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Woodland

Boxy, honky nasal sound.

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1 hour ago, Janito said:

 

With a very strong/thick back and the front thinner in the centre and thicker at the edges in C bout area? 

Sorry, I don't know.

55 minutes ago, GeorgeH said:

It is about proof, Jerry. It is not about the number of anecdotal "examples."

You guys are a terrible influence. The pastor just gave we a withering look for reading and posting in church during the pastoral prayer. :P

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On 1/4/2019 at 7:59 PM, Don Noon said:

An A string with a free length of 330 mm would need a lot more tension to vibrate at A if the free length was 350 mm.

If that's mystifying, I can't help you any further.

It helps to use a basic force diagram.  The fundamental concept is that the sum of forces must be zero, otherwise it would go flying across the room.  Likewise, the torques must sum to zero, otherwise it would spin.

803830744_Forcediagram.thumb.jpg.1067f392e9f7c6d13dd4897442e36c1e.jpg

Pick the black circle, where the top plate meets the neck block.  Sum the moments (torques) about that point, or force S (string) times lever arm X, plus force B (back) times lever arm Y.  The sum must be zero (Y is negative in this case).  Or, solving for B, 

B= S(x/y).  

Now, the sum of the forces must be zero as well, so T= S+B, or substituting in the above expression for B,

T = S + S (x/y), or T = S (1+ x/y)

So, the larger you make X  (the distance the string is away from the top), the larger the forces on the top and back will be.

 

 

I am having difficulty understanding the arrow directions.

The black circle is the hinge point, and as the upstand is increased it acts as a lever pulling on the nut. This would have the effect of compressing the top plate and stretching the bottom plate (assuming good fixture). I understand that Don is an engineer with good mathematical skills, and I would freely admit that I do not understand his formula, but purely from a pragmatic point  of view it appears that arrows B and T should be reversed.

I know that Don will soon put me right, but I find it much easier to understand with reversed arrows. :)

 

 

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21 minutes ago, Delabo said:

I know that Don will soon put me right, but I find it much easier to understand with reversed arrows. :)

S and b are both in tension , t is the fulcrum point. As the fulcrum moves up or down the force required for equilibrium on s and b change. Because s is further from the fulcrum, less force is needed to balance the pull of b. 

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3 hours ago, David Burgess said:

What is your source for the tensions and diameters of gut strings used 300 years ago?

No relevant ones, I definitly stand corrected on the modern to baroque string tension comparation in relation to the modern set up. Chicken/egg or cause/consequence question issues on my side.

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4 hours ago, Jerry Pasewicz said:

Michael this also brings up a good point of discussion.  It would seem that tops would be more likely to deform, and to a greater extent, in the way Don’s drawing illustrates if the post is set too loose.  It is the usual case that when we set a post in an instrument where the post is too loose, the adjustment holds for a very short time....when we readjust, it holds for longer....., and finally one more readjustment usually does the trick for an extended period of time.  If that sounds familiar, it believe it is the same experience as when a new fiddle is strung up (I do not know this first hand as it has been a long time since I made a violin, and I don’t recall being particularly conciencious about these things)

I also follow this approach and that's mainly for new work but I think  it applies to anything that has been taken apart and put back together or even an instrument that has been left without strings on for a while.

(By the way Jerry I don't regard you as a Bogie man at all! I have big respect for what you post here and always seek your post out. )

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8 minutes ago, Melvin Goldsmith said:

I also follow this approach and that's mainly for new work but I think  it applies to anything that has been taken apart and put back together or even an instrument that has been left without strings on for a while.

(By the way Jerry I don't regard you as a Bogie man at all! I have big respect for what you post here and always seek your post out. )

Than my apologies Melvin, and thank you.  I think most of us are on the same side, although the terms and techniques are different.

I have seen this as allowing the top to move back to where it should be...meaning, in the worst of cases when a post is way too short for way too long and maybe even in a very humid environment, the arching tends to flatten around the bridge.  After a new post and several adjustments, the arch is back to where there is no longer a noticeable flattening. 

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21 minutes ago, Melvin Goldsmith said:

I also follow this approach and that's mainly for new work but I think  it applies to anything that has been taken apart and put back together or even an instrument that has been left without strings on for a while.

(By the way Jerry I don't regard you as a Bogie man at all! I have big respect for what you post here and always seek your post out. )

Melvin, I seek your posts out too, and when you have deleted them before I have had a chance to read them, I think that I have missed something significant, regardless of whether or not the posts were ragging on me.

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1 hour ago, James M. Jones said:

S and b are both in tension , t is the fulcrum point. As the fulcrum moves up or down the force required for equilibrium on s and b change. Because s is further from the fulcrum, less force is needed to balance the pull of b. 

I am not sure why you see  the black circle, the fulcrum, (pivot point) moving up and down.

To my mind the black circle is static, and if it was anchored, it would be zero without tension being applied.

I see the tension exerted by "S", the strings, as this is obvious.

As  the black circle is the pivot point, then "B", is have a pulling effect in a normal pulley\leverage situation. The greater the height of "X" , the greater the leverage. :)

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4 minutes ago, Delabo said:

I am not sure why you see  the black circle, the fulcrum, (pivot point) moving up and down.

To my mind the black circle is static, and if it was anchored, it would be zero without tension being applied.

I see the tension exerted by "S", the strings, as this is obvious.

As  the black circle is the pivot point, then "B", is have a pulling effect in a normal pulley\leverage situation. The greater the height of "X" , the greater the leverage. :)

If x changes then t moves follows as well , given string tension remains the same. 

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6 minutes ago, James M. Jones said:

If x changes then t moves follows as well , given string tension remains the same. 

Don does not say what "T" is, but I assume it means "top". I also take "B" to be "back".

If tension is applied to "S" it would compress the top bi-bidirectionally because it is anchored to the tail piece.

For me "T" should have bi-directional arrows.

The arrow "B" would be  in stretching mode and it would pull the carcass diagonally because of the the tailpiece anchorage.

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1 hour ago, Jerry Pasewicz said:

 

I have seen this as allowing the top to move back to where it should be...meaning, in the worst of cases when a post is way too short for way too long and maybe even in a very humid environment, the arching tends to flatten around the bridge.  After a new post and several adjustments, the arch is back to where there is no longer a noticeable flattening. 

I suppose the scenario I hate most is a violin where the back is bulging badly around the post - often this is so bad that it's the highest point on the back.

When this has happened, there is no corrective approach that can be taken - short post, table moves down more, long post, bulge gets bigger. Pressing out the back is the only remedy, and I'm not sure how long that lasts as a fix. I suppose one-piece slab-cut backs are more susceptible, but it can be seen on 2-piece q/s backs too.

Looking at all the discussion we have had about torque and string angle, it does seem that raising the nut/bridge/overstand might contribute to this particular problem, even cause it in some cases. It's surely worth sharing the models and materials which are most at risk.

Or maybe it's just to do with overlong posts ...

 

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6 hours ago, Delabo said:

I am having difficulty understanding the arrow directions.

...from a pragmatic point  of view it appears that arrows B and T should be reversed.

I know that Don will soon put me right, but I find it much easier to understand with reversed arrows. :)

The diagram is of the neck, so I show the forces of other stuff (strings, top, back) on the neck.  If you wanted to look at the forces of the neck on the other stuff, then the arrows would be reversed.

The black circle is put where it is for ease of visualization and simplicity of coming up with the torque formula.  I reality, you could put the black circle on the moon, and the formulas would boil down to the exact same result... you'd just have a lot of very large unnecessary constants to cancel out.

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3 hours ago, David Burgess said:

Martin, bulging of the back  under the soundpost is inevitable (on a conventional violin), and begins the moment a new instrument is strung up.

Yes I'm talking about degree.

If you never pull the bridge back, the bridge will warp and then break. All sorts of potentially bad things are mitigated by care and forethought.

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1 minute ago, martin swan said:

Yes I'm talking about degree.

I would be interested in seeing a model or hearing a theory on what would cause or mitigate this distortion, seems to me it has to do with choice of materials, construction, and the very design.  

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I'm working on it, but based on the thread so far, high nut position, overstand and bridge, and an overtight post ... and enough time.

A weak top would contribute, a slab-cut back also.

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2 minutes ago, martin swan said:

I'm working on it, but based on the thread so far, high nut position, overstand and bridge, and an overtight post ... and enough time.

I could see high bridge.  The high nut, overstand, and flatter string angle over the bridge however I think would lessen the pressure on both the back and the top.  But hey, this wouldn’t be the only time I was wrong today.

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1 hour ago, Don Noon said:

The diagram is of the neck, so I show the forces of other stuff (strings, top, back) on the neck.  If you wanted to look at the forces of the neck on the other stuff, then the arrows would be reversed.

The black circle is put where it is for ease of visualization and simplicity of coming up with the torque formula.  I reality, you could put the black circle on the moon, and the formulas would boil down to the exact same result... you'd just have a lot of very large unnecessary constants to cancel out.

 

I am surprised that you do not view the black circle as the pivot point, as it is the obvious place where the X overstand lever acts upon. If I was going to design a fold-able violin the hinge would go there along with a two piece finger board and clip at the back of the neck. :)

To simplify things I am viewing Martins modified drawing as an old guitar with a tailpiece that I used to own. Its easier for me to visualize it this way. And then to imagine  adding a bridge and start tilting back the neck. Its using this model that I am trying to see which way the string tension energy is dissipated and  the direction of forces indicated by the arrows.

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21 hours ago, martin swan said:

This all makes sense to me, except that the move to a mortised neck joint came well before the arrival of metal or synthetic strings. Roger and others argue convincingly that necks just fail, and that the mortise was a way of facilitating repeated neck jobs. I think by 1800 it was obvious that early violins were not standing the test of time .... since they had already been around for 250 years or so!

Sorry, I can make only one homework at the time so it took me some time. Learning and verifying that my presumption about the lower tension of the baroque strings in comp. with more modern versions was wrong, was just a bit quicker. By that fact alone debating the mortice introduction in relaton to the string tension as I pressumed, is unnecessary and purely academic.

But anyway, (as far as I`ve bein able to read and some time ago learn when studying construction transitions in early Neapolitan mandolin) strings construction changes took place during the 18`th centurie from pure gut to wound gut (dated even earlyer),  twisted strings where introduced, gut and brass, , pure brass.... Those changes where slow but going, through the time where morticed neck on violin was similary slowly introduced, becoming a standard in new making in 19`th c.

Academic as I said, if modern mortice construction isnt a consequence of that.

I though, do wonder about, still just scratching the surface,  about the diferences (or the lack of it as Roger H. is sugesting) between barouque and modern geometry - neck  set/construction, load... 

 

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22 minutes ago, Marijan Radaljac said:

 

I though, do wonder about, still just scratching the surface,  about the diferences (or the lack of it as Roger H. is sugesting) between barouque and modern geometry - neck  set/construction, load... 

 

As I understand it from Don's drawings, the critical issue in relation to the torque on the top block is not the overstand per se, but the distance from the pivot point to the string directly above it.

We have been debating where the pivot point is, and I can't say I'm clear yet whether it's at the top of the table, some arbitrary distance down the top block, or even further down if we accept that the neck join itself really isn't elastic. Where the joint fails isn't really an indication of where the pivot point is, more to do with the relative shear strength of different bits of the neck. But wherever it is, the forces at play would appear to be the same however the neck is constructed. 

So that would leave us with string angle, stop length and string materials - Roger's articles suggested that there is little difference ...

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12 minutes ago, martin swan said:

As I understand it from Don's drawings, the critical issue in relation to the torque on the top block is not the overstand per se, but the distance from the pivot point to the string directly above it.

We have been debating where the pivot point is...

There isn't a pivot point for the torque exerted by the strings, just lots of different forces acting on every part of the instrument. The block is stable if it's properly fixed unless extreme humidity causes problems . If it wasn't stable it would have been designed to be deeper than it is.

This thread would be more useful if we discussed how to adjust the OPs neck projection.

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On ‎12‎/‎25‎/‎2018 at 2:07 AM, Don Noon said:

Fingerboard projection usually drops somewhat over time, so I wouldn't put too much effort into "correcting" it just yet.  Likewise, the sound of a freshly strung up unvarnished instrument is likely to change quite a bit with varnish and some settling-in time... so I wouldn't put too much effort into optimizing it now, either.

I'd say to varnish it, set it up, and play it for a few weeks... then adjust things when you know what you really have.

Why does fingerboard projection drop over time? My belief is that the neck and fingerboard bend gradually into a natural bow and that this makes by far the biggest contribution to the issue.

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Ok, here's a very simplified set of drawings for all the possible combinations of overstand and nut position, allowing for a consistent height of the string above the fingerboard

The drawing is heavily simplified, but I find it extremely helpful. Obviously not to scale, but I think the geometry remains the same. The horizontal line represents not to saddle.

86497311_overstand1.thumb.jpeg.b1960134df2c4a8419d025ab5171296c.jpeg 

And the conclusions are

image.png.0656915de3e0c13abc56a28bcd283b58.png

If anyone can point out any errors I would appreciate it.

The only question I have is whether raising the nut creates more leverage, or whether the measurement above the pivot point is the only relevant one?

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3 minutes ago, martin swan said:

Ok, here's a very simplified set of drawings for all the possible combinations of overstand and nut position, allowing for a consistent height of the string above the fingerboard

The drawing is heavily simplified, but I find it extremely helpful. Obviously not to scale, but I think the geometry remains the same. The horizontal line represents not to saddle.

86497311_overstand1.thumb.jpeg.b1960134df2c4a8419d025ab5171296c.jpeg 

And the conclusions are

image.png.0656915de3e0c13abc56a28bcd283b58.png

If anyone can point out any errors I would appreciate it.

The only question I have is whether raising the nut creates more leverage, or whether the measurement above the pivot point is the only relevant one?

A, Reduced string angle means less leverage/torque.

Forget about pivot point and aim for  string angle  fore and aft and bridge height by tweaking each measurement. In other words Martin, carry on as you did before this thread made everything more confusing than it should be.

 

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On ‎1‎/‎3‎/‎2019 at 1:57 PM, Michael Darnton said:

Well, I only comment that Rene made this comment about bridge height, only,  He didn't mention nut position or overstand. Whatever effect he was discussing, exactly, he was talking only about bridge height. I spent a couple of years thinking about this because it's part of the whole string path issue that's under discussion here. Like it or not, you guys are talking how the strings get pointed where, and what happens when you change something.

As I said, you appear to assume it's about forces acting on the end of the top; Martin hasn't clarified what it means to him. To me, as I said way back on the first page, it's about string angle, and repeating my more recent post, I'm not talking about downward pressure. I'm basically talking about the geometry issue that Don has mentioned, if I understand him correctly. 

But I'm not here to discuss that---I'm trying to get you and Martin on the same page so he can pull his tambourine out of the flames . :-) THEN you can both start trying to beat me with it.

Exactly.

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