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Simultaneous Joinery

Larry and I developed a set of simultaneous wood working joints about 20 years ago but never got around to documenting our work until now. We were inspired by a puzzle piece that had an intersection of three pairs of symmetrical elements. The puzzle was fascinating to look at but unfortunately it had very little structural value. It occurred to us that if we could build more structure into the design that it could be a true wood working joint.

We developed our simultaneous joints using a mixture of trigonometry and geometry. We prototyped the joints using clay models built over undercut sticks. Some of our first models had internal voids and unnecessary facets.

Making simultaneous joinery is a demanding task since exacting dimensions are critical. Poorly cut joints will either be loose or they will not close up properly. One could glue up simultaneous joints and get away with having looser tolerances but you would need an adhesive with a very long pot life and it would be a messy glue-up. Our pieces are all glue-less construction so they could be disassembled and repaired. We have a few examples of furniture made with glue-less simultaneous joints and they have held tight for about 20 years now.

Click here for a PDF document that will will outline the procedures we used to achieve the precision needed to produce simultaneous joinery. All of the cutting of parts is done one piece at a time and this is very time consuming. One could make jigs that were extremely precise and cut a large number of parts all at once but this is hard to justify unless you plan to mass produce a particular piece of furniture. The procedure we have outlined does work nicely for "one offs" and is within the scope of a small woodshop.