<!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 6.00.2800.1264" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY> <DIV><FONT face=Arial color=#800000>And you know, my limp expansion = gauge hasn't recovered yet.</FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>Having graduated from building = measuring jigs to building building jigs, I haven't even tried to replace my = failed endeavor. What I have done instead - and I'm quite happy with the = results - is to simply measure the size of the panel, cross-grain.</FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>To ensure accuracy of = measurement, I tap in a very small nail into the panel near one edge where the panel is = widest. I use one of my scale measuring tapes that David Sanderson or Jim Arledge = issues for measuring string scales. I place the tape end loop around the nail = (this ensures end placement accuracy) and measure to the nicely squared = opposite panel edge (put a pencil mark to repeat measuring spot). </FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>My shop is kept at a = consistent 45% to 50% RH. So I know my spruce panel's EMC is real close to 8.5%. I put the = panel in the hot box targeting around 6% EMC (adjusting heat to keep the RH = just below 30%). I measure the panel daily. Within a week the panel stabilizes. I = let the hot box RH go up to 30% and watch for a little bump upwards in the panel = width as the panel goes from something a little less than 6.5% back up to 6.5% = or so. That way I am doubly sure the panel's MC did indeed = stabilize.</FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>Across a typical width panel I = will observe about a 2.5 millimeter reduction in width during the course of drying = from 8.5% MC to 6% MC. So yes, you need to interpolate tenths of millimeters, but = with a big magnifying glass this is doable.</FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>Works for me. But I also think = your idea is great.</FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>Terry Farrell</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>----- Original Message ----- </FONT> <DIV><FONT face=Arial size=2>From: "Ron Nossaman" <</FONT><A href="mailto:RNossaman@cox.net"><FONT face=Arial size=2>RNossaman@cox.net</FONT></A><FONT face=Arial = size=2>></FONT></DIV> <DIV><FONT face=Arial size=2>To: <</FONT><A = href="mailto:files@ptg.org"><FONT face=Arial size=2>files@ptg.org</FONT></A><FONT face=Arial size=2>></FONT></DIV> <DIV><FONT face=Arial size=2>Sent: Friday, November 07, 2003 12:03 PM</FONT></DIV> <DIV><FONT face=Arial size=2>Subject: MC gage = experiment</FONT></DIV></DIV> <DIV><FONT face=Arial><BR><FONT size=2></FONT></FONT></DIV><FONT = face=Arial size=2>> <BR>> I apparently never posted this to the list, = intending to write it up <BR>> and submit it to the Journal. Since I still haven't = yet done that, and <BR>> someone asked, here's the gist of it.<BR>> = <BR>> After the demise of Terry's differential expansion gage, I got to = <BR>> thinking - and you know what kind of trouble that can lead to. As = <BR>> usual, what I started out doing was different from what I ended up = <BR>> doing, which was different from what I should have done from the = <BR>> beginning. After flailing around doing it inside out and backward for = <BR>> about a week, here's what I decided I should have done in the first = <BR>> place, and how I would do it if I were building another one...<BR>> = <BR>> I already had a $6 linear dial indicator from Harbor Freight that I had = <BR>> purchased last year for the inevitable dedicated tool I figured I'd be = <BR>> building before long, or just for general purpose confusement. It was = <BR>> just too cheap to pass up, and this looked like a fine use for it. I = <BR>> made a maple frame of "U" channel for a slip fit of the panel scrap I = <BR>> intended to use. So far so good.<BR>> <BR>> Choose a well = quartered 8mm plank, somewhat dense, with relatively <BR>> tight grain that's = uniform all the way across. If there's only a 50mm <BR>> width that's uniform, = rip it to 50mm. It should react slower than a <BR>> light loose grain piece, so = it won't get too far ahead of the wood in <BR>> the soundboard panel = when it's actually used as an MC gage. It <BR>> shouldn't move as far as the = loose grain stuff for a given MC shift <BR>> either, and your gage can be = longer for a given expansion scale to, <BR>> hopefully, increase measurement = accuracy. Now, what's the actual <BR>> expansion/contraction rate and = how to scale it to the dial indicator?<BR>> <BR>> Cross cut the chosen = plank into strips of the right width (mine's 50mm) <BR>> to fit in the channels = in  the frame pieces, leaving a couple <BR>> millimeters free top and = bottom so the strip won't bind. It's just <BR>> supposed to slide easily, but = not sloppy, in the tracks. Cut enough <BR>> strips to fill the frame = length. Stabilize them at some measured MC in <BR>> the hot box, house, or = shop; wherever the temperature and RH is stable <BR>> enough for a couple = of days until they quit moving. Somewhere around <BR>> 10%MC would be good. = Record the cross grain width of one of the pieces <BR>> as an indicator, and = mark it as the test piece. Or do them all for <BR>> comparison averaging. = Record the MC from temperature and RH%. Dry the <BR>> pieces in the hot box for = a couple of days until the test piece quits <BR>> changing dimension (and/or = weight) at around 6%MC or so. Record temp <BR>> and RH% with the same = instruments you used for the high MC measurement, <BR>> and figure the new MC. You = now have a dimension @ a specific MC for two <BR>> MC values that aren't near = the less trustworthy high and low limits of <BR>> your RH% measuring device. I = assume the error in an electronic <BR>> hygrometer will likely be in the = same direction and close to the same <BR>> rate for both measurements, so = the proportion of dimensional change to <BR>> computed MC% change should = be valid whatever the numbers actually are. <BR>> This may not be the case, = but it seems likely. If you have the <BR>> facilities to do this with a = sling psychrometer, that would probably be <BR>> better. Now the = scaling.<BR>> <BR>>  From the expansion figures I got, I figured I had room in = my frame for <BR>> a strip of the proper length to change 0.010" per = 1%MC. That seemed <BR>> sensitive enough to me to be useful, and simple enough = to figure out on <BR>> the gage without a conversion table. I can read it = directly off the <BR>> dial. From measurements taken on the test piece, find the = expansion <BR>> rate per inch per 1%MC increase, and glue enough pieces in line = to <BR>> nearly fill the frame, and mark the proper length to have a = piece that <BR>> will expand 0.010" per 1%MC. Put a thin maple cap on one end of = the <BR>> strip for the dial plunger to ride on without denting, and = mount it in <BR>> the frame with the gage so the gage reads what you've just = measured the <BR>> MC at. I mounted mine by driving a small wedge with a bit of = glue <BR>> between the frame edge and the panel at the mark I had made = indicating <BR>> the appropriate length. That way, the waste end can expand and = contract <BR>> without getting in the way of anything, and My frame can be a = bit <BR>> longer than actually needed in case I want to replace the panel = piece <BR>> some day. Now, start testing it against as accurate a = temperature and <BR>> RH% means as you have available at different humidity levels to = certify <BR>> it's accuracy.<BR>> <BR>> The sucker seems to be pretty = close, and since it's unconstrained, it <BR>> won't suffer compression set = either over time, or from extremes of <BR>> humidity like most of the = designs I've seen will. As long as I don't <BR>> overheat it or contaminate it = with something that affects it's moisture <BR>> capacity, it should last a = very long time. So far, I like it. Here's <BR>> the photo.<BR>> = <BR>> Photo:<BR>> <BR>> </FONT><A href="https://www.moypiano.com/ptg/files/attachments/28/96/b7/66/Dsc000= 01.jpg"><FONT face=Arial size=2>https://www.moypiano.com/ptg/files/attachments/28/96/b7/66/Dsc00= 001.jpg</FONT></A><BR><FONT face=Arial size=2>> <BR>> Alternate URL:<BR>> <BR>> = </FONT><A href="http://tinyurl.com/u4ah"><FONT face=Arial size=2>http://tinyurl.com/u4ah</FONT></A><BR><FONT face=Arial = size=2>> <BR>> _______________________________________________<BR>> = pianotech list info: </FONT><A = href="https://www.moypiano.com/resources/#archives"><FONT face=Arial size=2>https://www.moypiano.com/resources/#archives</FONT></A><BR><FON= T face=Arial size=2>> </FONT></BODY></HTML>