Dear List, Today I wrote Jim Coleman, Sr., about his contribution to the string breakage thread. I didn't want to waste everybody's time (and possibly make an idiot of myself) so I wrote him privately. I don't think I should keep what came back to myself, so I'm forwarding it. My comments are interspersed with his, so I've labeled them. >Date: Fri, 25 Apr 1997 16:01:55 -0700 (MST) >From: Jim <pianotoo@IMAP2.ASU.EDU> >Subject: Re: thanks >X-Sender: pianotoo@imap2.asu.edu >To: Susan Kline <skline@proaxis.com> [Susan:] >> There was one thing I wondered about, but didn't want to question in front >> of the list -- on the string breakage question. >> [Jim's post to the list, "string breakage" 4/8/97] >> >IMHO the reason there is less string breakage when one lowers the pitch >> >is that when you do bring it up with more confidence, you pass quickly >> >over the former place of corrosion. It has been my practice to use the >> >impact method of tuning hammer technique and especially on vertical >> >pianos the first stress on the tuning pin is downward counteracted by >> >the immediate turning of the pin. As the pin springs back the string is >> >tightened. The tightening of the string occurs during the spring back >> >instead of during the turning. Another consideration is that when one >> >uses a smooth pull technique, there is greater tension over a longer >> >period of time as one overcomes the frictional resistance, thereby >> >causing more breakage. String breakage has come almost to >> >a standstill since adopting the impact method. The same forces are at >> >work on a Grand if one tunes from the 9:00 O'clock position using the >> >impact method. I usually do not change position for grands, but rely on >> >the sudden movement of the impact method. >> > >> >Jim Coleman, Sr. >> > [Susan] >> This feels very counter-intuitive to me. I imagine wanting a paper towel off >> the roll, with one hand -- I give a sudden, sharp yank to separate it. My >> general feeling is that if you don't want to break something, you bend it >> gradually, and don't make any sudden moves. [Jim, today] >I should have emphasized that during the slow pull of an increased >tension, with the resistance at the Agraffe, there is even more tension >at the tuning pin end until the string renders thru the Agraffe. It is >during this TIME that strings break at the tuning pin. It takes a finite >amount of time for a string to break. There are two stresses involved at >the tuning pin. One is the bending of the string around the pin. The >other is the added tension from trying to overcome the resistance at the >agraffe. On a vertical piano with the tuning lever at about 2 to 3 >O'clock position, the first stress occurs before the second. After the >downward stroke of the lever, the pin springs up and increases the tension >of the upper portion of the string, breaking the resistance at the >Agraffe. During this action, there is no additional stressing of >the bending moment of the wire, only the addition of tension. Can you >envision these two things happening at different times? > >During a smooth pull, using even the same clock position, The string >bending moment is greater and also experiencing greater tension until the >point of resistance is overcome and the string renders thru the >agraffe or it breaks, whichever comes first. > >In studies which I did back in '67 using strain gauges to mark what >happens when a string breaks. When tension is gradually added to a string >without frictional resistances (such as agraffes) a string begins to >yield a bit before it breaks. This is where time enters the picture. > >Here are some examples of tests taken at the CGConn engineering labs while >I was there. > >wire size yield point break point > >13 258 lbs 290 >13.5 267 303 >14 317 355 >15 >16 347 398 >18 431 487 > >We didn't test every wire size. And sometimes there was some inconsistency >in that a larger wire would break before a smaller wire. We discovered >that work-hardening played a part in this. We also learned that preheating >wire would raise the yield point, but not affect the break point >appreciably. Also we learned that prestressing the wire twice to the >yield point would increase the yield point the third time, but not the >break point. > >From all of this you can see where time enters into the picture. There is >a measureable period of time between when the string comes to the yield >point and the point where it breaks. My impact method obviously >allows me to live somewhere between the yield point and the break point, >because I definitely do have less string breakage now than I used to have. > >Just today I had occasion to tune a piano which is very likely to >experience string breakage during slight pitch raise. This piano had >tuning pins which were very close to the bass V-bar. The pins were driven >to normal depth, however, bass V-bars are higher than treble V-bars on >console pianos. Typical examples of these are: Story & Clark consoles, >Acrosonics (bottom row of pins), Gulbransen spinets and consoles, and >the Chickering (which I did this morning). The string approaches the >tuning pin at such a high angle from the V-bar Agraffe pin that it tends >to climb over the previous coil on the pin. A brand new string can break >easily at that point of greater bend. Before raising the pitch of this >piano, I took the precaution of changing the angle of the coils on the >pin and tapping the string back down under the previous coil. In the past >before utilizing this technique, I have had as many as 4 or 5 strings >break on relatively new pianos. Experience is a great teacher. It's been >years since I have been caught by that trap. Even on harpsichords with >this coil jumping problem I have been able to avoid breakage by using the >sudden impact method. > [Susan] >> I don't see how there is a greater tension with a slow pull, either. There >> is tension all the time, and it gradually increases as the pitch is raised, >> and stays increased as long as the pitch is up. I don't understand how it >> can be higher as the pitch is being raised than it is when it is left at the >> higher pitch, unless there is a sudden jerk, when it would go extra high in >> the tuning pin segment while waiting for the tension to render through. >> [Jim] >There can be as much as 10 to 20 pounds greater tension in the segment >between the tuning pin and agraffe as there is in the speaking length >while pulling pitch up. The only way we judge tension is by the pitch we >hear. We don't hear the pitch of the upper segment. unless it goes BANG! >Oh, I hate that sound, don't you? We usually tune above where we want the >pitch to be in order to get the string tension equalized at pitch in the >two main segments. Then we settle the pitch down, set the pin correctly >and consider it a job well done. In my video tapes, I illustrate how it >is necessary to pull the pitch higher above the target pitch before >settling while using a slow pull method. With the impact method, one does >not need to go as far above pitch to have a stabilized string and pin. >On a vertical piano, more over-pitching is required for a 12 O'clock >tuning position than for a 2: O'clock position. Likewise, a left handed >9:00 O'clock position requires even a higher over-pitching before >stabilizing. Anyone can do this simple test by ear or using a SAT. >Once a person is convinced of this fact, then tuning vertical pianos from >a 2 to 3 O'clock position makes more sense in regard to string breakage >as well as to speed. In the 2 O'clock position, there is less over >stressing and less settling, hence less time, less danger. > [Susan, closing comment] >> I take your word for it that you are breaking fewer strings -- but I >> certainly can't see why! >> [Jim] >I hope some of the above will help you to see why. You may post any >of this to the list if you think it will help others. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ As you can well imagine, I think it will help others (!) so I've posted it _all_ to the list. Thanks, Jim. Susan Susan Kline skline@proaxis.com P.O. Box 1651, Philomath, OR 97370
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