Design Example: Joinery

As we assemble machines from individual parts, we need design methods to connect wooden parts to each other. The craft of joinery addresses techniques for rigidly connecting wooden parts together using feature more than fasteners.

A broader discussion of joinery appears in the section on Flat-Pack Joinery, but this page presents sample joinery designs illustrating several approaches.

These examples focus purely on single joints. But please note that joinery does not exist in isolation, it is the overall combination of structure and joinery constraint which produces a robust object.

The SolidWorks model files may be found in the joinery folder, or may be downloaded as a single file as joinery.zip. The sample parts are designed for 6 mm plywood but could be adjusted for other thicknesses.

Mortise and Tenon with M3 Captive Screw

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Rigid and strong joint created by the interference fits of two tenons in mortises (tapered tabs in slots) and a M3x20 captive screw to compress the tabs into place. In many applications the M3 screw may be omitted. A chief advantage of this joint style is the secure connection, high tolerance to dimensional varation, and ease of disassembly and reassembly.

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Dimensions of the tenon (tab) and captive nut slot. Note the tapered draft angle which accommodates cutting tolerance and provides a secure interference fit in soft materials.

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Dimensions of the mortise (slot) and captive screw clearance hole. Note the width clearance to accommodate variations in material thickness.

Mortise and Tenon with 1/4-20 Captive Screw

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Rigid and strong joint created by the interference fits of two tenons in mortises. This example is essentially the same as the previous but has a larger slot to accommodate a 1/4-20x3/4 screw and 1/4-20 nut for higher compression force.

Dowel Pins

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Demonstration of using manufactured wooden dowel pins to attach two plates in parallel, showing the 1/4 inch, 5/16 inch, and 3/8 inch dowel pins we commonly stock. The dowel pins do not precisely constrain the distance between plates or support significant shear loads; if this is an issue it is stronger to fabricate a laser-cut plate to join the parallel plates using mortise and tenon connections.

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Rendering of the dowel test plate.

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Dimensions of the dowel test plate showing recommended laser-cut hole sizes for the three sizes of dowel pin.

Snap-Fits

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Three examples of more unusual snap-fit assemblies. In each case, the flexibility of the wood is used to create stiff flextures which allow the parts to assemble but then provide hooks to retain the connection. None of these are very tight by themselves but can be effective when used in combination.