Wood Movement

[Dick Brown]

I made a 12 sided box for my daughter with the grain running vertical in the 12 sections. The lid fits inside with a lip over the top. The lid fits very snug. It is also 12 sections with each section running to a point in the center, grain running outer end to center. I live in the desert side of Oregon where it is VERY dry. She lives in the "Rain Forest" western side of the state. My question is, will the lid get tighter with moisture or will the expansion of the width of the side sections be greater than the expansion of the thickness and make it a looser fit? Opinions?? Forgot to mention, each side section is aprox. 2" wide by 1/2 thick, all joints glued.

[Dan Hahr]

If it finds itself exposed to high humidity, its likely that the box will swell and increase in diameter. The top will also swell but not the same as the box and will get looser and probably crack along some of the seams. Just guessing...

Dan

[Mike Ontko]

I could certainly be mistaken but I seem to remember reading in some book on cabinetmaking that the standard 2" to 2-1/4" width for rails and stiles was small enough that any expansion and contraction from changes in humidity would be negligible over time. I believe there's even a formula somewhere that can be used for calculating this on various wood types.

[Andrew Hughes]

I think it will get tighter. Alot will depend on the wood. Some woods are more stable then others.

[Mark Hennebury]

Got a photo?

[Marc Jeske]

I could certainly be mistaken but I seem to remember reading in some book on cabinetmaking that the standard 2" to 2-1/4" width for rails and stiles was small enough that any expansion and contraction from changes in humidity would be negligible over time. I believe there's even a formula somewhere that can be used for calculating this on various wood types.

Yes, but this is cumulative... OP has a 24" circumference total... so total circumference will increase same amount as one 24" wide board of that species.

Hopefully the bottom has a loose dado such as a frame for panel?

But then the depth of the dado (ie potential +- inside diameter change of the box wall) has to be calculated by particular species movement and off the cuff seems a 1/2" thickness may be shy.

In an extreme humidity change, 24 "box circum can change like almost an inch, so diameter ID would change almost 1/3"... so radius 1/6"... so OK... appears it could be done w 1/2" stock.. although seems the dado would be like 3/8" + deep or so... not leaving much meat remaining.

Did I make any sense to anyone ??

This is what happens when I stay up all night !

Marc

[Marc Jeske]

If it finds itself exposed to high humidity, its likely that the box will swell and increase in diameter. The top will also swell but not the same as the box and will get looser and probably crack along some of the seams. Just guessing...

Dan

Seems to me if the top is made of wedges like cutting a pie, it WILL absolutely crack when taken out of its equilibrium MC environment... whether higher OR lower humidity.

OK, now that I typed that I am second guessing myself.

I'm thinking the pie wedges will get bigger at the perimeter than closer to center, so will crack... BUT wait ! no, because it will all get bigger as a % change, so NO crack.

Brain spinning.

Dunno for sure... somebody HELP !! :confused:

Marc

[Marc Jeske]

The answer is......drumroll....... call Hoadley or Wengert !!

Marc :)

[Mark Hennebury]

It would seem that segments like you have mentioned could be problematic.
If a 30 degree segment changes to 29 degrees the cumulative effect could cause it to split. If the 30 degree changes to 31 it would appear that it would probably buckle and split as there is no room for it to expand.

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[Marc Jeske]

I wonder if this thread fits better in the Turners subforum?

Don't those Folks deal w segmented stuff quite often?

Certainly that pie slice lid anyway.

Marc

[John TenEyck]

I wonder if this thread fits better in the Turners subforum?

Don't those Folks deal w segmented stuff quite often?

Certainly that pie slice lid anyway.

Marc


I've made a couple of segmented bowls with pie segmented bottoms. The guys in the Turners Forum generally agreed the segmented bottoms were a bad idea and likely would crack when the RH changed. Those bowls are about 10 years old now and none have cracked. To be honest, the largest one has a bottom of about only 8", far less than what the OP is rightly concerned about.

John

[Marc Jeske]

Actually, OP diameter is about 8".


Marc

[Dick Brown]

I would love to post a picture but have had no luck in doing same. Would someone guild me through it please?
Thanks

[Frederick Skelly]

I would love to post a picture but have had no luck in doing same. Would someone guild me through it please?
Thanks

Oh rats. I think you have to be a Contributor to post pics now. But if you'd like to join and help support the site, it's only $6 to do so. Then you can see pics and post your own.

Fred

[David Utterback]

As mentioned, the wood species is important to determine the extent of wood expansion/contraction with changing humidity and temp. The grain orientation is equally important with less movement for quarter sawn versus flat sawn. What species is the wood and how is the grain oriented for the top? The more the orientation varies from wedge to wedge, the more stress on the glue joints, it seems to me.

[John K Jordan]

I made a 12 sided box for my daughter with the grain running vertical in the 12 sections...My question is, will the lid get tighter with moisture .

Forgetting for a moment about the possibility of the lid cracking and considering only the diameter, I think the lid will get looser. Wood shrinks the most in the tangential direction. It shrinks less but still significantly in the radial direction. Your pie segments could be either tangential or radial depending on how they are cut. However, wood shrinkage in the longitudinal direction (along the grain) is almost nothing compared to the other directions. My copy of Hoadley's book is in the shop so I can't look up the numbers right now, but here are some from the Wood Database: T:3%-12% R:2%-8% L:0.1%-0.2%

https://www.wood-database.com/wood-articles/dimensional-shrinkage/ Eric, the author, also has a reasonable explanation of what is going on. You can look up the actual T, R, and T/R numbers for the type of wood you used on the same web site. But I highly recommend Hoadley's book on Understanding Wood to anyone who works with and is interested in learning about wood: https://www.amazon.com/Understanding-Wood-Craftsmans-Guide-Technology-ebook/dp/B004WYO862

One way to answer your question (and others) is do a test. Put the box and lid into a sealed chamber/plastic bag and increase the humidity until it is close to the worst case numbers for the damp side of Oregon. See what happens when you wait long enough.

JKJ