Drop Leaf Table archive
Thursday 2 October 2008
Rule joints are used extensively in this table by Mark Ripley
This little dining table was commissioned by a couple who saw a photograph of a cherry coffee table on my website. It was featured in Makers' Gallery in F&C 107. When they visited my workshop to discuss the project we went to see a larger version in brown and tiger oak that belongs to a local client and they were very taken with the colours. The drop leaf was suggested as a way of maximising the usefulness of the table in a small space. The section is less than 1m square and will seat two comfortably or four at a pinch, but the easy lifting of either or both leaves extends the table to seat six comfortably. The collaborative discussion with my clients left me with the dimensions and specification which I then resolved into the design.
Timber choiceI supplemented some 65mm thick brown oak (Quercus robur) that I already had with a 42mm board to make the base. The top came from three 4m-long boards of 27mm which had been carefully selected at Timberpride and cross cut to make them easier to bring home, photo 2. The cutting list for the base was prepared and stacked while I concentrated on the top.
TabletopWork on the top begins with the preparation of a quarter template of the elipse which can be used to draw chalk outlines of the top onto various configurations of boards, photo 3. The template is drawn with a trammel which involves marking the short and long radii on a batten and striking off the perimeter of the ellipse as the trammel is moved along x and y axes. Having arrived at an arrangement that I liked, the positions of the rule joints, centreline and outline were accurately marked in readiness for edge jointing and biscuit slotting.
The top is glued up in three stages and faced off with hand planes and a portable belt sander. Once the parts are separated, they can be fine sanded on the pad sander. At this stage the top is left as a rectangle.
BasePrepare the legs, top rails and stretcher rails as rectangular blanks and mark out all the joints, then make a template of the leg profiles. The end legs are deeper than the side legs so mark the template accordingly.
With the mortises, including haunches, cut and profiles marked onto the legs, the rails are marked out. As the inner leg profile is quite shallow - it is straight for the top 100mm - and the stretcher rails are slim, the tenon shoulders do not need to be scribed into the curve. Conveniently, the angles are the same, meaning that only one tapered shim is required to present the rails at the correct angle to the spindle moulder's slotting cutters when cutting the tenon cheeks and shoulders, photo 4.
The haunches are cut on the bandsaw, photo 5, and the cross-halvings are cut before shaping, see Cross-halving methods.
Shaping stretcher rails and legsWith four curves to deal with, each occurring once, I decided to cut and sand the stretcher rails on the bandsaw rather than spend time making templates for spindle moulding. I also took into consideration the fact that the short grain at the tips of the tenon shoulders was very vulnerable to chipping off during moulding.
The legs are likewise bandsawn, photos 6-8, and sanded, along with other base components, to 120grit, and the base is dry assembled.
Rule jointThe top is marked with centre lines across both length and width. In order to minimise the break in the grain where the rule joint is cut, the top is cross cut at 40 degrees. Matching bearing-guided cutters of 16mm radius are required to cut the joint. Table hinges are made specifically for rule joints and are available from Isaac Lord.
Making a sample of the joint allows settings for routing and hinge fitting to be worked out and repeated on the work itself. Work slowly, removing small amounts of stock with each pass. Breakout at the edges will not matter as these are a long way from the finished edge, but dig-in or torn grain in the joint itself will be very difficult to rectify.
The centre and leaves are aligned for marking out the hinge positions. Slots for the barrel of the hinges are routed first and the recess for the leaves of the hinges are cut subsequently and squared off with a chisel.
Shaping the inlayOnce the rule joint is set up and working, the outline of the top can be marked and cut. As the pieces are fairly easy to handle, I cut the ellipse on the bandsaw and sanded in the curve. The template is now cut back and used as jig for routing the inlay groove, allowing for the inset required for the template-following bush in the base of the router.
The template is held in place, aligned with the centre lines on the tabletop, with clamps. Again this calls for some very careful routing, taking particular care not to run off from the template, or to try to remove too much stock with the delicate cutter; about 0.5mm at a time is enough, photo 9.
I used black walnut (Juglans nigra) for the inlay. In a dark wood like this, wenge (Millettia laurentii) or ebony (Diospyros spp) would have been suitable alternatives. Prepare strips 15mm x 4.5mm in section and hand plane them to a 3.5mm shallow chamfer either side of the centre line. At 15mm wide they are easier to handle before being bandsawn to 7mm strips with a tapered section. The arrangement of the top simplifies the inlaying process as single strips can be set without the need for any joints.
Apply glue to the narrow edge of the inlay and hammer it into the groove with a leather hammer, photo 10, then sand the inlay flush before the glue dries. Trim the ends with a dovetail saw and chisel to complete the inlay, photo 11.
Edge mouldingUsing the 16mm-diameter rounding-over cutter that cut the rule joint, mould the top edge of the tabletop. Change to a 6mm-diameter cutter for the underside. To avoid damaging the tips of the rule joint, stop the routing about 50mm short of the ends and cut in the moulding by hand with a block plane. Hand-saw the edge down to 240grit and pad sand the tops to 150grit. Random-orbit sand to 180grit and fine sand by hand.
Seal and oil the underside of the top ready for fitting, then rout a 6mm radius onto the outside edges of the legs then sand and seal these and the frame in preparation for gluing up.
Base assemblyFirst, assemble the cross halvings, then the end legs and finally the side legs. To prevent the stretcher rails from bending and possibly snapping under cramping pressure, clamp a strut between the halving joint and the top rails. Plane the top of the frame flush then level off the feet and round them over. Make slotted blocks to fit the top of the cross rail - this allows for movement across the width - and screw blocks for the long centre rail.
Leaf runnersRunners are made to support the leaves. A T-section runner is held between two L-section supports which are screwed to the underside of the top.
Rout a slot into the supports which correspond with turned pins fitted in the runners, acting as a stop.
Clamp the runners together with packing filling the T-cutouts and, using a core stock cutter, rout a finger-pull, photos 12-13. Sand and set the sets of supports/runners.
Finishing upSet up the table upside down, with the top resting on clean blankets. Screw the fixing blocks to the base, centre the frame and screw it to the top.
Prepare a small MDF panel to set the support rails a consistent distance from the centre rail. When fitting these, place a strip of thick paper between the supports and runners to ensure that the fit will not be too tight.
Screw curved pieces of wood under the leaves to meet the support rails. These will take up any slight drop as the rail is pulled out, ensuring that the leaves and top will always be level.
FinishingSand the top flush and round over the edges of the rule joint before sealing and finishing with a mixture of spirit-based - not water-based - polyurethane matt varnish, Danish oil and white spirit mixed in equal amounts. This is used throughout the process as initially the white spirit thins the finish, allowing it to penetrate the surface and later prevents overly thick and difficult-to-apply subsequent coats.
The first coat is applied by brush but wiped off after several minutes with a lint-free cloth. I coated the top every day for two weeks until delivery, lightly cutting back every two or three days.