<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html xmlns:o="urn:schemas-microsoft-com:office:office" = xmlns:w="urn:schemas-microsoft-com:office:word" = xmlns:st1="urn:schemas-microsoft-com:office:smarttags" = xmlns="http://www.w3.org/TR/REC-html40"> <head> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; = charset=us-ascii"> <meta name=ProgId content=Word.Document> <meta name=Generator content="Microsoft Word 10"> <meta name=Originator content="Microsoft Word 10"> <link rel=File-List href="cid:filelist.xml@01C5F061.CD233DE0"> <title>Recrowning - was Soundboard Crown measurement</title> <o:SmartTagType = namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="time"/> <o:SmartTagType = namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="date"/> <o:SmartTagType = namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="PostalCode"/> <o:SmartTagType = namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="State"/> <o:SmartTagType = namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="City"/> <o:SmartTagType = namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="place"/>  <style>  </style>  </head> <body lang=EN-US link=blue vlink=purple = style='tab-interval:.5in'> <div class=Section1> Fabulous, = Ron. Thanks so much for taking the time to keep us appraised. = I’ve had doing something similar in the back of my mind for about 10 years. I = have a couple of questions. <o:p></o:p> <o:p> </o:p> First, and maybe I already have the answer, why do you “straighten” the original rib top? Is it primarily to reduce the section at the tapered ends?  It seems like the pressurized = hose clamping set up would allow the piece you are adding to conform to a pretty steep curvature. <o:p></o:p> <o:p> </o:p> Second, I am curious why you = don’t employ a variation of your webbed ribs. Why not make your added piece wider = than the original rib to give it an I-beam effect? It could conceivably be made = wider under the bridge with the web tapered to the ends. = <o:p></o:p> <o:p> </o:p> <o:p> </o:p> <o:p> </o:p> <div> Dean<o:p></o:p></fon= t> Dean May       &nbs= p;     cell 812.239.3359<o:p></o:p> PianoRebuilders.co= m   = 812.235.5272<o:p></o:p> <st1:place><st1:City>Terre Haute</st1:City> <st1:State>IN</st1:State>  = <st1:PostalCode>47802</st1:PostalCode= ></st1:place><o:p></o:p> </div> <o:p> </o:p> -----Original = Message----- From: Dean May [mailto:deanmay@pianorebuilders.com] Sent: = <st1:date Month="11" Day="23" Year="2005">Wednesday, November 23, = 2005</st1:date> <st1:time Hour="18" Minute="56">6:56 PM</st1:time> To: = deanmay@pianorebuilders.com Subject: FW: Recrowning - = was Soundboard Crown measurement <o:p> </o:p> From:</spa= n> pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf Of Overs Pianos Sent: = <st1:date Month="11" Day="23" Year="2005">Wednesday, November 23, = 2005</st1:date> <st1:time Hour="16" Minute="58">4:58 PM</st1:time> To: Pianotech Subject: Recrowning - was Soundboard Crown measurement<o:p></o:p> <o:p> </o:p> <div> Hi all,<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> Some time back I mentioned on the list that = we have been re-crowning sound boards by firstly jacking crown back into the = board, then removing part of the ribs and building them up again with new = <st1:City><st1:place>Sitka</st1:place></st1:City> spruce to re-set the sound board crown. Dale Erwin expressed an interest = in seeing some images at the time.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> Many (probably most) of the sound boards in = service develop panel weakness, or have had it since the time of construction. = When a sound board looks to be in reasonable visual shape, I have proven to my satisfaction that it is possible to re-crown a board (and more = importantly stiffen it) to restore it to proper = function.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> I have re-sampled 8 images and uploaded them = to one of my webspaces (I hope you lads and lassies appreciate the 3 hours I have = put into this on this fine morning). Please find below links to the images = with accompanying text included in this post.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> <a = href="http://members.optusnet.com.au/ronovers/recrown1.jpg">http://memb= ers.optusnet.com.au/ronovers/recrown1.jpg</a><o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> This image shows the small jacks which I have manufactured, for using the back beams and cross braces to jack crown = back into the sound board. The piano we are operating on here is a Kawai KG6. We = have just started to rasp back the rib height in this image. The ribs on this = piano were quite deep and generously proportioned. The sound board panel is 10 = mm thick overall. It is quite surprising that such a seemingly robust sound = board should develop short tone and impedance problems. But this late 70's = instrument, in standard form, produced a most unpleasant and short shocky = tone.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> Last Tuesday I inspected another slightly = younger (1979) KG6 grey market piano at a venue one hour north of = <st1:City><st1:place>Sydney</st1:place></st1:City>. This piano had no compression ridges in the panel. The board was = virtually flat. The tone was simply appalling. Looks very much like this piano = might get a similar treatment to the one shown in these images.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> PLEASE NOTE:<o:p></o:p> </div> <div> The jacks must be placed directly under a = bridge to prevent the jacks pushing a hole in the sound board panel. The bridges = also act to spread the jack-pressure to ensure that the panel moves up as a = whole.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> <a = href="http://members.optusnet.com.au/ronovers/recrown2.jpg">http://memb= ers.optusnet.com.au/ronovers/recrown2.jpg</a> <o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> Once the crown is jacked up to what we deem = to be an appropriate level of crown, plus a couple of millimeters (to allow for = the sinkage which will inevitably occur when the jack pressure is released), = we take to the ribs with a half round wood rasp to remove the bulk of the = rib height we wish to replace. Bear in mind that the originally compression crowned = ribs are now pushed back into a curve. We remove the rib material to achieve = a straight bottom on the re-profiled rib. This means that we will be = removing more rib height from the ends and less in the middle. In the image, Wal Sullivan is using a specially made long sanding block (with 80 grit = paper glued to it) to straighten the rib tops and get them nicely trued up for = gluing the new rib extensions to the existing ribs. Notice that we aren't = re-crowning the first two ribs in the back corner. These ribs are subjected to much = lower stress than the middle order ribs. We also don't re-crown the highest = treble rib, since its nearly impossible to get to, and the bridge is so close = to the belly rail in the high treble that sound board collapse isn't a problem = at the very top end.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> In terms of structure, the extended ribs will = be significantly superior to the uniform height original ribs. A sound = board rib should be at its stiffest right under the bridge where it is subject to = the most stress, becoming gradually weaker towards the rim. The extended rib = will be deeper and stronger in the middle since we will have removed less = height to achieve a straight surface for attaching the = extension.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> <o:p> </o:p> </div> <div> <a = href="http://members.optusnet.com.au/ronovers/recrown3.jpg">http://memb= ers.optusnet.com.au/ronovers/recrown3.jpg</a> <o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> This image shows how we clamp the rib = extension to the original rib using a cheap-and-nasty piece of flat garden hose at 50 = psi. A radiata 4"X2" is clamped across the case to support the air = hose, with spacer blocks held in place between the back beams with masking = tape until the hose is pressurised. We use Titebond Extend for gluing the rib = extensions in place. When the pressure is applied the hose will push the board away = from the back beams so that it clears the jacks (we need to be careful to = leave the jacks in place so that the board remains jacked up when the pressure is released from the air hose). The rib extension for the next rib to be = glued is shown in the image. Notice that the feathering is already cut into the extension piece and that it is already sprayed with the acid cat lacquer = that we use for sealing sound boards.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> <a = href="http://members.optusnet.com.au/ronovers/recrown4.jpg">http://memb= ers.optusnet.com.au/ronovers/recrown4.jpg</a> <o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> With a 10 mm thick sound board panel, and the = bass bridge being so close to the inner rim, this piano in original form = didn't have much in the way of bass fullness for a 225 cm piano. In our customary = manner, we have trenched the sound board panel just adjacent to note no. A1. The = trench depth is 5 mm, half of the panel thickness.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> <a = href="http://members.optusnet.com.au/ronovers/recrown5.jpg">http://memb= ers.optusnet.com.au/ronovers/recrown5.jpg</a> <o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> Some of the original bridge notching on this = piano was pretty ordinary. C88, as shown in the image, was notched completely in = front of the pin-line. These matters need to be rectified in conjunction with a re-crown.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> <a = href="http://members.optusnet.com.au/ronovers/recrown6.jpg">http://memb= ers.optusnet.com.au/ronovers/recrown6.jpg</a> <o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> This view shows the sound board after = re-crowning and bridge notching, and the application of the acid cat lacquer sealing = coat. The crown on this sound board can be clearly seen in the = image.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> <a = href="http://members.optusnet.com.au/ronovers/recrown7.jpg">http://memb= ers.optusnet.com.au/ronovers/recrown7.jpg</a> <o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> This image shows a close up of the rear of = the sound board where the panel was trenched for bass = tone.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> <a = href="http://members.optusnet.com.au/ronovers/recrown8.jpg">http://memb= ers.optusnet.com.au/ronovers/recrown8.jpg</a> <o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> This image shows an underside view of the = soundboard after the rib-crowning operation. Two of the rib featherings near the = cut-off originally were very short. We lengthened these before fitting the rib extensions. The re-finished iron plate for this piano can be seen in the background.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> I'm just regulating the action at the moment. = The piano is only chipped up at present, but we've got a known good piano in = the workshop at the moment for its second rebuild, and after plucking the = strings of both instruments and comparing the sustain and tonal characteristics = I am very pleased with the re-crowned KG6. Looking forward to getting a = couple of tunings and some fine voicing into the hammers. We've fitted an Overs = action to this piano, and the Wurzen felted Abel hammers sound almost balanced = straight out-of-the-box.<o:p></o:p> </div> <div> <o:p> </o:p> </div> <div> Ron O.<o:p></o:p> </div> <pre style='margin-left:.5in'><x-sigsep>-- <o:p></o:p></pre> <div> </x-sigsep>OVERS PIANOS - = <st1:City><st1:place>SYDNEY</fon= t></st1:place></st1:City><o:p></o:p> </div> <div>    Grand Piano Manufacturers _______________________<o:p></o:p> </div> <div> Web http://overspianos.com.au<o:p></o:p> </div> <div> mailto:ron@overspianos.com.au _______________________<o:p></o:p> </div> </div> </body> </html>