This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment I have always been curious about the soundboard pre-stressing method of = targeting downbearing, but when I ask how much to push the soundboard = down, I get answers like: "enough", "not too much" and the like. The = idea of getting a feel for how much the soundboard will deflect under = load I should think would help target proper downbearing Now I see here = we are using some numbers. This is a good thing. You say David Hughes = deflects the board 3mm at the center strut. You state that you drive = wedges under each strut. How much do you deflect the board at each = strut? Now the other question I have is that I assume the reason one would = pre-stress the soundboard is to incorporate into your work how much the = soundboard will deflect under load. But if you deflect the soundboard = 3mm or whatever, wherever, for any given soundboard, what does that do = for you (i.e., you are pushing a stiff board 3mm down, and you would be = pushing a highly flexible board 3mm down - under strung conditions, = obviously the flexible board would deflect more under final strung = downbearing)? You could simply calculate the needed angles without = pre-stressing the board. Now if you could pre-stress the board with = downward pressure approximately equal to that of the final string = downbearing in the various regions of the scale, then we would be truly = simulating the soundboard's reaction to the strung-up load and = accurately calculate our desired string downbearing angles, etc. Of = course to do this we would need some sort of pressure gauge/device. What about a rig similar to a pneumatic rib clamp. Just use the half = with the fire hose. Clamp it to the rim above the bridge, inflate, and = there you go with measurable pressure applied all along the long bridge = in much the same manner as downbearing would be once the piano is = strung. You could also use four segments of fire hose to apply = appropriate variable pressure to each of the four sections (and one on = the bass if you want to do that). The result would be a board stressed = in very much the same manner as it would be after stringing. Then you = could set your downbearing exactly where you want it, armed with the = knowledge of exactly (or there abouts) how much the soundboard will = deflect! So now, readers..........you are thinking one of two things: Either = Terry Farrell needs to get his head screw on properly, i.e. it's a dumb = idea, or it sounds like a great idea, now go try it Terry and write us = back. So what do you think? Maybe it is the case that with a given soundboard construction, the = boards are consistent enough to yield predictable result when = pre-stressed 3mm or whatever. Is this the case, and thus would yield a = more accurate pre-stressing a waste of time? I guess I'm just thinking and probing for information. Any input would = be appreciated. I realize the thing to do is put in a couple dozen = boards, try some different methods, and see what happens. But boy oh = boy, that will be years, and I would fear, some tears. I'm just trying = to arm myself with as much info a possible before I screw up too darn = many pianos. Terry Farrell =20 ----- Original Message -----=20 From: Erwinspiano@AOL.COM=20 To: pianotech@ptg.org=20 Sent: Sunday, January 20, 2002 1:07 AM Subject: Re: Baldwin accu-hitch pins In a message dated 1/19/2002 9:15:16 PM Pacific Standard Time, = davidlovepianos@earthlink.net writes: Subj:Re: Baldwin accu-hitch pins=20 Date:1/19/2002 9:15:16 PM Pacific Standard Time From:davidlovepianos@earthlink.net Reply-to:pianotech@ptg.org To:pianotech@ptg.org Sent from the Internet=20 David David Hughes and I both drive wedges in uder each strut to compress = the board along its entire span. We start at the central strut then = first and last capo then bottom strut. Then the dime quarter nickel = business. I use 2.5 mm top treble 2.25mm first treble an bout 2mmin = tenor tapering to 1.5 or so down low on tenor. Bass is set with about = 1/2 degree at the top tapering down to 0 at the bottom. Pretty much the same. Dale Dale: My conversations and classes that I attended with David Hughes (if I = remember correctly) led me to believe that he prestressed the board = under the central plate strut by 3 mm and then set the bearing dime, = nickel, quarter, in low tenor, mid-range, treble, respectively. That = seemed to pretty much be his method without additional measurement. I'm = sure he arrived at this method by much experience, but he didn't seem to = sweat it beyond that. David Love Dale: ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/88/9f/71/74/attachment.htm ---------------------- multipart/alternative attachment--
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