The timing of Brad's post regarding ugly crack bowls was interesting for me, because I had just started a bowl and stopped due to cracks. In the photos below you can see what I started with and where I stopped. The pencil lines hightlights the crack on two sides. The bowl is 13" and at 6" I hadn't found the bottom of the crack. So for me, no more messing around with this piece of wood. Burn pile it goes. The crack was not evident when I started. I also don't like to glue up cracks or fill them in. But on the positive side, I got in some good practice with the bowl gauge making shavings. But that also meant cleaning up a big pile of shavings.
I have often suspected that trees that were blown down in a major windstorm were more prone to cracks than those properly felled. I think the twisting and whipping that goes on during the event is a set up for future hidden cracks. It seems more prevalent in maple. No science just a sense of more probs I have encountered with known blowdowns. Anybody else experience this?
One more thing that has a big difference in wood cracking is the time of the year it is cut or taken. It is always the best to cut it when the sap is down.
I cut a tree for squares in the winter and sawed them and then had an opportunity to get some more during the summer ( sap up ) sawed them the same and they bowed cracked twisted and etc. so if you have the chance get them during the winter.
What causes ring shake? (Where the wood separates between the rings.) That is what I hate the most. The wood looks great when sectioning then falls apart in the hand.
I had some beautiful chinese chestnut logs a couple of years ago that turned out to be mostly wasted due to ring shake. I've seen it in walnut too.
I would hate to burn that blank up. It looks nice otherwise. Couldn't you cut it up for box, bird house, ornament, pen blanks? Even if you just cut in two and gave it away. I'd take it.
I would cut it up for other uses myself. However with cracks that go like that you can often turn a vase or maybe you call it a bowl. I slowly cut wood away where the crack seems the worse being careful to keep the speed down so I don't explode it. I've found that quite often you can turn something that looks like a trumpet bell (think bowl from a board shape) This usually leaves the rim close to full size and you have a cone shape going down to a small foot. Not worth the effort if it doesn't have any great figure in the wood however I've painted and decorated a few like that.
The paper in the second link opens with the statement "There have been several explanations of the cause of shake, but none of them account for variability in the incidence of shake."
Some people will not like this---But this stuff grows on trees. The source of our enjoyment is perishable, very perishable. When you find a piece of wood like this, why waste your time. There is a risk of getting hurt. One of the turners in my club has 67 stitches up his arm from a piece like that. Best case scenario is you end up with a vessel with glued up cracks in it. In the time invested in this piece you could turn two good pieces with no cracks.
That is a check and Ring Shake is not wind related
Keith Newton
I have gotten trees which were taken down by a tree service, that had never lost a limb to wind, which had shake totally throughout, from base to 60' up, and there was no decay in it either. I inspected it with a hand lens, and there were fibers still connected to each side at both ends, which would indicate tearing, rather than decay related.
I cut it all to firewood length, and busted it up with a splitting maul. While I was performing that task, I was just baffled. What could have so totally broken the core of that tree away from the outside part without doing it some obvious damage to the outside? If it had happened just under the bark, surely this would have killed the tree.
Ah Ha, I thought, I remembered a very severe drought in 1980 where we had two and a half months over 100º, with no rain anywhere in the state. I could remember seeing standing tree with checks in them large enough to stick a finger in. I didn't think any of them would live. Then I set out counting growth rings. From the cambium back to the shake, came out on 1968. I lived in this city that year, and it was a normal year. So I went back to splitting.
This tree, which was about 30" diameter was the easiest tree of that size I ever split. With one swing, it would split in to the shake ring, then around to the back side and pop loose back there, leaving a perfect core. One unusual thing I noticed, was that sometimes it didn't stay on the same ring all the way around, it may jump over a couple of years.
As I continued my splitting, I recall looking over ahead at some of the sections which I had stood on end, and spaced so I could stand between them as I was splitting, when I noticed a detail which held the real answer to the mystery. The water in the sapwood was welling out standing 1/8" deep, while the heartwood was only moist. Ah Ha, I said again. This time I counted the rings of the sapwood, and there were 12 years, which was the amount needed to land on the year of 1980.
Everybody knows that when you dry wood in the round, it will check radially. The sapwood being on the outside of the tree is more absorbent, but also more desorbent as well, meaning it will dry faster. But it does rely on the heartwood as a sort of moisture sink. I believe that part of the reason for some of these extractives in heartwood, is that they slow the drying process, to keep trees from loosing all of their moisture too quickly.
Now when the drought ends, if a tree has lost so much moisture that it has shrunk in diameter, including the heartwood, the sapwood, being on the outside, and more absorbent, is going to get the moisture first, and will swell. As most people know almost all woods are stronger in compression than in tension perpendicular to the grain, so when the sapwood expands, it tears away from the heartwood.
I'm sure all of you turners have noticed that the heartwood often jumps a few years now an then, which would explain why this tree's shake ring jumped a few years occasionally.
It was really interesting to split this tree. Coming from a fine neighborhood, it had always been trimmed. All of the earlier limb scars had already healed over, so when they popped apart, there was a perfect mold and positive of where it was already separated, as well as in crotches higher up, even into limbs no larger than my wrist were totally checked.
The tree was in perfect health, and should have been left, except the previous winter during an ice storm, another tree had fallen onto the lady's roof, and she feared this larger tree would be next.
Since getting and studying that tree in the mid nineties, I have seen lots of ring shake in lots of trees around here. Sometimes it will only be partial, maybe due to the trunk being exposed more to the afternoon direct Sun, or beside a asphalt drive or road, which can bump the radiant heat up a lot higher than the ambient air level, contributing to faster drying on one side, over the rest.
There were other extreme years which show up a lot in big trees around here. Another was 1954, of over two months above 100º with no rain throughout the whole state of Arkansas. I wish I could afford to take a trip down into Texas to survey some of the area that went through a major dry spell, but I'm not a wood scientist, just a simple woodturner, maybe I can claim to be a self taught naturalist, or at least observer of Nature.
I've read a lot on the topic over the years, pretty sure I've seen the old paper you gave, and others including Wengart and Hoadley. The answer I keep getting is "nobody knows". Different researchers, experts, and self-appointed experts variously claim to know or strongly suspect that shake is caused by:
- wind, bending tree
- age
- size
- subfreezing temperatures
- extremely heat, excess moisture
- bacteria
- site/soil conditions
- growth stresses
- genetic factors
But what one expert claims, the next refutes. The science I've read was mostly from surveys rather than experimental such as creating conditions then waiting 100 years to see what happens. (I wonder why...) Wilson's bottom line is "cumulative growth stresses, rather than external action of wind or cold temperature."
Bacteria is often found in ring shake but no one is sure whether it caused the shake or moved up from the roots and grew in the damaged area.
The pictures I've seen of shake have shown, probably by necessity since otherwise there would be no picture, dark lines or obvious separation between rings. But what I ran into several times is not at all visible on a cross section - the wood looks perfect. However, it falls apart in the hand. Some texts describe shake that is not noticed until the wood dries. I assume here that drying shrinkage stresses cause visible separation.
As mentioned, I've seen severe shake in a walnut log and in a chinese chestnut tree. It makes the wood worthless for turning, but at least in the wood I had there was no danger of it flying apart on the lathe - it fell apart way before it could have been mounted!
I think shake is worse for woodturning since, in what I've seen, ruins the entire log. At least with drying cracks I get good wood between the cracks.
We get a lot of imported honey coloured New Guinea Rosewood here that has checks / cracks across the long grain which creates issues for spindle turning. It appears that the tree is heavily stressed at some stage during its growth then continues to grow on. The fractured grain can be surrounded by sound timber which seems to defy logic.
This is also something to be very wary of with timber in Far North Queensland as we have had a couple of Cat 5 cyclones (Larry & Yasi) in the past ten years. I recovered a Silver Quandong tree that fell at my brother in laws home in Cairns after TC Larry. Ordinarily the timber isn't that great for turning but it is useful so worth recovering however this tree had been heavily stressed by previous cyclones. As my BIL live at the foot of the Barron Gorge it gets a rather unique wind pattern either up or down the gorge. This tree had quite alarming damage under the bark on the down gorge side of the tree but had grown over & completely over the stubs of broken branches. Some of the damage was similar to the New Guinea Rosewood.
Yea, like Lyle said, it grows on trees. You may be able to get some end grain blanks off of it, and if I am looking for pieces for the clubs monthly wood raffle, I would cut that piece up. Other than that, into the fire wood pile. If the piece is highly figured or very rare wood, then I might make an effort to turn it. Most of the time, from a time/money point of view, it isn't worth the effort or risk.
Thanks Reed, I find it strange that the thread starts out with near 400 viewers but by the time it gets down to the end at this point there are only 128 viewers. Not very many people see the best parts of a lot of threads.
Firstly, I'm not claiming to be the expert here, just one guy's opinion is all I have to offer.
I'm a pretty low-tech sorta guy, so here's what I'd do with that particular blank. I would remove it from the lathe, set it on a rugged pallet I have made from 2x6's with 4" gaps between the "slats), and place my hatchet right on that crack, and beat it with a wooden mallet until I split it cleanly in two.
Now you'd have 2 smaller, odd-shaped blanks, which will make 2 perfectly good, albeit it smaller, bowls. I'd probably take a smaller mallet and a wood chisel to create flats for mounting it between centers, but with a little effort, I'd have 2 rough-turned bowls seasoning in a cardboard box.
I will only turn a piece with cracks in it if it's a burl, or a spalted piece with sound wood, and then sparingly, slowly, and wrapped in tape & Saran Wrap once the outside is shaped. I just roughed out a small Quaking Aspen burl hollow form that has some cracks and a few unstable inclusions, and it looks like its got some slight ring shake in the strait grain part attached that will rear its ugly head when seasoned, but it was frozen solid (and ice can be pretty good glue), and the rarity and figure of the burl motivates me to try to get something pretty out of this little burl. After shaping the outside and removing the center, I glued a few little cracks with CA, and my plan is to let it thaw, and assess the situation later to see if I can safely finish the little hollow form -- and the answer may be NO. Around here, Poplar (Aspen) burls are very uncommon, but that doesn't mean I have to take dumb risks to finish it. I have enough experience with burls in all states of decay to make a pretty good assessment, but I wouldn't be the first turner to be surprised by a piece of wood.
Just one fella's opinion, and worth exactly what you paid for it...
Like Brad, I wouldn't be the first turner to be surprised by a piece of wood either but its is a very good practice that you have developed - checking for cracks as you are turning.
