Minimising Cracking

Collated from newsgroup postings.

I've been looking everywhere for secrets about what makes wood crack and how to stop it. I've heard dozens of old maid tricks but none seem to work for me.

I use core blanks from veneer plants to turn on my wood lathe. Some of them are still wet. I store them in my unheated but dry shed. Once I'm done, I bring the piece in my house and the cracking starts. and What a crack it does!

The latest trick I heard was to soak my piece in linseed oil before bringing it inside. I haven't tried it yet.

Is there a better way to minimise the cracking and splitting of wood especially when I don't have one of those driers for wood?

They are wet because that is the best way to get the best yield from the log.

I store them in my unheated but dry shed. How do you know you are "done"? You got a moisture meter to check the moisture content of the peeler poles? Should be down to about 12% or so.

You got the heart of the log and that's the trouble. The Japanese have figured a way to prevent serious checking when they use poles for house building. They purpose saw a vertical, as in the long way or length of the log or pole, cut on the side most to be hidden and that relieves the stress on the pole but that doesn't help much for a turning piece.

PEG might be your best be but anti-freeze has been suggested as a cure for all things that can go wrong with wood.

Paint the ends to seal off moisture escape that way is done with planks but with those peeler poles I have no idea. Might be better than nothing and remember with all things equal, not wet as in peeler poles, air drying is usually rated at 1 inch per year!

You either need to drill out the centre (pith) of the log when making your piece, or split the thing before you start into thirds or quarters, and turn those.Pieces of any appreciable size with the pith in will split when drying.

I'll bet this problem happens more in the winter than in the summer. That's because the heater in your house is turning it into a desert. We use a humidifier in our house, to help a little with the problem of too dry air. This may also help with the cracking problem. In addition, you need to make sure that your wood is dried to a level compatible with your house.

Get a meter for humidity and check the humidity in your house, then in your "dry" shed. I'll bet the difference will be more than a few percent.

You have a couple of options. You can finish drying the wood in the house, or you can have it kiln dried. When you take it to the workshop to work on it, you may even need to bring it into the house each day, because your shop humidity may be too high for the house as well.

The radial cracks you're experiencing are because the heart is still in the veneer core. Two choices if you're trying to use the whole thing:

Buy a chainsaw and find other wood to work with.

the centre of a wet log is good for spurtle blanks and small items as the veneer place about the limbs and crotches. Make the long, linear cut as suggested, (it will look like a pie that is missing a piece in no time)

use a bandsaw to cut the blank into long pieces and turn these into spindle projects.

Avoid the Bullseye.

You have had some good answers, but how about we go for the simple stuff. You have essentially a five inch diameter log, i.e. the core from the veneer process. Probably pretty wood. Also it probably has the core still in it. Get rid of the core.

The easiest way I know is to cut the log through the centre with a chain saw or on a band saw and cut wide enough to remove the core. Alternatively, turn the core away. Either way it has to go. This will Relieve a lot of the stress that develops cracks.

Now turn the piece to oversize for the desired final shape. Conventional wisdom says to leave it one tenth inch thick for each inch of diameter. Put wax emulsion on the end grain or on the whole piece and put it aside in the shop to dry for three months or so. Remount and final turn, sand and finish. One of the most important tools for the turner is patience. "Tribulation works patience" may mean that a cracked bowl teaches us to take us easy. Just a loose (very loose) bit of theology.

You might try rough turning the 5" blank down to 1/2 to 3/4" thickness and then boil it. The theory is that boiling breaks down the cell wall of the wood and allows the moisture to leave more evenly thus preventing the cracking. I have never tried it but it sounds good. If you're talking about cracking from the pith, try turning the piece green, and when you get to final thickness (or sooner, if cracking begins at the pith) soak the pith area with thin CA glue, both inside and outside. Don't use the accelerator, just let it soak in deep. The CA glue is strong enough to hold the pith together and prevent it from cracking. Do this before final sanding. This is especially helpful in the darker woods, where the CA won't show as a stain on the wood.

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