I was choosing my next victims this morning, since it's still too wet to cut the grass (my story, and sticking to it), and decided to do a bit of photography to show how I dry turnings. I've learned a few things on the way to where I am, and if you're interested xxxx, you might want to try the DNAA method.
Don't bother weighing things after you turn them. It's not meaningful, and it takes a lot of time if you weigh every day or so. Use your tape to tell you when it's worthwhile to weigh. As you see in the photos, I'm a mortise man. Gives me full depth on my turnings, an uninterupted view of final shape when turning, and a quick and easy way to determine when it's time to weigh. Additional benefit, as you can see, is that the revised mortise can be turned to almost the same dimension as the original, allowing maximum contact with the jaws when roughing and working the dried piece. If you're a tenon guy you need to go a bit larger than optimum on the green rough so you can re-true to optimum after drying. I suggest the anticipated shrink plus the depth of penetration of the serrations if you use serrated jaws. That way you'll turn all the way to fresh and uncompressed wood to begin after drying. Dovetailers don't need to worry as much about compression, so they can start a little closer. I measure the contraction across the mortise to tell me when to weigh for stability. Since I dry with the bottom down, it's always the wettest part of the turning, so I may go a week more than I need to on a rush dry, but I can live with it. When I've lost about an eighth in two - 6.2% - I weigh and set aside for a week to weigh again. Equal or nearly so, I'm good. Also pretty close to the average tangential shrinkage for cherry of 7.1% (to 0%), which is a decent cross-check. Wood Handbook, chapter 3, downloadable for free from the FPL site.
Page 3-8 of that document has a couple of interesting figures on it. 3-3 is the direction of warp, which is determined by the annual ring orientation, and 3-2 is something that Ken might want to look at if he's still having trouble out there in Idaho. Look at the curve for initial desorption, and you'll see a fairly steep fall to 20% MC, which is around 80% RH. Even though the figures are for 4/4 boards, I find them a great help in preventing wasting a half-hour's investment roughing a piece. I keep things in that portion of my basement where the RH is around 75 or greater for the first week or two, looking at the larger diameter to see if it has begun to distort. One I see it, I can put it pretty much anywhere I can tolerate the RH. It's in the flatter portion of the shrinkage curve. It's not magic like wrapping in X thicknesses of paper, bagging or anchorsealing, it's something that I can see and use. Get a hygrometer and find a humid place, or enclose a big enough space to contain your roughs and the moisture they generate. Look and regulate by ventilation. Boring holes in an old transmitter crate is what I did in the bone-dry central valley of California. Didn't get too elaborate, just bored another when things were too high until I had a decent rate. I'm sure a fiddler or more scientific type could work something out by measuring inside and outside RH and opening and closing vents. That's too much work.
Note the larger diameter of the two turnings. The 14-incher shrunk 2.5%, the 10-incher 3.9%. Or, in simple terms, both shrunk about 3/8 of an inch. I've found that when a rough approximates the grain around the log, it really doesn't matter much what diameter the piece is. No 10% rule. Soft maple does a half, yellow birch a tad more, and with wilder grain, it can really get strange, which is why the bottom is where I look for my constant. Reason both shrunk about the same is that both turnings have approximately the same wall thickness and annual ring conformation. Thinner walls tend to lose less, because they don't have as much wood to pull against. Steeper sides with broader bottoms are under much more stress, because instead of having perhaps four inches of wood at the largest solid section, they can have much more. Makes them tougher to dry than a tapered shape.
How long does it take? At a tad over an inch, the larger cherry was one of a batch I monitored for grins, and the answer is five weeks to an EMC of 13% for five of the six roughs I did that day. One had an ugly knot that forced me into a near platter shape, and they dry more like the boards they are. Seven weeks. If you are in a hurry you can game the system by cutting thinner. Taking the 3/8 loss (or whatever equates to the wood in use) and adding your desired wall thickness to it is a good place to start, and leaves you a bit of recenter room, but not a lot to restyle. You can also buy a few days in the initial fast drop by blasting compressed air through the wood to eject moisture that didn't fling itself onto your uncovered tablesaw top. Strongly endorse this for mildew control on light-colored woods. Wood density is a pretty good predictor of drying rate. Bass and willow family are fast, cherry and birch in the middle, and maple slower. Stuff like white oak, with its closed tyloses can take even longer. One size, unlike some methods, does not fit all.
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