Controlling for hygroscopic expansion

[charlessenf]

I can across this interesting turning project and an issue the craftswoman had with the wood expanding. I thought to ask if there might be a (proven) way around this hazard and did.

Then I thought, "the turners on NC Woodworker might know," And here I am Mr, Dillion.

https://www.instructables.com/Turnreuse-Your-Glass...
" lid expanded and the glass broke"
I wondered if the expansion (percentage) might be correlated with the direction of the grain such that, by selecting for the grain direction (e.g. Quarter Sawn blocks) one might eliminate or significantly reduce the amount of expansion.

After I wrote the question, above, I thought "What if I turned them using Green Wood?" I mean, how swell can one get? right?

Or use that wood they make fence posts out of - hard as a rock - I can never recall the name when I need to. Or some of that exotic stuff I see advertised here and there.

Is there a way?

 

[Willemjm]

You can obtain pretty accurate numbers, by researching the species and the movement proportional to moisture content.

Or you can follow the simple process of allowing approximately 1/8” expansion per foot across the grain, for a moisture content change of 5%.

If this will be exposed to 100% humidity from the water in the container it fits, probably a tad more than 1/8” per foot.

Lots of good projects to turn from wet wood, but not for a lid fitting a glass container.

 

[mkepke]

Making a wood lid for a glass vessel is, I think, just a more extreme example of dealing with wood expansion and contraction. All the old guidelines around grain direction, species, control joints, etc apply.

One could, for example, make a lid out of segments of quartersawn material with slip joints between each segment.

At the other end of the spectrum, one has the humble test-tube with a tight fitting cork.

Sounds like a good monthly contest topic.

-Mark

 

[Mike Davis]

At the other end of the spectrum, one has the humble test-tube with a tight fitting cork.

Sounds like a good monthly contest topic.

-Mark

While cork may expand it is also very soft and somewhat pliable, most wood is not.

I would turn it smaller and apply a rubber or closed cell foam gasket.

 

[mkepke]

While cork may expand it is also very soft and somewhat pliable, most wood is not.

I would turn it smaller and apply a rubber or closed cell foam gasket.

..and corks are typically cut on a taper so they always fit, even if the cork shrinks.

Just using cork as an example of how this vase design problem is no different than any other where expansion/contraction needs to be considered. Pick a different/better material or design and the problem is radically simplified.

-Mark

 

[zargon]

You said: “Or use that wood they make fence posts out of - hard as a rock - I can never recall the name when I need to. Or some of that exotic stuff I see advertised here and there.”

I said, that would be “post oak” , using it for a fence post one would never notice the expansion and contraction… But trying to turn a lid or a part to be joined with a piece of glass. You might expect just as much movement from Postoak as any other wood… Maybe even more if it’s not kiln dried before you turn it.

The bottom line is: it’s really not a good idea to mix wood & glass.
& after looking @ the “instructable” — me thinks they might have glossed over the issue of wood expansion when it’s that close to large volumes of water. On the other hand, if you turn one of those and leave enough “slop” you might get away with it. All depends on what kind of wood & which way the grain is oriented.

years ago, I turned a bunch of bud-vases using test tubes inserted in drilled holes and the results were mixed at best. Many of them broke from expansion and contraction. ‘Won‘t be doing that again any time soon.