I'm in the process of constructing a benchtop that measures 244cm (8 feet) long and 55cm (22 inches) wide using two solid slabs that are each 13cm (5 ¹⁄₈") thick. The pieces I'm working with are both less than 3/4 of the total length, so they need to be joined end-to-end. My challenge is how best to join the end grain since these slabs are wider than they are thick. I need this connection to remain strong with the wear and tear of chiseling and hammering over time. I'm modeling this after Chris Schwarz's 'Anarchist's Workbench,' which is a Roubo-style bench. My bench will be supported by two legs with a non-laminated assembly, and I know there's an unsupported span of about 2.5 times the width. I've done some reading on the kanawa tsugi joint but am unsure if it's suitable for this orientation. Should I go ahead with the kanawa tsugi joint or consider other joining methods?
2 Answers
That thickness you’re working with seems quite hefty for a benchtop! Typical holdfasts are designed for tops that are around 2 to 4 inches thick, so just keep that in mind. I also think the choice of southern yellow pine might not be ideal for a workbench; have you considered using a different type of wood better suited for durability?
For wide slabs like yours, I'd be cautious about crowning over time. A simple half lap joint glued at the contact point could work, especially if you add a supporting truss underneath to keep everything tight despite seasonal movements. Personally, I suggest making a double breadboard top with a central batten instead. This method allows for better grain orientation and only requires you to fit the ends of the slabs into slots, which would help with seasonal expansion while keeping it flat.