<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 6.00.2900.3395" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT face=Arial>Gene - I've dried down and weighed more blocks of wood
than I care to admit. I never was able to get consistent results. IMHO, it may
be difficult to do oven drying with a softwood like spruce because a lot of
volatile organic compounds are outgassed during the drying process along with
the water and I think that tends to skew the results...... Anyway, I gave
up on that a long time ago.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Table 3-4, "Moisture content of wood in equilibrium with
stated temperature and relative humidity", in the USDA Wood Handbook is a table
that lists temperature dependant wood moisture contents (MC) at
various relative humidity (RH) values - i.e. wood that has come into
equilibrium with an environment at a certain temperature and RH will have a
certain MC.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>So you don't have to measure MC directly (wood moisture
meters do not work reliably at MC of about 6% and below - so don't bother buying
a moisture meter). All you need to do is to monitor your hot box environment for
temperature and RH. I suppose a cheap RH meter is okay, but I bought a good one
- about $200 - and comes with a certificate of calibration to some fancy-dancy
standard. So now you have your temperature and RH known, now all you need to do
is to determine whether the panel has equilibrated with the hot box environment.
There are a number of ways to do this, I use a direct and very simple method -
it's got a complex name - don't let it scare you - ready? - "Direct Linear
Measurement" - i.e., put a tape measure across the panel and measure
it.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Picture below is basically what I do - just estabilish a
measurement line across the widest part of the soundboard,
more-or-less perpendicular to the grain.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><IMG alt="" hspace=0 src="cid:006001c8ffc7$3c77d440$0701a8c0@DESKTOP"
align=baseline border=0></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV>
<DIV><FONT face=Arial>Tap in a nail near one edge where a small hole in the
panel will not show (actually, I guess I would normally do it on the curved side
- the side opposite pictured below). The nail will give you a very solid
repeatable measurement point to start from.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><IMG alt="" hspace=0 src="cid:006101c8ffc7$3c7f0030$0701a8c0@DESKTOP"
align=baseline border=0></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV>
<DIV><FONT face=Arial>Then just put a mark (pencil) somewhere convenient on the
other side of the panel and measure (actually, I usually don't use a mark, but
rather measure to the other side/edge - but then I usually cut out the forward
bass side of the panel where the cut-off bar would be - when I do that I have a
nice edge parallel with the grain to measure on - but I still mark the point
where I measure the edge - same difference either way). You'll find that, for
example, when the panel dries from 10% EMC to 6% EMC, the panel will
shrink several millimeters - enough that it is very easy to tell when it has
equilibrated with the hot box environment.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>All the above is nothing more than telling you to measure
the width of the panel perpendicular to the grain so that you can measure
the shrinking/swelling of the panel!</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><IMG alt="" hspace=0 src="cid:006201c8ffc7$3c7f0030$0701a8c0@DESKTOP"
align=baseline border=0></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>You can play with it also a bit - get your panel dried
down to where you want it and it appears stable. Lower the temp in the box and
let the RH go up a bit - observe the panel grow a millimeter or two over the
next day or so. Raise the temp again to lower the RH, the panel will shrink a
couple millimeters over the next day or so again - it really works well and is
no more difficult to do than laying a tape across the panel.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Hope this helps.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Terry Farrell</FONT></DIV></DIV></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><FONT
size=3></FONT> </DIV>
<DIV><FONT face=Arial size=2>I have been using the technique Bruce Hoadley
talks about - cut several samples of spruce (similar dimensions) to the same
weight - 100g is easy to deal with - oven dry one of them to get a dry weight
to compare the others with. Sounds straight forward enough.</FONT></DIV>
<DIV><FONT face=Arial size=2>Then I compare calculated mc using weighed
samples with my hygrometer and the EMC charts and the disagreement
begins.</FONT></DIV>
<DIV><FONT face=Arial size=2>If conditions are changing, certainly there is a
lag time for equalization but the disagreement continues. Also the samples
must be placed in the shop so they are representative - still the disagreement
continues.</FONT></DIV>
<DIV><FONT face=Arial size=2>Probably it would pay to get a much more accurate
hygrometer? </FONT></DIV>
<DIV><FONT face=Arial size=2>Is the weighing technique really accurate? How
would you determine if it was?</FONT></DIV>
<DIV><FONT face=Arial size=2>Would it be helpful to add a moisture meter to
the lot?</FONT></DIV>
<DIV><FONT face=Arial size=2>I am curious how shop folks gain confidence in
their technique to measure mc so that if the measurements are telling you the
mc is 7% it really is 7% +/- an irrelevant amount?</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I can give one example: I use my humidifier
to get the rh up to 40% at 95 deg f - this should get my weighed samples up to
about 7%rh but they insist on weighing in at 6.1%. Is this a typical
discrepancy between cheap hygrometer and weighed samples?</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Thanks for any comments. </FONT></DIV>
<DIV><FONT face=Arial size=2>Gene Nelson</FONT></DIV>
<DIV><FONT face=Arial size=2>Thanks,</FONT></DIV>
<DIV><FONT face=Arial size=2>Gene Nelson</FONT></DIV></BLOCKQUOTE></BODY></HTML>