Turnings that crack

[Gary Hupp]

Everyone seems to have good luck turning relatively green wood and having it turn out just fine. No pun intended. For me, whether it be oak or cherry or whatever, I get the piece turned and finished and about a week later, the cracks appear. What am I doing wrong?

[Joash Boyton]

Hi....

Generally, 85% of my turnings are turned green. I turn it to a little thicker than I want the finished thickness to be. Don't turn it to a thickness that you would when roughing out. Sand the base, becuase when you turn it green, there will be no way of resanding the base (unless you have a vacumn chuck or something) Then when it is finished, stick it in the freezer, no need to wrap it or anything, leave it in from 1 to 5 days depending on size and thickness, then again depending on thickness, after it has dried, put it in the fridge for 1-10 days, and then bring it out. You will notice that it will be covered in a layer of ice or frost, let it defrost before you put it in the fridge, or finishing it on the lathe. When defrosting, never stick it in the sun, this will cause a huge stress, and it may split, in the shade or in the workshop will be fine, keep it away from other pieces, because when it defrosts, the ice on the outside is frozen sap, that has come out of the timber, so when it dries, that liquid is as strong as a dye! Put it back on the lathe, and finish it, it will be slightly warped, take the warp out, sand and finish it. If you want a warped look, do the same as above, but stick it in the freezer, from 2-30 hours, depending on size, it will just dry it a little, and then when it has defrosted, stick it back on, and complete the process as described above. 1 in 100 of my bowls/platters/HF's will have splits that cannot be turned out.

This is a method that I have used always, I have changed, tweaked, expirimented, and this is what I have some up with. It is by far the easiest way to dry a piece, it only takes days instead of months. Take a look at some of my threads to see some finished pieces. All of my pieces are turned this way.

Hope this answers your question, try a piece, and let us know how it works out.

Please note, My method has only been tested and used on Australian hardwoods, your timbers may be different.

Joash

[George Tokarev]

Two major and one minor factor. Major are rate of drying and shape of the piece, minor the annual ring interval and orientation.

Good place to start is www.fpl.fs.fed.us/documnts/fplgtr/fplgtr118.pdf and the wood handbook at http://www.fpl.fs.fed.us/documnts/fp.../fplgtr113.htm

Explains a lot of what you'll need to know.

In thumbnail, you want to limit the loss of moisture from the surface to a rate which will allow the moisture from within to replace it, equalizing drying rate and minimizing drying stresses. You also want to monitor the shape of the piece, realizing that flatter bottoms and steeper sides will be more influenced by tangential shrinkage than pieces with narrower bottoms and more sloping sides. They're more influenced by radial. The influence of the annual ring orientations are shown in the figure of shapes within the log.

All kinds of methods out there to control the relative humidity of the environment around the wood. You have to assume the risks involved in particular shapes if that's your desired outcome.

There are some woods which have natural weaknesses, like the ray figure in your oak. It can be a bear to dry. Then there is the interlocked grain of the true poplars or elm which are almost split-proof, but can result in some interesting directions of distortion outside the norm you would expect if the tension were strictly developed by the annual ring orientation and tangential/radial shrinkage.

Start with some means of measuring the relative humidity. Little investment in money that will pay great dividends, and the best way to find the proper compromise between reasonable drying rates and possibile degrade. Avoid magic potions and fads. Some are simply silly, some result in slimy pieces which cannot be forced to accept a finish, others make for obscure grain and wierd discolorations. Stick with wood science and integrate it with your developing turner's eye to determine the best course of action for an individual piece.

[Gary Hupp]

The freezer/refrigerator idea sounds like a good idea. I will try it and get back to you. I still have a piece of the cherry that cracked most recently.

[Joash Boyton]

ok, look forward to seeing your first "trial and error" Let us know.

Joash

[Jim King]

I am an ABSOLUTE beleiver in boiling as the drying system of choice. I have never tried real alcohol as the best we have available here is moonshine from sugarcane and that was not real successful but a lot of people swear by it. I have a problem as my turnings travel 8 to 15 hours in an airplane and that is one of the driest and cruelist things you can do to wood . If the turnings are not VERY dry the kiln type action of a plane will crack them in three or fours and boiling plus patient drying has solved my problem.

I posted info on my web site about it. Try this.

http://www.exoticwoodworld.com/index...tic&sc=process

Jim

[Ron Sardo]

Check out Dave Smith's Blog http://alcoholsoaking.blogspot.com/
I use this method and it works well for me.

Another simple method would be to wax the endgrain of a rough turned bowl. Anchorseal is a popular product for doing this.

[Jon Shively]

I just watched yesterday on WoodTurning techniques on HGTV what he called a twice turned bowl. Like Joash described he rough turned it and left it thick, except he wrapped it in a brown bag and put it in a closet for a length of time. I liked Joash's description of the freezing and will be trying that as it sounds quite logical to me and when I can somewhat understand a process, it is easier for me to "tweak" the idea and make it work for me. Anyway, the one major item, Joash talks of sanding the base, well on the show the guy did have a way of sanding the base. On the second turning, after it has been dried, he took the bowl out of the chuck and slipped a piece of PVC pipe over the chuck (fits snugly) and it was padded on the end, put the inside of the bowl on this padded end and bring the tailstock back up and chuck it up and turn on the lathe and sand and finish to your hearts desire. Thought it was a neat setup. Good luck and thanks for the question as it has been in my head but didn't have a good way of asking.

[George Tokarev]

Interesting thread, as always. Enough reality in all responses to make them workable, but are they really different?

The refrigerator cools things down. Decreases absolute humidity, increases relative humidity, the component we're concerned with in drying wood. So why is it wood will dry in a refrigerator and the ten cords sitting under my spruce trees won't? The refrigerator removes water periodically by defrosting itself. http://home.howstuffworks.com/question144.htm More or less what happens when the condensate is withdrawn in the dry kiln process. If something's still making ice even at low vapor pressure, it'll dry. Not new, just different.

Boiling seems counterintuitive. How can you dry something by submerging it? Answer is, you can't. That's 100% relative humidity, just like wood held at the dewpoint by cold. So what would boiling do? Same as "getting boiled" of a Saturday night, reduce inner inhibitions and tensions. In this case, by softening the hemicelloses and the lignin which binds the fibers, allowing them to creep. The new tensions developed by changing the section of the wood in rough turning are allowed to equalize somewhat as they tug on plastic "glue" rather than solid. Of course the same takes place in drying non-boiled woods too. Just look at what new tensions do to those 2x6's at the home center. We bend wood all the time by steaming or boiling, and just as it sets in the form we force it into, it can set in its own stress-relieved form for further turning. Turners of delignified spalted wood know about this apparent increased stability too. How about drying? Well, there may be a tad of benefit here too. Soluble sugars will be taken away with the liquid, and it is the sugar that makes up cellulose or those feeding the tree which adsorb water. There's a bit less of this available after boiling. Of course, there's added unbound water, too. Real answer probably has to do with those pictures of Jim's place. Looks like high ambient humidity in that jungle, which will help keep the loss gradient gentle and the point of equilibrium higher that those of us in heated or air-conditioned dwellings. The purpose of finishing wood is, of course, to slow the uptake and loss of water, so a finished item has an advantage in short-term relative humidity changes like those at altitude. Not nabsolutely necessary to prefinish, as I know of a scofflaw who used to suspend northern hardwoods in the bomb bay of B52s for crews visiting from the left coast. Didn't hurt the boards a bit.

How about the alkies? Well, they bag or wrap the wood in paper, which is really more wood, just like all the people before them who put the piece in shavings or bags or boxes or dry kilns. That creates an envelope of higher-humidity air around the piece, or at least the portion under tension, if you only wrap outside. Nothing new there, nor different from painting the ends of a piece with anchorseal. Assuming that alcohol/water mixtures will lower the vapor pressure of the water and increase the rate of evaporation is silly, because if it were true we'd never be able to enrich the booze we drink by distillation. If alcohol replaced water bound to the sugars which make wood all the folks who put their beer,wine and spirits into wooden casks would just be watering it down. Hard to believe they'd have been doing it for thousands of years and never realized it.

Then there are the turn thin and warp in folks. They play the elastic limits, knowing a thin section of wood, having less to pull against, contracts, while a thick section can pull apart. Bit of what I mentioned above about discontinuities in the annual ring patterns being less likely to open up. Shape of the rough.

Fascinating.

[Claude Arragon]

Everyone seems to have good luck turning relatively green wood and having it turn out just fine. No pun intended. For me, whether it be oak or cherry or whatever, I get the piece turned and finished and about a week later, the cracks appear. What am I doing wrong?

Far from being an expert in green wood turning I noticed that if the walls of what your turn are thin enough, but above all constant in thickness, and if you do not have the heart of the wood any where in your piece you have a large probability that it won’t crack.

[Ron Sardo]

George are you Micheal Mouse?

[George Tokarev]

Some places.

[Joash Boyton]

I am an ABSOLUTE beleiver in boiling as the drying system of choice. I have never tried real alcohol as the best we have available here is moonshine from sugarcane and that was not real successful but a lot of people swear by it. I have a problem as my turnings travel 8 to 15 hours in an airplane and that is one of the driest and cruelist things you can do to wood . If the turnings are not VERY dry the kiln type action of a plane will crack them in three or fours and boiling plus patient drying has solved my problem.

I posted info on my web site about it. Try this.

http://www.exoticwoodworld.com/index...tic&sc=process

Jim

that's an interestinf site, I saw it a while ago, and always liked it, lotsa nice timber

[Bill Grumbine]

George are you Micheal Mouse?

Bit by bit the mask slips!

Gary, in my experience, there are a lot of factors involved, and one of the most important is the freshness of the wood you are using. Last week I had to turn a couple of bowls for a customer with wood he provided. The one has some cracks in it, and there is nothing to be done. It sat out for quite some time before I got it. On the other hand, wood that is turned soon after it is cut will often not crack if you get it down to 1/4" or less, and maintain a fairly uniform wall thickness. You can push the 1/4" a little fatter, but the thicker it gets, the more likely it is to develop cracks.

This can vary from species to species as well. Oak in its various species is one example of a wood that is harder to dry, even in controlled kiln conditions at lumber yards. Maple is much more forgiving. Cherry is pretty much a coin toss, at least the stuff I get. But as long as it is fresh and cut thin, you should do fairly well with avoiding cracks.

Bill

PS Hello George.

[Reed Gray]

Well, there are a lot of ways to do it. I am one of the ones that love warped bowls. I turn to about 1/4 to 1/2 inch thick, then dry, then after all warping is done (usually 2 weeks) I sand (power sanding and variable speed is a must) and finish. Local weather can effect things a great deal. You do need to make a micro environment for things to dry in. Too fast, and it will split. This is where the paper bags, plastic bags, and burying in the shavings piles come in. If you have a mild humid environment, shelf drying is fine, no fan, no sun, no extra heat. You may have to experiment a bit to find out what works for you. I have tried the DNA and LDD (liquid dishwashing detergent) soaks, and haven't found that it keeps the wood from moving at all, and in a measured test, found that it didn't change the rate of drying. I do like the LDD because it makes things a lot easier to sand. I haven't tried it with twice turned (thicker) bowls because I don't use that method. Also, some woods want to crack more than others.
robo hippy