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designing and building with wood channels my creativity and challenges my mind.
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Tuesday, August 21, 2012

Building a Large Trestle Table - Part 1

When I was commissioned to build a 9-foot trestle table and benches for a vacation home in Maine, my clients and I discussed the challenge of moving the piece which, being made of solid African Mahogany, was going to be quite heavy. Together, we decided to go for a "knock-down" design, which allow for the piece to be dis-assembled and re-assembled without damaging the joints. The other benefit of "knock-down designs is they provide for a very rigid construction that stays rigid, even during the dry, cold winter months, when wood furniture joints typically become loose due to wood shrinkage.

Now, Ikea furniture is "knock-down" furniture, but everybody knows it doesn't stay rigid over time. The difference between the Ikea version of "knock-down" and the fine furniture version is in the joints. Whereas Ikea furniture relies on dowels and screws threaded through particle board, the trestle table in question would be built with a matrix of lap and bridle joints, with a pair of wedged tenons holding the bottom stretcher tight in place. The resulting construction, weighted down by the heavy solid-wood table top, will result in a table that might get a bit shorter in the winter, but will always be tight and not wobbly.

Did I mention the table will be kept on a roofed-in (but open) deck? That means it will be exposed to rain, sleet, and relentless summer sun. This is a supreme challenge to a furniture-maker. But using a number of techniques and the right lumber, an heirloom piece is not only possible, but a welcome project.

This is the first post in a series, showing how I make the bridle joints for this table and bench set, which is still in progress.

Once the notches are cut, the legs are used to lay out the location of the notches for the cleats and feet, which get edge-notches as well as face-notches.

I use the actual pieces to lay out all my joints. It's the fastest and most exact. In furniture-making, one almost never uses measuring tape or free-hand marking. The most important thing is that things like multiple notches all be exactly the same depth. I achieve this with a scratch gauge.

I use a chisel and a Japanese saw to cut the notches. The better I get with the saw, the closer to the line I can cut. But I don't cut on my line: I use the chisel to pare away waste until a perfect drop-in fit is achieved.

Making Joinery Cuts with a Saw

Cutting joinery with a hand saw is an acquired skill. In the past, I would have spent a lot of time setting up jigs for power tools like my table saw or router, which would allow me to cut my joints simply by pushing a sled or a tool on a guided path. The result of using jigs and power tools is ideally a very accurate joint. But it is time consuming, especially for complicated joints (like the multiple bridles and lap in this table's trestle assembly). And power tools, while themselves accurate, are only as accurate as their setup, and for all but a narrow range of jigs, they are not accurate enough for fine-fitting furniture.

Much better is to develop a facility with a good hand saw and a sharp chisel. Here, I use the legs to lay out the size of the bridle joints on the cleats and feet. I use a marking knife to score the edge of the notch, then a saddle square to score a line all the way around the piece.

The line provides a track for the saw, with which I make a very shallow, long cut in the face of the feet or cleat. Once the cut is made, the shoulder of the face notch is defined, and the waste can be cut away with the chisel. The result is a shallow track, in which the leg joint slides home.

Reinforcing the Bridle Joints

The whole idea of this design is that it can be dis-assembled. So once the bridle joints are all fitted, I will put thick dowels inside the top joints, where the stretchers meet the cleats. This will make the cleat/stretcher joint extremely rigid, even though in winter the wood will shrink and a typical unglued joint would become loose. The cleat/leg/foot assembly will be glued together with titebond III, a water-proof wood glue. Later, I will add the arched, bottom stretcher (see design pics), which will have a wedged tenon joint at each foot. This wedge can be tapped in during the winter, when the joint will loosen.

Stay tuned for more about this project as it progresses!

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