[pianotech] re design

[Dean May]

John

Your posts are typically wonderful and provide the rest of us with graduate
level continuing education in piano technology. Thank you.

When you say a "treble with studs" are you talking about agraffes in the
treble? 

Dean

Dean May             cell 812.239.3359 

PianoRebuilders.com   812.235.5272 

Terre Haute IN  47802


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of John Delacour
Sent: Tuesday, February 03, 2009 4:32 PM
To: pianotech at ptg.org
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.