Nothing is Arbitrary in Bench Design
When you build a project for the first time, I’ve always found there are odd moments when you begin to doubt that what you are doing is correct. Sometimes these moments are followed by a makeshift bonfire in the yard to destroy the evidence of your blunder. And sometimes they result in a small but significant revelation.
As I was getting ready to assemble this Roubo-style workbench, there was a point where I began wonder where I’d hid the charcoal lighter fluid. This moment came right after I had cut all the joints for the bench’s base and the tenons that attach the base to the workbench’s top.
It just looked…¦ wrong. And though this sounds weird to say about a bench that has 5″ x 5″ legs, it looked kinda skimpy to me. The rails that run between the legs are about 4″ wide and they have massive 2-1/2″-long tenons on the ends. But when I saw all the parts in relation to one another, I began to worry that the bench would rack under regular planing pressure.
So I went back to the original drawing from Roubo’s book to see where I went wrong. The bench in that 18th century engraving had the tenons running all the way through the top, which is about 5″ thick. Then it hit me. All the strength in this bench comes from the top. I didn’t see this at first because all the tables I’ve built have their rigidity coming from the apron and rails that run between the legs. In a dining table the top helps the rigidity, but it is clearly playing second fiddle there.
Not so with this bench. The top is massively thick for three reasons: One, to add mass. Two, to provide stiffness so you don’t have to support it from below with an apron that will impede clamping. And three, to keep the entire bench rigid under grueling racking forces. It is, quite simply, ingenious.
To prove my point, I assembled the bench without mechanically securing the top to the base. It was pretty stiff, but when Senior Editor David Thiel shoved on the end I could see the legs sway the tiniest bit.
I hadn’t planned on my legs going all the way through the top (that’s a difficult joint to execute for beginners). But after looking at other 18th century benches I figured out exactly what I had to do to make things right.
– Christopher Schwarz