At 12:21 pm +1000 7/10/06, Overs Pianos wrote: >Have a look at my 280 concert grand line drawing on the 'for sale' >section of my website. The 280 has a bass bridge designed with >exactly this procedure. It really does make a lot of scaling sense >once you get used to it. Del Fandrich was, to my knowledge, the >first designer to scale basses in this manner. Hello Ron, I've had a look at the drawing for the 280 and it seems the lengths of notes 1 to 24 are roughly as follows: 1:213.5, 2:210.8, 3:208.1, 4:205.4, 5:202.8, 6:200.2, 7:197.7, 8:195.2, 9:192.7, 10:190.2, 11:187.8, 12:185.4, 13:183.1, 14:180.7, 15:178.4, 16:176.2, 17:173.9, 18:171.7, 119:69.5, 20:167.4, 21:165.2, 22:163.1, 23:161.1, 24:159.0 and that the length of the lowest trichord A-25 on the long bridge is 197.0 cm. Can you confirm these figures? If they are right, then a No.22 wire on note 25 will come to a tension of 390 lbs or so, or roughly 90% of the breaking strain. The strings are extraordinarily long and that is a dangerously high tension. As for the covered strings, I have mentioned elsewhere that I never design bass strings to exceed 70% of the breaking strain, for the simple reason that sooner or later they will snap, and often sooner. If I spin 0.15 mm (the thinnest) copper on a No. 20 core for your note 24, the tension will come to about 270 lbs., 72% of the breaking strain. A 0.20 cover will produce a 304 lbs, a dangerous 82% of the breaking strain. It is possible to make safe covered strings for such a scale only up to note 20, and I can't think why you have more than 20 covered string notes maximum on an 8'2" piano. 24 bass notes is what I would put on a 6'9" piano. Even if we risk covering the top 4 notes on the bass bridge, we still have a drop in tension when going from the lowest plain trichord to the first covered bichord; a huge drop in tension where every other piano I have met with has a considerable rise in tension, and for good reason. How is it possible to achieve a good break with such an arrangement? Perhaps I have made a gross error in my estimates of your speaking lengths, so I'd better say no more until you tell me they're about right. Besides that, I have not had the pleasure of seeing your pianos in the flesh, as some on the list have -- but that would in no way affect my analysis of the design principles, which I'm sure you will agree are unusual. JD
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