HALVED or halving joints in their various forms are much used in joinery for connecting two parts of the same thickness. The cross halving gives the parts a firm grip on each other and prevents either moving.
In marking out, the gauge is set to half the depth of the pieces,which are marked on both sides, from the faces which are to be in the same plane when the pieces are assembled. If this precaution be taken, it will not matter should the gauge have been set a trifle incorrect! . The width of the notches should be such as to make each part fit tightly into the other, for if there be any looseness the joint will be wobbly.
The slopped halving is used where there is no crossing and the end grain of one part is to be concealed. It comes in usefully for intermediate bars, as the tongue makes fixing with nails or screws easy.
The corner or angle halving is a favourite with amateurs, as it offers the simplest method of joining two pieces at right angles. But the angle bridle or open mortise is a stronger and more workmanlike joint, resisting twisting strains much better. The marking out is as for the through mortise and tenon see below).
The plain housing , is a square groove cut right across the grain of a surface (say, a side of a bookshelf) to take the end of a board. It affords excellent support, and the part let in can be firmly secured in the housing by screws.
To keep the cuts on each side of the housing to the same depth everywhere, the tenon saw should be blinded by two Btrips of wood screwed together beyond the ends of the blade, and set parallel to the edge at the requisite distance. The waste is chiselled out, working from both ends towards the centre: or, what is a much quicker process, removed in stages by a router. The fit should be tight. If the groove is too wide, the joint becomes unsightly.
Where the groove is not to be seen from one end, the slopped housing is used. This is more troublesome to cut, as part of the inner end of the groove must be chiselled out before a saw can be employed.
Nailing or screwing may be avoided – and this applies equally to the plain housing – if tenons are formed on the end of the housed part, and mortises cut in the other part, and the tenons are wedged .
The sloping-toe joint is an excellent one for the end of a strut, and the right one to use on a ledge-and-brace door. It is also very suitable for raking members in heavy timberwork.
The end of the strut is bevelled off from the point at which it meets the other part, and the extreme end is cut square to the non-bevelled side. The two parts are nailed, screwed, or, in the case of heavy work, bolted together.
A common modification of this joint is the bridle-toe joint, in which the end of the strut is forked like one member of an angle bridle , to fit a rib left between two notches cut on either side of it. The rib makes it impossible for the strut to shift laterally.
The wedged or keyed tenon is a very handy joint for bookshelves or other furniture which must be capable of being taken to pieces quickly for packing.
The hole in the tenon must have at least half an inch of wood between it and the end, and extend a little way into the mortise, so that the key shall not be gagged. The key must not be driven in hard, lest it should burst the end of the tenon.
The through tenon and mortise is one of the most useful of all woodwork joints. It is named after the fact that the tenon or tongue formed on the one part goes right through the other part, in which a mortise or socket is cut to fit it. The length of the tenon gives it a very strong hold.
The sightliness of the joint depends on the sides of both tenon and mortise being quite parallel to the faces of the wood in which they are formed. So some hints on the proper procedure will be given. In the first place, a mortising gauge is almost essential to accurate work. This has two marking points, one of which can be set any required distance from the other by means of a screw.
On the working face – this will be that on which the end of the mortise will show – mark the positions of the ends of the mortise, which will be as far apart as the depth of the tenon piece. Square lines across through these, and from their ends square lines down the sides, and join the ends of these on the fourth face.
Next, set the two points of the mortise gauge as far apart as the width of the chisel which will be used for cutting. This should be a proper mortising chisel, by the way,aboutone-thirdas wide as the working face of the mortise piece. The stock of the gauge is then adjusted so that the two points are equidistant frnni the edges of the working face. The gauge is drawn along with the stock kept in contact with one side of the piece, the marks being carried beyond the cross lines both ways. The opposite face is marked similarly – from the same contact face as before. All is then ready for cutting.
The piece having been fixed firmly on the bench, working face upwards, the chisel is applied near the centre of the mortise, bevelled side towards the centre, and kept perfectly upright laterally while driven in a little way. It is then turned for a similar cut on the other side of the centre, which will remove a triangular chip.
The opening is lengthened both ways in alternate cuts, to a depth not much exceeding half the thickness of the wood, until a good opening is obtained, and then kept bevelled side towards the centre until the end marks are reached. Then the piece is turned over and cut through from the other side.
Note – It is very bad practice to cut right through from one face. The chances are heavily against the direction being kept correct; and in favour of the wood being splintered by the chisel as it comes out.
If the tenon is to be wedged, the mortise ends are now extended on the slope to the wedge lines on the working face. A fiafc chisel may be needed to true up the sides of the mortise, which on no account should reach beyond the marks.
The chisel must not be allowed to undercut the ends of the mortise, and shapo them into shallow Ve, especially if wedges are to be used, since their effect would be thereby much reduced.
Where mortises are long, a good deal of time can be saved in cutting if holes are first bored into the wood from both sides with a bit of rather smaller diameter than the width. In any case a hole through the centre will expedite matters, notably when a square mortise has to be cut.
It will be noticed that the wood extends a little beyond the part needed for the tenon. This is to allow for chamfering off the end so that it may enter the mortise more easily, and to ensure a clean finish after the tenon is fixed, when the waste is chiselled and planed down flush with the mortise piece.
The same gauge-setting should be used for mortises and tenons, and the latter be marked from the surface which will be in the same plane as the guiding surface used for marking the mortises. Then, if the mortise be a bit out of centre, the tenon will be the same, and the parts will he flush.
The tenon piece, after being marked out in the same way as the mortise piece, is held upright in the vice while the saw is run down as close to the marks as is possible without cutting them out, until it just reaches the shoulder lines on both sides. The shoulders must be cut perfectly square across. Slight undercutting is not objectionable, and indeed 13 oftentimes used, as it ensures the shoulders making contact with the mortise piece.
A tenon should not press very hard, when driven, upon the sides of its mortise, if these are thin, lest the wood should be split.
A neat way of securing the tenon is to give the mortise a dovetail form in the direction of the grain. The tenon is then slit to take two wedges, which, when the tenon is driven home, expand it into dovetail form.
The bare-faced tenon is used where the tenon piece has to be thinner than the mortise piece, to save weight, or to give room on one side for boarding.
The square-haunched tenon is much used at corners, where the wood must be weakened as little as possible. The haunch increases the resistance of the tenon piece to twisting strains, and at the same time fills in a groove if one has been made in the mortise piece to take the edge of a panel. Where there is no groove the haunch may be sloped off from the shoulders to the tenon.
Wedges should always lie across the grain of the part which will have to withstand their force. The wedges, as well as the parts to be joined, are glued, and left till the glue has set before being cut off level.
To prevent the mortise pieces being burst by wedges driven in tonons near their extremities, it is advisable to allow a little waste length of wood at eaoh end. This is removed after the glue has set.