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  Wood Shrinkage Calculator  
     
  Carl Hgastrom 10/2/02 5:32 p.m.
I thought the visitors to this forum might be interested in a wood shrinkage calculator available at WOODWEB.com
To use the calculator, you enter the species and width, the current moisture content, and the expected "in service" moisture content, and the calculator computes the amount of shrinkage (or expansion) that will occur.
You can also enter the width of glued up assemblies - an important issue for wide panels or wooden counters.
For example: A 25 inch wide butcher block counter made out of sugar maple ... if it were assembled at 16% Moisture Content (MC), and installed, it would shrink nearly 3/4 of an inch in width when it reached an in service moisture content of 8% (8% is a typical "in service" value for the northeast US ... the southwest is slightly lower). If the same counter were assembled at 8% MC, and stored in a humid area where the MC increased to 16%, the counter would "grow" nearly 3/4 of an inch.
If you're interested, give it a try - if nothing else, it should tune you in to the importance of monitoring the MC of the material you're working with - particularly with large, glued up assemblies. It is also a useful tool when comparing the difference in shrinkage between species.
The calculator can be found at:
http://www.woodweb.com/cgi-bin/calculators/calc.pl?calculator=shrinkage
Regards,
Carl Hagstrom
Wood Shrinkage Calculator

Re: Wood Shrinkage Calculator
Gary Katz 10/2/02 6:30 p.m.
Thanks Carl. I could have used that caluclator a few months ago when we were installing bead board wainscoting.
Gary

Re: Wood Shrinkage Calculator
Jim Eggert 10/2/02 8:38 p.m.
Hey, Didn't they have a episode on "Shrinkage" on Seinfeld? :-)
To the point though, this is an area where I could use input, and the post above regarding "3/4" is way more than I care to either deal with or think about.
Can anyone put this is in a more everyday scenario? I really can't imagine ANY wood item I can build growing OR shrinking 3/4" for a 25" width of assembly.
Please continue....
Jim
Jim

Re: Wood Shrinkage Calculator
Al Constan 10/3/02 12:32 a.m.
Carl,
I always think about what will happen with the doors I hang when the "in service moisture content", like you call it, star taking place.
That is way I always tell my customers to paint the doors as soon as possible to avoid expansion by keeping moisture away from the door.
Al C.

Re: Wood Shrinkage Calculator
Carl Hagstrom 10/3/02 7:09 p.m.
Well - I'll address Jim's post first ...
>"To the point though, this is an area where I could use input, and the post above regarding "3/4" is way more than I care to either deal with or think about. "
I used an example of Sugar Maple (which, by the way, is probably the biggest "mover" out there) in a counter top situation (25") going from 16% to 8%. Yes, that's likely the most extreme event you'd encounter, but a real world possibility none the less.
Let's take a 12 inch wide chunk of cherry that starts out at 14 % MC, and ends up at 8% MC. This is a *very* realistic scenario (depending where you store you lumber ... or where it was stored before you got it), and it results in 3/16 inch of shrinkage ... enough to point out the importance of a moisture meter if you're really interested in heading off movement problems.
I live in NE PA, and humidity swings are radical compared to Gary's warm and dry state of CA. It's critical (for high end finish work) to monitor wood moisture content, and using "home stored" material in my area can really come back to bite you.
If you doubt any of the above, I'd suggest that you use the calculator, and enter the data that you think represents real-world scenarios for you. FWIW, I remember a job where the cabinet doors actually blew apart at the corner joinery because the doors had been made out of kiln dried maple that was *too* dry - turned out the material was damn near zero MC, and after the kitchen went in (spring, and lots of ambient on site moister), the door panels started expanding, and blew the frames ... 15 out of 30 doors ended up being repaired (the wider ones were the ones to fail).
It's been my observation that finish carpenters (as opposed to cabinet makers), tend to ignore the moisture issue .... some never run into problems, but when you do, you become an MC convert. If you've ever spend any time in a high end cabinet shop (east coast, at least), a moisture meter is the last tool a shop would want to be without.
As for Al's comment:
>"I always think about what will happen with the doors I hang when the "in service moisture content", like you call it, star taking place"
Moisture (humidity) swings dureing the building process can be crazy, and after the owner moves in, it's impossible to predict what they may do to alter typical "in service" MC's (like letting the dryer vent exit directly into the house to help reduce heating costs). Where I'm at, we hang doors "lite" in the spring (A dry door being installed in a humid environment), and hang them "heavy" in the winter (A maybe not-so-dry door hung when the heating is running full tilt).
However you look at it, ignoring the effect MC has on wood movement is just plain bad practice - anyone out there who considers themselves a finish carpenter, and isn't up to speed on how MC affects wood movement, should start doing some reading ... especially if you plan on installing any type of item that represent a serious glue-up (like that butcher-block counter top). FWIW, I've got a 30 inch maple counter in my office, and it moves back and forth about 3/8 of an inch each yearly cycle, and there's not a damn thing I can do about it (short of closing all the windows in my offoce in the fall and spring, and running a dehumidfier). I've got it fastened with lightly torqued screws that pass through fender washers, and have a backsplash detail that hides the movement. But this past week or to, I've heard the thing popping and creakin' every once in a while as the fall rains start to crank up the humidity levels, and the heat has yet to come on.
A drywaller once told me: "If it moves, grease it ... if it doesn't move, tape it".
Carl
Wood Shrinkage Calculator

Re: Wood Shrinkage Calculator
Jim Eggert 10/3/02 8:25 p.m.
Carl
I appreciate your example presented in the cherry wood. I will look into this much more closely.
To continue, can you provide input for the following.....
1. I know wood floors are notorious for cyclic changes in size, my own beech floor appears to have much more movement than other homes oak floors. That said, why is it we do not see this amount of movement in "most" furniture style pieces?
2. Is there a list of the best % reading for each species, sort of middle of the road?
3. Moisture meters? Just what I need is another tool, but are there suggestions for good, better and best?
4. Do some of these super glues cause more problems than they prevent? Titebond, Gorilla glue, etc..
Thanks
Jim

Re: Wood Shrinkage Calculator
Carl Hagstrom 10/4/02 9:45 a.m.
Jim:
>"....my own beech floor appears to have much more movement than other homes oak floors"
That's why you may find the shrinkage calculator helpful ... American Beech has a movement rate that's roughly 40% higher then Northern Red Oak (a 12 inch wide Beech board will move 3/16 of an inch between 13% MC and 8% MC ... a typical in-service moisture swing). An interesting note: most people think eastern white pine is a high mover, when in fact, it's at the lower end of the movement scale, and more stable then most hardwoods. Also, the "type of cut" matters. Flat sawn boards move more then radialsawn or quarter sawn boards. The calculator allows you to choose between the two. The difference is significant, and if you're not aware of what the difference is, an interesting exercise is to enter values in the calculator, and compare the difference between flat sawn movement and radialsawn movement.
>"That said, why is it we do not see this amount of movement in "most" furniture style pieces?"
I'm a little out my league here, but my understanding is that "quality" furniture incorporates design that accommodates shrinkage (along the lines of the way raised panels allow for the movement of wood).
>"Is there a list of the best % reading for each species, sort of middle of the road?"
All my reading indicates that *at the time of installation*, your material should be at 8%MC for the best continuing performance. And the **only** way I know of the be certain is to use a moisture meter.
>"Moisture meters? Just what I need is another tool, but are there suggestions for good, better and best?"
I would highly recommend visiting WOODWEB, and doing a search of the Knowledge Base on the following terms:
- wood shrinkage
- moisture meters
- moisture content
Over the last 7 year, we've been fortunate to have Professor Gene Wengert as a technical advisor - he is a professor emeritus at University of Wisconsin, Maadinso Campus, and is arguably the most respected source for issues involving wood and primary processing. Three of his titles will turn up in a search on "wood shrinkage":
- Wood and Water
http://www.woodweb.com/knowledge_base/Wood_and_Water.html
- I've Got that Shrinking Feeling
http://www.woodweb.com/knowledge_base/Ive_Got_that_Shrinking_Feeling.html
(this is the best article I've ever read explaining the process of how moisture "leaves" the wood after it is sawn, and dried)
- Measuring/Monitoring Moisture Levels (The hows and whys of monitoring moisture content in lumber.)
http://www.woodweb.com/knowledge_base/MeasuringMonitoring_Moisture_Levels.html
A search on moisture meters turns up 34 results.
For those who are truly interested in understanding moisture related wood movement, the above should be considered required reading. Understanding what's going on develops the skills to recognize problems *before* they happen.
- Carl
Wood Shrinkage Calculator

New Re: Wood Shrinkage Calculator
Jim Eggert 10/4/02 6:40 p.m.
Carl
Thanks
Jim
 
     
     
   
     
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