lpr5184

Amati Viola

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lpr5184   

I went through my lining stock and threw out the black willow I bought several years ago from Simeon Chambers. It was bought already cut, flat sawn to size. A quick test in the hands proved to be too much. It snapped like a potato chip.

Second, I tested some flat sawn willow from Old World Tonewood about the same age wood, and it remained flexible and had a good feel to it.

Third, I cut up the old Sitka...quarter sawn and It feels the best.

Like Manfio said, "lutherie is a bit like cooking, a good cook will make a good dinner with the ingredients he has"

I forgot how enjoyable the planing of spruce is. A lovely day in the shop.

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What a shame about your Chambers Willow. I have a whole bundle of it and after reading this I pulled it out and tested several strips. Mine seems to be ok, fortunately, but it was cheap enough that it wouldn't break my heart if I had to throw it out. 

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lpr5184   

It would be a shame if I hadn't checked and used the wood. I'm sure it would not have survived the bending iron. Pretty sure it was black willow. The OWT's willow I think may be a different type. It looks and feels very different. Oh well I'm happy with the Sitka so that's probably what I'll use. After 40 years of drying it still feels flexible and stiff.

-Sorry for the fuzzy photos. It's time to buy another camera.

 

010.JPG

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ctanzio   
21 hours ago, lpr5184 said:

My other thought is making the ribs too stiff is not good either so maybe flat sawn is better or am I over thinking this?

I've seen very few studies on the effect of "rib stiffness" on tonal performance. A general discussion on such a topic would probably be a mix of 1% science and 99% anecdotes. Of course, since the anecdotes would be informed by hundreds of years of viola making, one could argue that a lot of science might not be needed.

FWIW, here is some napkin engineering...

A typical viola rib size is about 40mm deep by 2mm thick. Linings seem to be about 8mm deep and around 2mm thick. So that is about 16mm out of 40mm of the rib reinforced to an additional 2mm thickness. I would suggest the rib is already significantly stiffened by such a lining regardless of the grain orientation. I would be more concerned about a mismatch in expansion and contraction due to humidity cycling. Maybe match the grain orientation of the lining to the ribs so the two have roughly equal stretch and contraction due to humidity?

Violin and viola linings seem over-engineered to me, speaking strictly from a structural loading perspective. The thought process an engineer would use goes something like this...

The glue surface between the rib and the plate represents a geometric discontinuity, and as such will see a local stress concentration near the joint. The challenge is to decide how much reinforcement is needed at the joint to reduce the stress concentration to avoid joint failure.

Let's assume that hundreds of years of viola making has taught us that a rib thickness of 1.3mm will last forever given the expected loads a viola will experience. So now the problem reduces to reinforcing the glue joint so that the stress concentration will be no worse than what the unreinforced rib would experience.

Select a wedge-shaped lining to glue into the joint. When the wedge thickness is about 30% the thickness of the rib (0.3 x 1.3mm = 0.4mm), experiments tell us the stress concentration tends to bottom out at around 2. So if we select a wedge that is 0.4mm thick or thicker, and that reduces the gross stress on the joint by 1/2, then the stress concentration (2) times the joint stress (1/2 the mid-rib stress) will be no worse than the stress near the middle of the unreinforced rib (which we know will last forever).

Basically, we need to double the "effective thickness" of the glue joint to half the stress. The effective thickness of a wedge is about 0.7x its actual thickness. So we want..

0.7xwedge thickness = rib thickness

to double the joint area.

Wedge thickness ~= rib thickness/0.7 = 1.9mm

Standard practice seems to be to make linings about 2mm thick. The question then is why are they made about 8mm deep? If the lining was also made 2mm deep, like a right triangle, standard engineering practice would be satisfied.

 

 

 

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lpr5184   
1 hour ago, ctanzio said:

 

FWIW, here is some napkin engineering...

A typical viola rib size is about 40mm deep by 2mm thick. Linings seem to be about 8mm deep and around 2mm thick. So that is about 16mm out of 40mm of the rib reinforced to an additional 2mm thickness. I would suggest the rib is already significantly stiffened by such a lining regardless of the grain orientation. I would be more concerned about a mismatch in expansion and contraction due to humidity cycling. Maybe match the grain orientation of the lining to the ribs so the two have roughly equal stretch and contraction due to humidity?

I did give some thought about grain orientation of rib and lining and how it would react to humidity cycling. Which is one reason I was leaning towards a quarter sawn lining, being that the ribs are the also quartered.

Another reason I like the Sitka is the dryness and stability. Most of the Sitka in the forests where I live was logged long ago for the aircraft industry. If Sitka is good enough for Boeing then that says something of it's stability. 

Maybe linings are over engineered, that I don't know. It is a subject that I have never really researched or seen discussed much.

Excellent post! Thank you.

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Woke up a bit paranoid about my stock of linings, so I fired up my iron. Feeling a bit better now! Spruce seems like a good choice especially for viola, being lighter. Looks like yours is lovely stuff at that.

IMG_20170330_132749.jpg

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lpr5184   

Yeah that looks like nice stuff you have there Jackson. It's willow you said? Looks very different from the willow I got from Simeon years ago.

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It is, or at least it was advertised as willow from Chambers. I doubt I could tell the difference between willow species so I'm not positive if it's black willow. It is fairly light, but not as light as some spruce lining stock I have. 

I'm not sure I have a preference for lining material, but I do favor willow for blocks. Carves like butter almost irrespective of grain orientation, though I make a point to have the grain run to the corner anyway.

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lpr5184   
2 hours ago, JacksonMaberry said:

 

I'm not sure I have a preference for lining material, but I do favor willow for blocks. Carves like butter almost irrespective of grain orientation, though I make a point to have the grain run to the corner anyway.

Horses of course. I didn't fall asleep through "the grain running to the corner class". I probably skipped school that day and went fishing. Glad I caught the class now. Your never too old too learn eh?

Good stuff

 :^)

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lpr5184   

Judging from the tight bends in Jacksons photo his lining wood appears to be flat sawn. The quarter sawn Sitka I have will not bend that tight of a radius at 2.0 mm thick.

So that tells me that quarter sawn linings are stiffer than flat sawn. Perhaps this is the reason all the linings I have purchased have been flat sawn. It is far easier to bend flat sawn linings. So I wonder what the effect of stiffer ribs will be on my viola?

This leads me to ponder the difference between a flat sawn and quarter sawn back on violas. If flat sawn has more flexibility then quartered,  then is that why a lot of violas use low density/slab cut backs?

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14 hours ago, lpr5184 said:

Horses of course. I didn't fall asleep through "the grain running to the corner class". I probably skipped school that day and went fishing. Glad I caught the class now. Your never too old too learn eh?

Good stuff

 :^)

I wasn't trying to flog a dead equine, sorry. I didn't even know why I did it that way until this thread, I was just following orders.

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I try to drawing instruments to train my eyes.  I drew out the Amati Estense viola when the book first came out, first the form, then the blocks, then the grain lines.  That's when I noticed  the grain lines going to the tips of the corners.  Also the end blocks have the grain lines angled.  Looking at the corner and end blocks with such consistent angle I thought, well this can't be an accident.  Good to have some reasoning on why.

-Jim

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ctanzio   

Mmmmm... Guinness spirit varnish. The secret of the Cremonese golden-brown finish revealed!

Do you use the same rib depth for the entire viola, or do you taper it slightly towards the neck?

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lpr5184   
10 minutes ago, ctanzio said:

Mmmmm... Guinness spirit varnish. The secret of the Cremonese golden-brown finish revealed!

Do you use the same rib depth for the entire viola, or do you taper it slightly towards the neck?

Yes the viola is tapered towards the neck by about 2mm.

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lpr5184   
10 minutes ago, Nick Allen said:

At the upper corners or along the whole instrument?

Hi Nick,  Here are the dimensions out of the book...

Treble side...38.4 bottom block tapering to 36.3 top block.

Bass side...38.4 bottom block tapering to 35.9 top block.

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ctanzio   

Is one side of the ribs kept flat, like the side glued to the back, while the full taper is left on the other side, like the belly? Or is the taper equal along either side of some hypothetical midline?

Assuming the glue surface of the top is carved flat, then gluing the top to tapered ribs would create a slight prestress in the plate. Given the asymmetrical stiffness of the top due to the base bar, that might result in some odd asymmetrical deformation on the plate after it is glued. Is that something that can be picked up by the eye and corrected by additional carving of the plate after it is attached?

The other theory I've seen put forth is that the taper is too small over the length of the instrument to have any real structural function. It is mostly visual. Sort of like how the expansive steps leading up to large temples and museums are subtly curved across the breadth of the steps to make them appear straight by offsetting a visual mirage that would make them appear curved.

 

 

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The Strad way is to taper the belly side gluing surface of the ribs from the top blocks on towards the neck block. Some violins have a straight line taper from the bottom block onward, eventually intersecting the plane of the back. I've never seen a back taper myself, but I imagine that it's not unheard of. Acoustic guitars have a back taper, for reasons structurally. 

To be honest, I've never heard a solid explanation as to why the taper exists. 

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lpr5184   

Hey Evan,

Hope all is well with you and hope you guys made it through the winter OK. My mom tells me they had A LOT of snow in Weiser this year with many buildings collapsing under the weight of the snow.

What are you working on?

 

E

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