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.
I will post a picture in ABPW of my stick. Comments should be made here.
I am glad that someone else found this useful. It sure is an easy and quick
way for me to be sure that I use enough allowance for wood movement. It
also shows how much wood moves in a relatively "stable" environment (my
humidity meter only has a swing of about 5%).
A year or two ago, a fellow woodworker brought in a device to the Cleveland
East Woodcraft store.
It was a board with a flatsawn stick mounted on it, one end was fixed and the
other was connected to a pivoted wire pointer. A card behind the pointer was
marked with dated and other info of interest.
IIRC there was a method of centering the pointer between max and min moisture
He said that he had these for the woods he used the most.
ps - what I mean by a flatsawn stick is that it is 3/4" thick, 3/4" long, and
about 15" wide wrt the grain of the wood.
If I was interested in measuring the "real" moisture content of the wood,
this would help. I am only interested in predicting wood movement relative
to current conditions so that I can make the "proper" allowance in furniture
construction. That extra 1/8" per foot of movement is possibly important
(especially since the moisture meter gives the same reading). It only takes
a few seconds to make the one measurement that interest me.
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