AW Extra 5/8/14 – Diamond Inlay Table
Diamond Inlay Table
Create striking patterns with a router.
By Peter Schmitt
This hall table posed a challenge, because it was built for a fundraiser. I wanted it to stand out, but I also wanted to limit the amount of time I invested in it. So I started with a tapered leg base—stylish, elegant … and easy to build. I planned to cover the top with figured veneer (an excellent way to make a top look special). Adding inlay—another sure-fire attention-getter—seemed out of the question until I came up with a simple method to complete the job. With its fiddleback mahogany top and contrasting curly maple inlay stringing, the finished table turned heads all night and drew substantial bids.
Build the base
Mill stock for the aprons and legs (see Fig. A and Cutting List, at left). Feel free to change the joinery. I used a mortiser to chop square mortises and then cut loose tenons to fit, but dowels, biscuits or even pocket screws would also work. Leave the legs (A) as square blanks until the mortises have been cut; then taper both inside faces on each leg. Cut the aprons (B and C) to final dimensions; then cut the mortises and drill the pocket holes. Make the loose tenons (D). Glue the legs and end aprons. Then glue the side aprons between the two assembled ends.
Veneer the top
Cut the top (E) to final size, making sure the dimensions are correct and the ends are square. Any variation will mess up the inlay pattern. MDF makes the best substrate for veneering, but hardwood-veneer plywood and solid wood can also be used.
I use traditional methods to lay up veneer. But instead of using cauls and clamps to glue the veneer to the substrate, I use a vacuum bag press. Here’s how to do it.
Cut a piece of 3/4" MDF slightly larger than the top to use as a pressure board inside the press. Cover this piece with rosin paper to keep the veneered top from sticking to it.
Use a small paint roller to apply even coats of yellow glue on both the top substrate and the veneer. Position the veneer on the substrate, using centering marks for reference, and tape it in position. Then place the top veneered-face down on the rosin paper-covered pressure board inside the bag. Close the bag, start the pump and maintain the vacuum pressure until the glue has dried.
Remove the substrate from the press and then remove any rosin paper that has adhered to the veneer—dampening the paper softens the glue and makes it easy to remove. (Note: sand the surface as little as possible to maintain the veneer’s thickness.) Trim the veneer flush with the substrate on all four sides.
Stabilize the top by applying veneer to the bottom side, following the same procedure. The veneer used for this side doesn’t have to be pretty, because it won’t show.
Lay out the inlay pattern
The veneered top’s inlay pattern consists of diagonals running from corner to corner and a diamond created by connecting the centerpoints on each side (Fig. B). The border is created by inlaid edging pieces (F-J) that surround the top.
Laying out the inlay pattern requires accurate measurements and precisely drawn lines. Mark the diagonals and the diamond on the veneered top. Then draw registration lines on both sides of each diagonal pattern line, spaced exactly 3/16" away (Photo 1).
Install the stringing
Use a plunge router equipped with a 1/2" o.d. guide bushing and a 1/8" down-cut spiral bit to rout the grooves for the inlay (six 1/8" wide x 3/32" deep grooves altogether, three in each direction). Use a 48" long template made of 3/4" plywood or MDF and cut exactly 6-1/16" wide to guide the router. (Note: Using a different size guide bushing changes two things: the spacing of the registration lines and the width of the template.)
Clamp the template on the first registration line and check the bit’s location at both ends of the top to make sure the template is properly located (Photo 2). In fact, you must make sure the bit bisects the pattern line before you rout each groove—and reposition the template, if necessary.
Rout the first two grooves from the same setup, using both sides of the template (Photo 3). If everything is correctly sized, you won’t have to reposition the template. To rout the third groove, move the template to the second registration line (Photo 4). Again, make sure the bit is properly centered on the pattern line before you rout.
Cut the 1/8" square inlay stringing (K) on the tablesaw, using a 48" long piece of maple (Photo 5). Set the fence 1/8" from the blade and make four passes with the board on edge. Then reset the fence and make four more passes to cut four 48" lengths of stringing.
Install the first three pieces of stringing (Photo 6). Apply a thin bead of glue to the bottom of each groove. Press in the stringing and tape each piece to hold it in place. After the glue has dried, flush the stringing with the surface, using either a card scraper or a sanding block with 80 grit paper. Then follow the same procedure to rout the three grooves that run in the opposite direction and install the stringing in them.
Attach the edging
Cut three 3/4" x 1-3/8" x 46" blanks of mahogany for the edging (one blank for each side and one for the two ends), along with three 45" lengths of 3/8" square maple stringing. Cut or rout a 3/8" x 3/8" rabbet in the top face of each mahogany blank. Then glue in the stringing (Photo 7). After the glue has dried, rip the edging blanks to their final 1-1/4" width—position each blank so the cut cleans the joint on the inside edge. Then scrape or sand the top inlaid surfaces flush.
Install a slot-cutting bit in the router table and rout grooves in the edging blanks and the top for the spline. Orient the pieces top-face down for routing and install a featherboard on the fence to keep the pieces firmly pressed against the table. Mill lengths of spline (L) to mount the edging. The spline should fit the grooves without binding or wobbling.
Mark the edging blanks and cut and fit the miters. Then glue on the edging pieces (Photo 8).
Apply a finish
Level the joints between the edging and the top with a card scraper or a sanding block. Then finish-sand the top and base to 320 grit. Apply a finish (Photo 9). I start by wiping on several coats of tung oil. Then, for added durability, I wipe on several coats of polyurethane.
Fig. A: Exploded View
Fig. B: Diamond Inlay Layout and Registration Lines
Click any image to view a larger version.
1. Lay out the inlay pattern on the top by marking a centered diamond and two end-to-end diagonals. Then precisely mark registration lines on both sides of each diagonal pattern line.
2. Center the bit on the pattern line. Clamp the template on the first registration line. Then position the router’s guide bushing against the template. The bit should automatically bisect the pattern line.
3. Rout a groove from end to end. Then move the router to the other side of the template and rout a second, shorter groove. You’ll have to reposition the end clamp before routing.
4. Move the template to the opposite side of the pattern line, align it with the second registration line and clamp it. Then rout a third groove.
5. Cut lengths of inlay stringing on the tablesaw.
6. Glue in the first three pieces of stringing. Scrape them flush after the glue has dried. Then rout the three grooves that run in the opposite direction and install the last three pieces of stringing.
7. Create the decorative edging by gluing a large piece of stringing into a rabbet cut on the inside edge.
8. Install the edging, using splines to level the pieces with the surface of the veneered top.
9. Apply a finish. I prefer to wipe on tung oil, followed by polyurethane.
This story originally appeared in American Woodworker February/March 2011, issue #152.