In the following section, we will cover some of the methods used by builders in joining wood.
PLANING AND SQUARING TO DIMENSIONS
Planing and squaring a small piece of board to dimensions is what you might call the first lesson in woodworking. Like many other things you may have tried to do, it looks easy until you try it. The six major steps in this process are illustrated and described in figure 3-40. You should practice these steps until you can get a smooth, square board with a minimum of planing.
JOINTS AND JOINING
One basic skill of woodworking is the art of joining pieces of wood to form tight, strong, well-made joints. The two pieces that are to be joined together are called members. The two major steps in making joints are (1) laying out the joint on the ends, edges, or faces and (2) cutting the members to the required shapes for joining.
The instruments normally used for laying out joints are the try square, miter square, combination square, the sliding T-bevel, the marking or mortising gauge, a scratch awl, and a sharp pencil or knife for scoring lines. For cutting the more complex joints by hand, the hacksaw dovetail saw and various chisels are essential. The rabbet-and-fillister plane (for rabbet joints) and the router plane (for smoothing the bottoms of dadoes and gains) are also helpful.
Simple joints, like the butt (figures 3-41 and 3-42), the lap (figure 3-43), and the miter joints (figure 3-44), are used mostly in rough or finish carpentry though they may be used occasionally in millwork and furniture making. More complex joints, like the rabbet joints (figure 3-45), the dado and gain joints (figure 3-46), the blind mortise-and-tenon and slip-tenon joints (figure 3-47), the box corner joint (figure 3-48), and the dovetail joints (figure 3-49), are used mostly in making furniture and cabinets and in millwork. Of the edge joints shown in figure 3-50, the dowel and spline joints are used mainly in furniture and cabinet work, whereas the plain butt and the tongue-and-groove joints are used in practically all types of woodworking.
Figure 3-46.-Dado and gain joints.
Figure 3-47.-Tenon joints.
The joints used in rough and finished carpentry are, for the most part, simply nailed together. Nails in a 90° plain butt joint can be driven through the member abutted against and into the end of the abutting member. The joints can also be toenailed at an angle through the faces of the abutting member into the face of the member abutted against, as shown in figure 3-5 1. Studs and joists are usually toenailed to soleplates and sills.
The more complex furniture and cabinet-making joints are usually fastened with glue. Additional strength can be provided by dowels, splines, corrugated fasteners, keys, and other types of joint fasteners. In the dado joint, the gain joint, the mortise-and-tenon joint, the box corner joint, and the dovetail joint, the interlocking character of the joint is an additional factor in fastening.
All the joints we have been mentioned can be cut either by hand or by machine. Whatever the method used and whatever the type of joint, remember: To ensure a tight joint, always cut on the waste side of the line; never on the line itself. Preliminary grooving on the waste side of the line with a knife or chisel will help a backsaw start smoothly.
A miter joint is made by mitering (cutting at an angle) the ends or edges of the members that are to be joined together (figure 3-44). The angle of the miter cut is one-half of the angle formed by the joined members. In rectangular mirror frames, windows, door casing boxes, and the like, adjacent members form a 90° angle, and, consequently, the correct angle for mitering is one-half of 90°, or 45°. For members forming an equal-sided figure with other than four sides (such as an octagon or a pentagon), the correct mitering angle can be found by dividing the number of sides the figure will have into 180° and subtracting the result from 90°. For an octagon (an eight-sided figure), determine the mitering angle by subtracting from 90°180° divided by 8 or 90° minus 22.5° equals 67.5°. For a pentagon (a five-sided figure), the angle is
Members can be end mitered to 45° in the wooden miter box and to any angle in the steel miter box by setting the saw to the desired angle, or on the circular saw, by setting the miter gauge to the desired angle. Members can be edge mitered to any angle on the circular saw by tilting the saw to the required angle.
Sawed edges are sometimes unsuitable for gluing. However, if the joint is to be glued, the edges can be mitered on a jointer, as shown in figure 3-52.
Since abutting surfaces of end-mitered members do not hold well when they are merely glued, they should be reinforced. One type of reinforcement is the corrugated fastener. This is a corrugated strip of metal with one edge sharpened for driving into the joint. The fastener is placed at a right angle to the line between the members, half on one member and half on the other, and driven down flush with the member. The corrugated fastener mars the appearance of the surface into which it is driven; therefore, it is used only on the backs of picture frames and the like.
A more satisfactory type of fastener for a joint between end-mitered members is the slip feather. This is a thin piece of wood or veneer that is glued into a kerf cut in the thickest dimension of the joint. First, saw about halfway through the wood from the outer to the inner corner, then apply glue to both sides of the slip feather, pushing the slip feather into the kerf. Clamp it tightly and allow the glue to dry. After it has dried, remove the clamp and chisel off the protruding portion of the slip feather.
A joint between edge-mitered members can also be reinforced with a spline. This is a thick piece of wood that extends across the joint into grooves cut in the abutting surfaces. A spline for a plain miter joint is shown in figure 3-44. The groove for a spline can be cut either by hand or by a circular saw.
A three-sided recess running with the grain is called a groove, and a recess running across the grain is called a dado. A groove or dado that does not extend all the way across the wood is called a stopped groove or a stopped dado. A stopped dado is also known as a gain (figure 3-46). A two-sided recess running along an edge is called a rabbet T (figure 3-45). Dadoes, gains, and rabbets are not, strictly speaking, grooves; but joints that include them are generally called grooved joints.
A groove or dado can be cut with a circular saw as follows: Lay out the groove or dado on the end wood (for a groove) or edge wood (for a dado) that will first come in contact with the saw. Set the saw to the desired depth of the groove above the table, and set the fence at a distance from the saw that will cause the first cut to run on the waste side of the line that indicates the left side of the groove. Start the saw and bring the wood into light contact with it; then stop the saw and examine the layout to ensure the cut will be on the waste side of the line. Readjust the fence, if necessary. When the position of the fence is right, make the cut. Then, reverse the wood and proceed to set and test as before for the cut on the opposite side of the groove. Make as many recuts as necessary to remove the waste stock between the side kerfs.
The procedure for grooving or dadoing with the dado head is about the same, except that, in many cases, the dado head can be built up to take out all the waste in a single cut. The two outside cutters alone will cut a groove 1/4 inch wide. Inside cutters vary in thickness from 1/16 to 1/4 inch.
A stopped groove or stopped dado can be cut on the circular saw, using either a saw blade or a dado head, as follows: If the groove or dado is stopped at only one end, clamp a stop block to the rear of the table in a position that will stop the wood from being fed any farther when the saw has reached the place where the groove or dado is supposed to stop. If the groove or dado is stopped at both ends, clamp a stop block to the rear of the table and a starting block to the front. The starting block should be placed so the saw will contact the place where the groove is supposed to start when the infeed end of the piece is against the block. Start the cut by holding the wood above the saw, with the infeed end against the starting block and the edge against the fence. Then, lower the wood gradually onto the saw, and feed it through to the stop block.
A rabbet can be cut on the circular saw as follows: The cut into the face of the wood is called the shoulder cut, and the cut into the edge or end, the cheek cut. To make the shoulder cut (which should be made first), set the saw to extend above the table a distance equal to the desired depth of the cheek. Be sure to measure this distance from a sawtooth set to the left, or away from the ripping fence. If you measure it from a tooth set to the right or toward the fence, the cheek will be too deep by an amount equal to the width of the saw kerf.
By using the dado head, you can cut most ordinary rabbets in a single cut. First, build up a dado head equal in thickness to the desired width of the cheek. Next, set the head to protrude above the table a distance equal to the desired depth of the should. Clamp a 1-inch board to the fence to serve as a guide for the piece, and set the fence so the edge of the board barely contacts the right side of the dado head. Set the piece against the miter gauge (set at 90°), hold the edge or end to be rabbeted against the l-inch board, and make the cut.
On some jointers, a rabbeting ledge attached to the outer edge of the infeed table can be depressed for rabbeting, as shown in figure 3-53. The ledge is located on the outer end of the butterhead. To rabbet on a jointer of this type, you depress the infeed table and the rabbeting ledge the depth of the rabbet below the outfeed table, and set the fence the width of the rabbet away from the outer end of the butterhead. When the piece is fed through, the unrabbeted part feeds onto the rabbeting ledge. The rabbeted portion feeds onto the outfeed table.
Various combinations of the grooved joints are used in woodworking. The tongue-and-groove joint is a combination of the groove and the rabbet, with the tongued member rabbeted on both faces. In some types of paneling, the tongue is made by rabbeting only one face. A tongue of this kind is called a barefaced tongue. A joint often used in making boxes, drawers, and cabinets is the dado and rabbet joint, shown in figure 3-54. As you can see, one of the members is rabbeted on one face to form a barefaced tongue.
The mortise-and-tenon joint is most frequently used in furniture and cabinet work. In the blind mortise-and-tenon joint, the tenon does not penetrate all the way through the mortised member (figure 3-47).
A joint in which the tenon does penetrate all the way through is a through mortise-and-tenon joint (figure 3-55). Besides the ordinary stub joint (view A), there are haunched joints (view B) and table-haunched joints (view C). Haunching and table-haunching increase the strength and rigidity of the joint.
Figure 3-55.-Stub (view A), haunched (view B), and table-haunched (view C) mortise-and-tenon joints.
The layout procedure for an ordinary stub mortise-and-tenon joint is shown in figure 3-56. The shoulder and cheek cuts of the tenon are shown in figures 3-57 and 3-58. To maintain the stock upright while making the cheek cuts, use a push board similar to the one shown in figure 3-58. Tenons can also be cut with a dado head by the same method previously described for cutting end half-lap joints.
Figure 3-57.-Making tenon shoulder cut on a table saw.
Figure 3-58.-Making tenon cheek cut on a table saw using a push board.
Mortises are cut mechanically on a hollow-chisel mortising machine like the one shown in figure 3-59. The cutting mechanism on this machine consists of a boring bit encased in a square, hollow, steel chisel. As the mechanism is pressed into the wood, the bit takes out most of the waste while the chisel pares the sides of the mortise square. Chisels come in various sizes, with corresponding sizes of bits to match. If a mortising machine is not available, the same results can be attained by using a simple drill press to take out most of the waste and a hand chisel, for paring the sides square.
In some mortise-and-tenon joints, such as those between rails and legs in tables, the tenon member is much thinner than the mortise member. Sometimes a member of this kind is too thin to shape in the customary reamer, with shoulder cuts on both faces. When this is the case, a barefaced mortise-and-tenon joint can be used. In a barefaced joint, the tenon member is shoulder cut on one side only. The cheek on the opposite side is simply a continuation of the face of the member.
Mortise-and-tenon joints are fastened with glue and with additional fasteners, as required.
The dovetail joint (figure 3-49) is the strongest of all the woodworking joints. It is used principally for joining the sides and ends of drawers in fine grades of furniture and cabinets. In the Seabee units, you will seldom use dovetail joints since they are laborious and time-consuming to make.
A through dovetail joint is a joint in which the pins pass all the way through the tail member. Where the pins pass only part way through, the member is known as a blind dovetail joint.
The simplest of the dovetail joints is the dovetail half-lap joint, shown in figure 3-60. Figure 3-61 shows how this type of joint is laid out, and figure 3-62 shows the completed joint.
A multiple dovetail joint is shown in figure 3-63; figure 3-64 indicates how the waste is chiseled from the multiple joint.
Box Corner Joints
With the exception of the obvious difference in the layout, the box corner joint (figure 3-48) is made in a similar manner as the through-multiple-dovetail joint.
Inside corner joints between molding trim members are usually made by butting the end of one member against the face of the other. Figure 3-65 shows the method of shaping the end of the abutting member to tit the face of the other member. First, saw off the end of the abutting member square, as you would for an ordinary butt joint between ordinary flat-faced members. Then, miter the end to 45°, as shown in the first and second views of figure 3-65. Set the coping saw at the top of the line of the miter cut, hold the saw at 90° to the lengthwise axis of the piece, and saw off the segment shown in the third view, following closely the face line left by the 45° miter cut. The end of the abutting member will then match the face of the other member, as shown in the third view. A joint made in this reamer is called a coping joint. You will have to cut coping joints on a large variety of moldings. Figure 3-66 shows the simplest and most common moldings and trims used in woodworking.
Figure 3-65.-Making a coping Joint.