hockenbery said:
DW
Keep turning the green wood.
Keep at it! A bowl with a nice curves and even 1/2" or less walls shouldn't crack.
- Al
That's it. Under 1/2" shouldn't give you cracking problems unless they were preexisting, you cut a shape which favors cracking, used a wood predisposed, or you just plain loused up in the drying.
Thickness of the bottom is
much less important than its shape. I have a lot of bowls that wouldn't stand on their own if the bottom wasn't an inch thick, because they taper to such a small bottom. Fortunately it's radial shrinkage which predominates with heart up, which normally means larger diameter, and that's usually half or less the tangential, which affects
broad, bark up bottoms. Thin wood will tolerate stress much better than thicker, but thicker doesn't necessarily mean wall thickness. It means
continuous wood in the direction of shrinkage. Thus a set of thinner, more vertical walls is much more likely to split than a thicker sweeping set of walls, because there is a greater distance of continuous wood to pull against, just as the broader bottom will take almost the full measure of normal shrinkage. Nature helps us again, though, because the bottom of a bark-up bowl is predominantly quartered figure, which moves less.
You want to believe your fingers or calipers over your eyes on wall thickness. Since the angle is changing, there's a naturally broader look as you begin to transition to the freshly cut portions of the bottom which can fool you into cutting too thin there. Sometimes you cut so thin you can't recover on the wings. Especially when the wood's already got problems like spalting.
Spin all the unbound moisture you can out of the piece prior to putting it into the paper bag or newsprint wrap. Even at that, you'll want to open it next day to make sure you're not growing mildew. I don't bag, but I'm not in the desert.
I find sanding a problem. The moist wood clogs up paper pretty rapidly, and wet wood doesn't show areas where the bevel compressed the surface, so I generally run a single 120 grit pass and sand after drying. Sanding with fine grits is a double pain, because I have to keep cleaning them, and the chances of making surface checks increases. So I sand after the wood is dry, where I can use a light touch more easily.