Setting Out The Joint
The principal 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 classed 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, , or as an external joint, as the upper rail of the same illustration.
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 ) 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 , 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.
Fig. 178.—Setting Out the Stiles with Marking Knife.
Fig. 179.—How to Saw the Tenons—First Operation.
The two Cross Rails , 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 .)
Set out the stiles with a marking knife or penknife and a try square, as shown at . In this sketch only one stile is shown for clearness of representation, but two or more stiles (as at ) 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 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 , 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. 180.—Second Operation in Sawing Tenons.
Fig. 181.—Cutting Channel at Shoulder of Tenon before Sawing.
To saw the tenons, place the rail in the vice as at and, with a panel, tenon, or hand saw, according to the size of the work, cut down the outside of the tenon line as shown. Reverse your position and cut as shown at , then place the rail in a vertical position, and you will find little or no difficulty in sawing down square with the shoulder line. Repeat the above methods of sawing until all the tenons are sawn.
Next saw out the pieces at the side of the tenon by the following procedure. Place the rail against the bench stop, or in the vice, and cut a small channel in which to run your tenon saw as shown at . If you have scored the line deeply with your knife when you were marking out the work, you will have little difficulty in removing a small portion with the chisel. The amount removed in the illustration is, of course, exaggerated. In the small channel thus made place the tenon saw and, guiding the saw blade with the finger so as to keep it upright or square , saw away the waste material. Remove the waste material at the sides of the tenons in a similar way, and then saw out the portion marked H, , lower sketch.
The Mortising of the stiles may next be taken in hand by putting the stiles edgeways in the vice and boring away the bulk of the waste wood from the mortise with a suitable-sized twist bit and brace. This method will save a great amount of noise, as to a great extent it does away with the use of the mallet. Take the mallet and chisel and chop down about 3⁄8 in. as shown at ; then turn the chisel to the position shown at and remove the small piece as shown. Continue these two operations until you are about half-way through the wood and then start in a similar manner at the line a, , after which turn the other edge of the timber uppermost and repeat the methods shown.
Fig. 182.—Sawing away Waste Material.
Fig. 183.—Using the Chisel and Mallet for Mortising.
shows the sketch of a mortise which has its side removed so as to show the method of successive cuts with a chisel when removing the core from a mortise; this, in conjunction with the other sketches, clearly shows the methods of working. In many woodwork examinations the examiners insist that the mortise shall be removed by successive cuts with the chisel, but we certainly advise the removal of much of the waste wood with a boring bit, provided the worker can keep straight and well within the limitations of his gauge lines.
Fig. 184.—Removing Waste of Mortise with Chisel.
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