Making a Bird’s Mouth Hollow Spar
In this episode, the Mastering Skills crew visits boatbuilder-designer Clint Chase at his shop in Saco, Maine, where Clint demonstrates the various steps in designing, building, and assembling a beautiful hollow spar using bird’s-mouth joinery. Good gluing technique is essential to this process and is addressed throughout the episode.
Clint begins the project on his computer, determining the spar’s dimensions while taking into consideration strength, weight, and stiffness. Once the specifications have been calculated and a drawing is produced, we head to the shop and discuss wood choices and tools required for milling the staves. Clint cuts the joints on a tablesaw, after making a few test cuts to check his setup.
Most spars are tapered to reduce weight and add beauty, and Clint demonstrates how to make a simple tapering jig for the tablesaw. After this, we prepare for the glue up by dry-fitting everything together using a simple jig Clint developed for this trial assembly. Once satisfied with the joinery, he discusses appropriate glues, tools for the glue up, the location and fitting of plugs and core, and efficient clamping techniques. When the glue has cured, he demonstrates the steps of shaping the spar, starting with a small power plane, switching to a bench plane and low-angle block plane, and then finishing with different grades of sandpaper to produce a perfectly round and smooth spar.