Arbor Day is everyday down at iFarm this spring. Brian and Shawn have been building an arbor that will support fruiting vines, like arctic kiwi, on this permaculture farm. Serpentine in layout, the arbor is constructed from black locust saplings with simple half-lap joinery on full-round material. Black locust is a choice species for use outdoors and in basements, because it has the density of white oak, and is even more rot-resistant.
The construction process is significantly more detail-oriented than square-rule timber-framing, but uses similar concepts to scribe-rule framing, which was used until the mid-19th-century (and which we most commonly reproduce in our buildings). The saplings are irregular, but the joinery and layout hews to an imaginary straight line through the center of the timber.
Brian’s Veritas double bubble scribe has seen a lot of action throughout this process. Brian screwed temporary shelves to the vertical posts and rested slimmer locust saplings between them, creating stretchers that follow the bents parallel to their course. When he is satisfied with the orientation of the stretcher, relative the the bent, he uses his bubble scribe to draw the outline of the vertical post onto the inside edge of the horizontal stretcher. The benefit of the bubble scribe over a regular compass is that it has two bubble levels incorporated into its arms, allowing Brian to keep the scribe level and plumb.
Even with this increased level of accuracy, Brian makes his first cuts a full quarter inch shy of his line. If he cuts directly to the line, the unevenness of the two timbers might cause him to carve a void where there needn’t be one. The imperfections and knots along the surface of the timber pose a challenge that makes it important to creep up on the joint.
After carving the initial lap, Brian refines the fit of the joint the way you catch a unique rabbit (u-nique up on it). Above, he demonstrates how a common compass can be used to create a tight fit between two fairly lumpy, cylindrical surfaces. Approaching the joint in this way allows him to achieve a complex and tight fit between the stretcher and post, and sometimes, with an additional stretcher.
The joints are fastened with lags composed of grade 8 steel. This metal will acquire superficial surface rust, and blend in with the wood, then stop rusting.
iFarm continues to be an exciting project, posing new challenges every season and demanding an expert level of attention to detail. We can’t wait to see the fruits of our arbor, and what new challenges await us around the bend.
More photos here.