Woodwork Joints Part 12

Fig. 266 shows a shutting joint used to prevent permeation of dust to the interior of a drawer. The drawer front is grooved and engages a suitably-formed slip which is screwed to the bearer as indicated in the ill.u.s.tration. Occasionally some difficulty is experienced when fitting the slip to a narrow drawer, but this can always be overcome by putting in the screws from the top of the bearer instead of from underneath.

[Ill.u.s.tration: Fig. 266.--Dust-proof Drawer, showing the Front grooved to engage a Slip which is screwed to the Bearer Rail.]

Shutting joints which are required to be "light-tight," such as those used in photographic work, are generally formed by slightly grooving the frame and inserting a strip of black velvet. The friction of the high pile of the velvet prevents the filtration of light through the joint.

When making air-tight showcases, one of the best and simplest tests is to place a lighted candle in the case and close all the doors; if the candle goes out within three minutes you have accomplished your object.

THE DOVETAIL JOINT

Nothing definite is known as to the origin of dovetailing, but a quaint and pleasing little story which is well worth repeating runs as follows: A farmer had called in the local "joyner" to do sundry repairs at the homestead. One day, whilst enjoying a humble meal, he sat watching some doves as they hopped about the yard. Struck by the movement of their wedge-shaped tails, it occurred to him to joint his timber by the interlocking method; hence we have _dovetails_.

[Ill.u.s.tration: Fig. 267.--A Single Through Dovetail.]

[Ill.u.s.tration: Fig. 268.--Through Dovetails on Carcase Work (P, Pins; T, Tails).]

THROUGH DOVETAILING.--One of the simplest forms of the dovetail joint is shown in Fig. 267, where two pieces of timber are joined by the method known as "through" dovetailing. This method is used in everyday practice for joining the corners of frames, bracket trusses, and a hundred and one other articles.

Figs. 268 and 269 show the method of through dovetailing as applied to the making of boxes, plinths, and general carcase work; it is used in positions where no objection can be taken to the end grain showing on each side of the finished work. In the case of plinths and furniture cornices the foundation frame is made of yellow pine or other cheap wood, and the more expensive and rare timbers are glued and mitred around in various thicknesses and shapes, thus saving the more costly material and strengthening the construction by the method known as laminating. In many cases all that is necessary is to veneer the face sides, thus covering and hiding any unsightliness.

[Ill.u.s.tration: Fig. 269.--Dovetails for Boxes, etc.]

[Ill.u.s.tration: Fig. 270.--Lap-dovetailing for Drawers.]

LAP-DOVETAILING.--Fig. 270 is an example of lap-dovetailing, such as is used where a drawer side joins with the drawer front. It is not permissible to allow the end grain of the timber to show at the front of a drawer, and this is why resort is had to the lap-dovetail. As the most general use of the dovetail is for this and similar purposes, we shall therefore deal fully with the methods of marking out and the making of this cla.s.s of joint.

ANGLES.--A most important point in the construction of a dovetail is to avoid having the angles of the pins and tails too acute. An inclination of one in eight is considered correct; no hard and fast rule need be obeyed, but the variation should on no account be less than one in six.

[Ill.u.s.tration: Fig. 271.--How to obtain Correct Angles for Dovetail Template.]

[Ill.u.s.tration: Fig. 272.--Squaring and use of Template.]

Fig. 271 shows a simple method to obtain the correct angle. Take a piece of timber and plane up the face edge (A, B) true and straight; mark out a line (C, D) at right angles to the face edge and s.p.a.ce off 8 ins. as shown; now measure a distance of 1 in. (D, E), and join E to point eight.

This will give the correct angle for the dovetails, and it may then be transferred to the joiners' bevel. Many workers who are constantly on dovetail work make a zinc template to the exact angle and keep it specially for the purpose (Fig. 272).

SQUARING.--Another important point to remember is that the drawer sides must be true and squared to an exact length and planed up to thickness; otherwise the finished drawer will be in winding and out of truth.

To true and square the ends of drawer sides, drawer backs and drawer front, a most useful little machine is the mitre trimmer; failing this, excellent results can be obtained by using the shooting board.

[Ill.u.s.tration: Fig. 273.--Method of Marking with Cutting Gauge.]

GAUGING.--After squaring up the timber accurate gauging of the ends is another important point. The gauge used should be a cutting gauge, so that the line is incised about 1/32 in. in depth, thus effectually cutting the cross fibres of the timber.

Fig. 273 shows the method of using the cutting gauge. The stock of the gauge must be held well up to the end of the timber. The gauge is a most difficult tool for the novice to use, and his trouble is generally caused by holding it too flat. Tilt the gauge a little so that the thumbscrew shown in the ill.u.s.tration goes nearer to the floor; the blade will then not bite so keenly, and better results will be obtained. The dotted lines indicate the positions which the dovetails will occupy when marked out.

The gauge is set a trifle less than the thickness of the drawer sides to allow for the thickness of the steel cutter, and a gauge line is marked on the inside of the front and all round the drawer back. The gauge is now readjusted so as to leave a 1/4-in. lap on the front, and a line marked on the ends of the front and all round the ends of the sides which will engage the drawer front. A glance at Figs. 270 and 273 will make this clear.

[Ill.u.s.tration: Fig. 274.--Removing the Waste Wood.]

The dovetail pins on drawer part and back are s.p.a.ced out and marked on the end with the aid of the joiners' bevel, the lines being then squared down to the gauge line by the method shown at Fig. 272--that is, by using the try-square and marking awl.

The drawer front is now put into the bench vice, and the pins are cut as indicated in Fig. 274. The drawer back is treated in a similar manner, but of course in this case it is not "lap" but "through" dovetailing, and the saw kerf goes through the timber and down to the gauge line.

[Ill.u.s.tration: Fig. 275.--Cutting away the Half Dovetails.]

We now come to the point where it is necessary to remove the superfluous material. Fig. 274 shows a method commonly adopted and known as sawing out the waste; the saw is held at an angle and part of the inside portion of the dovetail is cut away as shown. This is a good plan for the amateur, because it shows him at the commencement of his chopping out which will be the pin and which the tail.

[Ill.u.s.tration: Fig. 276.--Showing the Vertical and Horizontal Chisel Operations in Lap-dovetailing. A: The Preliminary Roughing-out. B: Vertical Chiselling; note that the first stab should be just outside the Gauge Line. C: Marking the Horizontal Cut.]

Fig. 276 (A) shows another method that answers well for soft woods such as pine, American whitewood and satin walnut. The drawer front is laid flat on the bench after it has been sawn, and with a mallet and sharp chisel the corner of the dovetail is knocked off as shown. This takes the bulk of the material away and the dovetail is then pared out square in the usual way. The ill.u.s.tration (Fig. 276) also shows how the chisel is held for vertical paring (B) and for horizontal paring (C).

[Ill.u.s.tration: Fig. 277.--Roughing-out by Boring.]

[Ill.u.s.tration: Fig. 278.--Marking Pins on Drawer Side.]

A third method is shown at Fig. 277. With hard, curly timbers, such as tobacco mahogany and satinwood, it is a laborious process to carefully chop away the timber in small pieces, and to overcome this difficulty we occasionally see the workman take a twist-bit and bore a series of holes as shown. A great portion of the timber may then be split away by inserting the chisel end-way into the grain, after which it is pared to a finish.

As dovetailing is chiefly used for drawer making, it will be of interest to give several ill.u.s.trations of variations of the joint and its uses.

Fig. 278 indicates the method of marking the position of the holes in the drawer side. When the paring out of the dovetails is completed the drawer front is turned over on to the side as shown, and the position of the recesses which will engage the pin portions are marked with the marking awl as ill.u.s.trated.

[Ill.u.s.tration: Fig. 279.--Marking by means of Saw Blade.]

[Ill.u.s.tration: Fig. 280.--Gauge Lines, Scores and Saw Cuts.]

[Ill.u.s.tration: Fig. 281.--Sawing the Drawer Side.]

[Ill.u.s.tration: Fig. 282.--Position of Chisel for Cutting Channel.]

The completed drawer back is marked on the sides in an exactly similar manner.

Another method of marking through dovetails is shown at Fig 279. The side is held in position on the end, and the dovetail saw is inserted and drawn out of the saw kerf, thus leaving the exact mark on the drawer-back.

Other workers prefer a pounce-bag instead of a saw. A pounce-bag consists of a piece of fairly open woven muslin filled with a mixture of French chalk and finely-powdered whiting; the muslin is tied up with a piece of thin twine like the mouth of a flour sack. All that is necessary is to place the timber in position and bang the bag on the top of the saw-cuts, when sufficient powder will pa.s.s through the bag and down the saw kerf to mark the exact positions of the lines.

SAWING THE DOVETAILS.--After marking out the pins on the drawer sides, we proceed with the next operation, that is, sawing the dovetails ready for chopping out the waste material. The drawer side is taken and firmly secured in the bench screw and sawn as at Fig. 281; it is most important that the saw kerf is kept _inside_ the line which has been scratched by the marking awl. See Fig. 280, where the dotted line represents the gauge line and the outside lines indicate the scores of the marking awl.

Failure to observe this condition will result in faulty dovetailing, and it will also prove the necessity for using a finely-toothed and thin-bladed dovetail saw.

To cut out the waste wood (or core), the usual procedure is to saw away the half-dovetails as at Fig. 275. With care, this can be accomplished with the dovetail saw, thus avoiding unnecessary labour and the use of the paring chisel.

After sawing, the drawer side is placed flat upon the bench, one end in contact with the bench to prevent the drawer side from slipping away; a chisel (preferably bevelled edged) of suitable width is now taken and a small channel is cut as at A, Fig. 282. The method of cutting this channel is shown in the same ill.u.s.tration. The chisel-cut is started about 1/8 in. from the gauge line; the cut is made right up to the gauge line, which (when gauging) was made 1/32 in. deep so as to cut the cross fibres of the timber. A small piece of waste wood will therefore come away as at A.

The object of cutting this small channel is so that, when the chisel is held vertically on the gauge line and struck with the mallet, the chisel will have no tendency to force its way backward and overshoot the gauge line. The waste or core is now removed by holding the chisel approximately vertical and applying sufficient power to drive it half-way through the timber. The drawer side is now turned over, the operation repeated, and the core pushed out. Care must be exercised whilst cutting away the core to ensure the chisel being held nearly perpendicular; if too much lead (or bevel) be given, a faulty and undercut dovetail will be the result. Undercut dovetails prevent a proper grip of the glue; they give a weak joint, and often cause the face of the drawer side to be splintered whilst driving up the joint. If it be necessary to ease one or two shavings from off the drawer side whilst fitting the completed drawer in the carcase, the joint will show a greater gap as each succeeding shaving is removed.

In common work, especially in soft timbers, many workers allow the pins of a drawer back to run through the sides about 1/16 in. and hammer down the pins of the dovetail. This is called "bishoping the dovetails," and is unnecessary if the work be properly made and fitted.