The Merged Table: 'widening' natural edged slabs

Words and photos: Craig Allison

Several years ago, I made a dining table from two bookmatched slabs of big leaf maple, a species native to the Pacific Coast of North America. In addition to the two slabs, I purchased a couple of smaller slabs of the same thickness, thinking they would be used to build the support structure for the table.

One of the smaller slabs was used in various ways, and another, about 2.5 metres long, stayed with me for several years. Recently I was asked to make a coffee table for a couple who were moving to the Pacific Northwest from California. The owners wanted an occasional informal dining table for two in front of their fireplace and television, and the leftover maple slab was the perfect length for a ‘waterfall’ table of about 1.25 metres.

Unfortunately, the slab was a bit too narrow and too irregular to function well as a single-sided dining table. Splitting the slab and adding a piece in the centre would have been easy, but it felt like ruining the slab, so I decided to add a straight piece to one side instead. The idea was to marry a piece of straight grained Douglas fir (another species native to the area) to the wild edge and grain pattern of the maple plank, thinking this would not compete with the grain pattern or shape of the maple slab.

The 40mm ‘feet’ seen in the photos of the finished piece are removable so the height of the table can be changed from a normal coffee table height to one that is easier to sit at with legs underneath.

Problem solving

I’ve been an amateur woodworker for a long time, with some definitely non-professional level skills. A long career in the construction industry, working with all types of design and construction professionals on new buildings and renovations of historic structures, has given me a background in problem solving and materials which exceeds my woodworking skills. The process of finding a process to fit the tools and skills I have available is always a fascinating part of any furniture design, and this piece was particularly challenging, because it isn’t one that I’ve seen before.

The easiest solution that came to mind was to simply match the leading edge of the slab to the fir plank, but because of the waterfall design both the top and the underside of the piece would be visible. This meant the joint would need to include the full 50mm thickness of the two pieces. After considering a number of options, I decided on the following process.

Beginning the process

The first step was to flatten the maple slab, which was substantially wider than the 300mm capacity of my combination jointer/planer. For this I used a shop-made ‘flattening mill’ – a router jig made from plywood and hardware store aluminum angles (photo 1).

I’ve looked at the commercial systems available in the market, but decided to go with my homemade version, primarily because I can easily dismantle and store the parts, using minimal storage area in between projects. The biggest drawback to this process is that the lack of effective dust collection requires that you wear a good mask and expect a time-consuming clean-up process afterwards, otherwise it works quite well.

I typically spend a good amount of time making drawings for a new piece, using Sketchup and hand drawings. I find that time spent drawing always reduces the time required to build the piece, and  results in fewer unforeseen issues along the way. In this case, however, a minimal sketch was the only working drawing needed.

Following the edge

The first step after flattening the maple slab to just under 50mm total thickness, was to cut a small, 6mm rebate along the live edge of the plank. I did this with a router and a 6mm bit, cutting freehand as closely as I could to the top surface without cutting into it and changing its shape.

The white pencil shading on the top helped make the exact edge visible (photo 2).

Then, using a hand-held jigsaw, I made a vertical cut outside of the rebate, removing as much waste as possible in preparation for pattern routing a vertical face (photo 3).

The pattern routing was done from the underside of the slab, using a long spiral bit with end-bearings (photo 4), making several light passes until the bearing contacted the small rebate along the top edge of the slab.

The acceptable result was a relief, as this step had lots of potential to go wrong (photo 5).

The profile of each of the three maple slab sections (top and two ends) was then traced onto a sheet of 6mm MDF, to be used as a pattern for routing the mating face of the Douglas fir plank (photo 6).

I cut this MDF sheet to the pencil line using a narrow bandsaw blade followed by a lot of hand filing. I made sure to get as close to the line as possible, as this step would largely determine the quality of the fit between the two pieces of the table (photo 7). I treated the profiled edge of the MDF with cyanoacrylate (CA) glue to keep it from being eroded by the bearing on the router bit.

I then taped the MDF pattern to the Douglas fir board using double- sided tape, traced it (photo 8)...

...and then repeated the pattern routing, first sawing close to the line (photo 9)...

then using a bearing-guided bit riding on the pattern to create a vertical mating surface (photo 10).

The fit was good, needing just a little hand work to produce a maximum gap of less than 0.5mm (photo 11).

Joining edges

A 1.5mm rebate was cut along the top edge of the Douglas fir, to be filled with epoxy at the finish. Even though the fit was good between them, the two pieces touched at some spots and had small gaps at others, so the finished appearance would have been uneven; a thin, consistent black line between them seemed better.

The maple and fir parts of each of the three sections were then glued together using a 6mm MDF spline cut from the template used to shape the Douglas fir parts (photo 12).

The groove for this spline was made with a slot-cutting router bit (photo 13). There is very little stress on this joint in the finished piece, so almost any method of attachment would have been okay, however this ‘over- engineered’ method was actually the easiest for me to do.

Creating the waterfall

The last operation to be completed before final sanding and finishing was to cut the mitres in each section and join them together. I cut the mitres with a large track saw set to 45° and joined them with dominos installed at 90° from the mitre faces (photos 14, 15). This method seemed awkward to me when I first tried it, but I’ve used it on a number of pieces, on material as thin as 25mm and as thick as 75mm, and it has been very reliable. It eliminates the need for manipulating clamps to close the mitres and keep the thin edges in line which was always difficult for me no matter what sort of clamps and jigs I used.

The endgame

Finishing this piece was simple. I filled the 1.5mm rebate between the two species with black epoxy and scraped it flush. I eased and tightened the sharp edges of the mitres using a  hard steel burnisher made for creating a hook on scraper blades. The entire piece was sanded to 320 grit and oil finished. I’m happy with the result, because the piece fits the program for its owner and made use of a gorgeous maple slab, one that I had been saving only with the hope that I could use it one day.

First published in Australian Wood Review, issue 120.

Craig Allison @craiga1128 is a lifelong woodworker and building contractor with 35 years experience leading construction projects. He lives in Marin County, California. Learn more at craigallisonwoodwork.com