Planning projects for wood movement - Router Forums
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post #1 of 28 (permalink) Old 10-11-2015, 08:02 AM Thread Starter
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Default Planning projects for wood movement

I have just a question or two, and a few comments, to make on wood movement.

I just finished reading a few of the pfd files I got from Stick on this subject, and one file states to take into account the season in which the project is built. I have never done this. Thank goodness I have yet to attempt anything with drawers or doors. What sort of mistakes might I have made if I had? Disasterous one!

Just so I understand, there's no secret way of accounting for wood movement beyond relative rules of thumb, right? I read a general rule to follow when using flat or plain sawn wood is to allow about 1/4" of movement for every 12" of width across the grain, and I understood to figure a general starting point of where that expansion/shrinkage currently is at based on the current season, and based on all this I concluded the following: in summer projects the wood is likely at full expansion now and may see about 1/4" shrink in winter, in wintertime projects the wood is likely at the lowest shrinkage as may be expected and may expand by 1/4" in summer, and spring/fall projects the wood is at about half expansion currently and will gain or lose as the seasons progress one to the next.

I also read that in quarter sawn wood, this expansion rate is about 1/8" instead of the 1/4" seen in plain sawn wood.

Do you all keep this in mind each time you cut a board to fit? If you wanted several finished pieces to be the same dimensions, would you alter your measurements per board in the same projects built in different seasons?

Up to date, I have made most of my things using just plain old pine lumber from Lowe's. 2x and 1x stuff. Mostly shelves and other solid objects without moving parts, so I haven't had a lot of ill effects of shrinkage/expansion yet. But, I would expect this type of wood to be the most susceptible to the effects as any wood type available. Also, based on my understanding of shrinkage from the pfd's, I believe warpage and twist, which I have seen a LOT of in the pine wood, is also related to how the wood expands and contracts unevenly. Is this correct?

Currently, I am working to build several sets of shutters across my living room bow window, but to avoid wood movement problems I chose to simply use baltic birch plywood and finish them with paint. I really want to learn to understand wood shrinkage for future projects though.

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post #2 of 28 (permalink) Old 10-11-2015, 08:36 AM
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Duane,

Age old problem. This is the reason why certain components are built/attached differently then the rest of the assembly. Examples; wide tabletops (kitchen tables, et. al.) are attached via slotted holes, retaining clips, etc. These allow for seasonal movements by allowing expansion or contractions, thus preventing a rigidly attached piece from tearing apart the other pieces.

Although your ratios are reasonable and can happen, I think that those dimensions generally excessive if the wood is properly prepared. This is the reason for striving for a lower moisture content in material prior to the build. If you properly acclimate the wood to the intended environment, then the wood movement is minimized and lowers the chances of detrimental wood movement in the finished product.

The saving grace for inside furniture is, that, the inside environment is fairly stable all year round and the movement that does occur is not generally noticed. You still have to take care when dealing with a large "field" but follow the rules and all should be well.

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post #3 of 28 (permalink) Old 10-11-2015, 08:45 AM
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Duane,
I think you're pretty much on the right track and have a pretty good understanding of the principles. However, there's one more monkey wrench to throw into the machinery of your calculations. Most shops aren't heated consistently enough to have relative humidity levels as low as inside the home. So, even if you build your project in winter, it is likely to shrink some more the first winter it spends in the house. Remember that all this swelling and shrinking is going on across the grain only, the board doesn't change in length. So, as long as you are using fairly narrow pieces (3 inches or less) it won't be a problem. The main places I have had issues with movement are I glued up wide panels instead of using plywood, and when I glued two pieces together with crossed grain. You don't have to over-think it too much as long as you remember to keep it in mind.

“We should be careful to get out of an experience only the wisdom that is in it and stop there lest we be like the cat that sits down on a hot stove lid. She will never sit down on a hot stove lid again and that is well but also she will never sit down on a cold one anymore.” - Mark Twain
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post #4 of 28 (permalink) Old 10-11-2015, 09:08 AM
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Quote:
Do you all keep this in mind each time you cut a board to fit?
yes....

if those windows get a lot of sun you'll not be happy down the road because of what the sun will do to your BB...
Blisters, wrinkles and separation being the most obvious and the opening salvo...

in the grand scheme of the things the dimensions of the pieces wood movement should be a minor issue if you select your materials well...
paint or stained, clear vertical grained (QS) basswood or most any true closed cell hardwood would be my choice(s) for wood blinds...

other woods....
Cherry...
maple...
pecan...
VGF...
Alder..
Beech...
Hickory...
Ash...
mahogany...

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #5 of 28 (permalink) Old 10-11-2015, 09:33 AM
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Quote:
Originally Posted by Duane Bledsoe View Post
I have just a question or two, and a few comments, to make on wood movement.

I just finished reading a few of the pfd files I got from Stick on this subject, and one file states to take into account the season in which the project is built. I have never done this. Thank goodness I have yet to attempt anything with drawers or doors. What sort of mistakes might I have made if I had? Disasterous one!

Just so I understand, there's no secret way of accounting for wood movement beyond relative rules of thumb, right? I read a general rule to follow when using flat or plain sawn wood is to allow about 1/4" of movement for every 12" of width across the grain, and I understood to figure a general starting point of where that expansion/shrinkage currently is at based on the current season, and based on all this I concluded the following: in summer projects the wood is likely at full expansion now and may see about 1/4" shrink in winter, in wintertime projects the wood is likely at the lowest shrinkage as may be expected and may expand by 1/4" in summer, and spring/fall projects the wood is at about half expansion currently and will gain or lose as the seasons progress one to the next.

I also read that in quarter sawn wood, this expansion rate is about 1/8" instead of the 1/4" seen in plain sawn wood.

Do you all keep this in mind each time you cut a board to fit? If you wanted several finished pieces to be the same dimensions, would you alter your measurements per board in the same projects built in different seasons?

Up to date, I have made most of my things using just plain old pine lumber from Lowe's. 2x and 1x stuff. Mostly shelves and other solid objects without moving parts, so I haven't had a lot of ill effects of shrinkage/expansion yet. But, I would expect this type of wood to be the most susceptible to the effects as any wood type available. Also, based on my understanding of shrinkage from the pfd's, I believe warpage and twist, which I have seen a LOT of in the pine wood, is also related to how the wood expands and contracts unevenly. Is this correct?

Currently, I am working to build several sets of shutters across my living room bow window, but to avoid wood movement problems I chose to simply use baltic birch plywood and finish them with paint. I really want to learn to understand wood shrinkage for future projects though.
now that I made a mess of your Wheaties....
don't over think this issue either....
it you get a lot more specif about what you are trying to build we'll address them....

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #6 of 28 (permalink) Old 10-11-2015, 09:36 AM Thread Starter
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Too late. :-) I already cut up all the pieces for them and edge painted them all. I plan to join them with brad nails and wood glue before face painting them, so the glue bonds well. The window is on a porch with a roof over it, and that only ever sees evening sun, and is shaded by a tree also. The window itself never gets any sun so I hope the shutters will be fine. All my parts are ripped to 2.5" widths. Hopefully this all means minimal problems, if any.
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post #7 of 28 (permalink) Old 10-11-2015, 09:40 AM Thread Starter
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now that I made a mess of your Wheaties....
don't over think this issue either....
it you get a lot more specif about what you are trying to build we'll address them....
Other than the shutters, I don't have a current project. Just trying to learn in advance for next time, that's all.
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post #8 of 28 (permalink) Old 10-11-2015, 10:17 AM
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Originally Posted by Duane Bledsoe View Post
Too late. :-) I already cut up all the pieces for them and edge painted them all. I plan to join them with brad nails and wood glue before face painting them, so the glue bonds well. The window is on a porch with a roof over it, and that only ever sees evening sun, and is shaded by a tree also. The window itself never gets any sun so I hope the shutters will be fine. All my parts are ripped to 2.5" widths. Hopefully this all means minimal problems, if any.
ask 1st...
glue doesn't hold well om painted surfaces...

Quote:
Originally Posted by Duane Bledsoe View Post
Other than the shutters, I don't have a current project. Just trying to learn in advance for next time, that's all.
Okay...
What is it that is giving you difficulty understanding...
you know each project has it's own particulars... species, type of sawn and grain orientation...
nothing in it's self will cover all bases for everything...

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #9 of 28 (permalink) Old 10-11-2015, 11:26 AM
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@Duane Bledsoe .....

thanks for reading the PDF's and thinking them through...
often wonder if anyone was really reading and using them...
swarfmaker and 1fizgig like this.

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #10 of 28 (permalink) Old 10-12-2015, 08:40 AM
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Take a look at this:

Estimate Wood Movement Calculator

Google Wood Movement and there is a lot of information on line that might help you.

Last edited by Garyk; 10-12-2015 at 08:42 AM. Reason: added text
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