One of the interesting experiences associated with building a slab-top Roubo workbench is the knowledge that while you’re aiming for tight, rock solid joinery when the bench is assembled, the nature of the slab top means that the joinery is unlikely to stay visually perfect for very long.
I assembled my Roubo bench on 24 November 2019 – almost exactly five months ago. And when I cleaned up the joints in the weeks that followed they were pleasingly tight and gap free. Now, I built this bench in full knowledge that the slab would move during the first year or so, as it slowly reached moisture equilibrium with my workshop. Most timber reaches this point relatively quickly, but the sheer mass of the slab means that it takes longer to reach equilibrium. The benefit, is that once the slab achieves equilibrium it will move much less than a thinner conventional benchtop. So while the movement can be more dramatic at first, the bench should be much more stable as time passes.
This week I noticed that those lovely tight leg joints were showing a consistent gap around the tenon, and that the tenons (which I had flushed when I flattened the bench top in December of last year) were now approximately 0.5mm proud of the bench top. This is to be expected, as the bench top shrinks around the leg joints. A quick check of the bench top with a straight edge showed that the top has started to cup a little, 4 months after I flattened it. I was expecting to flatten the bench top several times over the first 12 months of the bench’s life, so again this isn’t much of a surprise. The amount of cupping isn’t enough to interfere with using the bench, so I will leave it for a month or so before undertaking the first re-flattening of the year.
Do those gaps around the leg joints matter? Not in the slightest – the bench is still rock solid and the gaps are only cosmetic. Those joints are not coming apart any time soon, if ever. I will add wedges to fill the gaps when I next flatten the bench, and will flush up the joints. This is all part of life with a Roubo bench, and I’m ok with that.