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integral bass bar


nathan slobodkin
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2 hours ago, Mark Norfleet said:

I have varnished two part stacked plywood dams that I've been using for decades.  They aren't fool proof, but they save me a LOT of time over what I used to do.

Yup.  Nothing wrong with them... used to do something similar... and knowing you, I bet yours are very nice!  :)

I switched to rigid insulation because it allows me to make a very accurate cast quickly, following the outline and corners closely, by cutting out the tracing on the bandsaw... and it releases from the Tecstone or plaster easily once the cast sets up. With Tecstone 1 1/2" stock works very well for most casts. 2" for most cello applications.

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The cross grain bend strength of spruce is very low and I believe the one piece carved in bass bars follow straight along the grain lines thus the top is inherently weak along the bass bar.

I believe the glued on bass bars are installed at an angle to the grain such that a bar spans several grain lines.  This might reduce the incidence of bass bar cracks developing in the top plate.

 

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1 minute ago, Marty Kasprzyk said:

The cross grain bend strength of spruce is very low and I believe the one piece carved in bass bars follow straight along the grain lines thus the top is inherently weak along the bass bar.

I believe the glued on bass bars are installed at an angle to the grain such that a bar spans several grain lines.  This might reduce the incidence of bass bar cracks developing in the top plate.

 

I'd suspect you might be right, assuming they do follow the grain.  I recall a Kennedy 'cello withe grain of the top running off at a slight delta on the top... the glued in bar that was in it ended up following that grain rather closely (it was installed at what would be considered a correct angle otherwise).  It had a long crack on each side of the bar.

There was a late 19th/early 20th century Turin maker who produced instruments with carved bars. I've seen two that survived intact. He also glued in a pillar type support on the chin side of the lower bout rib.

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53 minutes ago, JacksonMaberry said:

You know, I had the same thought at one point. I soaked out a sprung bar I had just put in, and checked it when it and the plate had dried. 

Spring was still there. 

I was mostly thinking of after it had been in place for quite a while. I would also wonder what soaking it out and then re-drying it would do. The way to  test it might be to put a piece of release film on the inside of a plate, under a sprung fitted bar, and “glue” and clamp it. Remove the clamps after it dries and sits for a while, and see if the spring is still there. I might try that just for laughs.

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12 minutes ago, FiddleDoug said:

I was mostly thinking of after it had been in place for quite a while. I would also wonder what soaking it out and then re-drying it would do. The way to  test it might be to put a piece of release film on the inside of a plate, under a sprung fitted bar, and “glue” and clamp it. Remove the clamps after it dries and sits for a while, and see if the spring is still there. I might try that just for laughs.

Let me know what happens if you do! Always interested in these types of things. 

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On 9/27/2022 at 11:38 PM, JacksonMaberry said:

 

It is impossible to tell if a bar was fit with or without spring unless you have removed it. 

 

Several times in this thread, it has been emphasised that one cannot tell if a bar has been fitted with spring, unless one has removed it. Over the decades, I have gradually accumulated a drawer full of bass bars that I have soaked out of various fiddles. There are all sorts of lengths shapes and sizes, but one thing that they all have in common is that they, even after they have dried out a couple of days, do not “fit” at all, so that any pronouncement if they had had spring or not would have been reading tea leaves. Also the marotte that they had to fit flawlessly was definitely NOT shared by our 18th C colleagues, one can see plane and knife marks etc., and “near enough” was clearly the order of the day.

I remember my father having a period where he was convinced that fitting bars “on the slab” i.e. with the annual rings at 90° to the normal was the way to go. I thought “oh bloody hell, another nutjob”, but later I removed one and replaced it with a “normal” bar, and regretted it, since I found that it had sounded much better before I fiddled with it

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3 hours ago, jacobsaunders said:

Several times in this thread, it has been emphasised that one cannot tell if a bar has been fitted with spring, unless one has removed it. Over the decades, I have gradually accumulated a drawer full of bass bars that I have soaked out of various fiddles. There are all sorts of lengths shapes and sizes, but one thing that they all have in common is that they, even after they have dried out a couple of days, do not “fit” at all, so that any pronouncement if they had had spring or not would have been reading tea leaves. Also the marotte that they had to fit flawlessly was definitely NOT shared by our 18th C colleagues, one can see plane and knife marks etc., and “near enough” was clearly the order of the day.

I remember my father having a period where he was convinced that fitting bars “on the slab” i.e. with the annual rings at 90° to the normal was the way to go. I thought “oh bloody hell, another nutjob”, but later I removed one and replaced it with a “normal” bar, and regretted it, since I found that it had sounded much better before I fiddled with it

Sometimes I just want to "like" a post. :)

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On 9/27/2022 at 11:38 PM, JacksonMaberry said:

It is impossible to tell if a bar was fit with or without spring unless you have removed it. 

Sometimes one can see a sort of valley in the belly surface at the ends of the bar, and defintely knows if it starts to rattle after glue failing.

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15 hours ago, Jeffrey Holmes said:

I'd suspect you might be right, assuming they do follow the grain.  I recall a Kennedy 'cello withe grain of the top running off at a slight delta on the top... the glued in bar that was in it ended up following that grain rather closely (it was installed at what would be considered a correct angle otherwise).  It had a long crack on each side of the bar.

There was a late 19th/early 20th century Turin maker who produced instruments with carved bars. I've seen two that survived intact. He also glued in a pillar type support on the chin side of the lower bout rib.

The one that inspired this topic was straighter than I normally do but did cross the grain a bit. Not 100 percent  parralel.

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9 hours ago, jacobsaunders said:

I remember my father having a period where he was convinced that fitting bars “on the slab” i.e. with the annual rings at 90° to the normal was the way to go. I thought “oh bloody hell, another nutjob”, but later I removed one and replaced it with a “normal” bar, and regretted it, since I found that it had sounded much better before I fiddled with it

The bending stiffness of a bass bar doesn't care which way it is cut.  This can be easily checked by cutting a precise square cross-section bar and checking the taptone each way.

There might be some advantage of a bar cut "the wrong way" in that it should be stiffer in shear and vertical punch loads.  The idea that the annular rings act as "beams" is overpowered by the microscopic misalignment of the cell walls (the walls are better aligned in the "slab cut" bar). 

I use either cut, as I don't think it's a big deal.  Traditional cut is just a bit easier to fit.

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On 9/26/2022 at 9:01 AM, jacobsaunders said:

Yes, I did

Isn't this more work than glueing a bass bar on afterwards?

.... I realised after I read the responses that my question was obsolete. I still wonder why it was done so much? I assume that they got very quick at it.

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58 minutes ago, jacobsaunders said:

Spruce is far more bendy “on the slab” than it is with annual rings standing up, sod “tap tones”

If you're talking about crossgrain bending of tops, that's right.  Longitudinal bending doesn't matter, and that's what a bass bar is.  Top plate taptones are a combination of cross and longitudinal bending (and in-plane stretching), thus all affected by crossgrain stiffness, so a slab top will tap lower.  I don't know that anyone cares about the crossgrain bending of a bass bar.

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1 hour ago, Anders Buen said:

Don is right, the youngs moduluses of spruce in radial and tangential direction are fairly similar.

That's not quite right... the radial modulus is definitely higher than the tangential.  However, for pure longitudinal bending stiffness, it's the along-the-grain modulus that dominates, and it's the same no matter which way the other grain direction is cut.

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11 hours ago, uguntde said:

Isn't this more work than glueing a bass bar on afterwards?

.... I realised after I read the responses that my question was obsolete. I still wonder why it was done so much? I assume that they got very quick at it.

Indeed, a carved integral bar is more work than sticking one in afterwards. This tells us that it was the style and tradition of the area, and not a time saving short cut, as often ridiculously claimed. It finally became extinct when they started using milled plates. You are quite right, if you spend decades doing something day in, day out, you get pretty good at it

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1 hour ago, Marty Kasprzyk said:

Notice how cracks start at the sharp corners of the saddle's rectangular cut out.

I believe an elliptical cut out would be better. 

Interestingly this violin doesn’t have a “rectangular cut out” but an innovation that I hadn’t seen before, and wrote about here https://maestronet.com/forum/index.php?/topic/339564-seidel/&do=findComment&comment=789240

Perhaps we should all bow to the obvious and award David with the 1st. prise for his innovation, which is evidently head & shoulders above anything else:) https://maestronet.com/forum/index.php?/topic/328110-look-ma-no-saddle/


 

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22 hours ago, Don Noon said:

That's not quite right... the radial modulus is definitely higher than the tangential.  However, for pure longitudinal bending stiffness, it's the along-the-grain modulus that dominates, and it's the same no matter which way the other grain direction is cut.

No, but not far from. The tangential direction is about half the radial, while both are 5-13% ish of the longitudinal. So for all practical means, quite similar. The twisting modulus is also close to the radial modulus for spruce. Of course, there are variations from piece to piece.

i think the bending stiffnes goes as the modulusˆ1/2 so the numers does not need to be very precise for practical assessments.

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26 minutes ago, Anders Buen said:

The tangential direction is about half the radial...  So for all practical means, quite similar.

A factor of 2 is considerable.  Having made a slab-top violin, I can attest to the lowering effect on the taptones.  However, in the assembled instrument, the stiffness of the back and longitudinal stiffness of the top make the floppy crossgrain top not so important.  The B mode frequencies were only slightly low, and it sounded and played well.  Not a screamer, though.

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