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Michael Darnton

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Would you be willing to comment on the tension or spring that you put into the bar, if any? What is your manner of working this, how do you distribute the tension etc?

If you are willing to tell me this with details, I will post my own method, which is rather elegant to my mind and might be a good alternate method which also works well.

Tonewise, I am happy with my method. It has a bonus in that it provides a way to support the entire work.

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The frame is home made.

I put in bar tension the same as post tension--that is, up to the point where beyond it the force required would suddenly rise a lot. I think we talked about this in another thread. I do this by pressing on the center of the bar, down, and seeing how easy it is for me to make the ends contact. I put most of the curve in the center, and by the time the last couple of inches of bar are reached, the spring is essentially fully gone, and the ends just click down flat, so that there's no tension to kink the top there.

If you look behind the screw and pad on the fourth clamp (that is, the third visible screw) in the gluing picture you'll see a little block of aluminum. There's another on the outside, and they have a screw holding them together so that they clamp the upper wing across the gap of the f-hole so the wing can't move. Otherwise, this method of fitting results in a raised upper wing, pressed up by the bar pressure. That's another little Becker thing that isn't my idea.

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Thanks...... yes Perhaps we did discuss this, but I don't recall. My omission or perhaps it was in a thread before I started reading.

What I do is use a jig that clamps the plate endwise. The jig has a stationary anchor at one end and a hinged plate at the other. Both are slotted for convenient engagement of the plate. The "stationary" end can be moved to different positions for violas or children's violins etc.

The two ends are joined by a piece of all-thread with a wing-nut. I put in the plate and tighten the nut beyond snug to give an extra "sagitta" of 3-5 mm depending on my judgement of how stiff the plate is. The plate bends as it wishes, and I mount the bar with no spring. Somehow this seems as though it would automatically account for something involved with the strength of the arch. I have not noticed any displacement of f-hole wings. But I will be on the lookout in the future.

For Alex......... Here is where I got the idea: You know about Schmidt correctors in the popular Celestron telescopes etc. These have a spherical primary mirror. (I have the 9.5" one and love it.) For both you and Michael, an optics person, you both know that a spherical mirror will require a corrction to spherical aberation. The lens to do this is very slightly deviated from just a planar piece of glass. It used to be very difficult to make this corrector lens. In the mass-produced scopes, the glass is distorted by mounting somehow and pulling a vacuum on one face. The other face is then ground and polished flat. The resulting plate works very well and the result is execellent optics when well done.

I decided to try a similar idea with the top and bassbar. The mounting jig holds the plate in the air, and it is thus easy to work on and also to apply the clamps.

When the jig is removed, the bar is under tension. In addition, it will be in longitudinal tension, which I think may not happen in the conventional method of tensioning. I do not know if this is at all significant. Comments from anybody are certainly welcome.

There is a final thing of interest even apart from the bar fitting. Most tops simply bend away from the longitudinal direction (cylindrical bend). But some bend as a potato chip with the four bouts bending down disproportionately and sometimes a great deal. I am sure this will say something about the graduations and/or arching of the plate. I have found that I like the tone of violins which do not do this, but it is interesting just the same. I would be interested in anyone's opinion on this effect, what it might mean, or if it has any application to judging the working of a plate.

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What I do is use a jig that clamps the plate endwise. The jig has a stationary anchor at one end and a hinged plate at the other. Both are slotted for convenient engagement of the plate. The "stationary" end can be moved to different positions for violas or children's violins etc.

The two ends are joined by a piece of all-thread with a wing-nut. I put in the plate and tighten the nut beyond snug to give an extra "sagitta" of 3-5 mm depending on my judgement of how stiff the plate is. The plate bends as it wishes, and I mount the bar with no spring. Somehow this seems as though it would automatically account for something involved with the strength of the arch. I have not noticed any displacement of f-hole wings. But I will be on the lookout in the future.


Very interesting.

I use a jig like Michael's pix by 24mm plywood in repair works. Your jig plan is so good, so usefull to make and repair. I will and want take it. Thanks.

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Thanks, I think the word "organic" is not only a good description, but also a compliment.

I like to think that it bypasses a lot of things I cannot understand about stresses in the plate caused by a sprung bar. My bending also seems rather parabolic, because of the narrowing of the plate in the center. I think that both methods distribute stresses. These may not be the same, naturally. When the glueing surface is finished, I DO shape the upper part to close to the finished shape. I cut the ends plus top to 5mm as per Becker. The ends have a simple short circular taper for stress relief.

I will say that I have not had any problem with bumps on the outer surface, even with thin tops. I will continue to check for wing displacements, however. I am glad you mentioned this.

If you happen to try the method, let me know your opinion as to tone and whether it gives similar results to your method. As I said, I have no problem with the tone I get, but as I keep repeating, I am not an excellent player.

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I have been following the pictures and text also. I see many things

upon which Michael makes no comment. But I feel gratified in seeing

many unmentioned details that look VERY familiar. One for example is

the use of (band?) saw cuts into the blocks before the rough material

terminates at the socket into which they are set. I do this too. It is

a good insurance that one can use part of the block as the mould,

discarding the waste later.

Michael does not use a full-width mould as I do , so his ability to cut

away excess block may help give him slack to take the ribs out of the

mould. (To put on my back linings, I just slip the sides up the mould

and reclamp at the C-bouts.)

I have only one concern, and that is about string-length. A 14" violin

has a string length 328-330 mm, lets call it 329mm.

Scaling a violin directly to a 16.25" viola gives a string length longer

by a factor of 16.25/14 of course. This gives 381 mm which is 15". I

have even seen violas with a string length of 15.25" For me, this is

excessive. I am an avid violist with short fingers. In addition, many

players wish to switch from violin to viola. I have tried to keep my

string length to 14.5" (approx. 368mm, I work mostly in English units).

To do this, I enlarge the lower bouts a bit and reduce the upper bouts

slightly although not to the extremes of the Tertis model. This helps

the left hand in higher positions also.

I will ask Michael: Have you changed the stop and the neck length beyond

the violin proportions in order to accomodate a shorter string length?

I realize that my methods decrease string tension a bit. This may or

may not appeal to players, but in the shorter 16" versions I have often

used a Stark version of the Dominant string on the C stirng to give a

bit more punch. It seems to even up the balance I have had no

complaints.

Any other views appreciated.

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"For Alex......... Here is where I got the idea: You know about Schmidt correctors in the popular Celestron telescopes etc. These have a spherical primary mirror. (I have the 9.5" one and love it.) For both you and Michael, an optics person, you both know that a spherical mirror will require a corrction to spherical aberation. The lens to do this is very slightly deviated from just a planar piece of glass. It used to be very difficult to make this corrector lens. In the mass-produced scopes, the glass is distorted by mounting somehow and pulling a vacuum on one face. The other face is then ground and polished flat. The resulting plate works very well and the result is execellent optics when well done."

Thanks for that info, it's a very ingenious way to overcome what is normally a very time consuming task, because of the difficulty of correctly configuring a flat plate lens I never attempted one but instead made a Maksutov. Even though its correcting lens has extreme curvatures they are spherical, with the final correctional figuring done on a parabolic mirror, a much simpler task.

I never supposed that any of that type of information would ever be useful in instrument making, so when you mention a parabolic shape I can picture it clearly in my mind.

I suppose it wouldn't be impossible to fit a reflective material to it and check the exact shape using a Ronchi Test, a Foucault Test would be taking it to extremes.

No, I'm only jesting now, it's just that my mind kicked into overdrive as all the different possibilities started running through it from all directions.

Back to violin making mode again, do keep us informed of any other non traditional methods you use, as it shows that there's more than one way to skin a cat.

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Would someone comment on this bassbar tensioning thing: for exactly what purpose. Sacconi

did not mention it in his book, apparently he did not use it. The only experimental work

I know of was done by Croen/Altman. I remember that they said the optimum condition was

0.5mm gaps at both ends of the bar and the tension raised the high pitch output.

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Sacconi may not have mentioned it, but the Sacconi workshop tradition in which I was trained includes it. The renegade in this is Hans Weisshaar, who was the main proselytizer for no tension. . . and as a dealer friend of mine said to me, you didn't find all the great violinists running to him to have their violins set up, did you?

The idea is that the bridge pushes down, and the post and bar push back up to counter that, achieving a certain, admitedly-primitive equilibrium for the middle of the top. I know you wanted something more specific, and the only thing I can say is that players like the results, whatever they are. Perhaps freer response and broader tonal qualities could be guessed.

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I don't have his book--what was his remark? My gut feeling is that it will have exactly as much difference as it initially did in the altitude of the top--that is, *if* the top was pushed up .3mm by the sprung bar, in 100 years, it will probably still be .3mm higher, whatever that height is. That is, this isn't an issue of top collapse, but of tone.

Some people who've removed bars years later say the spring is still there. That doesn't make a lot of sense, until you realize that there isn't just expansion of the top going on, but also a sliding differential fit--like with a bimetallic strip.

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Michael

I would like to add my voice to the chorus of thanks for your viola-making demonstration - it is immensely instructive.

I was hoping someone would take up the following topic before me, because I find it difficult to phrase the questions properly, but here goes:

About the arching over the f-hole to make it "stand out" as you put it, I've noticed this on Strad posters and ascribed it to deforming, but looking again, with many examples showing the side view of the bass side where the soundpost won't account for this, I noticed the lower wing on the Betts (soundpost side) and the Archinto viola. This feature is also very pronounced on the small Gasparo viola and the Maggini violin. On the other hand, it seems to be hardly present on the three del Gesu posters I have (including the Cannone).

So, my questions are these:

1. Is this feature peculiar to Stradivari and some Brescian makers, or is it a feature of other Cremonese makers as well?

2. I've not read the C&J book, but no other reference I have mentions it - why does this seem to be overlooked in modern making, or am I getting the wrong impression?

3. A long shot, but do you think this feature might have any tonal repercussions?

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Stradivari made the most radical and graceful work of the f-holes of anyone, but you can see tendencies of it in any Cremonese maker of that time. One Strad thing is to leave eyebrows of raised wood over the tops of the fs. French makers exaggerated it (Derazey sometimes being one of the worst, I think) and it's really obvious on SOME of their violins. On Strads now it mostly expresses itself as a light halo just over the fs' upper edges that you will notice isn't usually there in, for instance, photos of del Gesus.

The reason you see the lowered wing on the treble side and not on the bass is because the post lifts the center and exaggerates the difference. Think about it a minute and you'll realize the opposite happens on the bass side--the arching has fallen, and now a formerly low wing becomes even. If you don't lower the wing just a bit in new making, you run the risk of a wing above the arching just below it in very short time. It's easiest to see on a real (Stradivari) violin how naturally the lower wing fits with the flow of the plate outside the f-hole, and is discontinuous with what's going on at the inside edge of the f. In fact, the lines of the arching on either side of the f's don't connect at all, in reality--I don't look at posters enough to know how well that comes across in the arching templates.

Sacconi hints at some of it in his figure 107 and the discussion around it, but misses some of it, too. I don't think he mentions the eyebrow that French makers noticed 100 years before him. Sacconi, as I keep saying, is far from perfect.

Del Gesu approaches the problem differently, and does less, with a different type of scoop on the lower wings. Other makers have their own style, too. I suspect you don't see this written about much because it's the stuff experts talk about because it's diagnostic for them and makers don't notice because no one told them it was there, and their schools didn't teach it. I didn't learn this from other makers--Bob Bein was the person who showed me the basics of it, on real Strads. There's nothing about any of it--even Sacconi's comments--in C&J, I don't think, and I don't believe the Biddulph del Gesu books don't deal with the peculiarities of del Gesu wings, either.

I don't think there's anything published about it, though I do know a number of American makers, at least, who are aware of these things and do them.

This is completely visual, not tonal, I think.

I don't know the history of sprung bars, but I do know that it's a quite a bit older tradition than from Sacconi's time. Bagatella advises for it in his book, which was printed in 1783, for instance. Without going to my library, I think Count Cozio may have mentioned it as well...

OK, curiosity gets the best of me--Cozio says a small amount of spring is necessary, but not so much as to distort the arch, whatever that means. I guess my 1mm or so could be called a "small" amount?

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