Last night I subscribed to the Yahoo clavichord group (http://launch.groups.yahoo.com/group/clavichord/, it's moderated, so you have to "apply" for membership), and this evening I did a bit of searching. Here is one detailed result of that search:
Thomas Donahue asked:
> What is anyone's experience with methods used to bypass the twist
of a clavichord caused by string tension?
I will spill the beans and declare my own 'secrets' - actually, not so
secret - here.
1. Build in a twist to start with: i.e., prepare the bottom with a
twist in the opposite direction. Build the case on top of this so that
it, too, starts off with the same reverse twist. If you judge the
amount of reverse twist correctly, the instrument will become
approximately flat when it is strung.
2. On large instruments, let the grain of the bottom boards run
parallel to the string band.
Andrew Nolan said:
> Many makers in historical times used a double layer bottom with one
layer glued obliquely to the other
I am not so sure about the 'many'. AFAIK this was a speciality of C.
G. Hubert. One of his contemporaries refers, I think, to
'improvements' he had made in the design of clavichords, and I suspect
this is one of them. I am sceptical about its effectiveness. Any
comments from those that have made Hubert clavichords?
Owen wrote:
> I've never found [diagonal] braces of much use, actually
They do seem to work well on the large Swedish clavichords. Those
instruments have large soundboxes, so the addition of a 'flying brace'
running from the front right corner ofthe wrestplank to a point inside
the soundbox close to the bottom and just to the right of where the
balance rail ends does not significantly reduce the enclosed volume or
affect the sound. A diagonal keywell brace then runs from this point
across under the keys to a point roughly half-way along the fall-back
rail; if continued in a straight line, it would arrive approximately
at the back left corner of the case. This keywell brace is not
attached to the bottom.
This system, used in conjunction with a thick bottom of dense
pitch-pine, must be adjudged a success in resisting twist. When I
restored a Lindholm clavichord of approx 1792 I was surprised and
pleased to note that before and after restoration it remained
absolutely flat. I'd be interested to hear if Andy Lagerquist's
instruments show the same twist-resistance. As far as I remember, a
somewhat similar system is described in David Tannenberg's MS.
Final point:
I think it is generally a mistake to try to take the twist out of an
instrument once it has occurred. (I was faced with this question when
restoring the 1784 Hoffmann at Hatchlands, which is severely twisted).
As an instrument twists, it actually becomes stiffer as all the joints
etc. jam up closer. If you pull it straight again, you are opening up
all these joints and the clavichord will lose tone and sustain as a
result, and probably be less stable. The aim, I suggest, should be to
stabilise the instrument in its twisted state, and adapt the action to
work well in this state. With severely twisted square pianos, I admit,
this may simply not be practical, in which case I suppose the only
option is to dismantle the instrument almost completely and re-build
it - preferably with a reverse twist!
Peter Bavington
Clavichord Maker
291 Sprowston Mews
LONDON
E7 9AE
Great Britain
Tel. & fax: +44 (0)20 8519 1170
E-mail:
peter@... http://www.peter-bavington.co.uk -------------------------------------------
Fred Sturm
University of New Mexico
fssturm@unm.edu http://fredsturm.net "The true sign of intelligence is not knowledge, but imagination." - Einstein
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Original Message:
Sent: 08-27-2012 23:40
From: Fred Sturm
Subject: repairing a twisted clavichord
I fail to understand what is meant by the "cross brace." The instrument structure is a rectangular box, with what I'll describe as bass side, treble side, front side and back side, the inner rim portions of them being structural, outer rim pretty much just decorative. Those are the only really structural members as it looks to me, slightly stiffened by the plywood "bottom" (not actually all the way at the bottom, but rather about a third up from the bottom of the sides) that holds the keyboard and the belly rail. The words "cross brace" imply being diagonal to me, but maybe I am misunderstanding. I don't think adding some kind of stiffening anywhere would have much effect on tone production: pretty much confined to the soundboard, best I can tell, the sides ("rim) being too massive to contribute anything, and they probably don't rob much. Anyway, all I want is to get it square enough that I can put it on some kind of stand and make it work.
BTW, I got the manual along with this instrument, and the following quote is somewhat amusing:
"I have not included the construction of the case as being critical, because the case as described here is much stronger than it needs to be. Old instruments sometimes had an outer case 1/4" thick and a slim liner (no inner case at all) and on this hung two sets of strings! The instrument described here has an inner case over 3/4" thick and an outer case 1/2" thick, plus sturdy braces. Even if your joints are far from perfect, nothing can happen. The strings pull the case together and "lock" it. And one set of light clavichord strings does not exert much of a pull."
Experience show he was wrong I guess.
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Fred Sturm
University of New Mexico
fssturm@unm.edu
http://fredsturm.net
"The true sign of intelligence is not knowledge, but imagination." - Einstein
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Original Message:
Sent: 08-27-2012 09:23
From: Richard Adkins
Subject: repairing a twisted clavichord
Hi Fred,
When this happened to my Zuckerman (kit I made in HS), I wrote Mr. Zuckerman. He recommended
lowering the tension and then use Angle Iron to reinforce the cross brace.
We had used double thickness Oak flooring and it still warped.
Another friend of mine has one of these, and it is warped as well.
We have another one upstairs, and it is also warped.
I think you can put it in playable condition by fixing the bracing as he recommended.
Others may have had more success. I think you'll always have a bit of warp, just not
as much.
You can put a small block of wood under the high end out of site to balance the case.
Cheers,
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Richard Adkins
Coe College Music Department
Piano Technician
Cedar Rapids IA
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Original Message:
Sent: 08-26-2012 23:32
From: Fred Sturm
Subject: repairing a twisted clavichord
I was just given a clavichord, built from a Zuckermann kit, that has severe case warpage. It is otherwise pretty nice and reasonably well made. I would like to make it a playable instrument, for piano students to find out a little something about what a clavichord is and experience playing one.
I am expecting to take it apart: unstring, remove outer case, try to get the inner case relatively square again, put it back together. I have actually done this once before with reasonable success, but it was pretty much invent as you go, and while it is quite functional, it still has a fair bit of warp to it.
I am wondering if anyone has done this successfully, and if you might have some tips for how to go about it, and how to keep it from twisting as much in future. This one has a turnbuckle installed (original), which seems to have done little or nothing (and tightening or loosening at this point seems to have no effect on the twist) - and I can see why, as it acts on the bottom of the case, and the twisting force is at the top.
The same thing happens on old squares. I have one of those, too, a Broadwood from 1803 or so, with severe twisting as well. I have puzzled over what could be done, and come up with no brilliant ideas (taking it apart and putting it back together is beyond my ambition). Any thoughts or leads on square pianos would also be appreciated.
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Fred Sturm
University of New Mexico
fssturm@unm.edu
http://fredsturm.net
"The true sign of intelligence is not knowledge, but imagination." - Einstein
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