I’m about to restring a Hubbard “French” double kit purchased in 1978 and restored in 2000 - with a new soundboard put in, new tuning pins, new strings, of course. There are currently no gap spacers, but I see small indents under the registers. Were these actual gap spacers, or simply supports for the registers? The instrument seemed to work fine without them. Is there any need to replace them?
Thanks.
My 1973 assembly manual states, ‘1/8" x 1" (high) register supports (sometimes called gap spacers) will be required under the slides at b-c, an octave below middle c, and c’‘-c#’', an octave above middle c. Make slips of hardwood 1/8" x 1" and of such a length that they can just be jammed in between the wrest plank and upper belly rail. Put glue on the ends and jam them in position exactly under the strings (standing perfectly vertical) so that they cannot interfere with the jacks. ’ Based on other types of wooden furniture, I would suspect the important reason for these is to protect the registers from gravity.
When I finished in 1974 my Hubbard French double kit, with the provided hardwood gap spacers (which as James say avoid the thin registers from curving downwards), after a while the gap in the centre of the range started to shrink, first 1mm, then 2mm, then more and it blocked the registers!! (most likely because at that time the instrument was strung for A=440Hz, but this issue has been reported for 415Hz as well). I resolved the issue in a way that later kit assemblers also did:
- I let all the strings down an octave, thus reducing their pull to 1/4th.
- After a week or so, the gap had opened and the registers were free again.
- I then inserted new gap spacers. These were made of iron, and were not pushing directly on the soft wood of the belly rail. Instead, I had 1mm-thick brass plates glued to both belly rail and wrestplank, and the iron spacers inserted between them at pressure (a bit of epoxy preventing them from “slilpping away” laterally).
The gap spacers are still there and the gap has not moved for 47 years now.
My Hubbard French kit is ten years younger than those of James and Claudio, but it had the same instructions for installing register supports/gap spacers. After 25 years or so I began having trouble moving the registers, which I attributed to ‘gap creep.’ When Anne Acker restored my instrument recently, she confirmed that the wooden spacers had begun to deform and replaced them with metal ones. Replacing them makes sense to me, both to hold up the long pieces of wood and to prevent the gap shrinking over time.
Claudio, I have the same problem, for the same reason, on the instrument that I am restoring. Are your brass plates wider than the spacer, to distribute the force over a greater area, and are they inset into the wrest plank and upper belly rail?
Indeed, James. The new gap spacers were obtained by sawing to length cast register levers included in Hubbard’s kit, which I did not use in the instrument. The cross section of the spacers is about 12x3mm. The brass plates were about 30mm wide by 40mm high, about 1.5mm thick. They were glued to both wrestplank and upper belly rail, just 1mm below the registers. This way the effect of the metal spacers is indeed distributed to wood areas near to it.
Once the strings were brought up to pitch, during a check years later it was visible how the spacers had sunk very slightly into the brass plates, which had undergone a minimal deformation. However, there is always more than 1mm of total free space in the gap, whereby the three registers move freely.
Many thanks, Claudio, James & David. This instrument has apparently been
working properly without gap spacers, but I will at least put wooden
spacers back in where they were originally.
Claudio,
As you discovered, 1.5mm of brass is too thin. 3mm would have been better (just lose 3mm of length on the spacer itself!), or steel of 1.5mm. Either material should be obtainable from a good metal supply shop, though the minimum quantity will probably be more than you need for one instrument, unless you can find off-cuts.
David
Indeed David, but it worked fine: perhaps 1mm of contraction in decades.
Dennis: I still believe that having a Hubbard kit with no gap spacers or wooden spacers is to invite disaster.
All the best
Claudio
The narrowing of the gap on modern instruments of historical design is interesting, and leads me to ask whether there is evidence of that happening with actual historical instruments?
David
Le 28/08/2023 18:10, David Pickett via The Jackrail écrit :
The narrowing of the gap on modern instruments of historical design is interesting, and leads me to ask whether there is evidence of that happening with actual historical instruments?
Not all modern instruments have gap spacers (or a narrowing gap). So the
real question is rather why some instruments suffer from this problem
and not others. How many historical instruments in playable condition
have either gap spacers or narrowed gaps? I do know that gap spacers
have often been added to historical instruments during their restoration
- for instance the Paris Musée’s 1652 Couchet, but have never seen
mentions of original metallic gap spacers.
Indeed. But if you have a modern instrument inspired in one that, according to my Taskin stringing page, was originally meant for about A=408Hz and you string it at A=440Hz, you are increasing the tension by the ratio squared, that is 16%. If you also have a treble scaling enlarged to improve sound under steel strings, as Hubbard clarified, you have an increase in tension over 20%!
On top of that, the case’s barring design is one by Hubbard and not the original typical French one! So here you have more than one explanation why the problem appears in Hubbard’s kit but not in Taskin’s originals or better copies, or even late Hubbard kits that were improved in this respect.
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I should have added that the instrument will be tuned to 415 and strung
accordingly - I don’t know what its pitch was previously.
With my builder’s hat on, I believe wood gap spacers are fine. Wood is enormously strong in lengthwise compression. There’s no need for metal. As far as European timbers go, nice Beech is fine.
They do serve two functions with one name. One is to stop registers sagging, and one to help brace the gap and keep it wide. But the first is the principal reason. If your gap is imploding then there are large structural problems in the instrument. I am no organologist but I think gap spacers historically were wood.
As to which instruments had them and which not, don’t forget that there is a whole class of harpsichords with box registers that mostly worked fine for very long times.
Out of interest, here is a good summary of properties of wood relating to strength. Mainly what we are looking at in relation to gap spaces is maximum crushing strength.
https://woodbin.com/ref/wood-strength-defs/
Wood has high internal damping and tends to suppress action noise whereas metal can transmit such extraneous sounds, too well.
Here’s Carey Beebe’s video on gap spacers:
Here’s a thread on gap spacer replacement:
With posts from one of our members Fred Sturm.
Thanks, Andrew, for all this. Much appreciated.
Hi Dennis. At 415 I am confident your instrument will be fine with wooden spacers. Do not incur onto future risks without them. And do not insert them straight in place, but have both wrestplank and especially not-that-hard upper belly rail covered by a strip of hard wood against which the gap spacer will press, spreading the tension.
Hi Andrew. Have seen that Beebe used “presses” to open the gap a little before inserting spacers. A good Idea, albeit perhaps a little bit risky. Since anyway these problems arise when first stringing (or re-stringing) a harpsichord, I prefer my method: lowering pitches by an octave, thus tension by a quarter, waiting a week for the case frame to settle thus re-opening the gap a little, then inserting the new gap spacers and only then bringing the strings up to pitch.
Needless to say, in a new instruments gap spacers should best be installed before stringing.
Re Material for Gap Spacers.
Hi Andrew again. You are correct, hard wood is perfectly fine for gap spacers, and historical.
However, when the instrument already has the gap shrunk due to excessive string tension (as in my previous post) and less-than-ideal frame design, and the belly rail is made of not-that-hard birch plywood, and you wish to insert the gap spacer with strong pressure to re-open the gap a millimetre or so, then the metal spacers are most helpful, and they certainly do no harm.
Le 29/08/2023 12:07, Claudio Di Veroli via The Jackrail écrit :
Hi Dennis. At 415 I am confident your instrument will be fine with wooden spacers. Do not incur onto future risks without them. And do not insert them straight in place, but have both wrestplank and especially not-that-hard upper belly rail covered by a strip of hard wood against which the gap spacer will press, spreading the tension.
Thanks, Claudio.
Hi Andrew. Have seen that Beebe used “presses” to open the gap a little before inserting spacers. A good Idea, albeit perhaps a little bit risky. Since anyway these problems arise when first stringing (or re-stringing) a harpsichord, I prefer my method: lowering pitches by an octave, thus tension by a quarter,
Don’t you mean to a quarter (i.e. divide it by four, 25% of the original
tension rather than 75%)?