Let me add that the rib after cutting and pressing had a 15M radius which yields 5.5 mm of crown for that length. A slight amount of compression might add something to that. The deflection on the rib for that load is 4.3 mm leaving about 20% of the crown. In actual practice with the panel installed and glued down the initial bearing of 1.5 degrees measured about half that once strung and pulled to pitch. That was right on target. I liked the sound too, but who cares about that. I listen to the engineering. David Love www.davidlovepianos.com -----Original Message----- From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of David Love Sent: Friday, December 21, 2012 10:11 AM To: pianotech at ptg.org Subject: Re: [pianotech] was GH-1s The premise of my load distribution is irrelevant in this case but it is not false. I believe your individually calculating the load of each rib based on how the unisons fall is incorrect, that the bridge does distribute the load. How much bearing you set at one end or the other of the piano can, of course, influence the load on each rib. But you push the bridge down on rib number 6 and rib number 4 deflects. It doesn't do that just to be respectful to rib number 6. The issue, however, is how we're designing them and the criteria we are using. If I anticipated the same load that you did, 25 lbs, that's how I'd build it. The premise of a rib in a piano that has 900 lbs of downbearing carrying only 25 lbs is a false premise unless you have a whole lot of ribs or not much downbearing. You want something more similar that's real world. Here's a rib in a piano I built, Steinway A, with a small cut-off bar. The rib is close in length to your sample at 810mm in length. The dimensions were calculated with a load of 65 lbs. The dimensions were 810 mm in length, 21mm w x 21.4 mm h. So let's put our thinking cap on, your slightly shorter rib carrying 40% of the load that mine is in design, is still 5 mm taller than mine (the 1 mm width difference doesn't make that much difference in load bearing). What more do you need to know? You build yours heavier. That, of course, is your prerogative, but for me, that's too heavy. If you don't think that answers the question then you don't want to know the answer. David Love www.davidlovepianos.com > > Yours: 25 lb load, 770mm x 20W x 26H, and a 9M radius > Mine: 25 lb load, 770mm x 15w x 16h, and a 9M radius > > (for approximately 50% deflection) I read that too, and it's useless because your rib loads are calculated on a false premise of equal distribution of load along the bridge, and you went with the cutoff. Size rib #6 of 18, at 1090mm long, or 999mm, or whatever is your personal preference at whatever load you calculate and specify, and I'll have something informational for comparison. Ron N
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