Round Cut Tops (Almost) Always Split
All wood splits, some more than others, but it all splits. It even splits when paid professionals try to make it not split. This is good news for those of you wanting to snuggle by a warm fire, but not such good news for connoisseurs of split-free wood. And, it is especially bad news for anyone wanting to make a round table top out of a slice of tree.
It seems easy enough to just slice a cookie, or coin, or round, or whatever you want to call it, off the end of a log and use it as a table top, but it rarely works out. The problem (especially when swimming) is shrinkage, and in the wood realm it’s uneven and unproportional shrinkage.
I talk to customers a lot about this uncomfortable subject, and even though it isn’t pleasant, someone has to do it. As woodworkers, it is critical to understand how wood shrinks (read an earlier post about shrinkage by clicking here), and as customers it is important to understand the limitations of wood.
Drying quartersawn lumber is easy, relatively speaking, and almost always produces wood that doesn’t split. Drying flatsawn lumber without splits is more difficult, but if the ends are sealed and the lumber is dried at a slow, consistent pace, it can be done reliably. Drying round cuts from the end of a log, however, is a totally different story, and almost always results in split wood, and not just a small split, but usually large, unsightly, unrepairable and often devastating splits. So much so, that I tell customers I will cut rounds for them only if they take the milled pieces directly from my sawmill as soon as they are cut. That way I can prove that I had nothing to do with them falling apart – they do that all on their own.
It all goes back to the way wood shrinks and the way it does so unevenly. As wood dries, it shrinks twice as much with the rings as it does from the center. When viewing a log at the end (not a round cut off the end of a log but an actual log), this produces cracks that resemble spokes in a wheel. Sometimes there are larger cracks mixed in with the smaller ones, but they are always in multiples. The end wood wants to split, but since it is attached to a log which is holding it in place, the end cracks with many smaller splits to even out the pressure.
If that piece is cut from the end of a log all bets are off. There is no log holding things together, so the end result is usually one large split that relieves all of the pressure at once. With wood that is known to split easily, like oak, the round cuts will not only have large splits, but will often just break in two or more pieces.
Here are some examples of dried wood cookies. All of these were cut from the end of the log when the wood was wet and then air dried slowly in the shop. They are all about 18″ in diameter and 2″ thick.
So, now you know that the cool round table that you were planning to build is probably going to split if you do nothing about it, but can you do something about it? Well, maybe, kinda, sorta.
One way I know to work, from personal experience and from other local sawyers, is to cut the rounds at an angle. This will reduce or completely eliminate the cracks because the stress is going more up and down than in a circle, but it will turn your round table top into an ellipse. And, while a piece that stays together is probably better than a piece that falls apart, an ellipse is not always acceptable. I personally expect to see a round piece of wood when you tell me it was cut from the end of a round log, and find the ellipse shape a bit unnatural.
Another alternative is to remove the pith (center of the log). Removing the pith can stop the devastating splits, but it obviously puts a hole in the piece of wood, and it is still a gamble because it is hard to tell from tree to tree how much pith needs to be removed to stop the splits from happening. A larger hole is better, but at some point the missing wood in the center will demand creativity, and perhaps more wood or glass to make a complete top.
The last and most widely used solution is to use a wood stabilizer like Pentacryl or PEG (polyethylene glycol). Originally developed to stabilize wood from archeological sites, Pentacryl works well to stabilize all kinds of wood from punky wood to crotches and will help with wood cookies. It works by replacing the water in the wood and keeping the cells at their original size, even when dry. Know that while Pentacryl will reduce and often eliminate cracks, wood cookies are by far the most difficult to dry and may still crack.
Pentacryl is not perfect. It works well, but it is expensive at $60 per gallon and adds a yellow tint to the finished piece. And, wood cookies which could normally be dried relatively quickly need to be dried extremely slowly. So slow, in fact, that thicker pieces could still take over a year to safely dry.
PEG is applied like Pentacryl, but has drawbacks that make it less than perfect too. Like Pentacryl, it is also expensive and the resulting wood surface may not accept the finish of your choice. It also takes extra time to apply and may require additional equipment to make it work correctly.
The bottom line is that you can make a table out of a round end cut from a log, but you’ve got to be prepared for failure and/or be prepared to throw plenty of time and money at the problem. I still steer away from cutting wood cookies and do my best to direct customers away from them as well. And, if I do end up cutting wood cookies for a customer, I literally cut and run.
About wunderwoodsHi! My name is Scott Wunder and I am the owner of WunderWoods Custom Woodworking. We build wine cellars, built-ins and furniture from local woods, here in St. Louis, MO. Recently, I finished a three-year term as the President of the St. Louis Woodworkers Guild, which had me writing a monthly article for our newsletter. I love to write, especially about wood, and found that I still had more to say. Every day I run into something wood related that I realize some of my customers don't know and this seems like a great forum for sharing what I have learned (instead of telling the same story to each person). The main thing to remember is that I try to keep it light and as my wife always reminds people that have just met me, "He is joking."
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