And, yes the board is more heavily loaded at the upper end and the bridge does some work to distribute the load. Were you to plot the stiffness coefficient of the ribs themselves it might look something like this. X axis are the rib #s and the y axis represents stiffness. Number 1 rib is the bass end, of course. Even though the #14 rib is smaller in cross section than, say #6 rib, it is much shorter and so therefore is much stiffer. In terms of the question at hand, in order for the board to deflect enough to crack the rib as it was pictured you likely wouldn't be able to achieve that level of deflection without doing some serious damage to the panel itself in the treble end. Even if the panel wasn't dried down enough (one suggestion) the amount of change in the crown radius that might take place seems hardly enough to crack that rib like that. Thus my guess that the rib was already damaged when installed. David Love www.davidlovepianos.com From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of David Love Sent: Friday, December 10, 2010 7:51 AM To: caut at ptg.org Subject: Re: [CAUT] strange rib damage That would be correct. It depends, of course, on how you set bearing and that may depend on the type of board and/or its condition. I often try and set bearing at the low end of the bass bridge at near zero with only slightly more pressure at the upper end of the bass bridge. Some set even more bearing at the upper end of the treble bridge than I have indicated. This is an average setting for me on the new boards that I'm doing (rib crowned with minimal compression) and I find it unnecessary, even counterproductive, to load the board more than this. In practice, at the very top of the treble bridge (last half of the upper section) I actually back off the bearing some down to more like 1 degree. The board is usually stiff enough up there without trying to achieve it by adding load and more problems come from too much stiffness or a restricting movement (jangles) than the opposite, I find. David Love www.davidlovepianos.com From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of Laurence Libin Sent: Friday, December 10, 2010 7:23 AM To: caut at ptg.org Subject: Re: [CAUT] strange rib damage Just to be sure I'm interpreting this correctly, each string of trichord Note 88 exerts a downbearing of 4.423 lbs (1/3 of 13.27 lbs), roughly 3.6 times more pressure than the single string of Note 1, right? And pressure is not evenly distributed across the bridge and soundboard but much more heavily loaded at the treble. Laurence Libin ----- Original Message ----- From: David Love <mailto:davidlovepianos at comcast.net> To: caut at ptg.org Sent: Friday, December 10, 2010 9:47 AM Subject: Re: [CAUT] strange rib damage Here's a typical Steinway B scale and resulting lbs. This totals out to 694 lbs. The lbs on each note takes into consideration the number of unisons. Using an average setting of 1 degree for every string would produce a total of 698 lbs. HTML probably helps to keep the chart organized. Note# / bearing deg/ lbs 1 0.25 1.22 2 0.25 1.21 3 0.25 1.19 4 0.25 1.19 5 0.25 1.16 6 0.25 1.15 7 0.25 1.11 8 0.25 1.11 9 0.25 1.78 10 0.25 1.74 11 0.5 3.43 12 0.5 3.41 13 0.5 3.36 14 0.5 3.31 15 0.5 3.24 16 0.5 3.20 17 0.5 3.19 18 0.5 3.13 19 0.5 3.04 20 0.5 2.99 21 0.75 4.99 22 0.75 5.29 23 0.75 5.41 24 0.75 5.74 25 0.75 5.85 26 0.75 6.28 27 0.75 6.32 28 0.75 6.37 29 0.75 6.62 30 0.75 6.49 31 0.75 6.65 32 0.75 6.44 33 0.75 6.53 34 0.75 6.56 35 0.75 6.54 36 0.75 6.55 37 0.75 6.52 38 0.75 6.55 39 1 8.84 40 1 8.35 41 1 8.43 42 1 8.54 43 1 8.57 44 1 8.55 45 1 8.67 46 1 8.60 47 1 8.65 48 1 8.33 49 1 8.45 50 1 8.47 51 1 8.73 52 1 8.45 53 1 8.31 54 1 8.49 55 1 8.63 56 1 8.72 57 1 8.77 58 1 8.90 59 1 8.72 60 1 8.84 61 1 8.84 62 1 8.77 63 1 8.81 64 1 8.89 65 1.5 13.23 66 1.5 13.06 67 1.5 13.12 68 1.5 13.26 69 1.5 12.79 70 1.5 12.94 71 1.5 13.09 72 1.5 13.24 73 1.5 13.40 74 1.5 13.55 75 1.5 12.92 76 1.5 13.07 77 1.5 13.22 78 1.5 13.38 79 1.5 12.73 80 1.5 12.88 81 1.5 13.03 82 1.5 13.18 83 1.5 12.51 84 1.5 12.66 85 1.5 12.81 86 1.5 12.96 87 1.5 13.11 88 1.5 13.27 David Love www.davidlovepianos.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/caut.php/attachments/20101210/43148c8b/attachment-0001.htm> -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: image/png Size: 13927 bytes Desc: not available URL: <http://ptg.org/pipermail/caut.php/attachments/20101210/43148c8b/attachment-0001.png>
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