<!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 6.00.2800.1106" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY> <DIV>Hi Ron. I ran across the following - don't know the source:</DIV> <DIV> </DIV> <DIV><FONT color=#008080>Air Drying: <BR>At MC lower than the fiber = saturation point (usually 35%), moisture change takes place by diffusion within the = wood. The standard diffusion equation may be written as <BR>t = L² / D = <BR>where <BR>D = 1x10-6 cm²/s transverse and radial, 1x10-5 cm²/s lengthwise, = <BR>L is the length along the direction of diffusion. <BR>t is the time to 1/e of the = moisture change, that is to 63% of the equilibrium change. <BR>So, if = you have a piece of seasoned wood 2 cm thick that is at the 15% MC of typical = outdoors storage here, and you want to estimate how fast it will come to = equilibrium in your workshop at 30% RH (7% MC) if exposed to air both sides, L = 1 cm = and the diffusion equation gives t = 1x106 s, 11 days. The equilibrium MC = change required is 8%, so in 11 days you can expect 63% of 8% = 5% lower MC, = that is 10% total MC. That leaves 3% to go, and you can expect 63% of that 3% to = take place over the next 11 days, to 8% MC. So, 3 weeks should be enough time = for 2 cm thick wood. If your wood is 4 cm thick, it will take 3 months, 6 cm = thick, 7 months. According to the literature, most seasoned temperate woods = change moisture at a rate within ±20% of this. </FONT></DIV> <DIV> </DIV> <DIV>According to this, I should be able to dry my 15 mm thick spruce = within a month from 40% MC down to 8% MC. We'll see what happens. Keep in mind, = this wood is not green (about 140% MC) - it is about 40% to 45% MC - so I'm not = drying from a green condition. I hope it will dry in a few weeks, as I need to = get cranking on these boards ASAP!</DIV> <DIV> </DIV> <DIV>I sealed the ends with a water-based polyurethane I had lying = around. We'll see how that works.</DIV> <DIV> </DIV> <DIV>I would love to see pictures of your hot box - let me know when it = is on your web site.</DIV> <DIV> </DIV> <DIV>I have pictures of cutting properly quarter sawn panel pieces from = poorly quarter sawn boards and stacking and drying spruce for my = first soundboard panel and ribs. I've got six relatively low resolution shots = if you are interested. </DIV> <DIV> </DIV> <DIV>You've got some good suggestions. I'll keep an eye on the edges of = my boards - interesting, your comments about compression set in this = area.</DIV> <DIV> </DIV> <DIV>Wow, a lot of new experiences today!</DIV> <DIV> </DIV> <DIV>Tomorrow, tuning spinets.  :-(</DIV> <DIV> </DIV> <DIV>Terry Farrell<BR></DIV> <DIV> <SPAN id=__#Ath#SignaturePos__></SPAN> </DIV> <DIV>----- Original Message ----- <DIV>From: "Ron Overs" <<A href="mailto:sec@overspianos.com.au">sec@overspianos.com.au</A>></DI= V> <DIV>To: "Pianotech" <<A href="mailto:pianotech@ptg.org">pianotech@ptg.org</A>></DIV> <DIV>Sent: Tuesday, March 25, 2003 4:49 PM</DIV> <DIV>Subject: Re: Wood Drying</DIV></DIV> <DIV><BR></DIV>>Terry,<BR>><BR>>Your most immediate danger is = too rapid drying through the end grain.  THe<BR>>dimensioinal change from differential drying through the end can create<BR>>checking that will = make large sections of wood unusable.  Don't waste a<BR>>second = getting some form of moisture-impervious sealant into the end of<BR>>every = piece.  Melted parafin wax works best, IMHO.<BR><BR>Or, if you have any wood = glue (out of date Titebond or rubbish PVA) <BR>lying about, that works very well = also. When sourcing local logs, we <BR>specify that the log is end-sealed as = soon as it is cut.<BR><BR>Your idea of breaking the log down into 1/2" boards is = a good one. <BR>Such boards will be ready to use in one year with just air = drying <BR>(ie. for the panel, rib stock will take at least two years, unless = <BR>you plan to make laminated ribs out of the 1/2" boards). When we <BR>break = down a log for sound board material, after the large boards (2" <BR>thick) have = been cut out, we break down all the small triangular <BR>flitchs into 1/2" = wide boards, so as to obtain the maximum of useable <BR>spruce from the log = (you will need a resaw with a tilting table for <BR>this purpose). The danger with = drying is moisture gradients. <BR>Therefore, the thinner cut boards will tend = to have less of a <BR>gradient problem, but they will be more prone to warpage. = As soon as <BR>you have cut your boards, they should be stacked with spacing = sticks <BR>(of say 25 mm by 25 mm section) between each layer of boards, spaced = <BR>at about 300 mm (1') for boards 1" or thicker. I would recommend that = <BR>the spacing sticks be set somewhat closer together for 1/2" boards to = <BR>reduce warpage. The entire stack should be covered with some kind of = <BR>roofing material and weighted on top (house bricks will do) to ensure <BR>that = the upper boards in the stack are held down to prevent them from <BR>warping. = Don't make the stack too high or the overall weight will <BR>cause the lower boards = to sustain crush damage adjacent to the spacer <BR>sticks.<BR><BR>I'll = photograph the drying stack I have at the house and send you a <BR>jpeg. Looking at = your location Terry (27 degress N, - I notice that <BR>you have another = Sydney a few miles east), I would recommend that you <BR>commence the drying process = during the winter months, since the <BR>summer heat will be very risky for = freshly sawn boards. It is the <BR>initial drying phase during which degrade from = moisture gradients is <BR>more likely to occur. Furthermore, quarter cut boards = will tend to <BR>lose moisture faster through the edge of the board compared to = the <BR>quartered face. This will occur with a quarter cut board since the <BR>medullary rays will be perpendicular to the edge and parallel to the = <BR>board face. We seal the edges of quarter cut boards as soon as they = <BR>come off the saw. This will greatly reduce the risk of stress damage <BR>at = the edge of a quarter cut board during the drying process. I have <BR>noticed a = tendency for belly wood to be more prone to compression set <BR>damage adjacent = to the board joints. While there may be a multitude <BR>of reasons why this = might be so, I have long suspected that the <BR>tendency for quarter cut boards = to lose moisture faster through the <BR>edge, particularly during the initial = drying phase, to be a factor <BR>here.<BR><BR>By the way folks, our new sound = board conditioning box is coming <BR>along nicely (the new box is big enough = to accommodate a Bösendorfer <BR>Imperial board). If anyone is interested = I'll be taking a photo of <BR>the assembly prior to fixing the last side of the = box, so that you <BR>can view the layout of the air ducting. I'll put in on the = web site <BR>and let you know when it is up.<BR><BR>Best,<BR>Ron O.<BR>-- <BR>_______________________<BR><BR>OVERS PIANOS - SYDNEY<BR>Grand Piano Manufacturers<BR><BR>Web: <A href="http://overspianos.com.au">http://overspianos.com.au</A><BR><A href="mailto:info@overspianos.com.au">mailto:info@overspianos.com.au</A= ><BR>_______________________</BODY></HTML>