Wood movement question

[PChristy]

This question might have already been asked but why does kiln dried wood move when it is glued together? I can understand the green wood moving but I can not understand why dry wood moves - how does furniture - cabinets - trim in your house not move - :icon_scra am I missing something or have I asked a stupid question:embaresse

 

[Trent Mason]

Phillip,

I think it has more to do with changes in temperature and humidity in your house/shop/etc. Even though it is dry, it can still be affected by those variables. :dontknow:

 

[Bas]

When it comes to wood - "panta rei" (everything moves). Trim moves, hardwood floors expand and contract, table tops crack and warp etc. The bigger the swing in humidity, the bigger the movement. It doesn't matter whether the wood is kiln dried or not. With green wood, movement is more obvious because the wood is losing a ton of moisture, a lot more than the 3%-6% swing (from the air) you typically get once the wood is completely dry.

Right now, the boards in my hardwood floor have gaps in between them. Come summer, those gaps will be gone. I have to recaulk the freshly installed baseboard soon, because after the paint dried completely the boards shrank a little, causing slight gaps in the caulk. Etc.

 

[PChristy]

So if I was to do a segmented pen for a customer they will eventually have some movement and feel the edge of the pieces that have been glued together -

 

[Mike Davis]

The pieces are so small in a pen it would be hard to notice the movement. Add to that the wood is all moving at the same rate and unless you have vastly different dryness in the pieces to start with they will stay pretty much the same as each other.

It is when you get into larger pieces that go cross grain to each other that you really see the movement or difference in shrink rate of one piece against another.

 

[PChristy]

The pieces are so small in a pen it would be hard to notice the movement. Add to that the wood is all moving at the same rate and unless you have vastly different dryness in the pieces to start with they will stay pretty much the same as each other.

It is when you get into larger pieces that go cross grain to each other that you really see the movement or difference in shrink rate of one piece against another.

Thanks Mike, Would there be a difference in movement in the hardness of woods - say Walnut with Hard Maple - or Purple Heart with Maple:dontknow: I have to make a rolling pen for my wife and I am thinking about the PH/Maple combo segmented - will that work:icon_scra

 

[CarvedTones]

I have a gift for oversimplification, sometimes to the point of being less than correct, but here is my simple understanding...

Wood moves for the reasons explained earlier. If it is constrained in it's movement, it builds up stress. When that stress is too much for the inherent structural integrity of the wood, it will crack or bow to relieve the stress. A big piece of wood is easier to bend/bow and has more stress, so you have to let it move. But you can constrain the movement in small pieces.

 

[Mike Davis]

Thanks Mike, Would there be a difference in movement in the hardness of woods - say Walnut with Hard Maple - or Purple Heart with Maple:dontknow: I have to make a rolling pen for my wife and I am thinking about the PH/Maple combo segmented - will that work:icon_scra

If you are very concerned about it you could get all the specs on the wood you want to use and compare the hardness, moisture content, specific gravity, glue holding ability and other significant aspects.


Or just make a rolling pin and see how you like it.

 

[scsmith42]

Thanks Mike, Would there be a difference in movement in the hardness of woods - say Walnut with Hard Maple - or Purple Heart with Maple:dontknow: I have to make a rolling pen for my wife and I am thinking about the PH/Maple combo segmented - will that work:icon_scra

Phillip, there are a lot of things that influence wood movement, humidity being number one (basically it swells as it gains moisture).

For the same species, the amount of movement varies depending upon the cut of the board, and how tight the growth rings are. The tighter the ring, the less movement. Quartersawn wood moves less in terms of width than it does in terms of thickness (percentage wise). Wood movement over the length of the board is still a different percentage than radially and tangentially.

Different species have differening percentages of movement, because the cellular structure differs.

If you really want to learn more about this, I have some kiln drying manuals that I can send you that are guaranteed to put you to sleep! :gar-La;

 

[PChristy]

Thanks guys for the info - I will make the pen and rolling pen and see what happens down the road:dontknow:

 

[Bas]

If you really want to learn more about this, I have some kiln drying manuals that I can send you that are guaranteed to put you to sleep! :gar-La;

Now, now Scott! You don't need manuals for that

OK, I know, ... :slap:

 

[scsmith42]

Now, now Scott! You don't need manuals for that

OK, I know, ... :slap:

:rotflm: :rotflm: :rotflm:

 

[Glennbear]

Thanks Mike, Would there be a difference in movement in the hardness of woods - say Walnut with Hard Maple - or Purple Heart with Maple:dontknow: I have to make a rolling pen for my wife and I am thinking about the PH/Maple combo segmented - will that work:icon_scra

I have seen many projects made by our fellow woodworkers with similar combinations that did not have problems including french rolling pins.:wsmile:

 

[PChristy]

I have seen many projects made by our fellow woodworkers with similar combinations that did not have problems including french rolling pins.:wsmile:

That is why I don't understand why my segmentations are moving and some of the other guys are not - I don't know what I am missing - I have furniture here that was built 30 years ago and not one single crack is in it where it has moved - I guess I will never understand it:eusa_doh: Looks like to me if it has been dried, cut, glued and nailed/screwed together, sealed ,sanded, stained and/or clear finished everything would be sealed from the humitity and therefore would not move - I just don't get it:BangHead::slap:

 

[Howard Acheson]

Let me first suggest you purchase a book that should be in every woodworker's library--Understanding Wood by Bruce Hoadley. Amazon will have it. This book is the bible of wood and will explain about wood movement and how to deal with it.

In simple terms, wood will always want to absorb or emit moisture as the moisture in the air surrounding it changes. As relative humidity seasonally rises and falls the wood will absorb or emit water vapor to reach what is called the "equilibrium moisture content". As it EMC changes the wood will expand or contract. It makes no difference whether the wood had be air dried or kiln dried.

Wood movement is different for each species of tree. There is no valid generalization that can be made about movement in hardwood versus softwoods. Wood moves little along the grain. Wood moves most across the grain. If the wood grain is parallel (flatsawn) the movement is greatest. If the grain is radial, the movement is about 1/2 the parallel movement.

A good source for estimating the amount of movement with varying relative humidity go to the Shrinkulator at: http://www.woodbin.com/calcs/shrinkulator.htm

 

[Mike Davis]

I don't understand why my segmentations are moving...

Phillip,

Can you show a picture of the wood that is moving? If not then explain what woods are together, type of glue, finish, grain orientation, etc. as much info as possible?

 

[Jeff]

+10 on Howard's suggestion about the "Shrinkulator". Look at their internal link "Understanding Wood Movement". :thumbs_up

I just got hooked up to it at his suggestion and I've gained a better understanding and appreciation for the hows and whys of wood movement. Yes, it is confusing, but not rocket science once it sinks into our cerebellar gray matter. :eusa_thin

I just bought a highly rated mini-Ligno E/D moisture meter for about $110. It's already proving to be a good spend.

 

[PChristy]

Mike these are moving - Don't look at the lines - I messed them up from the get go - I have sanded them both smooth and applied the Wood Butcher Block to the 2nd one - the movement is up and down - it is not much but it is there - BW and Cherry with one Maple

Howard thanks for the heads up about the book

View image in gallery

View image in gallery​

 

[Jeff]

Mike these are moving - Don't look at the lines - I messed them up from the get go - I have sanded them both smooth and applied the Wood Butcher Block to the 2nd one - the movement is up and down - it is not much but it is there - BW and Cherry with one Maple

Howard thanks for the heads up about the book

View image in gallery

View image in gallery​

Phil,

The up and down movement sounds typical of a quartersawn face (like a quartersawn table top). If you started with flatsawn wood, ripped it to width and thickness, and then turned the pieces 90 degrees to glue up your top then it's the quartersawn face that you're looking at and seeing that up/down movement. That's a radial movement (i.e., 90 degrees to the circular growth rings).

I've heard McRabbet mention "glue line creep", but don't entirely understand it. Maybe other members can enlighten us. :dontknow:

 

[Jeff]

Phil,

The up and down movement sounds typical of a quartersawn face (like a quartersawn table top). If you started with flatsawn wood, ripped it to width and thickness, and then turned the pieces 90 degrees to glue up your top then it's the quartersawn face that you're looking at and seeing that up/down movement. That's a radial movement (i.e., 90 degrees to the circular growth rings).

I've heard McRabbet mention "glue line creep", but don't entirely understand it. Maybe other members can enlighten us. :dontknow:

About glue creep. This merry band of woodworkers has discussed it before.

http://www.ncwoodworker.net/forums/f29/glue-creep-1343-post10586/

Keep us posted. :icon_cheers