Does wood shrink lenghtwise when drying?

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 once, cut twice. New website up.... lazylarrywoodworks.com.au

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.

-- Debt is nothing more than the 21st Century's form of slavery.

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

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

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"

I’m with Charlie and company Not much,

-- Jim from Heirloom Woodshop Southern Oregon

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.

-- Kent Shepherd * The goal is-----More Tools!

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 :-))

-- Debt is nothing more than the 21st Century's form of slavery.

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

-- Debt is nothing more than the 21st Century's form of slavery.

I hate shrinkage…..

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

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

-- JJ...... I guess you could say I'm a 54 year old "juniorjock". — Make things with wood.