Woodwork Joints Part 15

[Ill.u.s.tration: Fig. 325.--Use of Plane and Shooting Board for Mitreing.]

[Ill.u.s.tration: Fig. 326.--The Screw Mitre Trap.]

A simple method and one that should always be remembered because it is handy when working without a shooting board is shown at Fig. 328. Set the marking or cutting gauge to the thickness of the wood to be mitred at 45 degrees; then gauge this distance on the wood, as shown at B; draw from the line to the edge, as shown, and saw and plane to a finish. The diagonals of a square give 45 degrees, and this is the method used to mark out the work. The end of the wood must, of course, be square with its edges before marking out in this manner.

[Ill.u.s.tration: Fig. 327.--"Donkey's Ear" Shooting Board.]

[Ill.u.s.tration: Fig. 328.--Gauging for Mitres.]

[Ill.u.s.tration: Fig. 329.--Narrow Inner Moulding.]

[Ill.u.s.tration: Fig. 330.--Wide Mitred Moulding.]

Fig. 329 shows a bevelled framing into which has been mitred a narrow moulding M so as to show a correct margin around the panel.

[Ill.u.s.tration: Fig. 331.--Door with Curved Mitres.]

[Ill.u.s.tration: Fig. 332.--Method of Setting out for a Curved Mitre.]

Fig. 330 shows a similar framing, but with a wide moulding M mitred around it. To obtain a correct intersection of this moulding, the angles A and B are bisected. The bisection of the angles meets before the width of the moulding is cleared, therefore the angle C will again have to be bisected, and the finished joint will appear as shown. One of the simplest of mouldings with a large flat face has been chosen to ill.u.s.trate this. The moulding could be all in one width, as shown, or it could be built into the framing in separate pieces, the wide flat and the piece carrying the mould.

CURVED MITRES.--We now come to what are probably the most difficult of all mitres, viz., curved mitres, and the writer well remembers in his apprenticeship days his first experience of attempting to fit the mouldings around the door shown at Fig. 331 by using straight mitres at A. This, of course, is impossible if the mouldings are of the same section and it is desired to make all the members correctly intersect. If straight mitres are used the section of the curved moulding will have to be of a different shape from the section of the straight moulding, and in these days of machine-made mouldings this method is seldom resorted to.

It is better, cheaper, and easier to make curved mitres when the necessary machinery is at hand.

TO SET OUT A CURVED MITRE (see Fig. 332).--Draw a section of the moulding full size, A, as shown at the left hand of the ill.u.s.tration, and project lines round the framing, as shown V, W, X, Y and Z. Where the lines V, W, X, Y and Z intersect at the corner D, it clearly shows that a straight mitre will not cut all the points of intersection. A curved line will cut all the intersections, and a template made of cardboard, sheet zinc, or veneer, should be made to this shape. At the left-hand side the geometrical setting out is shown for obtaining the curve without having to resort to drawing it freehand.

Take half the width of the moulding, as shown by dotted line A, and where it cuts the approximation of the curved mitre place the point of the compa.s.ses and strike out a circle as shown; with the same radius place the compa.s.s point on B--that is, the inside point of the mitre, and cut the circle on the right and left with the small arcs shown at _aa_. With the same radius put the compa.s.s point at the junction of the circle and mitre line, C V, and cut the circle at right and left, viz., _ee_.

[Ill.u.s.tration: Fig. 333.--Template for Mitreing.]

Now rule a line through _aa_, and another line through _ee_, and where these lines cut each other it will give the correct radius of the curved mitre. The advantage of knowing the correct radius of a curved mitre is of great benefit to the skilled machinist, as it enables him to set up his machine so as to give a definite result.

MITREING A MOULDED DOOR FRAME.--Fig. 333 ill.u.s.trates the method of mitreing the moulded portion of a door frame where the joint is dowelled, not tenoned. A small wooden template is made out of beech or other hardwood, having its ends cut at 45 degrees. This template is placed on the rail, as shown, and held in position by placing both the rail and the template in the vice. The face of the template forms a guide for a wide chisel, and enables the worker to gradually pare away the moulding to the correct angle.

[Ill.u.s.tration: Fig. 334.--Using Panel Saw in Mitre Box.]

For sawing the mitres on large mouldings such as are used on the lid of a gramophone or wireless cabinet, a mitre sawing box and a panel saw may be used as indicated at Fig. 334.

JOINTS FOR CURVED WORK

Fig. 335 shows a circular frame made up in two thicknesses, the segments being screwed to each other and the joints crossed in two layers. This is a very strong method, and it is used for making circular frames and curbs up to 15 ft. in diameter. The segments can be either long or short, the only important condition being that they must be marked out and sawn to the correct radius. Fig. 337 shows a board marked out in segments for this cla.s.s of work. The longer the boards the better will they cut up, as it gives more opportunities of cutting one piece out of the other as at A A.

[Ill.u.s.tration: Fig. 335.--Circular Frame in Two Thicknesses.]

[Ill.u.s.tration: Fig. 336.--Circular Rim in Halved Segments.]

Fig. 338 shows how to begin to put the work together. To continue this, fit other segments in position and screw them to D and E respectively.

The completed work is ill.u.s.trated at Fig. 335.

[Ill.u.s.tration: Fig. 337.--Board Marked for Circular Jointing.]

[Ill.u.s.tration: Fig. 338.--Putting Circular Work Together.]

[Ill.u.s.tration: Fig. 339., Fig. 340. Method of Building up Semicircular Head of Door Frame.]

Fig. 336 shows a circular rim, or curb, made of segments which are halved together. This method is suitable for heavy work, where the timbers are of considerable size. The halvings are cut on the ends of the segments to any convenient shape or bevel, each one being marked so as to fit its fellow.

[Ill.u.s.tration: Fig. 341.--Part of Laminated Table Frame.]

[Ill.u.s.tration: Fig. 342.--Half of Laminated Core Box.]

When extra length is required, semicircular or circular work is built up out of four or five thicknesses of wood, and the method is called laminating. The method of building up the semicircular head of a door frame by this method is shown at Figs. 339 and 340.

The shaped framing for kidney-shaped writing tables and similar cla.s.ses of work is built up by laminating pieces of 3/4-in. or 1-in. wood, after which the face side is veneered so as to hide the glued joints. Fig. 341 shows a sketch of one quarter of an elliptical table frame levelled up and ready for applying the veneer.

LAMINATION.--If we apply to the dictionary for the word "lamination," we find that lamellar structure is the arrangements in thin plates or layers one over the other, usually having the end joints alternating, and it is a condition which allows of cleavage in one direction only. This method is used for nearly all descriptions of free or irregular curves, such as sweeps, bends, ogee shapes, and segments of circles. The timber is marked out in suitable lengths, rough-sawn and then planed true on the face, glued together, and when set the sides are cleaned up to the required shape. It is one of the strongest methods of construction, and necessarily costly. Pulleys, pulley rims, and a hundred and one other jobs are built by this method.

Fig. 342 shows one half of a core box built by this method, ready to be worked to the required shape.

MISCELLANEOUS JOINTS

Weather boards.--For outdoor buildings, such as garages, garden sheds, toolhouses, etc., "weatherboarding" is often preferred to ordinary matchboarding, chiefly because of the facility with which it throws off the rain. The boarding can be bought ready prepared. Three methods of jointing are shown in the sections at Fig. 343. The method indicated at A shows one of the most satisfactory types, its boards being planed and moulded as shown. The other two examples are more common. The boarding at B is rebated, whilst at C each board overhangs its lower neighbour. The boards for C and D are always cut tapered as indicated.

[Ill.u.s.tration: Fig. 343.--Weather Boards.]

[Ill.u.s.tration: Fig. 344.--Ladder Rungs.]

The end grain is usually protected by nailing on a strip of timber, chamfered on both edges.

LADDERS.--Fig. 344 ill.u.s.trates the method of fastening the rung (or stave) of a ladder to the side. At A the common method is shown, the stave being simply driven into the hole and wedged. At B a much better but more expensive method of construction is given. The stave here is socketed and the pin turned to a smaller diameter. In both cases the rung, or stave, is painted before being driven into the side and wedged.

[Ill.u.s.tration: Fig. 345.--Cornice Pole Joint.]

[Ill.u.s.tration: Fig. 346.--Veneer Keying.]

Ladder sides are made in two distinct ways. One method is known as "a plank side," the side being cut from a plank as shown at the section D; the other method is called "a pole side," and is constructed by cutting a straight larch pole in half and using half of the pole for each side of the ladder, as at section C.

HINGED CORNICE POLES.--Fig. 345 shows a hinged joint for cornice poles and should be of interest to those who are frequently removing from house to house. The joint will adapt itself to fit any bay window (even a square bay) and it is formed by turning and cutting the two pieces shown.

To fix a cornice pole to a bay window one of these joints is required for each angle of the bay, the pole being cut into suitable lengths and fixed to the hinged joints by the use of the dowel screw and a little hot glue. It is perhaps needless to remark that the diameter of the joint should be of the same diameter as the cornice pole, to enable the rings to easily slide over the surface.