Roger Hill

Thanks, everybody. I've made a decision not to decide until I carve that area down closer to finished shape.

Starting the back plate for my next violin and encountered this discolored area along the upper bout. Wasn't apparent until I band sawed the curve. The dark area seems as hard as the rest, just discolored. What do guys recommend as the preferred course of action? One option is just to ignore it and have a violin with a quirk. Another is to toss it and start over with a new plate. Wood is a very nice soft maple from Mario Landry. Also, the wormhole is about 1" deep, .050" in diameter and may impact the flute area.

Loen's normal practice is to show plates from the outside. He says this in his "Path Through The Woods" article regarding the del Gesu graduations.

Didn't intend to come off as having knickers in a knot, only to praise Luis as one of our most helpful contributors and let you, a newbie here, know that he has posted a lot on this subject. Also look for his tutorials on scrolls, corners, etc. Everything Luis posts is helpful and on point.

He has told us a number of times. Just do a search of his posts for keyword "ground". Basically an old varnish formula plus something gritty.........Manfio is VERY free with his help. Just like Michael edit: Well, I was typing as Luis was typing. Think we got it covered.

Didn't mean to ignore you, Torbjörn, you just got caught in the middle of a discussion of purely mathematical esoterica. John mentioned on the other thread the mathematical properties of the curve for the long arch that he is seeking. I thought that my favorite curve, the inhomogeneous catenary, would satisfy what he was looking for. Turns out, I was wrong. Nothing more to it than that. Now, if John wants to dissect your favorite curves, you can egg him on

If anyone would like to see what the curves, slopes and curvature look like , send me an e-mail and I'll send you a (very) small Excel spreadsheet with plots. Be warned, it is nothing fancy. dryfly_6x at msn dot com

Wonderful news, Dean. As soon as she gets her tummy rubbed and finds a dead garter snake, I'm sure she will be her old self again Dogs are resilient, but we all get upset when that resiliency requires help from the vet. Now you know how truly important to you she is, although we sure wouldn't wish this on anyone to figure that out. My wife has been an Old English Sheepdog breeder for 30 years. Been through the misery you suffered way too many times. I've cried like a baby every time we've lost one.

I don't believe the slope is discontinuous, only the second derivative. Substitute x = Xo in the equations above to see this. I will have to study this some more before I am filled with the great certainty I normally exhibit

Hi Dean: Know how much losing a pet can hurt. My thoughts are with you and with your puppy. Hope she is home soon and asking for a tummy rub.

Hi John: H cannot be discontinuous at the join, otherwise and we do not obtain static equilibrium. Thinking about extreme examples with kevlar thread and heavy chain, we could obtain a curve that is for practical people a square function. It will clearly tend to buckle at the bends, which are in reality corners. I suspect that your intuition is in fact, correct and I am wrong. Looking at the article in the link, the author does an integration to obtain y'. If we divide the curve into two sections demarked by Xo, to get the curve for points x <= Xo, we must do the integral up to Xo and y' = sinh(wx/H) the ordinary catenary shape. for x> Xo, y' = sinh (wXo/H + w'(x-Xo)) and you quickly discover that the second derivative is discontinuous at Xo. I Bow to your superior intuition

Thanks, William. This one: http://www.ams.org/notices/201002/rtx100200220p.pdf seems to be on point, although I have yet to digest it. Michael, I am only quibbling over mathematical esoterica. I think John is looking for the smoothest analytic function that looks strad-like. I think the inhomogeneous catenary accomplishes what he wants, but then again, it may not. It certainly is composed of more than one analytic function, or perhaps none at all if I am wrong about each of the chain sections hanging as individual catenaries, with only the join position as determining which two specific catenaries would result from the hanging of a two section chain. I will continue playing with such minutiae in preference to corners, scrolls, beestings, and the things that more normal violin hobbyists obsess over

Continuing from the Marilyn Wallin thread: QUOTE (Roger Hill @ Mar 27 2010, 07:28 PM) I am not convinced of this, John. Each chain section hangs as it would if alone and suspended at the end-points, i.e. the tension is continuous. I don't think you will find a kink there. If so, it would be visible to the naked eye and it is not. Try it and see. John Masters There is no kink because the first derivative or slope is continuous. But is the second derivative continuous? I find that hard to believe if the sections suddenly change density. Well, John, let me expose my thinking regarding catenaries and buckling and second derivatives. If there is an error in my thinking I am sure you and a dozen others will point it out. I am a big boy, I promise to neither stamp my feet nor cry if I am wrong. First, lets consider a chain of length S, attached at the origin at one end and hanging from a second attachment point some distance away at height h. (We are assuming, of course, that s is greater than the distance from the origin.) The shape of the chain is given by y = H/w(cosh wx/H – 1) y’ = sinh w/Hx where H is the horizontal component of the tension in the chain and w is the weight per unit length. If you follow the derivation given here: http://mysite.du.edu/~jcalvert/math/catenary.htm you find that H = (w/8h)(S^2 - 4h^2) And y’ = sinh(wx/H) Substituting for H gives y’ = sinh(8hx/(S^2 – 4h^2) independent of the weight per unit length of the chain, from which I conclude that y” is also independent of the weight per unit length of chain. (But I think we already knew that, all catenaries are created equal and their shape depends only on their length and vertical separation of the ends.) Now, suppose we make an inhomogeneous catenary of kevlar thread of length Sk and and logging chain of length Sl. Attach the kevlar thread to the origin and attach the logging chain to an attachment point at some height h, less than Sl. The logging chain and the kevlar thread each assume catenary shapes which have their slopes continuous, essentially zero at the point of connection. Neither slope has any dependence on its weight/length, only on the vertical separation of it’s end points and length and the same is true of its second derivative. The catenary of the thread thinks that there is a near infinite amount of kevlar thread running outward in order to get the tension it experiences at the attachment point, while the logging chain thinks that it is attached to the origin directly. If we can find some Unobtainium thread, having zero weight/length and infinite E, the inhomogeneous catenary becomes simply the catenary of the chain, displaced to the right by the length of the Unobtainium thread. I just do not see how a discontinuity in the second derivative arises due to the property of all catenaries that the weight/length cancels out of the equations. Another way of saying this is to note that all the forces are proportional to the mass/length. Of greatest importance is the property of the catenary that it attempts to make all loading forces co-linear with the curve of the arch, thereby inhibiting the buckling. If the second derivative were discontinuous, this property would not obtain for the inhomogeneous catenary, but I just don’t see how that happens. Thus, I am still a proponent of the inhomogenous catenary for the long arch shape. If I have a "kink" in my thinking, please explain it to me.

Speaking of rocket science, I used to do studies on the Poseidon nuclear missile systems carried by our submarines. Are you aware that the nose cones on those systems are made of Sitka Spruce? Must be for some good reason.

I wasn't suggesting that anyone was bashing Fry, only that a typo is simply a typo and not reason to cast doubt about the contents. There is plenty to bash about the book. Firstly, the covers are of terrible material and warped right out of the box. Secondly, the printing of some of the figures is equally awful. The printing and binding were done by a publisher which (I believe) specializes in cheap copies of expensive textbooks. I do find Fry's ideas appealing and plan to test them. Fry himself is about 90 and doesn't use a computer. I think no one can blame him for not wanting to hand write a manuscript. While Wali is certainly devoted to his friend (having been a PhD student of Fry's in 1958) I don't find his praise for the violins that far out of line in a world which seems able to either praise or take Nagavary with a grain of salt. Knowledgable readers will know how to measure the words. Without Wali taking the time to do this, Fry's knowledge would probably have been lost. Wali certainly is not going to get rich for his effort. The ultimate judges of the violins are the students and teachers who have his violins, all of which were made by someone else (thus limiting what Fry could do with them) and at very little cost. Just listening to the DVD was an eye opener for me.

I am not convinced of this, John. Each chain section hangs as it would if alone and suspended at the end-points, i.e. the tension is continuous. I don't think you will find a kink there. If so, it would be visible to the naked eye and it is not. Try it and see.

or will they simply be in a configuration in which the forces are balanced? i.e., can't we have a situation in which one set of stress's balances another?

a less revealing photo of the violin: http://karengomyo.com/

it really is

besides being a very pretty violonist, the violin is a strad. Photo gives a very nice reflection around the treble f-hole. Of particular interest to me is the eyebrow running straigt to the narrowest part of the C-Bout. http://chicagoclassicalreview.com/wp-conte...ian_steiner.jpg Sorry 'bout that title. Don't know how to edit it.

Yes, it is all bound up in a neat little package.

After reading on page 39: "Purfling consists of three thin strips glued together with the central black strip made of hardwood (like ebony) and thinner layers of maple (or occasionally willow) on both sides. The whole strip is 1/2 to 1/3 mm thick", I wonder how accurate the other information contained in this book is or how much else is back to front? Cheers, Peter I'm sure you've noticed that the period key (ie, the decimal point) and the slash "/" are adjacent on your keyboard. Such a typo doesn't alarm me much. My comment is that Fry has laid out one scheme, typical of only some of Stradivari's graduation schemes, which works for him and which he explains. I have talked to Jack on a number of occasions and he will tell you in unequivocal terms that the old masters tuned their violins by ear. They knew what to listen for and how to improve what they heard. The DVD simply illustrates his point.

You might want to try a three segment chain, the inhomogeneous catenary, as a perfect example of this

the article is here: http://web.archive.org/web/20040902121230/...onInViolins.htm

I am not skeptical about the importance of material properties, only skeptical about which properties we should be concerned about. I think that when most everyone (but not unanimously) says they hear a difference between their violins in the white, and the same violin varnished, we should have greater concern for the wood/varnish composite. Sam Z says he wants a ground to "glue all those fibers together" and give the sound a "sizzle." Seems to me that there should be a concern primarily for cross grain E when varnished. I suspect that along grain E doesn't change too much with varnish, but I have never measeured it. IIRC, Schleskes measurements of the effects of varinish are only for cross-grain properties.