I was expecting maybe at least Don might respond to this post I made a couple days ago. I see Don is back. What is your read on this? Terry Farrell ----- Original Message ----- From: "Farrell" <mfarrel2@tampabay.rr.com> To: "Pianotech" <pianotech@ptg.org> Sent: Sunday, February 16, 2003 9:11 AM Subject: Re: Wood Well, that is more-or-less what I did Del. My aim was to calibrate a panel-type MC gauge, so RH and MC stability were my aims, not necessarily measuring rate of change. But I do have some data that might shed some light on this subject. I took 2 to 6 blocks of wood (approx. 8 mm x 100 mm x 100 mm - my 0.01 scale only goes up to 100 grams, so I needed to stay with block of less than that - they were all between 50 and 95 grams) - mostly spruce, but some mahogany and hard maple (all pretty much reacted the same except the maple was slower to change MC overall). I placed blocks in my hot box and varied RH and left it at different levels for several days to be sure wood MC had stabilized. I would weigh blocks every day. Experiments ran (I actually did several) up to 34 days. If anyone wants the raw data, I can send it to you. Some approximations follow (I looked for a near-equilibrium conditions, a rise or fall of RH, and then near-equilibrium conditions again): RH DAYS = MC 20% drop 2.5 2.7% drop 14% rise 5.0 1.3% rise 12% drop 5.0 1.3% drop 9% rise 4.0 1.0% rise These data represent fairly stable endpoint conditions (both hot box RH and MC, except for the 20% drop, the wood had not stabilized before the hot box RH went back up a bit, but MC did in fact drop 2.7% in 2.5 days, it had simply not yet reached equilibrium). >From these data, it looks to me like wood looses moisture as easily as it gains it. Terry Farrell ----- Original Message ----- From: "Don" <pianotuna@accesscomm.ca> > Can someone suggest a better protocol for such an experiment? ----- Original Message ----- From: "Delwin D Fandrich" <pianobuilders@olynet.com> Yes. Put a piece of wood--since we're interested in piano tuning stability, let's make it a Sitka spruce panel about 8 mm thick by, say 250 x 250 mm--in a hermetically sealed environment stabilized at 70º F (or 90º F, or whatever, just so the temperature remains stable throughout the experiment) and 50% RH. With the wood sample placed on a very precise and accurate scale, monitor its weight until it has stabilized. Rapidly raise the RH to 70% and periodically monitor and record the weight change over time until the weight of the sample has again stabilized. Rapidly take the RH back down to 50%, again monitoring the weight change at the same time intervals. Following the same procedure take the RH further down to 30% and then back up to 50%. If you take weight readings frequently enough this should give you a pretty good idea of the rate at which the sample absorbs and desorbs moisture. In the end I expect you'll find it's about the same both ways. Del _______________________________________________ pianotech list info: https://www.moypiano.com/resources/#archives
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