Confused about wood movement

Alan,

There are 3 different wood movements.
1) Longditudinal, this is about 0.1% from green to dry and so can be
virtually ignored.
2) Tangental, to the center of the tree, this is where most of the change
occurs and is about 2x the next.
3) Radial.

As most wood is slab cut the majority of the planks, except the center ones,
are tangental thus percentage wise the width will vary much more than the
thickness, the exact amount will depend on the particular wood. For example
rock maple shrinkage, from green to 12% is 5.0% tangental and 2.5% for
radial (from the 'Handbook of Hard Woods').

Ply-wood because of it's construction is for all intents and purposes
stable.

Bernard R

"Toller" <[email protected]> wrote in message
news:[email protected]...
>
> "Alan Bierbaum" <[email protected]> wrote in message
> news:[email protected]...
> > Yes you need the slotted holes to allow for wood movement. Most North
> > American hardwoods will move about 1/4" per foot of width, across the
> > grain, between 6% and 12% moisture content. Your work can experience
> > this range of moisture (depends on where you live and move to). A
> > concrete example follows (quote from a past post by me, you can look
> > up the series and pictures in google).
> >
> How much does it move with the grain?
> How about plywood?
>
>

On Fri, 05 Mar 2004 21:06:09 GMT, "Toller" <[email protected]> wrote:

>
>"Alan Bierbaum" <[email protected]> wrote in message
>news:[email protected]...
>> Yes you need the slotted holes to allow for wood movement. Most North
>> American hardwoods will move about 1/4" per foot of width, across the
>> grain, between 6% and 12% moisture content. Your work can experience
>> this range of moisture (depends on where you live and move to). A
>> concrete example follows (quote from a past post by me, you can look
>> up the series and pictures in google).
>>
>How much does it move with the grain?
>How about plywood?
>

Lengthwise - almost nothing - you can consider it nothing.

Flatsawn - across the grain (common lumber available) - about 1/4" per
foot from 6% to 12% moisture content. About half of this amount
through the board thickness on flatsawn boards. Reverse these numbers
for quatersawn lumber.

Plywood can be considered as stable enough that you do not need to
worry about movement (only warpage).

Invest in one of the many good books on wood properties (at least
borrow one from the library and read it).


Alan Bierbaum

web site: http://www.calanb.com

SOP is to run a regular-sized hole at the point you want to stay fixed - in
drawers, the front, and float the back.

Traditionally, Norm bashers aside, nails were used to attach cross-grain
moldings, because they bend. Screws won't, so give 'em room.

with frame and panel, as you noted, the dimensions don't really change much,
but in solid wood carcasses, you can get into trouble unless you're fully
climate-controlled.

"Toller" <[email protected]> wrote in message
news:[email protected]...
> I am loosely following some plans for a chest of drawers. They say the
> drawer rails have to have oversized holes to allow for wood movement,
since
> the grain in the rails is perpendicular to the grain on the panels they
are
> screwed to.
>
> That makes sense, but I have done it wrong many times without anything
going
> wrong. I have put trim around the base of cabinets where the trim grain
is
> horizontal and the cabinet is vertical, put shelf or drawer rails where
the
> grain is perpendicular, etc. Rail and stile frames have to be
> perpendicular. Everything has survived okay.

Nope.

http://www.fpl.fs.fed.us/documnts/usda/ah531.pdf

And other sources give the tables in RH.

"Fred the Red Shirt" <[email protected]> wrote in message
news:[email protected]...
> Alan Bierbaum <[email protected]> wrote in message
news:<[email protected]>...
> > ...
> > This is in response to several questions on wood movement. Almost
> > everyone here knows that wood moves with relative humidity; ...
>
> I think it moves with absolute humidity.
>
> --
>
> FF

Alan Bierbaum <[email protected]> wrote in message
news:<[email protected]>...
> ...
> This is in response to several questions on wood movement. Almost
> everyone here knows that wood moves with relative humidity; ...


How much is wood movement effected by finish? If something is sealed, stained and covered with three
coats of polyurethane on all surfaces, is the moisture level going to vary as much as unfinished
wood? Do I have to worry as much about wood movement for this case?

Scott

Are you by any chance related to Swingman?

You're sitting in front of a reference cardfile. I suggest you use it.
You'll learn more with your brain open than your mouth.

http://www.umass.edu/bmatwt/publications/articles/humidity_tempature_wood_moisture_content.html

Remember your elementary science? Heat is energy, energized molecules are
more active, therefore disperse through the wood at a more rapid rate. All
of which, had you the inclination to read for information, rather than
affirmation, would have been explained to you on page 8 of the document.

"Fred the Red Shirt" <[email protected]> wrote in message
news:[email protected]...
> "George" <[email protected]> wrote in message
news:<[email protected]>...
> > Nope.
> >
> > http://www.fpl.fs.fed.us/documnts/usda/ah531.pdf
> >
> > And other sources give the tables in RH.
> >
> > "Fred the Red Shirt" <[email protected]> wrote in message
> > news:[email protected]...
> > > Alan Bierbaum <[email protected]> wrote in message
> > news:<[email protected]>...
> > > > ...
> > > > This is in response to several questions on wood movement. Almost
> > > > everyone here knows that wood moves with relative humidity; ...
> > >
> > > I think it moves with absolute humidity.
>
> If you are refering to figure 8, I suggest you review it. The
> plot is EMC vs Relative Humidity AND Temperature. Note the
> slope of the lines of constant EMC.
>
> --
>
> FF

The one with the number eight at the bottom.

Lots of paper collections were numbered like that. They were called
"books."

"Fred the Red Shirt" <[email protected]> wrote in message
news:[email protected]...

All
> > of which, had you the inclination to read for information, rather than
> > affirmation, would have been explained to you on page 8 of the document.

> You still have neither confirmed nor denied that your argument is
> based on Figure 8. When you reference a 68 page document, it is
> helpful to be a bit more specific as to what part of it supports
> your argument.
>
> No, I don't know who Swingman is.
>
> --
>
> FF
>
> PS You were right.

That's where the combined RH/OAT tables come in. They show how rapidly the
untreated wood will gain moisture. And it _will_ gain or lose, regardless
of finish, eventually, so smart money finishes inside and out to help
equalize the rate.

FWW had a test (Jeff Jewitt?) of the rates through various finishes. Think
shellac was the best.

"Scott Duncan" <[email protected]> wrote in message
news:[email protected]...
>
> Alan Bierbaum <[email protected]> wrote in message
> news:<[email protected]>...
> > ...
> > This is in response to several questions on wood movement. Almost
> > everyone here knows that wood moves with relative humidity; ...
>
>
> How much is wood movement effected by finish? If something is sealed,
stained and covered with three
> coats of polyurethane on all surfaces, is the moisture level going to vary
as much as unfinished
> wood? Do I have to worry as much about wood movement for this case?
>
> Scott
>
>
>

"Alan Bierbaum" <[email protected]> wrote in message
news:[email protected]...
> Yes you need the slotted holes to allow for wood movement. Most North
> American hardwoods will move about 1/4" per foot of width, across the
> grain, between 6% and 12% moisture content. Your work can experience
> this range of moisture (depends on where you live and move to). A
> concrete example follows (quote from a past post by me, you can look
> up the series and pictures in google).
>
How much does it move with the grain?
How about plywood?

"Toller" wrote in message
> I am loosely following some plans for a chest of drawers. They say the
> drawer rails have to have oversized holes to allow for wood movement,
since
> the grain in the rails is perpendicular to the grain on the panels they
are
> screwed to.
>
> That makes sense, but I have done it wrong many times without anything
going
> wrong. I have put trim around the base of cabinets where the trim grain
is
> horizontal and the cabinet is vertical, put shelf or drawer rails where
the
> grain is perpendicular, etc. Rail and stile frames have to be
> perpendicular. Everything has survived okay. Admittedly I just started
> woodworking a couple years ago and nothing has stood the test of time; but
I
> just checked out a 100 year old desk (mahogany?) and a 25 year old table
> (cherry), and they both have perpendicular grains fastened together..
>
> Plywood is stable, so if you put plywood in with wood going both ways
> (vertical on the side and horizontal on the top) it has to be wrong one
way
> or another. Doesn't it?
>
> Have I just gotten lucky, or is wood sufficiently stable in a
> winter/humidified summer/airconditioned house that movement is no longer
an
> important factor? Or do I have a profound misunderstanding of the
process?
>
> The issue at hand are the drawer rails for the cherry chest. Putting in
> oversized holes seems wrong, but I don't want to have it crack apart, now
> that I am warned.

Oversize, or slotted holes, are easy to do, where they are called for, and
will generally give you some insurance against inevitable movement. Cross
grain face gluing, in particular, is asking for eventual trouble, IME.

Wood movement is MOST definitely a concern in furniture/cabinet making ...
disregard it at your eventual peril. The effects can often take years in the
same climate, or days/weeks in a new climate. Your projects have likely not
been around long enough ... try moving them across country to a different
climate and they may actually fall apart.

Time may be everything in this regard. Remember, "The oxen are slow, but the
earth is patient."

A good book on the subject is Bruce Hoadley's "Understanding Wood."

--
www.e-woodshop.net
Last update: 2/28/04

"Fred the Red Shirt" wrote in message

> No, I don't know who Swingman is.

Neither does "George", but complete ignorance of a subject hasn't stopped
him from posting his assumptions yet.

--
www.e-woodshop.net
Last update: 3/05/04

Alan Bierbaum <[email protected]> wrote in message news:<[email protected]>...
> ...
> This is in response to several questions on wood movement. Almost
> everyone here knows that wood moves with relative humidity; ...

I think it moves with absolute humidity.

--

FF

"George" <[email protected]> wrote in message news:<[email protected]>...
> Nope.
>
> http://www.fpl.fs.fed.us/documnts/usda/ah531.pdf
>
> And other sources give the tables in RH.
>
> "Fred the Red Shirt" <[email protected]> wrote in message
> news:[email protected]...
> > Alan Bierbaum <[email protected]> wrote in message
> news:<[email protected]>...
> > > ...
> > > This is in response to several questions on wood movement. Almost
> > > everyone here knows that wood moves with relative humidity; ...
> >
> > I think it moves with absolute humidity.

If you are refering to figure 8, I suggest you review it. The
plot is EMC vs Relative Humidity AND Temperature. Note the
slope of the lines of constant EMC.

--

FF

"George" <[email protected]> wrote in message news:<[email protected]>...
> Are you by any chance related to Swingman?
>
> You're sitting in front of a reference cardfile. I suggest you use it.
> You'll learn more with your brain open than your mouth.
>
> http://www.umass.edu/bmatwt/publications/articles/humidity_tempature_wood_moisture_content.html
>
> Remember your elementary science? Heat is energy, energized molecules are
> more active, therefore disperse through the wood at a more rapid rate. All
> of which, had you the inclination to read for information, rather than
> affirmation, would have been explained to you on page 8 of the document.
>
> "Fred the Red Shirt" <[email protected]> wrote in message
> news:[email protected]...
> > "George" <[email protected]> wrote in message
> news:<[email protected]>...
> > > Nope.
> > >
> > > http://www.fpl.fs.fed.us/documnts/usda/ah531.pdf
> > >
> > > And other sources give the tables in RH.
> > >
> > > "Fred the Red Shirt" <[email protected]> wrote in message
> > > news:[email protected]...
> > > > Alan Bierbaum <[email protected]> wrote in message
> news:<[email protected]>...
> > > > > ...
> > > > > This is in response to several questions on wood movement. Almost
> > > > > everyone here knows that wood moves with relative humidity; ...
> > > >
> > > > I think it moves with absolute humidity.
> >
> > If you are refering to figure 8, I suggest you review it. The
> > plot is EMC vs Relative Humidity AND Temperature. Note the
> > slope of the lines of constant EMC.
> >

As you will recall from your high school physics the partial pressure
of a vapor over a liquid increases with temperature. The relationship
is typically non-linear, that holds true for water. Thus if the
EMC of wood tracked with Absolute Humidity the lines of constant
EMC in Figure 8 (above) would be significantly curved.

It's a bit hard to tell on my monitor, I always have trouble with
graphical representations of non-geometrical data, but they look
pretty straight to me. That the lines of constant EMC have constant
slope in Figure 8 shows that the EMC tracks (linearly) with Relative
Humidity, not Absolute Humidity.

You still have neither confirmed nor denied that your argument is
based on Figure 8. When you reference a 68 page document, it is
helpful to be a bit more specific as to what part of it supports
your argument.

No, I don't know who Swingman is.

--

FF

PS You were right.

On Sun, 07 Mar 2004 14:30:04 -0500, Scott Duncan
<[email protected]> wrote:

>
>Alan Bierbaum <[email protected]> wrote in message
>news:<[email protected]>...
>> ...
>> This is in response to several questions on wood movement. Almost
>> everyone here knows that wood moves with relative humidity; ...
>
>
>How much is wood movement effected by finish? If something is sealed, stained and covered with three
>coats of polyurethane on all surfaces, is the moisture level going to vary as much as unfinished
>wood? Do I have to worry as much about wood movement for this case?
>
>Scott
>
>
Finish slows down the moisture movement into or out of the wood; it
does not stop it. You should still allow for the movement.

Alan Bierbaum

web site: http://www.calanb.com

Yes you need the slotted holes to allow for wood movement. Most North
American hardwoods will move about 1/4" per foot of width, across the
grain, between 6% and 12% moisture content. Your work can experience
this range of moisture (depends on where you live and move to). A
concrete example follows (quote from a past post by me, you can look
up the series and pictures in google).

This is in response to several questions on wood movement. Almost
everyone here knows that wood moves with relative humidity; some just
don't know how much. Since I work mostly in maple (it is similar to
oak, hickory, cherry and other American hardwoods), I used a maple
table top end offcut as a gage. My shop is air conditioned in the
summer and central heated in the winter (typical of local house
conditions). I measure the stick about once a month and record the
length, date and moisture content with a moisture meter. The meter
always reads 8% (yes it does work and gives different readings on
purchased wood); the date and length do change. Today the
length is 25 7/8". The minimum recorded is 25 7/8 and the maximum
recorded is 26 3/32".



On Fri, 05 Mar 2004 16:47:23 GMT, "Toller" <[email protected]> wrote:

>I am loosely following some plans for a chest of drawers. They say the
>drawer rails have to have oversized holes to allow for wood movement, since
>the grain in the rails is perpendicular to the grain on the panels they are
>screwed to.
>
>That makes sense, but I have done it wrong many times without anything going
>wrong.
snip
>
>Have I just gotten lucky, or is wood sufficiently stable in a
>winter/humidified summer/airconditioned house that movement is no longer an
>important factor? Or do I have a profound misunderstanding of the process?
>
>The issue at hand are the drawer rails for the cherry chest. Putting in
>oversized holes seems wrong, but I don't want to have it crack apart, now
>that I am warned.
>

Alan Bierbaum

web site: http://www.calanb.com