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Rib Taper hypothesis #43,759


sospiri
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20 hours ago, David Burgess said:

So far, I am more inclined to go along with Bruce's theories of it being an aesthetic consideration. But I am not prepared to rule out that it might have been some sort of superstition.

It has been entertaining to see people try to arm-wave their way into some idea that taper will do something magical for sound, strength, or stiffness.  The theory I am familiar with says it's all a family-sized package of baloney, and apparently verified by Andreas' accidental experiment.  Aesthetics, left-hand feel, or superstition are what I'm left with, but since it's a traditional and expected feature, that's what I do. 

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On 10/23/2020 at 8:01 PM, Michael_Molnar said:

A bend increases stiffness.

In some situations, it does. In others, it weakens the structure.

15 hours ago, David Beard said:

We don't know why.

Agreed. I am favoring an explanation more along the lines of Jim Bress's "grandma's ham". I have not yet discovered any sonic or player comfort benefits.

Still, I do it, for the same reasons Don has described.... that it's a traditional and expected feature. This is not to claim that I am totally free of superstitions. I can post photos of "orbs" running around in my basement, snapshots from the motion-sensing security camera. :o

I've been hoping that they are "good spirits". :)

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7 hours ago, Don Noon said:

It has been entertaining to see people try to arm-wave their way into some idea that taper will do something magical for sound, strength, or stiffness.  The theory I am familiar with says it's all a family-sized package of baloney, and apparently verified by Andreas' accidental experiment.  Aesthetics, left-hand feel, or superstition are what I'm left with, but since it's a traditional and expected feature, that's what I do. 

The plates are stressed in all three planes are they not?

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Let's remember, not seeing or comprehending a physical reason for something is different than knowing there isn't one.  Completely different.

 

Here is an illustration of one structural difference:

1552374827_ribreduction.thumb.jpg.4120b3a18657bd884acbc2972cec2929.jpg

 

A second physical change is that such manipulations of block and rib heights can alter the relationship between the neck angle and the overall effective plane of the top plate.

 

And, a third physical change if the top block is lowered and the others aren't is that an out of plane torque is applied to the plate.   Some have suggested that the plate would simply bend out under this influence and the torque would fade and vanish with time.  I don't think this is a reliable hypothesis.  While suspecting some change in this direction with time, expecting the effect to full disappear is much less certain.  This is equivalent to saying wooden springs will cease to give resistance with use.  I'm not sure this is a reliable fact.

Regardless of uncertainties about why it might have been done, it also isn't clear when, how, or at times if it was done in Cremona work.

We can point to clear examples in later Cremona makers and say: here the ribs were tapered from the front from the center bouts to the top block.  In other cases we can say the ribs taper, but is it from the back or front?

In many earlier cases, it isn't necessarily clear if there was any taper. And when there is taper, it often appears even along the length of the plate.   Is this because some helpful later restore gave the plate a flat seating by correcting the ribs and blocks?  Or was this an earlier approach to tapering?

There's a lot we can't honestly claim to know on this issue.  

 

We can absolutely say that the idea of tapering from the back in low instruments is very old in North Italian making, and extends beyond the violin family.

1081860117_1500sBassZanettone03376_ZanettoViolaDaGambaBodyView_012.thumb.jpg.910db19737a48ff1ec571ca564b43cd9.jpg

 

 

 

 

725657881_1580BassdaSalo(5).thumb.jpg.7135111e554849b5af28c16752216d64.jpg

 

1464384558_1600cGambadaSaloBresciaG20080606_a05a3b8df7a1e7cc4694jBn4kZIGcicq.thumb.jpg.6310a20f48a8c36c94f218535efb05a3.jpg

 

 

 

 

 

 

 

 

 

 

When did Cremona makers apply a tapered rib concept to their viola and violin making?  I say we don't know.

In the Cremona/Strad molds believed to be dated after 1689, we consistently have the two rib heights marked with a center point and two arcs scribed directly on the molds, as here with the G mold:

g-3.thumb.jpg.5bbe3f8c151a863ae57c57b87b3c3b12.jpg

 

But, in the earlier MB mold, we don't have these two scribed rib guides:

mb-1.thumb.jpg.7a6ed7b90f09251160e5d57af79dd339.jpg

 

Instead, we have this one lone circle:

mb-2.thumb.jpg.7e26d0090afbc7590d9ea1490a51df0a.jpg

 

Is this some earlier alternate way of marking rib height?

The similarly early P B mold overs us both markings:

1917913195_PB.thumb.jpg.4987737f91a2f2975a6f82ff0c020283.jpg

 

I want to show one last mold.  If I haven't confused things, this is the viola mold believed to be from 1672c or earlier.  This mold shows what I think are an earlier and likely original single marking of rib height in the center position of the mold, then two later double sets of rib heights in the newer style.  Likely from later uses of the mold, but with rethought rib heights.

800878125_-00-Violapre1672nems55398.jpg.6b981cb272c64128af17c178d76678e0.jpg

 

To me, these things suggest that the concept of two rib heights may have changed/begun or at least formalized post 1689.  

???

 

 

 

 

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20 minutes ago, David Beard said:

When did Cremona makers apply a tapered rib concept to their viola and violin making?  I say we don't know.

In the Cremona/Strad molds believed to be dated after 1689, we consistently have the two rib heights marked with a center point and two arcs scribed directly on the molds, as here with the G 

To me, these things suggest that the concept of two rib heights may have changed/begun or at least formalized post 1689.  

???

 Hellier Strad from 1679 had a 2mm taper. However, the fact that it wasn't sold until 1734 makes me wonder when it was started and when it was finished?

The fact that he continued to use the taper to me suggests that he had a reason. I don't believe he did it for traditional or aesthetic reasons. He was an innovator as much as a follower.

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On 10/24/2020 at 7:44 AM, uncle duke said:

Scribe your 31.75 mm all around, bring upper ribs down to where they are all even height and then taper from upper belly corner blocks to neck to at least a one mm taper - a little more if you think you can.  Then taper the bottom ribs around a 1/2 mm or leave flat. 

Tapering of ribs is the least of your worries.

So I read thru the Heron-Allen manual about rib taper.  I don't believe Chanot had a full grasp of the situation or old Ed didn't comprehend correctly - the placement of the figures don't make sense.

My interpretation would be to flatten the bottom ribs/blocks first and then proceed to scribe the 31.75 mm all around from upper corner to upper corner.  Go ahead and bring it around some. 

Next is their suggested taper - a measurement difference of 2.381 mm.  I'll tell you now that will be a lot of work making that taper from upper corners to the neck block.  They suggest a two piece, full height mold and taper the mold first.

And be forewarned that if one chooses to purfle first and then try to fit a belly plate to a 2mm taper there will be a greater edge overhang as compared to what it should be - it will be well over 3mm approaching 4mm? when the edge overhang should be around 2.5 or so mm's.

Two choices come to mind.  The Conor method where you use cig papers between the ribs and belly, glue belly to ribs, make the edge overhang adjustments, release the belly from the ribs carefully and then cut for the purfling.

The other method would be maybe another Conor method - simply glue the belly to the ribs, clean them up and then cut for the purfling after the belly is glued to the ribs.

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On 10/25/2020 at 1:33 PM, Jim Bress said:

The tapering of the upper bout ribs always reminds me of the "grandma's ham" story. I see examples of violins where the c-bout ribs appear to have less height than the bouts. Just pictures, so no measurements support what's actually happening, but it's not a good look. For me, this lends some credibility to Buce's hypothesis. I taper the top from the upper blocks, but see no reason to get fussy about a precise amount of taper.  It's just turned into a working practice at this point.

Grandma's ham:

A young girl was watching her mother bake a ham for a family gathering and noticed her mom cutting off the ends before placing it in the oven.

“Mom, why do you cut the ends off before baking the ham?” she asked.

“Hmmm… I think it helps soak up the juices while it’s baking. I’m not sure, though. That’s just the way your grandma always did it, so I’ve just always cut them off. Why don’t you call grandma and ask her?”

So, the little girl phoned her grandma and asked “Grandma, mom is making a ham and cut off the ends before placing it in the oven. She said that it’s probably to help soak up the juices but wasn’t sure. She said you’d know because she learned how to cook from you.”

“That’s true. I do cut off the ends of the ham before baking. But I’m not sure why either. I learned how to cook from my mom. You should ask her.”

So, the inquisitive little girl called her great grandmother and asked “Great grandma, mom and grandma said they learned how to cook a ham from watching you. Do you cut off the ends of the ham to help it soak up the juices?”

The great grandmother chuckled. “Oh, no sweetie. I just never had a pan big enough to hold a whole ham, so I always had to cut off the ends to make it fit.”

So you sayin them Cremonensisians dint have no grasp o fizix?

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9 minutes ago, sospiri said:

So you sayin them Cremonensisians dint have no grasp o fizix?

Not sure how you got to that conclusion from what I wrote. For clarity, I have no idea what the masters we follow were thinking. The ham story reminds me of us following a practice established long ago for reasons we speculate about. 

Which reminds me of another quote:

The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge  

Cheers,

Jim

 

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I don't see my reply to Mr. Darnton for some reason.

Anyways, I need to say that I don't recall tapering more than 1.5 mm - to me it was simply too much extra work making the neck block match the taper for a good gluing surface. 

I'll try the extra 1/2 mm the next time around.

I'm on moderator approval these days Mr. Darnton and others not in the know.  Punching Stross and Dan S, in the nose on a daily basis some years ago didn't set right with a few others apparently.  I can live with it.

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3 hours ago, Jim Bress said:

Not sure how you got to that conclusion from what I wrote. For clarity, I have no idea what the masters we follow were thinking. The ham story reminds me of us following a practice established long ago for reasons we speculate about. 

Which reminds me of another quote:

The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge  

Cheers,

Jim

 

So let's make an effort to at least try and  understand the physics at a basic level.

Don't you think that the taper introduces both tension and compression into the wood in all three dimensions?

Does it matter that it doesn't amount to much force, when the wood, varnish and glue are slowly drying, thereby increasing the tension and compression forces in the belly?

Wouldn't they have been taught this?

 

 

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46 minutes ago, sospiri said:

 

So let's make an effort to at least try and  understand the physics at a basic level.

Don't you think that the taper introduces both tension and compression into the wood in all three dimensions?

I'm not an engineer or a physicist, and it's been a while since I stayed at a Holiday Inn. Force is certainly applied to the wood to bend down to the ribs. I'm not sure tension and compression would be the correct terminology.  Maybe bending moment? It's not important to me because I think the force is both negligible and reduces over time.

Does it matter that it doesn't amount to much force, when the wood, varnish and glue are slowly drying, thereby increasing the tension and compression forces in the belly?

Unverified assertions concerning time, materials, and outcomes. You could design experiments for these.

Wouldn't they have been taught this?

The only working time machine that I know of is owned by Roger Hargrave. However, I don't know when it is right now.

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5 hours ago, Jim Bress said:

Not sure how you got to that conclusion from what I wrote. For clarity, I have no idea what the masters we follow were thinking. The ham story reminds me of us following a practice established long ago for reasons we speculate about. 

Which reminds me of another quote:

The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge  

Cheers,

Jim

 

So what is your take away from the Gramma story?  Since they don't no why they shouldn't keep repeating the tradition?

Maybe that isn't your take away? It isn't mine.

I believe that kind of recipe tradition has the potential to result in 'design by cultural evolution of a tradition'.   

Traditional regional cheeses and meat curings are I think examples of this sort of thing.  The people carrying out the tradition get a certain cheese.  They need to what to do to up hold the tradition.  They need to repeat those things.  But they don't need an accurate understanding of how or why it works. They could have no understanding, or even a fictitious or superstitious understanding.  If they follow the tradition faithfully enough, they get the cheese.

 

In such traditions, and especially in bring such a tradition from one town to another, then some degree of variation might get introduced. If the variation happens to produce acceptable cheese, ok.  If it actually produces cheese that somehow is seen as better, than there is motive to make the new variation the new tradition.  If the cheese isn't as good though, then there is motive to restore the older proper tradition.

Thus, a mindless devotion to repeating and honoring a tradition can lead to the most sophisticated design regime of all: evolution.  This is the kind of design work that today's most sophisticated A.I. is chasing after.

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On 10/23/2020 at 3:19 PM, sospiri said:

I don't  agree with Bruce Carlson's aesthetics hypothesis. If it was done to improve the look, then why not taper all the way from the lower corners. 

If you taper the ribs all the way from the lower corners you will not get the same visual effect. I don't believe that you read my explanation very carefully.

Then again one might question what is happening to the bassbar which is already glued to the inside of the plate.

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On 10/27/2020 at 5:37 AM, uncle duke said:

And be forewarned that if one chooses to purfle first and then try to fit a belly plate to a 2mm taper there will be a greater edge overhang as compared to what it should be - it will be well over 3mm approaching 4mm? when the edge overhang should be around 2.5 or so mm's.

Two choices come to mind.  The Conor method where you use cig papers between the ribs and belly, glue belly to ribs, make the edge overhang adjustments, release the belly from the ribs carefully and then cut for the purfling.

The other method would be maybe another Conor method - simply glue the belly to the ribs, clean them up and then cut for the purfling after the belly is glued to the ribs.

I'd say it's the other way around, as with the rib taper the gluing surface lengthens, so the edge overhang would decrease instead of increase. In addition to the two systems you have already mentioned that would work perfectly to avoid any problems with the edge overhang , there is a third that I use, to be able to put the purfling before gluing the top :

 

Whatever the method, if you trace the outline on the top plate with the taper already in place, it is not possible for the edge overhang to change due to the taper itself.

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13 hours ago, Bruce Carlson said:

If you taper the ribs all the way from the lower corners you will not get the same visual effect. I don't believe that you read my explanation very carefully.

Then again one might question what is happening to the bassbar which is already glued to the inside of the plate.

I'm sorry Bruce, I just don't believe the aesthetics hypothesis. It seems too frivolous and dismissive. For true craftsmen it was never form over function, always form and function together.

Isn't the bass bar being slightly stressed also? And don't the stresses build over time as the wood shrinks, as long as the glue isn't softened in extreme humidity?

I enjoyed reading this article by Ben Hebbert

https://violinsandviolinists.com/2017/12/08/baroque-bass-bars/

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4 hours ago, sospiri said:

I'm sorry Bruce, I just don't believe the aesthetics hypothesis. It seems too frivolous and dismissive. For true craftsmen it was never form over function, always form and function together.

Isn't the bass bar being slightly stressed also? And don't the stresses build over time as the wood shrinks, as long as the glue isn't softened in extreme humidity?

I enjoyed reading this article by Ben Hebbert

https://violinsandviolinists.com/2017/12/08/baroque-bass-bars/

Violins with ribs of equal height all around or with a continuous taper from the end block to the neck block, IMHO, lack a lot as regards the overall appearance of the violin. This however is a totally subjective aesthetic judgement but in Stradivari it is there, and it is that way. We will never know what Stradivari was thinking but to exclude or ridicule it because we can't get a handle on what the function was is ridiculous. In violin shapes form is aesthetic so if you prefer to use the word form ok. I'll let you figure out the function.:lol: I still don't think you read my explanation very carefully.

Ben's article is a good read even if there are a couple of errors (minor).

 

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