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Monday, March 1, 2010

Preserving a Memento From Your Tree

Many of us have a cherished old tree on our property that, unfortunately, has to be cut down for some reason, or has fallen in a storm. We may want to have something made from its wood, particularly if the tree holds nostalgic significance. Or, maybe we just think the wood is beautiful, so why not have something made from it?

If you're considering having a woodturning (or other object) made from your freshly cut tree, here's some information to help you get the most from its wood. Since I'm a woodturner, I'll discuss it from a woodturner's point of view.

There are a lot of things that can be turned on a lathe from a chunk of wood. Some common ones are bowls, vases, platters, candle sticks, and hollow vessels (eg, urns). There are many more. Obviously, the larger the object that you want, the larger the chunk of wood must be; conversely, the larger your piece of wood is, the larger the turned object can be. Small limbs generally aren't very usable. But some of the most attractive wood figure ("grain") comes from areas of the trunk where a branch exited ("crotch" figure). If your tree happens to have a sizable burl on it (see the blog post about burls), that might be a very desirable piece to have something turned from, particularly a bowl.

Before you cut your downed tree into smaller chunks, it's important to consider some things. As freshly cut wood dries, it shrinks; as it does, something has to give, and that means the wood will very likely crack. And that lessens its usability, generally relegating it to the firewood pile. It would be better to leave the tree in log form than to cut it up into many small chunks that will then be left to dry and crack.

Better yet, if you know the length of the chunk that will be needed to make your desired object, cut the log somewhat longer, and seal the ends of the chunk to prevent rapid drying. Wood dries fastest through the end grain of the log, and slower thru the sides of the log (think of the log as a bundle of straws packed tightly together, side by side; water can leave the straws easily via the ends, not so easily thru the straw walls). The goal is to have the wood dry evenly, from the inside out. If moisture is allowed to escape rapidly thru the end grain, the drying will be uneven within the wood, and internal shrinkage stresses will build up, causing the wood to crack.

What do you seal the ends of the wood with? Well, there are commercial products designed specifically for that purpose, but you could use melted paraffin wax, or any latex paint. You want to paint the sealer onto the cut ends of the chunks as soon as possible; amazingly, the freshly cut wood can crack within minutes on a dry day. Just look at the ends of your firewood... see how each piece has "checked" (ie, cracked)?

Even with the ends quickly sealed, a section of log that's still in the round (ie, has not yet been split down its length) will most likely crack at the ends. Why? Because, although you've slowed down the drying rate by sealing it, the wood will still be drying, and due to the structure of wood, it will want to shrink. When it does, the shape of the log will want to distort, and stresses build up in the round log; those stresses are most often relieved by cracking. Splitting the round section at least in half will allow those halves to shrink with less chance of them cracking (as long as the ends are sealed), although there's no guarantee they won't. Some species of wood are more difficult to dry successfully without cracking than others (like apple, for instance).

So, now what? Well, the answer is ... don't leave the cut chunks "in the round". The best thing to do is to split the chunk (or saw it) right thru the "pith", which is the very center of the log, as viewed from the end. Actually, it may not be the center of the circle formed by the end of the log, but rather, it's the first year's growth ring, which may be offset from the center of the log. The annual rings form more-or-less concentric "circles" on the ends of the log, but the pith may be offset to one side, depending on the tree's growing conditions. At any rate, you should split the chunk thru the pith. You don't want the pith to be left in the chunk of wood that will be used to produce a turning, because it's almost guaranteed to crack, outward from the pith. Look again at a piece of firewood that's still in the round. More than likely, there's one or more cracks radiating out from the pith.

Now that you've split and sealed the ends of the log chunks, you're in much better shape to have something made from them. Be sure to cut the chunks significantly longer than needed, so that if the ends do crack, they can hopefully be trimmed back to uncracked wood.

If you want a bowl made, its diameter can't be greater than the diameter of the half-log chunk; and of course, the chunk's length must be at least as long as its diameter. These diagrams show two possible bowl orientations on the end of a log, with the pith (small circle) at the center. Each bowl would be made from one half of the log, which will be split across the pith so that the pith will be discarded. In the first diagram, the rim of the bowl is oriented nearest the bark side of the log, with its base nearest the center of the log, so its rim diameter will be smaller than the log's. In the second diagram, the bowl's rim is placed near the log's diameter, so it can be larger than the first. The point of all this is just to demonstrate the fact that you don't want the pith to be in the finished item, with rare exceptions.

If you're interested in having a woodturner make something from your tree, probably the best course of action is to contact the woodturner before the log is cut up. A discussion with him of what you'd like will give him a chance to plan the best cuts to be made, and he can advise on the proper handling of the wood.  But most importantly, remember--you must take steps to prevent the improper drying of the wood. If you do nothing else, at least cover the wood with a tarp, and keep it out of direct sunlight until it can be gotten to the woodturner.

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