Troubles drying bocote

[Dave Mount]

I acquired some 3"x3" bocote that was sold as unseasoned. I have a pin-type moisture meter and it was difficult to get the pins to penetrate, but the reading I got was 20% MC -- not sure I 100% believe it, but I treat readings in that situation as "at least as wet as **%". I turned three spheres from it, then put two generous coats of Anchorseal on them and put them in a paper bag to season, along with comparable spheres made from bloodwood, purpleheart, and sycamore. I've been monitoring the weight of those spheres over the three weeks since I turned them; they are losing weight slowly (or what I would call slowly), losing about 0.7% in weight per week. Living in northern MN, the humidity is low in the shop, but I only heat it to about 52 F, so it's not as dry as in the house. These conditions are very favorable for drying rough turned bowls in the same way (in paper bags, with or without anchorseal depending on the species), as I have for many, many years without much wood failure (except for redbud -- a separate story).

Last night I weighed the spheres and was disappointed to see serious drying checks in the bocote spheres, though the other species are fine. There are checks in both endgrain (radial) and along the "face" grain. I superglued them all, put on yet another coat of Anchorseal, and put them into a second paper bag inside the primary bag.

The fact that they checked clearly shows I was drying them too fast. . .but my question is, how slow is slow enough? I would have thought that losing about 0.7% MC per week would be plenty slow enough. Green spheres of the same size from three other species with the same treatment (bloodwood, purpleheart, and sycamore) are drying at the same rate without checking, though it is possible they are still above the fiber saturation point and haven't actually started shrinking.

I have no prior experience with bocote, so I don't know if it is just a problem with that particular wood (as I have experienced with redbud), or if I'm drying too fast for most any wood. When drying bowls, I don't follow their weight, I just ignore them for several months. On the other hand, bowls aren't as thick as a 3" sphere. Any thoughts or experiences that would speak to this?

Best,

Dave

[Mike Nathal]

I have no direct experience with bocote, but here are some ideas. 1. Do not use CA glue until the spheres are fully dry. Some cracks close up on their own upon further drying and CA glue will interfere with that. 2. Try microwave drying. I have done this with thick sections like spheres, up to 6 inch diameter, (domestic species) with some good luck. My thinking is that you heat up the water/wood so that the wood is steaming hot, and it not only accelerates the drying but it relaxes the internal stresses in the wood. Three hints for microwaving: 1. don't use your main kitchen microwave, 2. have a digital scale to weigh the piece frequently. 3. Initially, use short increments like 2 minutes, check to see if it is hot, almost too hot to pick up, add minutes until it does get hot. Once it is that hot, I let it cool outside the microwave, and then weigh it and record the numbers. And then repeat. As the wood dries out, the weight loss per cycle will start to diminish. At this point, you need to reduce the microwaving time so that you don't start to burn the wood. If you do start burning, it may smolder for quite a while: I only did this once when drying a bowl, it was quite smoky and the smell remained in the microwave for about a month.

[John K Jordan]

Dave,

I've dried a lot of exotics including Bocote but I go about it differently. Don't know if it's a better way but I haven't had any cracks. The down side is it's not fast...
Since the blanks are usually smaller than bowl blanks I dry the entire blank before turning.
I make sure the blank is well sealed then put it on the shelf to air dry, weighing every few months. When the weight quits changing, the blank is dry. Sometimes this takes months, sometimes years, depending.

I do use a moisture meter a lot for quick checks but more with domestic wood than exotics. Mine is a pinless meter which requires on knowing the density/specific gravity and on having a big enough flat are on the blank.

If I wanted to turn first, then dry, I would probably do as you mentioned - seal well then dry. I haven't tried this so I've no idea if it would be successful. Perhaps in your case the other spheres were much drier and were pulling moisture from the bocote too fast? Just a wild guess. I probably wouldn't use CA on the checks, just more anchorseal. But unfortunately, a solid sphere is not going to dry gracefully like a rough turned bowl drying from both sides of relatively thin walls.

BTW, I've found anchorseal covers more to suit me if I let it thicken considerably before use. I pour a couple of inches in a plastic coffee can then leave the lid off long enough so the stuff loses some water and gets a lot thicker - goes on thicker this way. Another thing you might try in the future is the method wood dealers often use - coat the entire blank with paraffin. A dealer I know keeps a vat of hot wax and dips the blank 1/2 way, then turns it around and dips the other half. I wonder if this would work with turned pieces like your spheres.

I'm wondering how deep the checks are and if the spheres are going significantly out of round. Perhaps they will turn away when final turning the spheres.

BTW2, I have some larger blocks of both domestics and exotics I'm drying this way too, but that really requires patience (the largest is 9x9x13"), some on the shelves for over 10 years now. As I'm getting older every year, I should probably put some of these in my will.

JKJ