John, Thank you so much for the detailed explaination. I had no idea that treble strings intentionally slope to the bridge on this type of piano. I am curious if it is reasonable to make the treble string slope angle determinations by comparison to the level of the strings in the lower sections? Gene ----- Original Message ----- From: "John Delacour" <JD at Pianomaker.co.uk> To: <pianotech at ptg.org> Sent: Tuesday, February 03, 2009 1:31 PM Subject: Re: [pianotech] re design > At 19:15 -0800 2/2/09, Gene Nelson wrote: > >><<The typical hammer for note 88 with agraffe is small compared with the >>normal in my experience. I do not necessarily want a larger than normal >>hammer - but at least normal - probably an Isaac hammer or equiv. I >>believe that the typical agraffe hammers at the top note/s are small >>because of strike point issues? Hammer hitting agraffe/plate so they get >>reduced in size? No, I do not like thuddy/knocking sound up there. > > A treble with studs can sound wonderfully strong and clear if the proper > measures are taken and if very careful measurements are taken before > boring and gluing on the hammer heads. I am working on two such pianos at > the moment, a 1924 Bechstein C and an 1865 Kirkman Style 2. Neither piano > had any useful sound in the high treble when I took them in. Both the > Bechstein had and the Kirkman hammers were original. I ordered VFG > hammers for the Bechstein and hammers with a special Wurzen felt for the > Kirkman. In both cases the top hammers, from Abel, were considerably > fatter than the originals, but I'm used to that. They can be slightly > sanded down as needs be. > > Though the Bechstein is well made generally, the metal frame under the > agraffes was very rough. The hammers in the whole top section and a few > below had been fouling the frame and must have done so almost from the > beginning. > > There is one big difference between this Bechstein and this Kirkman. The > high strings on the Bechstein are, most unusually, almost horizontal, and > the strike height is almost uniform throughout the scale, whereas on the > Kirkman they slope up to the bridge at more than 5 degrees, reducing to > about 2 degrees at the first break. The latter configuration is far more > common and requires a lot more thought, as I will explain. > > There is _one_ optimum strike point for the hammer in the extreme treble > and that is roughly 1/16 of the speaking length, say 3mm for note 88. If > the string is struck by the hammer head at a perfect right angle at this > point, you will get the best sound for that hammer head. If you plan to > remove felt from the top of the hammer, this must be taken account of > _before_ the hammers are bored. Better than removing felt to increase > hardness is to inject a little dope round the tip of the moulding. That > said, I have needed to use no dope on either the Kirkman or the Bechstein > and the extreme treble on both is excellent. I hardly ever use dope. > > Now, neither the Kirkman nor the Bechstein ever sounded or behaved as well > as they do now, and the reason is that the original finishers did not take > account of the individual characteristics of the instruments as regards > strike height and string angle. > > There is a good reason for the gradually increasing upward slope of the > strings in the top section of grands that use studs, and that is that it > allows more clearance between the near side of the hammer-head and the > metal frame, since the hammer, in order to strike the string at a right > angle must be cast forward at the same angle as the strings' upward slope. > Thus a wider hammer-head can be brought to strike the string at the proper > point than if the strings were horizontal. I don't think Bechstein ever > quite worked this out; on the older grands the top hammers are > exceptionally thin and spindly in order to clear both the belly and the > metal frame, and by the time they made this 1924 piano they were still > sending out pianos that after a little playing would have problems with > treble tone. > > The boring length should follow the differences in strike height, so that > if the strike height is, say, 200mm at note 40 (strings horizontal) and > the design requires the head to be at 90 degrees to the shank (not by any > means the rule), then for a hammer centre height of 150mm, the bore length > is 50mm if you make no allowance for wear. If the strike height is 196 at > note 85/88, then the bore length must be 47... > > ...But then there is the important question of the _angle_ of the head to > the shank, which must be altered following the slope of the strings. If > in the above example I went ahead and bored all the hammers at 90 degrees, > my top hammers would understrike considerably and not only would I need to > thin the hammer-head to stop it fouling the frame but also I might still > not hit the proper strike point, even at the wrong angle, and tone would > suffer. > > Back to the Kirkman, where the original hammers were bored roughly > respecting the strike heights, but all at the same angle, from the point > where the strings began to slope upwards to the bridge, I gradually change > the bore angle and, when gluing on, gradually increase the length from the > hammer centre to the centre line of the hammer moulding. The result is > that, for a string slope of 5 degrees and a bore length of 50mm, the > hammer head is glued on 4.36mm further out than the head of note 40. > > This is just a worked example, which supposes that the strike line is > exactly parallel to the hammer rail. > > I am sure that if restorers, and even makers, were to learn these things > and put them into practice, we'd hear a lot less about dope and hammer > weights. > > JD > > > > > > > > > > > > > > > > > > > > > > >>That said, I have experimented with larger - or should I say heavier >>hammers in the high treble with very good results. They just need to be a >>bit harder. I have an idea that more hammer mass up there will allow the >>strike point to be lengthened slightly but I cannot prove it just yet. > > >
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