This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment Hi Dale, An uneducated guess here. Are you also reducing the size of the rib = some, seeing that it is also stronger? Joe Goss RPT Mother Goose Tools imatunr@srvinet.com www.mothergoosetools.com ----- Original Message -----=20 From: Erwinspiano@aol.com=20 To: pianotech@ptg.org=20 Sent: Saturday, February 18, 2006 9:04 PM Subject: Re: laminated ribs Ok, now this is an interesting discussion. Admittedly not being a = math guy I'm still interested in putting some numbers on some scales of = things I've seen as a bench marks for comparison. Let's just take one case I have first hand knowledge of. I = rebuilt & 1960 Stwy L 3 years ago that lived in a Fresno area church = from the beginning of it's creation to the present so it has survived = wonderfully well. I was keenly impressed by the balance of sound, both in power & = sustain. I measured the bearing with a lowell gauge & though I don't = have numbers any more to give you my recall is that the top capo had = over 2 degrees of deflection & the 2nd capo about 2 or more & the = middle was 1 1/2 degrees tapering down to 1/2 in the bottom & the bass = had positive but minimum bearing as it should be with a cantalever. The = crown string stretched across the boards underside revealed lots of = residual crown in the strung condition & more than any other C.C. board = I've ever seen up to that time. All that to say it was in my opinion a = text book Steinway/belly set up both in terms of crown & bearing. = These are IMO the kinds of observations that are important to make when = we find something that is working really well.=20 The Stwy L scale as I recall has an average treble tension at 160 = lbs per string. It is obvious to see that the majority of the bearing = pressure on the long bridge is increasing gradually the higher up the = scale we go.=20 So knowing all of the above, what is the equation that will = calculate an approximate string bearing load under the conditions I = describe? If it's the one- 40th rule for simplicity then 40 divided into 160 = strings equals 4 pounds per string. Let's remove most of the bass = strings from this equation for now, since theoretically there isn't much = bearing there & we have approx. 160 strings times 4 pounds equals 720 = lbs. add in say 80 lbs for the bass & it's about 800 total pounds give = or take There is a much more accurate & glamorous formula for this but I = dont' have it at my finger tips. If the scale tension averages 180 lbs = per string then we're talking 4 1/2 pounds per string which bumps total = bearing load up another 100 ish pounds. My point in all this is that if we are using stronger engineering = materials & principles which building better stronger rib structure, = which we are, then surely our rib crowned & supported boards will = survive as well & IMO longer than this example of a C.C Steinway L I = cited above=20 Don't you think? Dale Erwin Consider a basic scale of moderately high tension. Say 40,000 lbs. = overall. With this string tension 1,000 lbs of string down force equals = 2.5% of scale tension. That is quite a lot considering that most = companies are claiming string down force more on the order of 0.5% to = 1.5% of string tension (which would be 200 to 600 lbs). I thought I was = setting my initial string down force pretty high at around 1.0 to 1.5%. = I don't like thinking about what I'd be doing to a board loading it up = to 2.5%. I can't imagine it being happy enough at that level to want to = stay there. Del ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/05/10/5a/69/attachment.htm ---------------------- multipart/alternative attachment--
This PTG archive page provided courtesy of Moy Piano Service, LLC