Releaseing internal tension

[Mike Vickery]

This might be a stupid question, but is their a way to decrease or release the internal tension in wood prior to final turning.

To give you a little background I was final turning a ficus last night down to 3/16th's. I was doing the inside in thirds and it went way out of round to the point where I could not blend the sections together. I measured the outside and it was 8 inches at the smallest point on the rim and a little over 8 1/4 at the widest. Most of the wood I use is pretty stable so this is new territory for me.

Thanks in advance.

[George Tokarev]

Could be it wasn't dry. That would make for a piece that contracted across the grain. If you were cutting along the grain, the differential between radial and tangential shrinkage can oval a piece as it dries as well.

Then there's technique, where you're "riding" the bevel up over the end grain and into the softer face. Shows a rim of unequal thickness, as does sanding while resting the paper on the piece, since the face is abraded more rapidly than the end grain. You can also spin so fast that you start to distort the piece along the grain if you're cutting a cross-grain bowl.

Only way to help yourelf is to make your cuts fine and well-supported. Ditto the sanding. A steady can help against bevel riding and centrifugal effects as well. The final method is to cut outside inside outside inside, where your medium thickness turning is re-trued once hollowed, then trimmed inside to final thickness.

[Mike Vickery]

Thanks for the response. I have considered that the wood may not be completely dry, but all indications was that the wood was dry we did have some high humidity for about three days before I turned it so that may have effected it since my environment is usually so dry (like a desert).

I have a fair amount of confidence in my cutting technique and the bowl wall thickness was consistent. When I cut it it was round but went out of round after it was cut pretty rapidly. I rever actually sanded it, it just seemed like a waste of time. It is now being used to test some pyrography on. The only reason I asked is I have 4 more roughouts from the same log wating for final turning.

[George Tokarev]

Grain orientation and object shape determine the direction of shrink, with the magnitude depending on the moisture differential. The fibers are pulling against each other in kind of an equilibrium that we disturb with our reshaping, which is why with really thin stuff we use the outside inside outside inside method. As the the stresses show themselves, we remove their effect.

And we never set up the grain with a wet rag on really thin stuff ... anymore. :mad:

Not to constitute an endorsement, because I have only only a theoretical explanation, but Steve Russell claims that boiling a rough will help stabilize it. Since lignin will become plastic below the temperature of boiling water or microwave boiling, which also dries the piece, you might try warming it up as a modestly oversize turning. Let it assume a shape of its own choosing, presumably the one which relieves the most tension. Only works well with green wood, but even once dried will gain some plasticity with steam.

[Barbara Gill]

Sometimes when I have that problem, I will take a little off of the inside and outside and then put the piece back on the shelf to stabilize.