[CAUT] strikeweight

[Ed Sutton]

Re: [CAUT] strikeweightDavid-

Once the hammers are hung, the "pitch" of the shank/hammer will be altered, so I don't see how the "shank tone" as such is significant.
However, when all other factors are the same, it may be an indicator of the stiffness of the wood, which may influence the response of the action. 
For example, my sense in a short trial of Bruce Clark's action with carbon fiber shanks was that it was fast and even in response and delivered easy power for the effort. But that was a short trial by a low-skilled performer, and there are many other creative adaptations in his design that make it work so well.
Nevertheless, those carbon fiber tubes should be able to deliver a very perfect and even "plinck" line. not to mention even weight and stiffness.

Ed Sutton
  ----- Original Message ----- 
  From: David C. Stanwood 
  To: College and University Technicians 
  Sent: Wednesday, May 14, 2008 6:03 PM
  Subject: Re: [CAUT] strikeweight


  Dear Albert,


  Great work and very interesting and important ideas you are working with!  My comment: Most of the dead weight is concentrated in the flange and flange/knuckle end of the shank and I would imagine that for that reason the dead weight value might relate so much to it's effect on tone...  


  I would be very interested to see additional data using Shank Strike Weight (SS) instead of the dead weight of the Flange/Shank assembly.   This value measures the weight of the shank tipped on a roller bearing with the flange oriented vertically so that it's weight is not measured.  The end of the shank rests on the scale.  Values are usually aroun 1.4g for narrow shanks and 1.8g for regular shanks.  We routinely sort shanks, within each type, by weight, then hang the hammers, then measure Strikeweights, then add or subtract hammer weight to smooth the strikeweights to a curve of our choosing.


  The "thinking" is as follows:  Shank Strike Weights can very within a shank type within a set by as much as  0.6g.  These variations don't show up in the StrikeWeight measure but when we measure the Strikeweight and make changes in hammer weight to smooth the curve we may be changing hammer weight to compensate for a variation in SS.   .6g of SS will not have the same inertial moment as .6g of hammer weight because the center of weight is different.   (a physicist could explaing this more eloquantly than me).  So by sorting the SS by weight we theoretically make the inertial moments of the shank/hammer more even as related to smooth Strike Weights.


  Here is a drawing of the setup:


  http://www.stanwoodpiano.com/ss.jpg


  Hope this helps.


  David Stanwood 




    Hello List

    Chris Solliday <csolliday at rcn.com> wrote ('way back on Feb 20):

      Alot of good ideas and ways for producing some very refined work are being floated regarding shank radius weight and hammerweight which combine to produce strikeweight and  the action's main contribution to overall tone. ...
      ...I pre-sort the shanks heavy to light bass to treble before I channel them and then again after channeling them. I too find that this reduces the quantity of the variation if not the relative variation. I do not make a spreadsheet until that point after the second sorting. ...
      ...I may be going over the shanks twice but I have much less work in the end.
      I am intrigued at the possibility of working shank tone into the equation and will be first looking for a correlation between pitch and weight.
      Thanks,
      Chris Solliday



    This is my first posting to this list, so I hope at least some of you find what I have to say interesting and/or useful.  Back around mid-February a series of threads ran on this list entitled "Shank to Hammer weight spreadsheet", "strikeweight", and "Shank Pitch".  The comments at the very end of Chris Solliday's post (see above) particularly caught my attention, so I thought I'd do a little "tinking" and weighing to generate some data which Chris (or anyone else) might find useful.

    My data-gathering proceeded as follows:

    Taking a box of new Renner shanks with flanges for Steinway, I first separated the "regular" from the "thinned" shanks; the set contained 59 and 31 shanks respectively.  Then I listened to the pitch of the shanks and arranged them in order from lowest to highest.  Interestingly, both groups of shanks fell into the same overall pitch range, i.e. the major third A#5 to D6.  The thinned shanks covered a slightly narrower range, but that is probably due to the fact that there were fewer of them.

    Next, I weighed each shank/flange assembly and recorded its weight, to the nearest tenth of a gram.  This was just the dead weight of each assembly on the scale.

    Next, using a Correx gauge, I measured centre pin friction, also to the nearest tenth of a gram.  This involved some estimating and averaging, but I used a consistent technique, so I think the numbers are pretty good.

    I entered these data into an Excel file, and generated charts from them in order to visually illustrate whatever correlations might exist.  The file is attached, including charts - have a look.  The data series with the connected blue dots represent the regular shanks; the unconnected pink dots represent the thinned shanks.  The lowest- and highest-pitched thinned shanks are numbered to correspond with the regular shanks which had the most closely matching pitches; the rest of the thinned shanks are distributed as evenly as possible between those two extremes.  Distributing them this way enabled me to plot them all on the same graphs in a somewhat meaningful way.

    Finally, to further explore the relationships of shank thickness and shank length to shank pitch, I altered three regular shanks as follows.  The first one, which had an initial weight of 7.0 g (including flange), I thinned substantially, removing 0.5 g of material.  The pitch of this shank dropped by about a minor 2nd.  The second one, which had an initial weight of 6.9 g (including flange), I shortened by approximately 24-25 mm, equivalent to 0.4 g of material; the pitch of this shank rose by about a perfect 4th.  The third one, which had an initial weight of 8.5 g (it had a larger flange attached), I first thinned by 0.5 g, which lowered the pitch by a little less than a major 2nd.  Then I cut off shorter segments of approximately 7 mm each (each weighing a little under 0.2 g); each of these cuts raised the pitch about a major 2nd; the cumulative effect of these three cuts was a pitch rise of about a tritone.  Altogether, this last shank ended up thinner, shorter, and about a major third higher in pitch than where it was at the beginning.

    Some observations/conclusions:

    1. As I mentioned above, both the regular and thinned shanks fell into the same overall pitch range, i.e. the major third A#5 to D6.  Hence, if one is going to sort shanks strictly on the basis of pitch, the regular and thinned shanks will end up being interspersed.

    2. There is a significant amount of overlap in the weight ranges of the regular and thinned shanks.  So if one is going to sort shanks strictly on the basis of dead weight, again the regular and thinned shanks will end up being interspersed.

    3. The trendlines in the "Pitch vs. Weight" chart seem to indicate that, as a general rule, heavier shanks have a higher pitch.  For two reasons, I suspect that the variations in pitch are primarily a result of differences in wood density from shank to shank.  First, because the substantial thinning I did on two of the shanks I altered resulted in pitch changes of less than a major 2nd, I doubt that the slight dimensional variations which may exist after Renner's precise manufacturing process are likely to result in pitch differences amounting to a major 3rd.  Second, the fact that the regular and thinned shanks produce pitches that fall within the same range suggests that something other than dimensional variations are responsible for the pitch variations.  Another obviously potential source of variation in the weighing process is differences in the weights of the flanges.  But I suspect that if one took the trouble to weigh the flanges separately, although there would be some variation, the data would generate a flat trendline.  Anyone wishing to test this hypothesis is welcome to do so; right now I don't have time.

    4. The random distribution of tighter and looser flanges throughout the entire range of pitches, and the flat trendlines in the "Pitch vs. Friction" chart seem to indicate that the pitch of the shanks is not affected by the pinning (although I do believe the pinning does affect the tone in the piano).  To test this conclusion a little further, I took a relatively tight assembly, treated it with CLP to reduce the centre pin friction, and listened to the pitch again; there was no change in pitch.

    5. Removing material from the end of a shank has a significantly greater effect on the shank's pitch than does removing an equivalent amount from the sides.  Whether this is something that needs to be taken into account when sorting shanks may be worth considering, because when the shank ends are trimmed after the hammers are installed, they aren't all necessarily shortened by the same amount.

    The really tough question now is, what am I going to do with these things?

    Albert (Bert) Picknell
    Head Piano Technician
  The Banff Centre
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