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Keeping fresh wood from cracking

Joined
Jun 13, 2011
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I just harvested a large white oak. Beautiful wood. I turned out some nice bowls but continue to have issues with it cracking while drying out. Any advice or suggestions would be appreciated. Thanks!
 

Steve Worcester

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Ahh, the eternal question.
Personally, I would rough turn them to 10% wall thickness of the diameter, date it on the bottom, and wax the entire bowl. Put it up out of draft and sunlight, then go turn another bowl.
There is an issue with lighter woods that the remaining moisture content and sugars can further promote spalting, but it will lessen cracking.
There are 100 other ways, boiling, alcohol soaks, paper sacks, burying in shavings (ok, I am 94 short), but I just use the easy route.
I store them upside down so if my shed leaks (it does) they don't hold water.
Well, how do you know it's dry? Weigh it. If after about a week of consecutive weights that are relatively close together, it is probably dry enough to turn.
However, it still does not guarantee that it won't crack. Why? There are more factors in bowl cracking that just moisture loss and movement. Another reason is there is pent up stress in the wood and when you release it by cutting it away, it will still move.
My $0.02
 
Joined
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White Oak checking

As Steve said there are many strategies to avoiding checking, but until you understand the physics of how it happens you won't know which approach would be most useful for your particular purposes.

Checking/spliting or cracking is basically the uneven drying of wood. Cells shrink as they loose moisture and pull away from the less dryed cells. Usually this occurs with the end grain drying faster than side grain. With Oak being an open grained wood the end grain will dry much faster than the side grain.
So, in your case I would bet your oak bowls are spliting within 12 hours after they are turned, with checks at the lip of the bowl on both sides where the end grain is.

The thicker the wood the more likely that the wood on the ends and on the surface will dry faster than the wood in the middle. Therefore the thinner the piece of wood the closer both surfaces are to the middle and more even the drying will be. So roughing out bowls to 10% of final thickness facilitates this to some degree but less so with Oak. Generally, the slower a piece of wood dries the more evenly it will dry, so placing it in a paper bag or covering in wood shavings or wax addresses this issue, and some form of slowing technique is needed even if rough turned. Whatever method you use, place it in an area or container that will minimize air movement, sunlight and temperature changes around the object to slow drying. The faster wood dries the more it tends to move also.

With Oak one approach that has worked well for me was to turn the bowls with an endgrain orientation and make sure the bowl has a uniform thickness throughout. The benefit of this approach is that the entire bowl has an endgrain orientation instead of half of it. That way it dries more evenly. The other advantage is that the pronounced growth rings of oak will be shown off in this orientation. For larger objects that take longer to turn, I will turn the outside, cover with sanding sealer, and then turn the inside. I have had Red Oak split while I was turning it because the endgrain when 1/16" thick will dry in minutes not hours.

Another cause of checking in already turned objects (particularly bowls or vases) is that the outside usually dries faster than the inside causing tension in the wood. Sanding sealer on the outside before hollowing tends to fix this too. Placing the object in a paper bag so that the sides of the bag are against the sides of the bowl with the top partially open can accomplish this also.

When turned, don't leave it on the lathe. A few hours elevated by your lathe in the middle of a room will be all that it will take to crack if it was green when turned. And harsh sanding that heats up the wood will also dry the surface while leaving moisture in the center. Hope this helps!
 

Steve Worcester

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One thing I did not mention is that regardless of species, orienting the grown ring to the spacing between rings is as even across the bowl as possible helps to. If the space between rings on one side is 1/8" and the other side is 1/2" (because of growth pressures, leaning, compression/contraction), there is more stress to release unevenly and will likely result in more warping and cracking.
Trunks are easier to do this with than branches because of the compression/contraction (always tell the sawyer you want from the ground to the crotch and no branches).
In my bowl 101 classes ( or 100 for non-majors) orientation of the block in the log is one of the first things I teach. And I always turn side grain bowls, just don't like turning end grain bowls.
 
Joined
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I just harvested a large white oak. Beautiful wood. I turned out some nice bowls but continue to have issues with it cracking while drying out. Any advice or suggestions would be appreciated. Thanks!

White oak is a bit of a problem because it has those large rays, which are a built-in plane of weakness. Why it's so easy to split for the firewood stack.

Shape is the biggest factor in promoting drying stress. It's going to drop either side of the heart bisector (radial shrink), and it's going to contract across the annual rings (tangential shrink). Won't move much at all along the grain (longitudinal shrink) as The Wood Handbook, available free at http://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_id=100&header_id=p shows.

See how it moves in ch4 http://i35.photobucket.com/albums/d160/GoodOnesGone/LogEnd.jpg

So try not to leave the bottom too broad, or you'll break open along that bisector at the base area. Don't make the walls too thick or you'll increase the risk at the rim. 10% is about 25% too much for most any wood, so give yourself some shorter dry time and remove more wood while it's wet and easily sheared at the same time. Centering the heart is fine, and visually appealing, but not vital. Avoiding reaction wood will deny you some of the prettiest figure, so accept that it may, very occasionally, find a way to warp that will force you very thin or maybe keep you from getting back to round altogether. Difference will be proportionally greater around the edges of a larger piece, so you might have to settle for smaller. Such is life.

I don't buy the bit that a larger tenon or mortise is required to hold a large piece, because I turn over the bed with the help of the tail, and I don't hack, but slice, which puts less stress on it overall. Allows me to make narrower, more survivable bottoms, where the shorter distance to the air through endgrain allows a rate of loss and therefore shrinkage more in sync with the walls. I even leave a pillar in the center of the hollow side for ease of remounting after drying. It's tough to remember the last drying failure I had. Probably the first time I turned beech, five-six years ago.

I do watch the relative humidity and air circulation, though I don't coat or wrap. Basement floor and a neglected corner work to bring things down easy, shelves to bring them fast. RH never below ~60% for the first month. Week or two at the controlled 50% in the workshop finishes them for final turn.

If you're going to turn once and let them warp, get your thickness under about 3/8" and let them dry in the shop.
 
Joined
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wood checking

Steve,

John's mentioned his article above, he also has a video on the subject. It is quite informative for those who are learning to overcome this challenge and I would highly recommend it to you. However, some of the reasons he doesn't have problems will not apply to everyone. For example, he stores his wood outside in Georgia. Here in Chicago last week it had rained nearly every day, for the previous two weeks, then reached 96 degrees for two days and two days later was in the 40's. add chicago's constant wind and this area has challenges not present in other locations. But watch his video it was very well done and is informative. Plus you will learn plenty on the practical and visual aspects of grain orientation.
 

john lucas

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Pretty much everyone has to arrive at a slight change to figure out what works for them. You read as much as you can about why wood checks and what other people are doing, and then you adapt what you can to your environment.
 

Steve Worcester

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how much faster will the wood dry on the lathe while it is spinning

Some of the unbound moisture will spin out, giving you a shower (species and moisture content dependent).
BUT if you leave it thick, that isn't as much as a problem. BUT it also depends on the environment and maybe speed, but probably not too much of a factor also.

Ultimately, we give guidance to shorten the learning curve, but you (young Jedi) must complete the task. It is all about experimentation and what works for you.
 
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I use compressed air to drive out moisture in my warp-and-go stuff. It helps get things dry enough on the surface to keep the paper from loading rapidly. Haven't been weighing and fussing, but I'm going to doubt it makes a day's difference at ~1/4".
 
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