The workbenches we built this week at the Marc Adams School of Woodworking this week are a little different than the French benches I’ve built at other classes. The biggest change: We attached the top to the base with four through-mortises instead of the combination mortise-and-dovetail joint I’ve used in the past.
Why? Time and volume.
We had to make 17 8’-long workbenches in only five days using 6,000 pounds of material. In past classes we’ve done this class in six days, built shorter benches or let the students worry about vises when they got home.
So I set out to engineer a design that was suited to our material – 6×6 Douglas Fir beams – the limited number of workshop hours when we could use the machinery – 42 hours – and for a class that was made up of mostly beginners.
The above design is what I drafted, and it almost worked.
I eliminated the four sliding dovetails and increased the size of the four through-tenons. I’ve seen this feature on surviving benches so I know it works. And it saved us hours of handwork to cut the dovetails. The through-mortises in the top were cut before assembly by kerfing the extents of the mortise and removing the waste with a mortiser. This worked remarkably well. All the benches slid together with few problems.
The real star of the class was the material itself – 6×6 beams of kiln-dried Douglas Fir that the school purchased from the J. Gibson McIlvain Co. The material arrived in our hands with an actual dimension of 5-1/2” x 5-1/2”. My hope was that we would be able to plane the stuff down to 4-1/2” x 4-1/2”. The stuff was remarkably stable and well-behaved. We surfaced almost every stick down to 5-3/8” x 5-3/8”, so it wasn’t very twisted, cupped or bowed.
That saved time on machining and emptying the dust collector.
So where did my plan stumble? I think we all ran out of energy by the fifth day and didn’t push hard enough at the end to get everyone’s vises on. Everyone who wanted to assemble their bench got it assembled (I think that’s correct). But most of them only got a start on their vises by the time we started cleaning up by 2 p.m. Saturday.
I’m quite happy with the design of this bench and the material. It was darn clear and almost entirely free of heart, so it didn’t split as much as some construction timbers. If I had an extra day, I might add the dovetail back onto the design, just because it looks so nice. But I don’t think the addition of the dovetail or the lack of it will change the usability of the bench.
— Christopher Schwarz
P.S. You can download a SketchUp drawing of this design from Google’s 3D Warehouse using this link.