Wood dimension changes with season

Re: Wood dimension changes with season

Mark Meier (Ann Arbor, MI)

>Yes, certainly in the case of Walnut it is well known that it is exceptionally stable once seasoned with only negligible movement.

Mark

Re: Wood dimension changes with season

Alan Bierbaum

>This is a repost of rec.woodwprking post that I made a few months ago. I use the same (non-certified, non-traceable) tape for each measurement.

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".

I copied this method from someone else (don't remember who or when) and use it to determine how much movement to allow for in a finished piece of work. You can look up (several good sources) how much your wood will move with changes in relative humidity. Knowing the starting point (the stick and present humidity) and possible end location (humidity range) will let you build to allow for that movement. This is a simple gage to assist in determining what will happen to your project when it leaves the shop. Wood must be acclimated to the shop humidity for this to work.

Re: Wood dimension changes with season

CONGER - The Irish diaspora in Munich

>I have current experience with wood movement.

I have stored milled maple (indoors - heated basement room) for over 2 years.

I made up a board with bread-board ends last May. I glued (yes... GLUED) the BB end to the plank (2" thick) and fixed it with splines (a sorta bomb proof bread-board, built by an engineer who had switched off his thinking capability) and left the project rest while I was on holiday.

I came back to finish the project, only to find visible movement of about 1/8" at each end of the BB... or rather the plank had expanded, leaving the BB behind.

Happily, in this case not critical... but still a chastising experience.

I recall my phsyics teacher splitting granite rocks by stuffing wooden(?) pegs into a slit in the rock, and then pouring on water on the end grain. Two minutes later... pop... leaving two half rocks!

Wood moves... even after being acclimatised.

I guess if I lived in the desert I would be more confident... until the day it rained!

-g-

questions

Bill Tindall, E. TN

>Your test piece is now as narrow as it has ever been. You state that at some time it was more than 1/4" wider. I would have thought that the humidity would be as high now as ever and hence, the test piece should be near its maximum width.

Under what conditions did it reach its maximum width? Does it go to this width often? What width is it most of the time? What is the typical range of widths during the course of a normal year?

Re: Wood dimension changes with season

Paul M. in San Diego

>My first WW project was a solid-wood chessboard, with a mitered border. Each square was 2" and the border was about 3" wide. The squares were made with oak and poplar, and were doweled together for strength and alignment.

About 6 months after I made this, I heard a loud explosion in my living room (where the chess board was located). I looked around and found that there was now a 3/16" gap running right down the center of the board where the wood shrank but the mitered edge did not allow movement. Over the seasons, this gap opens and closes like clockwork.

I keep this chessboard on my shop wall to remind me to take wood movement into mind whenever I design a project.

Re: questions

Alan Bierbaum

>"Your test piece is now as narrow as it has ever been. You state that at some time it was more than 1/4" wider. I would have thought that the humidity would be as high now as ever and hence, the test piece should be near its maximum width.

Under what conditions did it reach its maximum width? Does it go to this width often? What width is it most of the time? What is the typical range of widths during the course of a normal year? "

I retreived the stick from the shop and have it in front of me now. The first date is 8/12/01 and the last is 8/21/04. It is four flat sawed boards edge jointed for a table top. It is a 1 1/4" wide cut off from the end of the table top. The two center boards have the grain curve up and the outer boards grain down (not alternate pattern). It lays flat on my desk (I do not normally check flatness). What I am measuring is actually movement across the grain in a flatsawn board.

Since my shop is climate controlled; yearly variation is not as severe as ambient conditions. Colorado has very dry (humidity wise) winters and relatively wet spring times. Without a plot of readings; it appears that Dec. to March is lowest and May to August is highest (I may need to crank up my humidifier more for the winters). I have consulted one of the himidity/temperature charts and the stick does seem to follow closely (I do this each time that I record the measurement). I do not record the temperature and shop humidity on the stick. Shop humidity/temperature is checked with one of those cheap three instrument home weather stations (not high accuracy). Normal shop conditions are humidity at 35-40% and temperature at 65 -75 degrees. This is FAS kiln dryed wood.

Does this help; or just cloud the issue for you?

Alan

Re: questions

Alan Bierbaum

>Correction - Shop humidity is 35-45% not 35-40%.

Re: Wood dimension changes with season

deanj

>

Discussion: I have read that lumber becomes more stable after kiln drying. If true it would explain why the tables overestimate dimension changes in kiln dried wood, because the tables are average changes during the initial dryig process.

Forest Products Lab and Hoadley in 'Understanding Wood' do not agree that kiln drying makes wood more stable. Wood still reacts to changes in RH by desorbing or adsorbing moisture. How dry the wood was at one point makes no difference in any text I have seen on the topic.

Your numbers seem to jive with the FPL documents.

From Table 12-�5. Coefficients for dimensional change as a result of shrinking or swelling within moisture content limits of 6% to 14% (CT = dimensional change coefficient for tangential direction; CR = radial direction)

Elm: CT = 0.00144 CR = 0.00338

Walnut: CT = 0.00112 CR = 0.00308

So Elm will change ~ .01728" close to 1/64"

Walnut will change ~ .01344" close to 1/70"

I picked American Elm, wasn't sure. Also, the

table assumed a moisture change from 6 to 12, where as you would have a change from ~8 - ~14

Tweak as needed.

See Chap 3, and Chap 12 for the numbers I used.

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

Re: Wood dimension changes with season

Adam Cherubini, NJ

>Bill

In accordance with the US forestry tables, I calculated my very wide walnut board would vary in width approx 1/8�. As it was not fully dry when I purchased it from the mill, I thought I would do a test to not only predict movement, but determine when the board was ready for use. Not having an accurate and verifiable rule in my 18th century shop, I did the next best thing. I scratched a mark 1/8� in from one edge. That was 10 years ago and the edge of that board still hasn�t moved over to that mark!

Adam

Whew;-)

Dan Donaldson

>Had to think about that one for a second;-)

I like that one.

ROFLMAO!

Alan Hamilton

>

Subtle beyond belief. Dry, wry...

Dean Burke - The Yakima Debunker

>

more data please....

Bill Tindall, E. TN

>You have some very valuable data that I would like to study in detail. Let me ask for what I need another way........

Please give me the long dimension of this test piece during Fall and winter of 2003 and spring and summer of 2004, a total of 4 dimensions? (Approximately October, February, May and July dates.)

Naming the long dimension of the test piece is a confusing. As a stick it might be called the lenght, but it is actually the width of the panel and that is why I used the term "width" in my original question.

Maybe it shrunk from the other edge :-)

Mike Lietzow

>

Re: more data please....

Alan Bierbaum

>"You have some very valuable data that I would like to study in detail. Let me ask for what I need another way........

Please give me the long dimension of this test piece during Fall and winter of 2003 and spring and summer of 2004, a total of 4 dimensions? (Approximately October, February, May and July dates.)

Naming the long dimension of the test piece is a confusing. As a stick it might be called the lenght, but it is actually the width of the panel and that is why I used the term "width" in my original question. "

Sorry for the confusion; I figured that saying it was an off cut from the end of a table told you that it was across the grain.

I don't know how the formatting will work; however here is the info in date - length (my moisture meter read 8% for everything.

08-17-03 26 1/16

09-27-03 26 1/32

10-19-03 26

11-22-03 25 15/16

12-20-03 25 27/32

01-21-04 25 7/8

02-22-04 25 7/8

March - no measurement

04-21-04 25 15/16

05-22-04 26

06-24-04 26 1/32

07-27-04 26 1/16

08-21-04 26 1/16

Re: Wood dimension changes with season

David Hammond, in Powder Springs GA

>Man, that took me a second... Such wonderful humor here on the Dark Side! You guys are great.

David

A big thanks for practical data

Bill Tindall, E. TN

>Great data. Thanks much. I have never been able to find practical data like this in the woodworking literature. It helps answer the question of how much does typical wood move under typical living conditions. The Forest Products Tables show how much it can move, but I always suspected that I over estimated movement from these Tables.

Re: A big thanks for practical data

Alan Bierbaum

>Glad I could help. One additional data point: Story follows.

I earned a living for eleven years remodeling kitchens at a kitchen-per-week. We had problems with double doors swelling shut. A pair of doors (fully finished) would grow 1/8" within a few weeks of someone turning on a swamp cooler. This is almost 1/8" movement across 9" of wood - four 2 1/4" stiles. We solved the problem by spacing the doors at 1/8" instead of 1/16". This is in red oak, maple, hickory, cherry and alder. The doors were custom made from 6-8% wood and completely finished. No statistics are available.