So this was just a bit of fun!
I had this little piece of birch log, only about 8" long and completely hollow...
..so it was like a scaled up version of a baked-bean tin. It's saving grace was a lump of burr on one side, so I sliced down through the log and saved a lump of the sapwood and bark, with the burr on it, then set about turning it into a bowl, but it was falling apart, so once the outside of the bowl was shaped, I hollowed out a lump of firewood-log such that the bowl sat confortably into it, and used it as a compression chuck ...
Next came the problem of how to know how much wood to turn away, given that there was no way of getting a calipers in there. What I did was to mark the outside of the bowl wall in increments of 1cm, and measure its diameter at each increment. I drew this up, freehand, on a sheet of graph paper, deducted about 12mm off each measurement to represent the wall thicknesses, then used it as a guide, constantly hollowing/measuring etc etc.
Once I'd got the shape that I wanted, using this system of measuring, I could begin to see through the splits and cracks and bark-inclusions, confirming that i'd got the thickness that I wanted, and when I popped the bowl out of the compression chuck I was happy with what I'd got.
With such a natural piece, an over-worked finish would have been just wrong, so I sand blasted the tool marks away and then gave it a single coat of Danish Oil, wiped off almost as soon as I'd painted it on. All the cracks were then sewn together with 2mm leather thong, the knots being sealed with ca glue.
It'll never win any prizes, but all who handle it appreciate its natural charm....so I'm happy that the experiment paid off and I learnt a fair bit from it.
Les
