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. 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. 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. 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. 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. 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. 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! 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. Hope this helps. Terry Farrell ----- Original Message ----- 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. Then I compare calculated mc using weighed samples with my hygrometer and the EMC charts and the disagreement begins. 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. Probably it would pay to get a much more accurate hygrometer? Is the weighing technique really accurate? How would you determine if it was? Would it be helpful to add a moisture meter to the lot? 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? 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? Thanks for any comments. Gene Nelson Thanks, Gene Nelson -------------- next part -------------- An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/20080816/e101cc2e/attachment-0001.html -------------- next part -------------- A non-text attachment was scrubbed... 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