When my grandfather repaired a broken chair leg, he bored a few holes in each side, then glued in some pins. While there were jigs to help align the holes in either side of the material, positioning was critical in both dimensions, and flush repairs on complex parts were really tough. Also the cross-section of the pins didn’t provide enough strength for demanding locations like the rail-to-stile join. These pictures show chairs with stiles broken at the rail.

In 1955, an engineer and woodworking hobbyist, Herman Stiener, developed a system to replace the dowel with a small oval plate of wood. He also created a unique self-indexing saw which could precisely carve vertical slots in the joining faces. This was the Plate Joiner, also known as a Biscuit Joiner. The combination of the much stronger “biscuit” and the easily aligned joining tool, made impossible repairs simple. Bear in mind that the ‘biscuit joiner’ is really just a ‘biscuit slot cutter’, we still have to do the joining with biscuits, glue, clamps, straps, jigs, and friends.

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I used two biscuits in each stile, aligned to maximize load distribution from front to back, where the stiles are subjected to the greatest stress. In the center picture, above, and here you can see the biscuits dry-fitted in their slots.

After gluing and clamping, and some minor surgery to replace wood lost from the splat, the two chairs are strong as new, only waiting for a little touch-up where material was splintered off the breaks.

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