaded with a pencil as indicated; this will prevent mistakes arising whilst cutting the work, especially by one who is not thoroughly familiar with the joint.

The distance A B, in Fig. 84, must not be less than the distance A B in Fig. 83.

[Ill.u.s.tration: Fig. 83., Fig. 84. The Two Parts of the Joint Marked.]

BORING AWAY WASTE.--Examine Fig. 84; the shaded portion in the centre has to be cut away, and it will greatly facilitate the removal of this waste piece by boring a hole with a twist bit at the position shown. The twist bit should be about 1/8 in. less in diameter than the width between the gauge lines G. The easiest method of boring out this hole is shown at Fig. 85, which gives the correct position of the worker.

[Ill.u.s.tration: Fig. 85.--Vertical Boring previous to Chiselling.]

SAWING.--The wood should be put in the vice as Fig. 86. Taking up a saw, with the index finger on the side of the handle, commence sawing, and proceed until you come to the position indicated by the dotted hand and saw A; this will leave a saw kerf or cut running diagonally from the shoulder line to corner of the wood. Release the vice and refix the wood so that it leans in exactly the opposite direction to Fig. 86; then reverse your own position and repeat the sawing, so as to cut another diagonal saw cut from the shoulder line to the corner. Fix the wood upright, as shown at Fig. 87, and saw as shown, when you will find that the saw has no tendency to run out of the guide cuts already formed by the method used at Fig. 86. Remember, when commencing to saw at Fig. 86, that it is necessary to saw inside the gauge line; otherwise the joint will be too slack, owing to the amount of sawdust removed by the thickness of the saw blade. The index finger on the side of the saw, pointing in the direction of the saw cut, will greatly help the worker to saw in a straight line, as it is natural to point with this finger to any object that is to be aimed at.