[CAUT] strange rib damage

Sat Dec 11 07:11:19 MST 2010

Might have been weakened when the rib was still a tree.
Consider the stress when the bridge pins were pounded in. I believe Steinway likes to bottom out the bridge pins. Perhaps enough shock to split a rib made of shake-damaged wood. (Were other ribs made from the same stock?)
Meanwhile, we don't know if the mid-range noise Kent reported has anything to do with this rib.
Ed Sutton

-----Original Message-----
>From: David Love <davidlovepianos at comcast.net>
>Sent: Dec 10, 2010 11:06 AM
>To: caut at ptg.org
>Subject: Re: [CAUT] strange rib damage
>
>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
>
> 
>