Hi David,
Just out of curiosity and if it’s not too much trouble for you: how long is the sounding length of f2# in both instruments?
Have a nice week,
Chris.
Hi Claudio,
For my calculations I use a spreadsheet which shows how many semitones I’m from the breaking point of a string of certain material/diameter/tension. It might seems counter intuitive, but strings with a smaller diameter are stronger than those with a thicker diameter. The smallest diameter I have is 0.19 mm and even then we’re way too close to the breaking point.
Quite a while ago I had similar problems with a horrible harpsichord made from plywood. I had to transform the instrument into a triple transposer (392/415/440) in order to get it restrung using Rose wire.
Have a nice week,
Chris.
Indeed Chris, I have brass wire where the manufacturer-specified strength is quite uniform for large sizes, but then in the small sizes the strength increases. Read somewhere that this is due to surface tension, but if I remember well, Owen once said this was due to the way the molecules arrange when the metal is drawn to produce the string coil.
Incidentally, I find it illustrative to make “destructive experiments” measuring the strength of the wire (better outside the instrument!). You bring the tension up, continuously checking the pitch, and when the string breaks you produce the customary calculations. Of course, there are two different ways of doing this:
- The technical material-science way: the wire is held by one vise or similar apparatus at every extreme, then the vises are separated very slowly carefully measuring both the free length and the sound frequency until the material breaks.
- The harpsichord technician way: you produce a “sonometer” with a plank of wood, replicating everything in a harpsichord: hitchpin, bridge, nut and wrestpin. You install the string and carefully measure the pitch as you very slowly turn the tuning hammer until it breaks. Actually, once you have reached a pitch and the string did not break, you should turn the hammer counterclockwise about 90º, say, then slowly pitch up again: you should do this quite a few times. This will duplicate the string “fatigue” as the string’s curves change in the eye and around the wrestpin.
As we all know, method 2. gives the realistic strength we need. This is always less than the “technical” one (because as we know the string mostly breaks either at the eye because of movements inside it, or else when the string curves around the wrestpin).
Dear Chris
I prefer the simple empirical approach. Like medicos, it’s sometimes too easy for us to become lost in looking for a cure and forgetting the actual patient.
In this case, we have the following:
- A twenty-seven year old brass-strung example of an established Grimaldi-school design from a prominent Parisian workshop.
- The present owner has been frustrated by repeated breakage of Malcolm Rose wire in the treble, and insists you restring using the new P-wire brass.
- Your analysis of the treble string lengths concerns you (and others) about the suitability of brass for this purpose.
I can observe the following:
- The brass-strung instrument is well due for restringing.
- We don’t know the circumstances under which the instrument is kept.
- Nor do we know the tuning or string replacement skills of the present owner.
- Other instruments of the same design and not dissimilar string lengths give good service.
It has been suggested:
- That you reduce the overall pitch to increase your calculated safety margin. (That is relatively easily done if the owner doesn’t desire to play @ A440, making a two-way transposer do A392/A415 instead of A415/A440.)
- That you string the treble in iron. (Which cannot be expected to give the quality of tone required.)
Where the maker of an instrument is still active, it’s nice to give them opportunity for input as Matthew originally suggested. Under separate cover, I’ll post the response I received after forwarding this entire thread to Marc & Julien.
(What Claudio is remembering about “surface tension” is the phenomenon of tensile pickup, a case-hardening and alignment of molecules as wire is progressively drawn down to smaller diameters, and a greater cross-sectional area of the wire is hardened. This can be useful, but not so much in this instance, where your theoretical input of ever smaller brass diameters does not solve your safety margin concern.)
Regards
CB
Hello everyone
Atelier Marc Ducornet would like to give a detailed reply to your question on the stringing of our Grimaldi. Of course, that instrument is designed to be strung entirely in yellow brass at A415, with the keyboard in its central position if three-way transposing.
Note that when strings are made, the wire is progressively drawn through smaller dies until reaching its desired diameter. As well as producing heat, the exterior of the wire is hardened which makes the iron stronger, but the brass not so much. That’s why small diameter iron strings (0.21mm) are very tough and useful for the treble in iron-strung harpsichords, but it also explains why small diameter brass was not used by builders in any local tradition because brass strings under 0.25mm are quite fragile.
Considering this, we decided few years ago to change the stringing schedule of our Italian models, increasing the diameters in the treble. At least 8 new and old Grimaldis were strung with Malcolm Rose wire to this new schedule.
Three things were noted:
- The tonal quality is improved, with more fundamental, power and character. The result is particularly beautiful on instruments more than ten years old.
- String breakage is reduced.
- Tuning stability is increased.
Here is the new schedule for our Grimaldi at A415, using CuZn30 wire. The structure of the instrument is sufficiently strong for the increase in tension. (Take care when making your hitchpin loops in brass wire, because the brass is slippery!)
| Number | Note | mm | inch |
|---|---|---|---|
| 1,2 | GG,GG# | 0.52 | .020 |
| 3,4 | AA,AA# | 0.48 | .019 |
| 5-8 | BB-D | 0.44 | .017 |
| 9-12 | D#-F# | 0.40 | .016 |
| 13-17 | G-B | 0.36 | .014 |
| 18-22 | C-e | 0.33 | .013 |
| 23-27 | f-a | 0.30 | .012 |
| 28-36 | a#-f#’ | 0.27 | .011 |
| 37-57 | g’-d#’’’ | 0.25 | .010 |
Marc Ducornet & Julien Bailly
Hi everyone,
This is just to share my experience.
We owned this model (Grimaldi by Marc Ducornet) for ca 10 years. We used it at home, for concerts and recordings, in different pitches. We replaced it by an earlier model only for stylistic reasons.
There hasn’t been any problem of broken strings, as far as I remember (and I would have remembered, since I’m not used to replace chords : we always had extremely stable instruments (except one I won’t mention here, which was excellent but unstable).
If it helps/confirms Carey’s contribution.
All best
M
Thanks very much Carey for drawing attention to this best-practice principle. I feel it’s not only “nice” but a fundamental ethical question (more on this below), and most of the time also the easiest way to obtain the relevant information, where third- or fourth-person second-guessing just doesn’t do the job.
My story of the day about harpsichord-repair ethics: I think it was Reinhard von Nagel who (at least for a while) made a very useful document available on his website about how-to-act-responsibly-when-repairing-another-builder’s-instrument (I searched for the text later and couldn’t find it again, maybe my fault. No matter). I found it a good and helpful document, especially as I at the time when I first read it (early 2013) just had returned from revising one of my father’s double-manual Franco-Flemish harpsichords which had been sold in perfect condition to a professional organist in the late 1980s, and was re-sold in 2012 in what turned out to be a substantially altered state – ironically the alteration (dated 1992) was signed by someone who at the time of the repair just had set up his own shop after working in the von Nagel studio.
Basically the whole coupler mechanism had been ripped out, and replaced by von-Nagely nylon threaded coupler stickers (however, installed with a too loose fit, and leaning this way or that way, something that never can be seen in V-N’s own instruments). The repairer also apparently didn’t understand why the key-frame was suspended on hooks at the rear to compensate for case-shrink or expansion (Owen has described the principle not so long ago in another discussion), and so found it necessary to cut off all the jacks at the bottom in order to install adjustment screws.
The touch now being heavier because of the added metal screws, the keys were cut thin from below almost to a triangular cross-section. The depth of touch was increased by (imprecisely) cutting the jackrail deeper with a table saw (which at one point went out of alignment, messing up the cut while also getting hot), and a new cloth was stapled in place (some staples colliding with some jacks). And so on.
Some of the work was pretty meticulously done, other parts not at all, and every bit of it was absolutely unnecessary. I remember working three angry days full tilt to get everything at least approximately in order again. I never showed my father (who was still alive in 2013) the pictures I took…(just to be clear, I applied my own principle and actually got in touch with the person who had made the changes, signed and dated them, asking some polite neutrally-phrased questions. He confirmed that he had done all this work, because the keyboard “was a bit heavy”. The removed action parts had not been saved…).
The larger point being, when that “repair” was done in 1992, my dad was still very much alive and active, and could, or rather should, have been contacted to discuss measures like increasing touch-depth, reducing touch-weight, and the underlying basic philosophies about suspending the keyboard, and the question of not using adjustment screws in wooden jacks in a transposing instrument: nothing would have been lost and a (doubtless costly) irreversible action-refurb would have been avoided.
This kind of thing is not only stupid, it also always hurts.
Soo…It’s good to make the community aware of the concept of repair-work ethics and about that there are some thoughts about best practice out there in the more professional end of the pond (doubtless there are variations but still). Thanks again for that!
Cheers,
Tilman
Hello Carey,
Thanks for this information!
Have a nice week,
Chris.
Hi,
Today I broke some strings on the Grimaldi. I very slowly pulled up the f2# and as expected it snapped after barely 1 semitone. Similar results for the e2 & f2 string. All were strung in Rose wire 0,23 mm.
I’ve replaced the f2# with a brand new Rose string (bought in 2019) with diameter 0,25 mm as suggested. To my surprise the string snapped just before I got it up 1 complete tone. Normally it should have done this also after barely 1 semitone.
Assuming that we can get the temperature/moisture at a constant level, this might work. However the instrument will be dragged around for concerts, sit in cold cars, then in warm/dry concert halls. If you’ve tuned in concert halls, you know how this play havoc with the tuning. So knowing the conditions in which this instrument will be used I’m still going to opt for that little bit of extra safety. Now, don’t shoot me 
Have a nice week,
Chris.