Ply ribs glued into grooves in the legs above the maple trunk block seemed the best solution to the bendiness problem. Quite thin and simple, “low-rise” ribs, glued into routed grooves in the legs would have done the job, but this seemed like an opportunity to do something a bit more dramatic which would further enhance the view through the glass panel in the tabletop. To that end, it seemed natural to use a contrasting material for them – bandsawn American black walnut veneer on 9mm birch ply. The shape settled upon was one that rose from its lowest point about 75 mm above the “trunk” block to a point flush with the tabletop and just outboard of the glass panel. A solid walnut addition to the ply enabled the formation of satisfying curves on the edge which would be visible through the glass. While, in this view, the rib appears somewhat heavy and bulky, this is not apparent when they are seen, as intended, through the glass panel in the tabletop.
The first step was to create templates for the shape of the curves needed to fit accurately into the legs onto white faced hardboard. A separate template was need for each leg to accommodate small differences in curvature between each leg. As can be seen from the photograph, the legs were already prefinished ready for final assembly and glue-up at this stage, so the need to stiffen them was quite a major setback to progress.
With the curvature of the leg surface traced, the inner curve, where it would fit into the groove, was created by marking a parallel line 12 mm inside it for the section to fit into the groove of that depth. These brass discs in various thicknesses (bought as a set from Axminster) were perfect for this and have been invaluable over the years for setting depth stops and jobs like this – much easier than trying to mark from a 6” rule.
Routing the 12mm grooves in the completed legs was rather more exciting than I would ideally have liked given the amount of time and effort already invested in them.
Careful hand shaping was needed rebate the tip of the rib so that it overlapped the groove and merged seamlessly into the curve of the leg. The fiinished detail can be seen inthe photo at the top of this post – I love this sort of stuff!
Here are the four top ribs showing the solid walnut blocks, Domino jointed onto the ply ribs, before shaping.
These concerns about excessive flexibility in the upper part of the legs led me to decide to create further ribs to prevent flexing in the lower section of the legs – the last thing I wanted was to get the whole thing glued up and then find there was still a problem. Without the need for a clear section in the centre, the lower ribs could be simplified by making those for opposing legs in one piece with a cross halving joint in the centre; these can be seen at the back in the photograph. An added benefit of the bottom ribs is that they further the tree inspiration by blocking the view through the legs (roots) without adding visual bulk. Of course, they also eliminated the need for the stainless stays, but I decided to keep them anyway.
One of the lower ribs with halving joint cut.
Glue-up next time.