Cloth linings on cello ribs


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3 hours ago, edi malinaric said:

New thought: Maybe the fabric just serves to hold a thicker layer of HG against the rib and its that thicker HG layer that supplies the major "shrinkage" effect across the rib

That shrink of hide glue is very powerful. I've read that in some craft traditions it's use to put bend into archery bows, and to break and texture the surface of glass.

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3 hours ago, edi malinaric said:

Once the thread are encapsulated in a matrix you are dealing with another material.

Normal fabric is usually the same warp to weft.

However the directional property of the material can vary between warp and weft depending on...

i) the number of threads/inch in each direction.

ii) the material properties of the threads in each direction.

For instance glass, carbon or kevlar  cloths used in laminating a multi-layer panel can feature layers from 50/50 warp/weft (equal properties in both directions) to 90/10 (usually referred to as uni-directional). This allows you to tailor the end-panel  very closely to the applied loads.

cheers edi 

However, taking into account the shrinkage of the cloth, the 45 degree skew would lessen the strength across the grain which is where the strength is an issue.  It lessens the strength due to the fact the strands are shorter....essentially luthier created grain run out.

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I'm not sure that I understand the problem you see. 

I have a template for cello grafts made from a scrap of poplar rib. The heel got cracked so I put a patch over it the next time I was lining a set of ribs. It didn't even bend the 1.5mm thick flat piece of poplar. 

The patches aren't stretched in. They're just laid in like wallpaper. The ribs don't distort much at all. If they did you'd have a problem because they'd be deeper at the blocks, where they're held tight. But when you skim the surfaces to glue on the plates, they're still pretty level.

 

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I am not sure where there is a problem.  We utilize linen when re-enforcing ribs because it adds a great deal of strength while at the same time retains flexibility.  We had a cello where a dancer kicked in a rib, and the only place that had a hole or even a new crack,  was the one place on the cello where the ribs were not re-enforced with linen.  It is my experience that ribs re-enforced this way when new will bulge slightly in the center, which I do not believe is a bad thing.

BTW, in restoration we varnish the linen surface, treat it to render the hide glue non-water soluble, or both to keep the  linen held tight  and not buzz.

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When laminated wooden (core) bows (archery) are backed / topped with fiberglass strips, there are strips that specifically have 45 degree weave and others that have 90 degree. I'm not sure which , but one is supposed to go on back (tension) and the other on the oposite side of laminated bows... the direction of weave makes it more or less elastic.

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10 hours ago, Jerry Pasewicz said:

However, taking into account the shrinkage of the cloth, the 45 degree skew would lessen the strength across the grain which is where the strength is an issue.  It lessens the strength due to the fact the strands are shorter....essentially luthier created grain run out.

Hi Jerry - that is correct - but (these "buts" can be a nuisance) that's only half the story.

OK let's start with the cloth placed with the fibres oriented at 0 and 90 degrees to the crack. Only half the material, the 90 degree fibres, do anything. The fibres at 0 degrees are just along for the ride.

 When we turn the cloth through 45% we also reduce it's strengthening effect of the 90 degree fibres by ~ 30% (actually 29.3% - but 30% is easier to remember).... but (said it was a nuisance) we have brought the other half of the cloth into play.  The other half when moved from 0 degrees to 45 degrees raises its contribution to crack resistance from 0 to ~70%.

Now we have two layers, each supplying 70% of the strength of the one layer at 90 degrees. The patch with two sets of thread running at 45 degrees is 40% stronger than when half of the fibres run parallel to crack and contribute nothing.

Also - being clever luthiers - we have effectively cancelled the run out. :-)

cheers edi

Hi Conor andJerry - I should have read all the threads before answering Jerry's (thread-3) :-)

 OK - are we all agreed that glue/cloth shrinkage plays only a small part in strengthening the ribs but (here we go again) a patch does do the job and makes the rib more resistant to damage from ballet dancers?

cheers edi

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Hi HoGo - yes - but that only occurs in the layer of material that was oriented at 90 degrees to the crack. By rotating the patch 45 degrees you have brought the other layer into play. So you end up with a 40% greater force due to shrinkage than before.

Conor has run a test on that (read his post above) and has shown that shrinkage doesn't seem to be a factor.

It maybe that the- greatest effect comes from the increase in thickness of the rib.

The stiffness of a beam is proportional to the cube of its depth (d x d x d)

If we assume that the fabric/glue combination adds 0.15mm to the rib thickness and the rib is 1.6mm thick. The stiffness changes from 4.096 (1.6 x 1.6 x 1.6) to 5.35 (1.75 x 1.75 x 1.75) which makes it ~ 31% stiffer just due to the greater thickness.

OK - now we are all confused - let's agree that adding patches on the insides of cello ribs does no harm.

cheers edi

 

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56 minutes ago, edi malinaric said:

 

Conor has run a test on that (read his post above) and has shown that shrinkage doesn't seem to be a factor.

It maybe that the- greatest effect comes from the increase in thickness of the rib.

 

OK - now we are all confused - let's agree that adding patches on the insides of cello ribs does no harm.

cheers edi

 

I wouldn't say that I've run a test exactly.

And it's not really about rib thickness. Thin cloth lined ribs are vastly stronger than thicker ones, and much more suple and lively.

If wood cracks it's because fibres have separated, either by tension due to shrinking, or impact. It's common sense that if you glue in a piece of cloth that acts against the stress, the thing won't crack as easily. 

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1 hour ago, edi malinaric said:

Hi HoGo - yes - but that only occurs in the layer of material that was oriented at 90 degrees to the crack. By rotating the patch 45 degrees you have brought the other layer into play. So you end up with a 40% greater force due to shrinkage than before.

Conor has run a test on that (read his post above) and has shown that shrinkage doesn't seem to be a factor.

It maybe that the- greatest effect comes from the increase in thickness of the rib.

The stiffness of a beam is proportional to the cube of its depth (d x d x d)

If we assume that the fabric/glue combination adds 0.15mm to the rib thickness and the rib is 1.6mm thick. The stiffness changes from 4.096 (1.6 x 1.6 x 1.6) to 5.35 (1.75 x 1.75 x 1.75) which makes it ~ 31% stiffer just due to the greater thickness.

The value of fabric reinforcement is less about an increase in stiffness, than it is about keeping more of the rib in compression, when it is deflected from the opposite side (the outside). As Conor mentioned or implied earlier, cross-grain wood is much more tolerant to compressive loads, than tensile loads.

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1 hour ago, David Burgess said:

The value of fabric reinforcement is less about an increase in stiffness, than it is about keeping more of the rib in compression, when it is deflected from the opposite side (the outside). As Conor mentioned or implied earlier, cross-grain wood is much more tolerant to compressive loads, than tensile loads.

 

Hi David - I wish we could all be sitting face to face around a bench somewhere. With long pauses between replies, one loses track of the conversation.

I was trying to limit my input to the mechanics of material orientation - showing that laying the fabric with the warp and weft at 45 degrees improves things by 40%.

The act of adding the material serves to change the properties of the laminate.  The patch improves the tensile strength of the inside face of the rib. Andrew Carruthers' clip of silk-on-ribs demonstrates just how much the tensile strength on the inside has been improved by the silk patch.

I morphed into the increase in stiffness because I was wondering how much the addition of the patch would affect  the acoustic behaviour of the rib and was trying to estimate the added mass and stiffness and it was on the top of my mind.  Just goes to show - one should know when enough is enough.

cheers edi

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2 hours ago, Conor Russell said:

I wouldn't say that I've run a test exactly.

And it's not really about rib thickness. Thin cloth lined ribs are vastly stronger than thicker ones, and much more suple and lively.

If wood cracks it's because fibres have separated, either by tension due to shrinking, or impact. It's common sense that if you glue in a piece of cloth that acts against the stress, the thing won't crack as easily. 

Hi Connor - as I've just replied to David these backwards and forwards notes separated by long gaps are a pain.

What I had extracted from your original post was that repairing your neck template with a patch  showed no distortion due to shrinkage. Re-reading your post, I realise that I had assumed a material patch. Mea Culpa.

cheers edi

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16 hours ago, edi malinaric said:

Hi HoGo - yes - but that only occurs in the layer of material that was oriented at 90 degrees to the crack. By rotating the patch 45 degrees you have brought the other layer into play. So you end up with a 40% greater force due to shrinkage than before.

But is the movement proportional to the force or to the actual shortening of the fibers? I would tend towards the later. Think of bulldozer pushing air balloon. The force of bulldozer is huge but it will move the ballon just as far as a kid would with much smaller force. Of course there is some "resistance" of the wood to deformation where force may get into account, but I can't believe it will change things too much.

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I've been kind of watching this conversation from afar and was wondering why it seemed to keep going on and on. In luthiery there is always the answer to the apprentice's "why" which is "because it works and I said to do it that way". The reason for using linen strips on cello ribs is that it works. The only thing I would add to the discussion is that the strips should be slightly unraveled at the edges to provide a gradual transition of stiffness and I position the strips so they come up the sides of the blocks a few milimeters as well as over lapping the linings to prevent two stiff areas with a weakness in between which could encourage cracking.

Don't over think this stuff folks. Remember, illiterate workmen in leather underpants made most of the violins we hold so dear today.

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51 minutes ago, nathan slobodkin said:

 illiterate workmen in leather underpants made most of the violins we hold so dear today.

Curiously, should you go into the archives, and try to research what the life of these 18thC. artisans must have been like, you will discover long probate inventories that list (and appraise) all of their artifacts, jewelry, furniture, pottery and clothes down to how many handkerchiefs they had, and how much they were worth (second hand), but there is no mention of any underwear at all. Perhaps  leather underpants could be an American Tradition?:)

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1 hour ago, nathan slobodkin said:

I've been kind of watching this conversation from afar and was wondering why it seemed to keep going on and on. In luthiery there is always the answer to the apprentice's "why" which is "because it works and I said to do it that way". The reason for using linen strips on cello ribs is that it works. The only thing I would add to the discussion is that the strips should be slightly unraveled at the edges to provide a gradual transition of stiffness and I position the strips so they come up the sides of the blocks a few milimeters as well as over lapping the linings to prevent two stiff areas with a weakness in between which could encourage cracking.

Don't over think this stuff folks. Remember, illiterate workmen in leather underpants made most of the violins we hold so dear today.

I think if there is something to learn I like to analyze things. Understanding how the cloth lining work helps creating new and prehaps better ways. Of course on "tradiitonal" instruments one will expect the simple cloth reinforcement in the "correct style" but modern maker may try something better (think of the addiitonal SP patches on new instruments and similar tested by modern makers)...

Similar cloth backing has been used in archery and everyone knows it adds strength against breakage but modern methods led evolution to the modern compound bow that is tailored to perfect performance and old traditional bows just cannot compare. (but it is still cool to shoot tradiitonal long bow).

SLightly related to the topic..., I came across use of thin fiberglass backing on simle wooden bows I made for my boys. It's the nonwoven (no-stick) thin tape used on joints of drywood panels. They are 0.1mm thick tape of thin fibers held together with tiny amount of some kind of binder, the 10 meter roll weighs almost nothing. I tested it's performance and glued it onto heavily curly piece of maple rib (slightly tapered but approx. 1.6mm thick, curl going right through) with superglue and tried to bend it - to my wonder I was able to bend the piece dry and cold to diameter smaller than 5cm before it broke. I could glue it on with HHG, but would have to wait till it dries and late rI found the binder can be removed by fire - just light it and iti will burn instantly leaving just clean glass behind (though now very fragile without the binder). Could be good candidate for reinforcement for more adventurous makers... I intend to use it to help bending some highly "uncooperative" rib stock in the future.

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3 hours ago, nathan slobodkin said:

I've been kind of watching this conversation from afar and was wondering why it seemed to keep going on and on. In luthiery there is always the answer to the apprentice's "why" which is "because it works and I said to do it that way". The reason for using linen strips on cello ribs is that it works. The only thing I would add to the discussion is that the strips should be slightly unraveled at the edges to provide a gradual transition of stiffness and I position the strips so they come up the sides of the blocks a few milimeters as well as over lapping the linings to prevent two stiff areas with a weakness in between which could encourage cracking.

Don't over think this stuff folks. Remember, illiterate workmen in leather underpants made most of the violins we hold so dear today.

I don't know why the threads keep going on and on, but I'm glad they do because the gold nuggets of information tend not to come from a single pan.  I did read about slightly unraveling the edges on Triangle Strings https://trianglestrings.com/repairing-rib-cracks/ .  Hearing it from a second trusted source is nice.  Over lapping the blocks was new and important.  The Triangle strings article also mentions coating the dried strips with varnish, (e.g., shellac) to reduce the rate in which the linen takes up and releases moisture.  Thanks for getting frustrated and adding your two bits. :)

-Jim

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On 5/23/2018 at 3:39 PM, nathan slobodkin said:

I've been kind of watching this conversation from afar and was wondering why it seemed to keep going on and on. In luthiery there is always the answer to the apprentice's "why" which is "because it works and I said to do it that way". The reason for using linen strips on cello ribs is that it works. The only thing I would add to the discussion is that the strips should be slightly unraveled at the edges to provide a gradual transition of stiffness and I position the strips so they come up the sides of the blocks a few milimeters as well as over lapping the linings to prevent two stiff areas with a weakness in between which could encourage cracking.

Don't over think this stuff folks. Remember, illiterate workmen in leather underpants made most of the violins we hold so dear today.

FYI: Here is an excellent example of post-modern arrogance. The age of Stradivari saw the most far reaching advances in the advancement of reason, science, technology, mathematics, philosophy, etc. And historians identify northern Italy at the time of Stradivari as an early modern society for a number of reasons, especially the spread of literacy.

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3 hours ago, mrbadger said:

FYI: Here is an excellent example of post-modern arrogance. The age of Stradivari saw the most far reaching advances in the advancement of reason, science, technology, mathematics, philosophy, etc. And historians identify northern Italy at the time of Stradivari as an early modern society for a number of reasons, especially the spread of literacy.

No..your post is. 

 

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17 hours ago, mrbadger said:

FYI: Here is an excellent example of post-modern arrogance. The age of Stradivari saw the most far reaching advances in the advancement of reason, science, technology, mathematics, philosophy, etc.

The knowledge existed, but how much of it trickled down to the common craftsperson?

The knowledge exists today to put a man on the moon, and more, but I wouldn't expect most violin makers, craftspeople, or artisans to know how to do it.

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On 3/2/2019 at 4:19 AM, David Burgess said:

The knowledge existed, but how much of it trickled down to the common craftsperson?

The knowledge exists today to put a man on the moon, and more, but I wouldn't expect most violin makers, craftspeople, or artisans to know how to do it.

I know how to get to space! it doesn't require math and it's legal now! :lol::rolleyes:

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11 minutes ago, David Burgess said:

Even in Michigan. :lol:

I know! I can't wait to move back in a couple years, it's getting way to progressive for me, as apparently "progressive" root word "progress", seems to mean allowing everything to go to hell in a handbasket

Living in Marin I need not go to the city much, so it had been awhile since I'd been there, I was shocked and appalled  by how much it had changed for the worse, like bad, like really , really bad. Beyond the feces, needles and quadrants of homeless, the city streets are in such a bad state that I regretted driving the Cooper and wished I drove the 4x4 as the potholes were so frequent and large that it literally became a slalom course.

So if all goes well, someday in the future, I hope to come back to the big mitten. There is an exodus from this state and there are many reasons why. 

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