Fig. 29.
You will remember how you were taught to wedge up mortice and tenon joints with glued wedges, which, becoming part of the tenon, and rendering it larger below than above, prevents it from being withdrawn from the mortice. Now, a single dovetail has the same effect, and is in point of fact of the same shape and size as the tenon with its wedges attached. See Fig. 29, A and B, the first being a wedged tenon, the second a dovetail.
We shall begin with a single dovetail, which is applied to the construction of presses used by bookbinders and others, and also domestically for house-linen. In these there is a strong tendency to draw the sides upwards, and to tear them from the bottom—a strain which this form of joint is exactly calculated to withstand. The same is also used in making many kinds of frames, where similar strength in one direction is necessary. If you have no special need of such at present, you should nevertheless make one or two for practice, and to give you a better insight into their construction. Indeed, if you cannot make single dovetails well, you will hardly succeed in making a whole row of them exactly alike, for joining together other articles, as drawers, boxes, and cabinets. C of this fig. represents a bar of wood truly squared up, and ready for being marked out. The square is laid across it as seen, and a line drawn on each side by its assistance, as far from one end as is the thickness of the other piece to which it is to be attached, and a little over (say one-eighth of an inch) which will afterwards be neatly planed off. This is allowed merely because the extreme angles at e e sometimes get damaged in cutting out the dovetail, and if they are, they will have to be removed. Having drawn the above line all round the piece, divide it into three by the aid of your compasses, as shown, on what we may call the front and back, and then on both these sides draw lines, e e, to the angle. You now have the dovetail, or rather the pin of the dovetail, marked, and with a fine saw you have only to cut out this piece as you see at D, taking great care to cut accurately close to the lines, but to leave them, nevertheless, on the edge of the piece you are about to use.
If you can saw truly, you should not have to touch these pieces with a chisel, but if not, you must take a very sharp one, and pare the wood exactly true to the lines which you have marked. Now the dovetail made by dividing the width of the stuff into three, as given here, will not answer so well for pine, which is liable to split off in the line H H of the fig. D; but for ash, beech, elm, and such like, it is a good proportion. If the material, therefore, is pine, divide it into four instead of three, as seen at E, and draw lines to the angles from the two outer marks; or, without any such division, set out equal distances from each side, so as to give about this proportion to the pieces which are to be cut out.
Where there are a row of dovetails to be made (as in cabinet work), even this latter measurement into four would make them too angular, as you will learn presently. You must now fix upright in your vice the piece in which is to be cut the dovetail to receive this pin; and laying the latter in place as it will be when the frame or other work is put together, draw round it with a sharp pencil or scriber, as seen on the end of K (the lines c d, at such distance from the end of the piece as is the thickness of the pin, and the perpendiculars, a b, are to be drawn with the square); and if the angles of such pin do not reach the angles of that in which the dovetail is to be cut, as will often be the case, the lines on the opposite side similar to a b must be also drawn with the square. So you see that I was quite right in directing you to add a square to your box of tools, even before many other requisites of carpentry.
If it is not considered desirable that the dovetail should reach the extreme angles of the pieces, as a b, fig. K, the pin piece is first marked as if for an ordinary tenon, and the dovetailed pin marked on this, as M. When the fellow-piece is cut out, it will then appear as N. The effect will be the same as the last, except that the end of the pin will be more conspicuous. A great deal depends upon the material, and on the intended use of the finished article, therefore you must use your own judgment, or consult that of others better acquainted with the art than yourself. L shows the dovetailed joint complete as last described.
Fig. 30.
We now recur to the row of dovetails and pins—or dovetails and sockets, as the part is often called which is to receive the pins. The most common kind is that represented by A B, Fig. 30; and as you ought now to be thinking of a larger tool-box, and would not like it roughly nailed together like the first, you might try your skill by constructing one more worthy of the name, and with a drawer or two in it. You must begin, as before, by marking the two lines across your work by the edge of the square, or, if you prefer it, by your gauge, which, when set to the thickness of one piece, will mark the others correctly; and remember to mark both sides. Then set out your dovetails, but do not make them so angular as you did the single one; for remember you have a whole row of them to assist in holding the work together, and when glued, this will be of necessity a very strong and reliable joint, if well made.
Always make the pins before the sockets, and mark round them as closely as possible, and take great care when sawing not to break them, and if possible keep their angles also very sharp and clean. It is solely care in these particulars, and accurate cutting just to the gauge lines and no further, that makes carpenters’ work generally so superior to that of amateurs, and boys especially are generally careless, and in too great a hurry to get the work done, that they may go to something else. Remember, therefore, that when you begin to hurry your work, you begin to spoil it.