Slate Top Coffee Table - Canadian Woodworking Magazine

Furniture Project: The rough texture of slate, combined with the smooth polished surfaces of wood, creates an interesting element in coffee table design. 

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Slate Top Coffee Table



Illustrations by Mike Del Rizzo

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For this table I used three slate tiles for the main surface. I have found that slate tiles from various sources are not always exactly the same size or necessarily square. For this reason, it's best to purchase the tiles before beginning any construction.

The top of this table is a lamination of two oak frames, with walnut trim set between the two frames. The tiles sit in a rabbet on top of the frame, offset by textured walnut trim. You could, of course, select a different wood combination, such as cherry and maple or maple and wenge.
 

Select the Lumber
•   Select lumber based on where it will be used on the table. Try to choose grain patterns that enhance the overall design. The place where this will be the most noticeable is on the top. If the grain forms a curve that is opposite to the curve on the piece, the top will lose its sense of harmony.

•   Choose the four oak boards that will make up the top frame (B, E). These should be your four best boards with the most appropriate grain.

•   Mark the face side in chalk to avoid mistakes later. I used 1 1/16" thick rough stock and milled the boards to a final thickness of ¾". Look at the edge grain on these four boards and try to select matching boards (C, F) with a similar pattern for the lower frame. The lower frame boards are 1" thick.

•   When selecting wood for the walnut banding (A, D), try to find pieces that have a consistent dark colour, at least at the ends where the corners will meet.

•   Prepare the walnut banding. The final thickness of this will be ¼" but at this point leave the material 1/32" thicker.

•   Using a table saw or a jointer, cut a ¼" x 2" rabbet into the top outside edge of the bottom frame boards (C, F).
 
Laminate the Frames
•   Glue the slightly oversized walnut banding (A, D) into the rabbet. It is not critical that the joint at the back of the rabbet be exact, but be sure to use enough clamps to ensure a tight joint along what will become the curved edge. Let the glue set.

•   Remove the clamps and hand plane or use the thickness planer to remove the last 1/32" off the walnut. This will result in a clean surface for the next lamination.

•   Prepare a pair of 2" wide spacer blocks.

•   Clamp one spacer to the inside edge at each end of the lower frame boards (C, F). Spread glue on the underside of each of the top frame boards (B, E) and clamp the boards together against the spacer.

•   Set them aside and let the glue cure.
 
Lay Out the Mitre Cuts
•   Confirm the actual measurements on your tiles before cutting the mitres for the table top frame.

•   Cut the mitre joints (I use a table saw with a sled). By making the first cut on one side of the blade, and the second cut on the other, any slight errors are eliminated resulting in a perfect 90º joint.

•   Lay the laminated boards on your workbench, as they will be assembled. If the joints are not perfect, now is the time to tune them up.

•   When you are satisfied with the arrangement, use a band clamp to hold the four boards together in order to lay out the biscuits and outside corners.

•   From the inside corner, measure out along the mitre joint, and mark a line across the joint at 7 ⅜". This defines the four outer corners of the table.

•   Place a mark for a biscuit across the joint at 5".

•   After removing the clamp, I used a Veritas saddle square to transfer these lines to the other side.

•   Each of the mitre joints is held together with three #20 biscuits. To locate the two bottom biscuits accurately, it is important to transfer these marks to the underside.

•   On the underside of the boards, measure back three inches and mark the location for the third biscuit.
 
Curve the Outside Edge of the Laminated Frame
•   Draw a curve along the outside edge of the four laminated boards. Clamp a scrap of wood at the outer corner on the mitre. The curves I used have a total rise of 1" on the long sides and ½" on the short sides. I used a ¾" wide piece of ½" plywood as a drawing aid on edge, held down at the center with a clamp.

•   Remove the waste with a bandsaw, jig saw, or jointer, but do not go right up to the pencil line. If using a jointer set it for the lightest cut possible, place the heel of the board on the outfeed table, and lower the edge down onto the knives at the halfway point. Make each subsequent cut slightly shorter until you reach the required curve.
 
Assemble the Laminated Frame
•   Dry fit everything once to be sure that all the mitered ends go together smoothly.

•   Assemble the pieces with glue and band clamps, and set them aside to dry.
 
Aprons
•   Mill material for the upper rails (L) and aprons (M) from 4/4 stock to a thickness of ⅞". The aprons are 38 ½" including a 1" tenon on each end. The upper rails are 16 ½" with a ¾" tenon.

•   Cut a slot on the table saw along the inside of the upper rails and aprons to receive the "z" clips.

•   Attach the top to the upper rails and aprons with the "z" clips.
 
Lower Rails and Stretcher
•   Mill the lower rails (J) and stretcher (K) from 5/4 stock to a thickness of 1⅛". This allows for a slightly beefier look that adds visual weight to the bottom. The rails have a 1¼" tenon on each end, and the stretcher has a ¾" tenon on each end.
 
Legs
•   Select 8/4 (2") material for the legs (I). Pay attention to the grain, ensuring that it runs the same way. Mill the leg blanks to a cross section of 1 ⅞" x 1 ⅞".

•   Lay out and cut ten mortises for rails.

•   Mount a 45º chamfer bit in your router table and rout a ¼" chamfer on the sides of the legs. This streamlines the legs, improving the look.

•   Reset the bit and rout a ⅛" chamfer around the bottom of the leg. This reduces the chances of the edge of the leg splintering if it is pushed over a surface.


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Steps in cutting mortises on legs
 
Assemble the Base
•   Assemble the base without glue. If everything fits, disassemble the base and sand all of the parts for finishing. I prefer to finish as much of my project as possible before I assemble it; accidental glue squeeze-out is far easier to remove from a finished surface than raw wood. Apply a coat of oil to all of the parts being careful not to get any on the tenons or in the mortises.

•   When the finish has dried, assemble the base with glue.

•   After the glue has set, remove the clamp from the top and clamp the top to a stable work surface.

•   Use a sander to complete the final fairing of the curve. A random orbital or finish sander is best for this, since a belt sander can remove material too quickly; it is much harder to monitor the progress using a belt sander.

•   When all four curves are fair, sand the top and bottom of the frame.
 
Slate Trim
•   Place the three tiles up against two sides of the opening in the top and measure the amount of the left over space. This number divided by 2 represents the width of the raised and textured portion of the slate trim (G, H).

•   Cut the walnut trim 2" wide and 13/16" thick. The extra thickness allows for some surface variation in the slate tiles.

•   Cut a rabbet into the walnut trim along one edge, so that the remaining section that is 13/16" thick is one half of the space between the oak and the tiles. This part can be a little tricky if the tiles are not perfectly square.

•   Cut the mitres on the ends and fit the slate trim into the top frame.

•   When everything fits together, tiles included, remove the walnut inner frame pieces and clamp them to your bench.

•   Texture the walnut frame in order to provide a transition from the smooth surface of the oak to the rougher surface of the slate. (see sidebar: Simple Texturing).
 
Attach the Top to the Frame
•   Use some black #8 x ⅝" wood screws to attach the laminated frame to the top with the "z" clips. Sometimes slate tiles will not sit perfectly flat because of the way they are cut. This was the case with the center tile in this table. In order to level the tile, I used a black #4 screw under the corners that needed to be adjusted. By adjusting how far the screw projected out of the inner frame I was able to raise or lower each corner until I had satisfactory fit.
 
Final Finishing
•   To protect the tiles from stains, they must be properly sealed. Remove them from the top and apply an appropriate sealer.

•   Apply a final coat of oil to the top and base, followed by a couple of coats of a good quality wax.

•   When the sealer on the tiles has dried, insert them in the top, sit back on the sofa and admire your work.
 
Simple Texturing for Inner Walnut Frame
Texturing is an effective way of adding visual interest to a project and is not a difficult technique to learn. The most important thing to watch for when texturing wood in this manner is the direction of the grain. It is no different than using a hand plane or a chisel. For this project I used a Bebe 5/16" Micro Scorp from Lee Valley. The scorp will cut most effectively when the fibres in the wood are under tension rather than in compression. Cutting with the grain in the walnut will result in a smooth, almost waxy surface while cutting against it will lead to tear out and splintering. Choose your wood for these pieces carefully; straight-grained wood is best. Highly figured wood will only cause problems. Hold the scorp by the handle with one hand, and place the other hand lower down on the shaft and, with a twisting motion, remove little divots from the surface. Practice on a few scraps before trying it in your prepared stock.
 

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MICHAEL KAMPEN
Michael Kampen