I made a router support board to clamp onto my folding workbenches. Having drawn around the sole plate I routed to half the depth of the 18mm/ 3/4" plywood. Extending the router bit slightly
in the collet had allowed me to reach full depth of cut. I suppose I could lay the board flat instead of on edge to remove the shoulder. I may try that anyway to see if I can go on cutting a little deeper. [It made almost no difference.]
Here the wooden board has sunk below the edge of the flange. Though still not quite as deep as I had hoped. The worktop timber must be some kind of oak. Its weight is quite incredible!
This image shows the miters joining neatly just inside the studs. I pulled one flange bearing back to expose the end of the two adjoining boards. Otherwise it would not have been possible to see exactly what was happening.
In theory the miters could be enlarged until the original edges disappeared altogether. Though this would weaken the edges where the miters are eventually glued together. A half and half width would probably be optimum for maximum corner strength. The purpose of the solid timber 'tubes' is primarily structural rather than purely decorative.
The rough sawn ends from the rusty circular saw blade are clearly visible here. These surfaces are not visible once the bearings are in place.
I had to bring out my collection of metal block planes to continue widening the miters. The grain on the boards had quickly become ragged using Stanley No4 & 5 bench planes. Even with the miters equal in width to the sides the boards did not sink in very far. As can be seen in the image at left, above. It would be ideal if the tops of the boards were brought in just flush with the studs. Then the second layer of boards can be added to conceal the studs. Even with the alloy spreader plates sandwiched between the bearing flanges and the hardwood boards I'd still like some compression on the outer boards. Compressing just the inner boards might set up stresses between the two layers.