I've been turning bowls for almost a year now and have run across this problem several times. I usually turn wood I collect from the yard or woods nearby. I've made several bowls that had checks in them, some have even broken on the lathe. I just roughed out a 10" bowl in beautifully spalted silver maple and found a check that runs from the lip all the way to the bottom nearly to the center. The bowl is wet now and as it dries I'm afraid the check will grow and ruin the bowl. Is the bowl doomed or is there a way to save it? FYI... I slow dry my bowls in a paper bag filled with shavings, usually from the bowl just turned.
Soft maple is a bad actor in this respect. Since, as you know, the long grain portions of the bowl will drop either side of annual ring centerline, and contract at 90 degrees to that as well, the crack is going to open more on the rim and outside and close on the inside of the bowl. Makes it possible, but not probable that it will close well enough to save the piece.
It's a low percentage play, but if it's a particularly nice piece, and the shape permits, make a big wide double or triple layer glued plywood circular cutout, modestly tapered, and drive it down to make a circular clamp around the outside. Set the rim on a sturdy surface, add a couple four clamps to keep the ring tightly wedged down toward the rim, and wick some CA into the crack.
Protect under a newsprint tent for a couple of weeks and you'll find out pretty much what you're going to get. If you're not in a heated place where the relative humidity is below about 65-70%, you can forego the tent.
First--when I dry my bowls, I try to encourage the interior to dry first and to discourage the exterior. To that end, I put them in a plastic shopping bag, loosely tucked (not sealed) into the bowl top, but with as much of the interior exposed as possible. I figure that if the INSIDE dries and shrinks while the outside is still a bit wet and pliable, cracks will be avoided. That sort of works. As the wood loses moisture, I eventually remove the plastic bag and let it fully dry.
When the lip is cracked, I shudder, because there is a lot of stress there.
But when I have cracks, I hit them with CA glue, right at this stage, trying to get the pieces to adhere. As I remove wood, I add more glue, on the theory that I might just have turned away the only part that is glued. And finally, in this situation I'd turn a thicker rim than usual because no matter what you do it will be weak.
Finally, if I do end up with a crack, and it's a weak bowl, I stop before making the very last cut inside and out and patch it with epoxy glue. If there is a void there, I will put a masking tape dam on the inside or outside. I've added some oil artists colors to the glue to try to make it look like the tree filled in the crack, not me, and it helps. It's a messy process, and I get dribbles all over, which turn off very nicely on the final cut.
I really haven't lost too many, and I've turned some really wet wood.
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