Julian Cossmann Cooke

Integral bassbars

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OK, I'll explain it in a couple of days, but I want you (plural) to think of yourself.

(Please post your idea here if you want.)

The real reason is very simple but not understood correctly by many makers.

To understand why we put gaps, you should understand why we put the bass bar in the first place.

Of course these two are closely related.

Thanks,

 

Koo Young

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An interesting question to me would be ...

if you came across something like a Giorgio Gatti (Turin C20) with its original integral bassbar, would you re-bar it?

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1 hour ago, martin swan said:

An interesting question to me would be ...

if you came across something like a Giorgio Gatti (Turin C20) with its original integral bassbar, would you re-bar it?

If it ain't baroque...

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On 9/1/2017 at 0:56 PM, chungviolins said:

OK, I'll explain it in a couple of days, but I want you (plural) to think of yourself.

 

Were you thinking that most of us hadn't already thought about it?

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On 9/2/2017 at 9:53 AM, David Burgess said:

Were you thinking that most of hadn't already thought about it?

I don't know what you had thought unless you tell me.

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On 9/1/2017 at 3:09 PM, martin swan said:

An interesting question to me would be ...

if you came across something like a Giorgio Gatti (Turin C20) with its original integral bassbar, would you re-bar it?

It depends. I have, but if I had no good reason to, I'd leave it alone.  

For those who haven't seen one, Gatti integral bars weren't all that neat and tended to be skinny and low.  

As much as I kinda' like the crude little device he put in on the lower rib to support pressure from the chin-rest, I'd most likely pull that out too (if the violin were to be used professionally), but I'd save it.  They come (vibrate) loose and buzz up a storm over time.

395335_10200599658687505_1257187902_n-1.jpg

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I haven't managed to get a night's sleep since chungviolins promised to explain bassbars - I do wish he'd hurry up and post.

I was really hoping for something tonight - I've been sitting at the computer all night waiting - but it's now nearly 1am so I'm going to take a couple of valium washed down with a large glass of Macallan in the hope that I can get a few hours shuteye. 

I will be back here at dawn ...

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1 hour ago, curious1 said:

So I guess you have nothing to say.

That's how it's looking to me, too.

"Curious 1" has compiled a really good track record, and really valuable posts, despite not relying on his real name. While I haven't always agreed with him 100 percent, I consider his posts to be a very valuable resource.

That's some of the sorting process one needs to go through, on almost any forum.

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On 9/1/2017 at 11:56 AM, chungviolins said:

OK, I'll explain it in a couple of days, but I want you (plural) to think of yourself.

(Please post your idea here if you want.)

The real reason is very simple but not understood correctly by many makers.

To understand why we put gaps, you should understand why we put the bass bar in the first place.

Of course these two are closely related.

Thanks,

 

Koo Young

Koo Young,  I am very interested to hear what you have to say about springing/tensioning bbars.  I'm still on the fence about the whole thing.  Thanks!

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I'm sorry that it took me a while.

Bass bar is one of the things which is not fully understood, when we teach/learn violin making , emphasis is usually on "how to" not "why".

(Another being the neck angle/ string angle on the bridge but that's another topic for another time.)

When we string up a violin, a few small changes happen on the violin. (These changes are very small, but unless it's addressed it'll get amplified over the time.)

     1. Finger board goes down.        (Please see the attached diagram. Black lines before strung up, red lines after)

     2. Upper and lower portion of the arches bulges out (goes up) and middle portion of the arch is goes down a bit (at the bridge).

     3. Upper block and lower block area buckles slightly inward.

     4. Back plate bends very slightly but it's much lesser degree than top plate so I didn't indicate.

Without BB, the changes I described above is so great that violin (top and FB) wouldn't be stable.

So the main reason (#1) for installing BB is that it counter-balances the force of the strings, and make the violin shape more stable.

Other reasons are,

    #2 : BB supports the bridge foot area on the bass side (Treble side; sound post).

    #3 : BB connects the upper bout and lower bout, reinforces the breathing mode of the violin.

    #4 : Incidentally BB raises the tap tones of the plate so that we can make the top thinner but this is not the reason we install BB.

 

From above, now we know why we put gaps when fitting BB.

With full string tension, top bends upwards, so when we press down the both ends when we fitting BB,

we simulate the change of the top shape which will occur when the violin is strung up.

But we have to remember that this gap and tension of it will dissipates in time no matter how big gap you put it.

(After BB is shaped after glueing  the tension becomes much smaller than you felt when you were fitting,

and as the wood dries and the whole violin settles the tension will eventually be nonexistent,

so argument of whether we put gaps or how much becomes a moot point after many years.)

 

Koo Young Chung

 

 

 

DSC_5705.JPG

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4 hours ago, chungviolins said:

 

From above, now we know why we put gaps when fitting BB.

I'm still not seeing it, from your explanation.

Sure, by putting in a "tensioned" bar, we can redistribute some loads, reinforcing the central section (with the side affect of causing more bass bar distortion in the upper and lower bouts, which are weaker (since they are trending toward "end grain")). This is distortion which tends to be masked by the presence of the fingerboard and tailpiece. What do you think has been accomplished by shifting the distortion to a different place? Have you really thought this through thoroughly?

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with the side affect of causing more bass bar distortion in the upper and lower bouts, which are weaker (since they are trending toward "end grain")

--->  You are correct, that's why we have to fit very well with tension distributed evenly along the BB, that is BB rolling evenly and fast, when you're doing tensioned BB.

        Tension or bending is more concentrated in the middle area where it is thicker than upper or lower bout area, in the both ends of the BB

       where is more gap than in the middle, there are supposed to little less tension: it just moves more when you are fitting it.

         

       And you're not supposed put too much tension any way.

What do you think has been accomplished by shifting the distortion to a different place? Have you really thought this through thoroughly?

---> As I said in the OP , we fit BB in a slightly deformed curve so that it is better fit and much less tension in the BB itself when it's strung up than that of a top w/o               tension:

      suppose if you fit BB without tension and glued only at the end point (this is just a Gedanken experiment), when this violin is strung up you might see a gap in the           middle because of the bending of top due to string tension.

      I've been thinking this thoroughly for many years now, I'm convinced this is the actual reasoning behind the BB;

      But it's possible that whoever came up with a tension BB long time ago, he might not have realized the reasoning I described in the OP.

 

K Y Chung

 

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Don Noon   
6 hours ago, chungviolins said:

...as the wood dries and the whole violin settles the tension will eventually be nonexistent, so argument of whether we put gaps or how much becomes a moot point after many years.

Not only that, but even the initial deflection from string pressure is high enough that I doubt springing the bar is going to do a whole lot.  I think to really have an effect you would either have to: 1)  Carve the corrective curve into the top to start with, or 2) Use a distorted counterform and clamp the top/bassbar into it with a very huge pressure (and who knows what shape you'll  have when you unclamp it).

Has anyone seen a brand new violin go saddleback right after putting the strings on?  I haven't, so I'm presuming that this is a long-term creep issue.  Then the question is:  how distorted do you want the initial shape to be, and how much distortion do you want to allow and the end, and when is "the end"?  Personally, I'd rather have it distorted later rather than now.

Anyway, from what I know of structures, it appears futile to try to counteract the saddleback tendency by springing the bass bar installation, no matter how fancy you contour the gap.  So I don't.

12 minutes ago, chungviolins said:

we fit BB in a slightly deformed curve so that it is better fit and much less tension in the BB itself when it's strung up than that of a top w/o tension

I would like to see your finite element analysis to confirm this arm-waving reasoning, which I believe is incorrect.

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I'm not even going to mention that there are certain (old, dead) makers who's instruments I make efforts not to spring the bar much if at all... like fitting the bar while the top is in a cast.  OOPPPS... I guess I mentioned it. :) Other's I'll spring just a bit.

Three things (among others) having little to do with the bar itself that I watch carefully for stability when restoring an instrument is the the arch (shape/grads), the integrity of the plane (of the glue surface) of the ribs, and how well the end block surfaces contact the top plate's glue surfaces.  All have a significant effect on stability and resistance to (further) distortion.  If you squint a little, Koo Young's drawing illustrates why I tend to pay attention to these areas.

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11 hours ago, chungviolins said:

 

 

  suppose if you fit BB without tension and glued only at the end point (this is just a Gedanken experiment), when this violin is strung up you might see a gap in the  middle because of the bending of top due to string tension.

I don't think you will. Try the experiment the other way around, gluing the bass bar only in the center, and see what happens.

In the bass bars you've seen which have partially come loose, where did they come loose, and where was the resulting gap?

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4 hours ago, David Burgess said:

I don't think you will. Try the experiment the other way around, gluing the bass bar only in the center, and see what happens.

In the bass bars you've seen which have partially come loose, where did they come loose, and where was the resulting gap?

David,  have you ever tensioned your bassbars?  I'm curious to know if you've noticed any difference in instruments of yours that you've seen years down the road.  My guess is that over the years you've not noticed any unwanted changes to your older instruments that you can attribute to the tension-less Bbar or you would have rectified the situation.

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Don Noon   

If you want to avoid the creep distortion shape shown by the red line, then you will necessarily need to have a distorted original shape shown by the green line (assuming you don't do something like use a super-stiff carbon fiber bass bar).  And, while we're at it, the soundpost side will need some tweaking too... carving in a depression (viewed from the outside) on the back to account for the bulge later on, and carving the top into a complex S-shape to account for the bulge at and behind the post and the depression at and above the bridge foot.  It just sounds like too much diddling to me, and would end up with a funny-looking new instrument so that it could look like a better instrument 300 years from now.  No, thanks.

distorted.JPG.686b22c273819c217642d8aad87cdf1a.JPG

 

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16 hours ago, Don Noon said:

Has anyone seen a brand new violin go saddleback right after putting the strings on?  I haven't, so I'm presuming that this is a long-term creep issue.  Then the question is:  how distorted do you want the initial shape to be, and how much distortion do you want to allow and the end, and when is "the end"?  Personally, I'd rather have it distorted later rather than now.

Anyway, from what I know of structures, it appears futile to try to counteract the saddleback tendency by springing the bass bar installation, no matter how fancy you contour the gap.  So I don't.

 

I have a couple of modern instruments (by well known living makers) which come in and are sunken on the bass side.  One in particular that I have in mind was made by a vocal critic of "springing" bass bars.  These are instruments in the 5+-year old range and I'd be very surprised if the makers made them that way.  I've check the top graduations and they have all been in the normal range, so I can only assume that the bass side of the top is somehow not being adequately supported by the bar.  Whether or not this is because of lack of spring or just a light bar I can't say, but visually the bars look fairly normal.   The sinking is not drastic, but when the bass f hole wing has sunk 1-1 1/2 mm on a newish instrument I tend to wonder about the future of the top.

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On ‎13‎.‎09‎.‎2017 at 4:19 PM, chungviolins said:

I'm sorry that it took me a while.

Bass bar is one of the things which is not fully understood, when we teach/learn violin making , emphasis is usually on "how to" not "why".

(Another being the neck angle/ string angle on the bridge but that's another topic for another time.)

When we string up a violin, a few small changes happen on the violin. (These changes are very small, but unless it's addressed it'll get amplified over the time.)

     1. Finger board goes down.        (Please see the attached diagram. Black lines before strung up, red lines after)

     2. Upper and lower portion of the arches bulges out (goes up) and middle portion of the arch is goes down a bit (at the bridge).

     3. Upper block and lower block area buckles slightly inward.

     4. Back plate bends very slightly but it's much lesser degree than top plate so I didn't indicate.

Without BB, the changes I described above is so great that violin (top and FB) wouldn't be stable.

So the main reason (#1) for installing BB is that it counter-balances the force of the strings, and make the violin shape more stable.

Other reasons are,

    #2 : BB supports the bridge foot area on the bass side (Treble side; sound post).

    #3 : BB connects the upper bout and lower bout, reinforces the breathing mode of the violin.

    #4 : Incidentally BB raises the tap tones of the plate so that we can make the top thinner but this is not the reason we install BB.

 

From above, now we know why we put gaps when fitting BB.

With full string tension, top bends upwards, so when we press down the both ends when we fitting BB,

we simulate the change of the top shape which will occur when the violin is strung up.

But we have to remember that this gap and tension of it will dissipates in time no matter how big gap you put it.

(After BB is shaped after glueing  the tension becomes much smaller than you felt when you were fitting,

and as the wood dries and the whole violin settles the tension will eventually be nonexistent,

so argument of whether we put gaps or how much becomes a moot point after many years.)

 

Koo Young Chung

 

 

 

DSC_5705.JPG

I think one could spend the whole evening fruitlessly arguing about this. For instance if the fingerboard “goes down” or in fact the belly comes up,. Although I get laughed at when I say it, a violin, unromantically viewed, is a wooden box under tension, where the back (longitudinally) gets stretched, and the belly clinched. One result of this, when one has to judge if an antique violin is composite, or if all the bits belong together, is that the belly length should measure roughly a mm or two shorter than the back.

 

There are two (main) schools of thought re. the bass bar. One (for instance Möckel in his book) thinks that the bass bar is a spring, which pushes back against the string pressure transmitted from the bridge,. The other, like me, conceives the bass bar more as a strengthening strut. I think an advantage of an “integral carved” bar, is that it by definition has 0% “Tension”, which is what I always try to achieve when fitting and glueing a new one.

 

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Don Noon   
47 minutes ago, Philip Perret said:

The sinking is not drastic, but when the bass f hole wing has sunk 1-1 1/2 mm on a newish instrument I tend to wonder about the future of the top.

What would you think of a new instrument where the F hole wing was 1 - 1.5mm raised from the rest of the top?  That's the pre-distortion you'd need to have to counteract this problem, and it seems to me that a bit of spring installing the bass bar isn't going to do it.

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30 minutes ago, jacobsaunders said:

 One result of this, when one has to judge if an antique violin is composite, or if all the bits belong together, is that the belly length should measure roughly a mm or two shorter than the back.

 

 

Jacob, I get this, a lot, but always figured it  was that the spruce shrank (along the grain, mostly) more than the back,  especially in that we are releasing that tension (created by shrinkage) every time we pull the top.

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