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Does wood shrink lenghtwise when drying?

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Forum topic by TopamaxSurvivor posted 05-28-2009 08:04 AM 10895 views 0 times favorited 11 replies Add to Favorites Watch
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TopamaxSurvivor

17671 posts in 3141 days


05-28-2009 08:04 AM

Topic tags/keywords: wood shrinkage drying lenghtwise

I am wondering how much, if any, wood shrinks lenghtwise when it dries? I know it shrinks significantly laterally. Today I was out a the Tree Farm, I needed a couple of 11” +/- 1×1’s to prop up the canned goods shelf when I moved the 5th wheel.. I split them from a piece of maple that had been cut about 6 months ago. It is oibviously still wet! I am just wondering if they will shrink to uselessness as they dry??

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence


11 replies so far

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degoose

7196 posts in 2820 days


#1 posted 05-28-2009 08:12 AM

TS there will be a small almost insignificant reduction in the length of the timber ,,less by far than across the grain… depending on the species of timber. and the profile and size.
Personally would worry overly about it.
Larry

-- Drink twice... and don't bother to cut... @ lazylarrywoodworks.com.au For lovers of all things timber...

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TopamaxSurvivor

17671 posts in 3141 days


#2 posted 05-28-2009 08:20 AM

I know it will be a lot less if any, but having been accused of having an insatiable curosity, and admitting I do :-)), I thought I’d throw it out and see if anyone has anything definite on it. I did a little search, but drew a blank before I posted this.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View ajosephg's profile

ajosephg

1878 posts in 3026 days


#3 posted 05-28-2009 11:28 AM

TS – now you’ve done it – giving me something else to wonder about.

I Googled “Does wood shrink lengthwise” and got about 5000 hits and now my poor mind is really messed up.

The short consensus seems to be about 0.1 to 0.2% but with a disclaimer “that it all depends.” They talk about “juvenile” wood, “reaction” wood (compression or tension) as things that can cause longitudinal shrinkage to be much greater. And, of course, what part of the log it’s cut from. I guess when you think about it, uneven longitudinal shrinkage is what causes boards to bow or twist.

One of the books that popped up is “The Encyclopediia of Wood” which is written in farmer language if you are inclined for further investigation.

PS – Here is another book that looks good. “Understanding Wood: A Craftsman’s Guide to Wood Technology” by Bruce Hoadley. I think I will buy this one!!

-- Joe

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David A. P.

28 posts in 3029 days


#4 posted 05-28-2009 02:10 PM

Here’s a handy calculator for wood shrinkage, for both radial and tangential shrinkage, by species and allowing tweaking of assumed (or measured) moisture content: http://www.woodbin.com/calcs/shrinkulator.htm.

Of course, that doesn’t answer your original question, which was about longitudinal shrinkage. This is because, as Larry said above, it’s insignificant compared to both tangential and radial shrinkage (on the order of 1-2%).

HTH :).

-- David A. P. -- Ars Arboris ("Art of the Tree") -- ArsArboris.com

View CharlieM1958's profile

CharlieM1958

16242 posts in 3683 days


#5 posted 05-28-2009 04:10 PM

Longitudinal shrinkage is usually not significant, but it can be under certain circumstances. The linked article is rather dry and technical, but does address your question.

http://ir.library.oregonstate.edu/jspui/bitstream/1957/5234/1/Why_Wood_Shrink_ocr.pdf

-- Charlie M. "Woodworking - patience = firewood"

View a1Jim's profile

a1Jim

115202 posts in 3042 days


#6 posted 05-28-2009 05:14 PM

I’m with Charlie and company Not much,

-- http://artisticwoodstudio.com Custom furniture

View Kent Shepherd's profile

Kent Shepherd

2718 posts in 2751 days


#7 posted 05-28-2009 05:44 PM

Usually with kiln dried lumber, shrinkage is very minimal in the length. However, I have done some rough cedar beams in the past that opened up a lot on the ends. The wood was not very dry when I put it up.

-- http://shepherdtoolandsupply.com/

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TopamaxSurvivor

17671 posts in 3141 days


#8 posted 05-28-2009 10:41 PM

Thanks guys. I guess .1 to .2% will not realy be noticable. If the 11” stick were to shrink 1/8”, it wouldn’t be tight enough any more and could possible pop loose during travel. An eight would be a full 1%.

ajoseph, I probably typed it into the site search box instead of the google. When this site is up the two are a together under the address bar. I automatically go into the bottom box when searching. I thought it was a bit odd that nothing popped up :-))

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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TopamaxSurvivor

17671 posts in 3141 days


#9 posted 05-28-2009 10:49 PM

Charlie, that article isn’t that long. Good reading and interesting.

David, I went to the Shrinkulator too, but it doesn’t do the lenght, just radially and tangent

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Gary Fixler's profile

Gary Fixler

1000 posts in 2847 days


#10 posted 05-28-2009 11:45 PM

Joe – I have both of Hoadley’s books (the other is “Identifying Wood”), and they are great. He’s a scientist from MIT who specializes in the science of wood. He knows his stuff!

As for bowing of wood, this is almost non-existent in woods that are quartersawn. Here’s a handy graphic. Riftsawn is even better, but rare, because so much wood is wasted. In these boards, the growth rings are more or less perpendicular to the face of the wood, so each side is essentially the same. In plain or flat sawn lumber, you usually get one side with much more open growth ring separation than the other, and longitudinal contraction of even a small amount pulls one side tighter than the other.

In Hoadley’s books, and in all the other places I’ve read, longitudinal swelling (remember, boards also swell back up when moved to more ‘moist’ environments!) and shrinkage is considered a non-issue. It’s not entirely true, but the figures I’ve always read are 0.1%-0.2%. Still, I suppose it’s always good to build for it, just in case. Things like mortises, and floating panels give some room for things to shift a little without tearing projects apart.

-- Gary, Los Angeles, video game animator

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juniorjock

1930 posts in 3231 days


#11 posted 05-29-2009 01:37 AM

bentlyj, just blame it on the cold water….......

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