wood movement even after sealing and aging wood

[Roger Chandler]

Hi all,
I still have a lot to learn about wood movement. For example, I turned a cherry bowl 3 days ago, on a piece of wild cherry, cut back last may, sealed with anchorseal immediately upon slicing it in half on my large bandsaw, and left to dry until I pulled it out in November to do a turning, which is when my old lathe broke, and when I got my new one, I returned to it and finished it into a bowl, where originally I was going to do a lid for another vessel I had turned.
In the 3 days since I turned it earlier this week, it has gone out of round by over 5/16 of an inch. Should I have done a "rough turning" and let it dry more in a paper bag and gone back to it some weeks from now; and should I have re-sealed it with anchorseal?
One thing that may be a factor is that here in Virginia we have had a wet winter so far, and the humidity levels have been fairly high. My wood is kept in a storage shed that is not heated.
Any thoughts that might help would be appreciated.

 

[Steve Worcester]

Yes and no.
Logs generically require aboiut a year per inch of thickness to dry, so in log form most wood will never dry to the level you need it.
That said, twice turned (rough, drying period, finish turn) is a better way to go. That does not mean that even perfectly dry wood will not move. Movement is also caused by releaving the stress in the wood as you cut and some movement may not be avoidable

 

[john lucas]

Even dry wood will move very slightly when you cut away some of it. It depends on the stresses that were in the wood originally. Box turners will frequently rough out a box and let it sit for a while before fine tuning the fit. This is even with dry wood used for the box turning.
It sounds like your wood was not completely dry and there fore move a little after you turned it.

 

[MichaelMouse]

The piece was nowhere near "dry" if you sealed it up. The usual method for dealing with the problem of wood splitting in the large is to rough out your piece and dry it without a load of unwanted wood in it. Most woods can be turned green to a general thickness of about 3/4 of an inch, depending on shape, up to 16-18" diameter. They will lose dimension across the grain and the sides will drop from center if you cut heart up, but you'll be able to work to ~3/8 wall thickness anyway.

That said, some woods are worse than others in the dimension and direction department. Yellow birch can be a real surprise, as can elm and other woods with interlocked grain. Leave yourself an extra eighth to a quarter to work with. I wouldn't go much over an inch wall thickness, even with a tapered shape, because there'll be a lot of contiguous wood to contract and the risk of cracking increases.

Turn/Dry/Turn is the procedure. Let the blank cure until the tenon or mortise on the bottom has lost about 6-7% across the grain, weigh it, and then a week later. If same or nearly so, it's as good as it gets for the situation it's in. It will continue to take up moisture in wet conditions and lose in dry, but unless you're filling it with water or putting it in the sun in New Mexico, movement will be minimal.