CARCASE JOINERY

T

here are many ways of joining car­case panels together. The pages that follow will examine three of the most popular choices: dovetail, rabbet and plate joinery. As shown in the photo at right, the interlocking pins and tails of a through dovetail joint give both solidity and distinctive appearance. Cutting such a joint with the tradition­al hand tools is considered a rite of passage for aspiring woodworkers. It requires skill and practice to perfect. It also leaves room for creativity, since it allows you to choose the width of pins and tails to give your joints an

esthetically pleasing look. The same joint can be executed in far less time, but with equal precision, using a router and a jig; that approach is demonstrated in the Drawers chapter (page 80-81). You may also want to try the half­
blind dovetail, which is examined on pages 82-84.

If you prefer somewhat simpler forms of joinery, try either the rabbet or the plate joint (page 34-37). Both are ideal for joining plywood pan­els, which are not suited for dovetails. Whichever type of joinery you select, you must plan ahead for the later stages of your cabinetmaking projects, such as installing back panels, shelving, edge banding or drawers. Some drawer-hang­ing methods, for example, require you to rout a groove in the side panels before the carcase is assembled.

DOVETAIL JOINTS

Waste Shoulder line

Outlining the pins

Mark the outside face of each panel with a big X, then set a cutting gauge to the thickness of the stock and scribe a line along the ends of the four panels to mark the shoulder of the pins and tails. The panels that will form the top and bottom of the carcase will be the pin boards. Secure each one in turn in a vise and use a dovetail square to outline the pins on the ends of the board as shown in the sequence above. Start with half-pins at each edge, making sure that the narrow ends of the pins are on the outside face of the board. Next outline the waste sections adjacent to the half-pins, then mark the center of the board end.

Outline a pin at the center mark, then outline the remaining pins (above, right), marking all the waste sections with Xs. (You can also use a sliding bevel gauge to outline the pins; set an angle of about 1:6 for softwood or 1:8 for hardwood.) There are no rigid guidelines for the number of pins or for the spacing between them. But evenly spaced pins that are at least one-half the size of the waste sections around them make for an attractive and solid joint. Use a combination square to extend all the dovetail marks so that they reach the shoulder lines on both faces of the boards.

2 Cutting the pins

Secure the first pin board in a vise so that the outside face of the panel is toward you. Use a dovetail saw to cut along the edges of the pins, working from one side of the panel to the other. Some woodworkers prefer to cut all the left-hand edges first, then move on to the right – hand edges. For each cut, hold the panel steady and align the saw blade just to the waste side of the cutting line. Use smooth, even strokes, allowing the saw to cut on the push stroke (right). Continue sawing right to the shoulder line, making sure that the blade is perpendicular to the line. Next, use a coping saw (step 3) or a chisel (step 4) to remove the waste between the pins. Repeat the procedure at the other end of the board and at both ends of the other pin board.

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Removing the waste with a coping saw

Stand on the other side of the panel and begin cutting away the waste wood between the pins. At the side of each pin, slide a coping saw blade into the kerf and rotate the frame without striking the end of the board. Cut out as much of the waste as you can while keeping the blade about Уіб inch above the shoulder line. Cut (left) until you reach the kerf on the edge of the adjacent pin. Pare away any remaining waste with a chisel (step 5).

4 Removing the waste with a chisel

Set the panel outside face up on a work surface and clamp on a guide block, aligning its edge about Vie inch to the waste side of the shoulder line. Using a wood chisel no wider than the narrow side of the waste section, butt the flat side of the blade against the guide block. Hold the end of the chisel square to the face of the panel and strike it with a wooden mallet (left), scoring a line about VWnch-deep. Then turn the chisel toward the end of the panel about Va inch below the surface of the wood and shave off a thin layer of the waste (below). Continue shaving away the waste in this fashion until you are about halfway through the thickness of the panel, then move on to the next section. When you have removed all the waste from this side, turn over the panel, and work from the other side until the pins are all exposed.

5

Final paring

With the panel outside face up, align the edge of a guide block with the shoulder line on the panel and clamp it in place. Butt the flat side of a chisel against the block, and using your thumb to hold the blade vertical, gently tap on the handle to pare away the final sliver of waste (left). Repeat the process between the other pins until there is no waste beyond the shoulder line.

6 Preparing to outline the tails

Set one of the tail boards outside face down on a work surface and clamp a guide block on top of it with the edge of the block flush with the shoulder line. Then hold the end of one of the pin boards against the guide block with its outside face away from the tail board. Fasten a handscrew to the pin board and use another clamp to hold it firmly in position (left).

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Marking the tails

Use a pencil to outline the tails (right), then remove the clamps and use a combi­nation square to extend the lines onto the end of the board. Mark the waste sections with Xs, then outline tails on the other end of the board and at both ends of the other panel.

8 Cutting the tails and removing waste

Use a dovetail saw to cut the tails the same way you cut the pins (step 2). Some woodworkers find that angling the board, as shown rather than the saw makes the cutting go easier. In either case, saw smoothly and evenly, and stop just a fraction of an inch before you reach the shoulder line. Remove the bulk of the waste with either a coping saw (step 3) or a chisel (step 4), then pare away the final bits of waste down to the shoulder line (step 5).

9

Dry-fitting the carcase

Before gluing up the carcase, assemble it to check the fit of all the joints. Stand one of the pin boards on a wood block, then align a mating tail board with it; support the other end of the tail board with a sawhorse. Press the joint together by hand as far as it will go, then tap the two ends the rest of the way into place, while protecting the workpiece with a scrap board. To avoid binding and damaging the pins, close the joint evenly along its whole length (left). Join the other pin and tail boards the same way, tapping only on the tail board. The joints should be tight enough to require a little gentle tapping, but avoid using excessive force.

If the joint is clearly too tight, mark the spot where it binds, then disassemble the panels and use a chisel to pare away a little more wood. Dry-fit the carcase again and make further adjustments, if necessary. If there is any gap between a pin and a tail, insert a thin wedge to fill it (page 32). At this point, you will need to see to the other requirements of your project, such as installing a back panel (page 38) and edge banding (page 39), if desired, then preparing the sides for shelves (page 41) or drawers. Once that is done, glue up the carcase (step 10).

Ю Gluing up the carcase

To apply proper pressure when tightening the clamps, use four wood pads specially notched for dovetail joints. Make the pads the same length as the carcase panels are wide, and cut away little triangular notches so that the wood will only make contact with the tails and not exert pressure on the pins. Apply a thin bead of glue on the faces of the pins and tails that will be in contact when the joints are assembled. Use a small, stiff – bristled brush to spread the glue evenly, leaving no bare spots. Assemble the car­case and install two bar clamps across the faces of each of the pin boards in turn. Tighten the clamps a little at time (left) until a little glue squeezes out of the joints. Remove the excess glue (page 23), and keep the clamps in place until the glue is dry.

SHOP TIP

Dealing with a defective dovetail

Even a slight error in cutting dovetails can result in a small gap between a pin and a tail. If the gap is small, fill it with a thin trian­gular chip of veneer or a wood shav­ing cut from the panel stock. To make the wood chip less obvious, cut it so that its grain will run in the same direction as that of the pins. Use a dovetail saw to straighten out or deepen the gap, if necessary. Apply a little glue in the gap and insert the chip, which should fit snugly.

CARCASE-SQUARING BLOCKS

Unless you are installing a back panel on a carcase, it can be diffi­cult to keep the four sides square during glue up. A shop-made car­case-squaring block (right) placed on each corner will help a great deal. For each block, cut a piece of 3/4-inch plywood into an 8-inch

square. Fit a drill press or an electric drill with a 2-inch-diameter hole saw or circle cutter, then bore an open­ing in the center of the block. (The hole will prevent glue squeeze-out from bonding the block to the car­case.) Next, outfit your table saw with a dado head that is the same width as the thickness of the stock,

and cut two grooves at right angles to one another, intersecting at the center of the block.

To use the jig, apply the glue and assemble the carcase, then fit a block over each corner (left), centering the hole at the point where two panels join. Make sure that the dadoes on the blocks fit snugly around the edges of the pan­els. Install and tighten the clamps.

SHOP TIP

Checking a carcase for square

To prevent clamp pressure from pulling a carcase out of square dur­ing glue up, measure the diagonals between opposite comers immedi­ately after tightening the clamps.

The two results should be the same. If they are not, the carcase is out-of-square. To correct the problem, loosen the clamps, then slide one jaw of each clamp away from the joint at opposite corners

as shown. Tighten the clamps and check again for square, shifting the clamps as necessary until the carcase is square.

Quick and easy to cut and assemble, the rabbet joint is ideal for both solid wood and plywood carcases. The joint is made up of a board or panel that fits into a rabbet cut on its mating piece. The width of the rabbet should be equal to the thickness of the stock. In a carcase, the joint is best cut into the side panels so that the end grain of the top and bottom will be covered. Although stronger than simple butt joints, rabbet joints frequently require screws or nails for reinforcement.

SHOP TIP

Invisible nailer

To conceal nails driven into a car­case panel, use a blind nailer.

The commercial device works like a mini-plane, lift­ing a thin wood shaving under which a nail can be driven. The shaving can then be glued right back down to hide the nail head. Set up the nailer following the manufacturer’s instruc­tions—usually for a Vfc-inch-thick shaving. And practise on a scrap board before using the nailer on an actual workpiece. The shaving you raise must be long enough to let you drive the nail comfortably. A strip of tape will hold the shaving down while the glue is drying.

Gluing up the carcase

Dry-fit the carcase, then make any other necessary preparations, such as installing a back panel or preparing the sides for shelving. Then, apply a thin bead of adhesive in the rabbets and on the contacting surfaces of the top and bottom panels. Use a brush to spread the glue evenly, leaving no dry spots. Assemble the carcase and install two bar clamps across the top and bottom panels, protecting the workpieces with wood pads. Tighten the clamps a little at a time until glue starts to squeeze out of the joints. Reinforce the joints with screws about 1 inch from the edges of the top and bottom panels; for additional strength, drive more screws in the middle. If you wish to conceal the screw heads with wood plugs, bore holes in two stages using an electric drill fitted with two different bits. First, use a spade bit wide enough to make holes for the plugs; then switch to a twist bit slightly wider than the screw shanks for making clearance holes. Bore the clearance holes deep enough to reach the side panels; angle the drill slightly toward the inside of the carcase to increase the grip of the screws. Then, drive the screws into place (right).

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Installing wood plugs

To secure the plugs, apply a dab of glue to the screw heads, then insert a plug into each hole (left), aligning the grain with that of the panels. Tap the plugs in place with a wooden mallet, then use a wood chisel to trim the pro­jecting stubs flush with the surface of the panels. Finally, remove any excess glue (page 23).

PLATE JOINTS

Although it lacks the allure of hand-cut dove­tails, the plate or biscuit joint has grown in popularity in recent years because of its strength and simplicity. The joint is cut with a plate joiner, shown in the photo at left. The tool works somewhat like a miniature circu­lar saw, with a retractable blade that plunges into mating workpieces. Glue is applied and an oval-shaped biscuit of compressed beech is inserted into matching slots on each piece. The carcase is then assembled. Since the blade projects from the tool only while it is cutting, the plate joiner is very safe to use. Guide lines on the base plate of the machine make it a sim­ple matter to align the slots in mating boards. The slots are cut slightly larger than the bis­cuits, permitting a small margin of error while still ensuring a properly aligned joint.

1 Marking the location of the joints

Identify the outside face of each pan­el with an X, then mark location points for the slots along each of the four corners. Start with one of the side panels outside face down on a work surface and hold the top panel at a 90° angle to it. Use a pencil to mark lines that overlap the face of the top piece and the end of the side panel about 2 inches in from each corner; make a third mark midway along the edge. Wider panels will require addi­tional biscuits; in general, there should be one biscuit every 4 to 6 inches. Mark similar slot location points on the other three corners of the carcase.

Cutting the slots

Leaving a side panel outside face down on the work surface, set the top piece outside face up on top of it. Offset the ends of the two workpieces by an amount equal to the thickness of the stock. Make sure that mating slot location marks on the two panels are perfectly aligned. Protecting the top panel with wood pads, clamp the two workpieces in place and set in front of them a support board the same thickness as the stock. This set­up will allow you to cut all the slots for one corner of the carcase without moving the panels. Follow the manufacturer’s instruc­tions for setting the depth of cut on the plate joiner; it usually
depends on the size of biscuit being used. Resting the plate joiner on the support board, butt the machine’s face plate against the end of the top panel and align the guide line on the faceplate with a slot location mark on the stock. Holding the joiner with both hands, cut a slot at each mark (left). To cut the mating slots in the side panel, butt the join­er’s base plate against the top panel and then align the center guide line on the base plate with a slot location mark on the top panel (right). Follow the same procedure to cut slots at the other slot location marks.

Gluing up the carcase

Once all the slots have been cut, dry-fit the panels and install a back panel if that is part of your design, or make ready for shelves or drawers. Then glue up the car­case: Set the side panels outside face down on a work sur­face, and squeeze a bead of glue into each slot and along the surface of the panels between the slots, inserting bis­cuits as you go (left). Repeat for the top and bottom panels, this time omitting the biscuits. To prevent the wooden wafers from expanding before the panels are assembled, do the gluing up as quickly as possible, fitting the side panels on the bottom panel and then adding the top. Install two bar clamps across the top and bottom panels and tighten the clamps exactly as you would when gluing up a carcase with rabbet joints (page 35).

INSTALLING A BACK PANEL

1 Routing a rabbet for the panel

Fit the panels together and set the carcase on a work surface with its backside facing up; install a bar clamp with a support board across the top and bottom panels, as shown. Install a %-inch rabbeting bit with a ball­bearing pilot on your router, then set the depth adjustment to cut Vie inch deeper than the thickness of the back panel you will be installing. Starting at one corner, rest the router’s base plate on the support board with the bit just clear of the workpiece. Grip the router firmly with both hands and turn it on, guiding the bit into the panel. Once the pilot butts against the stock, pull the router slowly toward the adjacent corner, keeping the base plate flat. When you reach the corner, turn the router off. Reposition the support board and cut rabbets along the edges of the three remaining panels in the same manner (above).