Apprenticeship Day 22
Jarrod's still willing to have me as an apprentice after all those libellous comments I made about him. Happy days.
More bowls today. Fortunately we didn't lose any more finished bowls to cracks. Seems like removing the central heartwood is working. For now.
Jarrod and I had a cracking chat about, well, cracking. A couple of months ago he lost about 12 cups out of a batch of 30 to cracking. They all came from the same tree, which Jarrod thinks was a little too punky. It smelt faintly of mushrooms. An indicator that the 'agents of decay' were at work. The decay eats away at the lignin in the wood, which compromises it at a cellular level. Had he known, Jarrod could have tried to compensate by leaving the cups a little thicker, which would add strength. If only it were that simple though! With that strength comes rigidity. As wood dries it shrinks, which causes movement in the wood. This movement has to happen. It can either warp the shape, or, if it's too rigid, tear fibres to move.
With objects like Jarrod's end grain cups, the base is thicker than the walls. The walls are thin at the rim, thickening down to the base. He was wondering if the thinner rim allows for greater movement, which might cause more stress at the thicker bottom. So a thinner rim might make a cup more likely to split. Or not. Jarrod liken wood to that nasty ex-girlfriend you might have had. She was mean to you, but you kept going back for more.
After I'd roughed out two bowls for Jarrod, he set me an apprentice challenge. It was a two parter. Part the first: fully turn a nested bowl. Part the second: Shape the bowl to the template. WITHOUT USING THE TEMPLATE.
*Gasps of shock and horror from the audience*
It was a good challenge. Unfortunately It had a rocky start. For there was only one blank left in the bag. The ugly blank. The chunky, misshapen blank I was kind of secretly hoping I wouldn't have enough time to get to. No such luck.
In this case, having to remove the punky heartwood was a nice thing to do. Turning big, heavy blanks is a bit of a task. Especially at the end of the day. So chopping a little off the top helped. It was fun to actually see how much of the shape I'd been turning had stuck with me. I 'finished' the outside and it didn't quite look right. I couldn't figure out exactly what was off, but I could at least tell it wasn't going to perfectly match the template. I faffed around with it a little longer, then decided I didn't want perfect to be the enemy of done. It was good enough. Time to hollow.
I've been practicing undercutting on all the bowls I've roughed out to templates. With those however, It was always better than I left more material than take away too much. I had to go all the way with this bowl. The biggest problem with that was I didn't have a hook which would allow me to do that. There would reach a point where the coring hook I had couldn't reach any further under the core without hitting the rim. At that point I'd have to borrow a hook with a tighter curve to the neck.
The undercutting wasn't done completely alone. Jarrod took over at one point to show me a couple of moves. In the short time he was at the lathe he removed a fair amount of material. Most importantly for a beginner like me, he left a smooth surface for me to attack. Once you start getting dig-ins, they tend to catch the hook, making the cutting surface rougher. You need to move the hook extremely slowly, clamping it down rocksteady.
In the end, I prematurely undercut the bowl. I didn't realise it was so close, so I hadn't tidied up the inside bottom of the bowl. It was fine, though, it just meant more work with the hook knife. Jarrod mentioned that it's a legitimate technique, to remove the inner bowl quickly and tidy up with the knife. Sure, it's great to turn it down to a small nub and have a nicely turned surface. If that's taking you an extra 15-20 minutes, compared to popping if off the lathe and doing some extra knife work, then in terms of production work it's not worth it.
In the end there wasn't time left to finish the inner bowl. So I popped it in the freeze, ready for when I get back on the 8th of January. I did grab the template and compare it to my work. What do you think?
I'm going to try and do some more writing during my break. There's a lot of my own stuff that I want to have a go making, so I'll be sharing that too.
Hope you all have a Merry Christmas and a Happy New Year.