Designs on a grand scale

[John Delacour]

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