Woodwork Joints Part 7

DOVETAILED AND WEDGED TENON (Fig. 157).--When two pieces such as the cross rail and leg of a carpenter's bench are required to be held together by a mortise and tenon, and to be readily taken apart, the tenon is dovetailed on one side and the mortise is made of sufficient width to permit the widest part of the dovetailed tenon to pa.s.s into it. When the tenon is in its position a hardwood wedge is driven in above the tenon, as shown.

[Ill.u.s.tration: Fig. 157.--Dovetailed and Wedged Tenon.]

[Ill.u.s.tration: Fig. 158.--Method of Fox-wedging.]

FOX WEDGED TENON (Fig. 158).--This is the method of securing a stub tenon by small wedges. The mortise is slightly dovetailed and two saw cuts are made in the tenon about 3/16 in. from each side. Into each saw kerf a wedge is inserted and the joint glued up. The cramping operation forces the wedges into the saw cuts, thus causing the end of the tenon to spread and tightly grip the mortise.

MORTISE AND TENON WITH MITRED FACE (Fig. 159).--This is a useful method of jointing framing which has square edges as shown; and it is equally useful even if the face edges have moulds worked upon them. If the joint has square edges a rebate may be formed to accommodate a panel by fixing a bolection moulding around the frame. A section of the bolection mould planted on the frame is shown in the lower figure.

[Ill.u.s.tration: Fig. 159.--Tenon Joint with Mitred Face.]

[Ill.u.s.tration: Fig. 160.--Rafter Joint.]

[Ill.u.s.tration: Fig. 161.--Roof Joints.]

ROOF JOINTS.--Fig. 160 shows the method of tenoning the princ.i.p.al rafter to the king post, whilst Fig. 161 ill.u.s.trates the tenoning of the struts to the king post, and the king post to the tie beam. Both these examples are used in roof work. (See also Fig. 71.)

[Ill.u.s.tration: Fig. 162.--Drawbore Pinning.]

[Ill.u.s.tration: Fig. 163., Fig. 164. Operation of Pegs in Drawbore Pinning.]

DRAWBORE PINNING.--At Fig. 162 is seen the method of securing a tenon by drawbore pinning, employed when it is not convenient to obtain the necessary pressure by using a cramp. The joint is made in the usual manner, and a 3/8-in. twist bit is used to bore a hole through piece A.

The tenon is driven home and the hole is marked on the side of the tenon (B); the tenon is then withdrawn and the hole bored about 1/8 in. nearer to the shoulder than as marked on the separate diagram at C. When the tenon is finally inserted the holes will not register correctly, and if a hardwood pin be driven into the joint it will draw the shoulders of the tenon to a close joint and effectually secure the parts.

SASH BARS.--Fig. 165 shows how to tenon a moulded sash bar to the rebated cross rail. In this ill.u.s.tration both shoulders of the moulded bar are shown square, but in the best cla.s.s work these shoulders may be slightly housed into the cross rail to prevent side play. This type of joint is used for horticultural buildings, etc. If the lower rail be moulded with the same members as the sash bar, the end of the sash bar will have to be scribed on to it to make a fit.

[Ill.u.s.tration: Fig. 165.--Tenoning Moulded Sash Bar.]

[Ill.u.s.tration: Fig. 166.--Tenon with Tongued and Grooved Shoulder.]

[Ill.u.s.tration: Fig. 167.--Detail of Table Framing.]

TENON WITH TONGUED AND GROOVED SHOULDERS (Fig. 166).--The object of the tongues and grooves here is to prevent the face of the work casting, or becoming warped, and thus spoiling the appearance of the surface of the work. If framing is to be veneered on the face side this is an exceptionally good method.

TABLE FRAMING.--Fig. 167 indicates the framing of a rail to a dining-table leg. In cases similar to this the tenons run into the leg and almost touch each other. They are therefore mitred on the end as shown in the inset. Chair frames often call for similar treatment.

TWIN TENONS with haunch, as used when the timber is of great thickness, are shown in Fig. 168.

AN OPEN SLOT MORTISE at the end of a right-angled frame is seen in Fig.

169. Fig. 170 shows an open slot mortise and tenon joint at the end of a frame of 60. Both these joints are occasionally called end bridle joints.

[Ill.u.s.tration: Fig. 168.--Twin Tenons for Thick Timber.]

[Ill.u.s.tration: Fig. 169.--The Open-slot Mortise Joint.]

HAMMER HEAD TENONS.--At Fig. 171 is shown the method of jointing framing having semicircular or segmental heads. The left-hand diagram indicates the method of wedging the joint so as to draw up the shoulders; the right-hand view shows the tongueing of the shoulders, which is necessary if thick timber has to be wrought. The sketch depicts the stile when taken apart from the shaped head of the frame.

CLAMPING.--Fig. 172 shows the method of tenoning drawing boards, desk tops and secretaire falls. This is commonly called clamping. The method is used to prevent wide surfaces from winding. A variation of the joint is shown at the left-hand side, the corners in this example not being mitred. Fig. 173 shows the tenoning of a wide to a narrow rail when the joint is at an angle.

INSERTED TENONS (Fig. 174).--Where two pieces of timber run together at an acute angle it becomes necessary to use inserted tenons. Both pieces of the timber are mortised and the inserted tenons are secured into the widest piece. On the left is shown the inserted tenon, secured by the method known as fox-wedging; on the right the inserted tenon has been let into the wide rail from the edge. The narrow rail is secured by wedging the tenons from the outside edge in the ordinary manner.

[Ill.u.s.tration: Fig. 170.--Open-Slot Mortise at 60 degrees.]

[Ill.u.s.tration: Fig. 171.--Hammer-Head Tenon Joint.]

DREADNOUGHT FILE.--At Fig. 175 is a sketch of a portion of a dreadnought file. This has superseded the old-fas.h.i.+oned home-made float used to clean out the sides of a mortise.

[Ill.u.s.tration: Fig. 172.--Clamping.]

[Ill.u.s.tration: Fig. 173.--Tenoning Narrow Rail.]

[Ill.u.s.tration: Fig. 174.--Inserted Tenons.]

[Ill.u.s.tration: Fig. 175.--Dreadnought File.]

[Ill.u.s.tration: Fig. 176.--External and Internal Joints.]

[Ill.u.s.tration: Fig. 177.--Setting out Stiles and Rails for Tenoning.]

GENERAL RULE.--In practically all cases where a single tenon is used the thickness of the tenon should be one-third the thickness of the timber.

This leaves the timber at each side of the mortise the same strength as the tenon.

Mortise and tenon joints for inside work may be united with glue. If, however, the work has to stand the weather a better method is to unite the joint with white lead, which is run down to the required consistency with good outside varnish.

SETTING OUT THE JOINT.--The princ.i.p.al use of the mortise and tenon joint is in the construction of various types of framing, such as door and window frames. In one or other of its many and varied forms it may be cla.s.sed as the most important joint in the general woodworking trade. The joint may be used as an internal one, as shown at the lower rail, Fig.

176, or as an external joint, as the upper rail of the same ill.u.s.tration.

Whatever type of framing has to be made, it is necessary that the face side of the wood be planed up straight and out of winding, and the face mark (as shown in Fig. 176) pencilled upon it. The best edge of the timber should next be planed up true in length, and square to the face side, and the edge mark (X) clearly placed upon it.

The marking gauge is now set to the desired width, and gauge lines are marked on the wood, after which the waste wood is planed off until the timber is the required width. The thickness is gauged and treated in a similar manner, except in such cases where the finished work is to be of a rough and ready character.

THE TWO STILES (or uprights) have their faces turned to touch each other, as shown at Fig. 177, and their length may be anything from 1 in. to 3 ins. longer than the required finished size. This waste wood at each end of the stiles (see arrow HO) is of importance to the work, as it prevents to a great extent the bursting of the mortise whilst cutting the hole or when knocking together the work. The small projection is called the "horn," and it is cut off after the frame has been put together.

[Ill.u.s.tration: Fig. 178.--Setting Out the Stiles with Marking Knife.]

[Ill.u.s.tration: Fig. 179.--How to Saw the Tenons--First Operation.]

THE TWO CROSS RAILS (Fig. 177), have their faces placed together as shown in the sketch. These rails may with advantage be left 1/2 in. longer than the finished size, and the portion of the tenon (which will protrude through the stile 1/4 in. at each end) may be cut off after the work is put together. (See Fig. 92.)

Set out the stiles with a marking knife or penknife and a try square, as shown at Fig. 178. In this sketch only one stile is shown for clearness of representation, but two or more stiles (as at Fig. 177) may be marked out at the same time, provided a 12-in. try square be used; in fact, marking out the stiles in pairs is to be recommended, as all cross lines will be exact owing to their being marked at the same operation. The cut made by the marking knife should be lightly carried all round the work as the mortising is cut from each edge of the stile, the cutting of the mortising being finished in the centre. The lettering on Fig. 177 is as follows:--HO, horn; M, position of mortise; H, position of haunching; A, inside line, or sight size, as it is occasionally called.

Set out the cross rails as at Fig. 177, lower sketch. The lettering in this figure is as follows:--T, tenons; the small piece of the tenon lettered J is called the haunch, and the shaded portion H is cut away to allow the haunch J to fit the haunching of the stile.

THE TENONS (as already stated) are generally one-third the thickness of the timber, thus leaving the same amount of substance at each side of the tenon as the tenon itself is composed of. The mortise gauge is set to the required distance and used as in the case of the marking gauge (Fig.

82).

[Ill.u.s.tration: Fig. 180.--Second Operation in Sawing Tenons.]

[Ill.u.s.tration: Fig. 181.--Cutting Channel at Shoulder of Tenon before Sawing.]