Coring Backwards???
A Pictorial Article by Bob Hamilton
This is a method for getting a deeper bowl out of your stock than the thickness of the stock would normally allow. It is similar to the “Dovetail Bowl” technique but the ring(s) are one piece instead of two piece. Due to the width of the kerf from using a parting tool to cut the rings this is only practical using blanks that are fairly thick to start with. In this article I am using a 15” disk of 12/4 soft maple with a few ambrosia streaks through it. Judging by the amount of overlap I achieved with this one I would think that a similar process would work with 8/4 stock.
The blank is mounted on the lathe using the woodworm screw in my Talon chuck and trued up across the face and edge.
Photo 1: Blank
mounted on the lathe and trued up.
I then start parting into the face of the disk, angling out towards the rim.
Photo #2: Parting cut
I keep widening the cut as I go to keep the parting tool from binding. As the cut gets deeper the amount of tool overhanging the tool rest creates a considerable amount of leverage against the tool handle, so I keep slowing the lathe down and clearing the shavings as I progress. By the time I cut through and the ring comes free I am right down to the lowest speed my lathe will go, 100 rpm.
Photo #3: Ring parted off
It has been my experience that no matter how “dry” a thick piece of wood like this is there will still be some moisture gradient between the outer surfaces and the inside. On the first one of these I made the solid disk developed two very deep checks before I was ready for finish turning, so on this one I coated the freshly exposed surfaces with end sealer right after this picture was taken.
Photo #4: This shows the amount of overlap available for the glue joint.
Since the parting cut was made at an angle I will now be able to stack the two pieces and glue them together. The seam between the two pieces will always show, though, so I will accentuate it with a “feature ring” glued up from some contrasting woods. In this case I assembled an octagon from strips of walnut and lacewood and some anigre veneer. I glued the octagon to the wider face of the base section and once the glue had dried I re-mounted it on the lathe and dressed the face of the ring flat for gluing on the top section. This was a rather awkward cut since it was on the headstock side of the blank and I wound up removing rather more of the upper walnut layer than I would have preferred before I was satisfied that it was flat enough for a glue joint. I also applied a piece of the anigre veneer to the bottom of the upper section so that the feature ring would have the same veneer on both sides.
Photo #5: Blank stacked and glued
The lower section has remained mounted on the screw chuck the whole time.
Photo #6: Chuck still in place
I screw the assembly back on to the lathe spindle and proceed to turn, sand, and finish the outside of the bowl. I also make a dimple in the centre of the mounting tenon to make it easier to get the bowl running true when I come back to turn off the tenon.
Photo #7: Outside of bowl complete
I reversed the bowl on the chuck and turned, sanded and finished the inside, then mounted it on my vacuum chuck to remove the tenon and finish turn the base. The completed bowl measures about 14 ¼” in diameter and stands 6” high.
