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TimRobinson

What's more important - weight or thickness?

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I'm finishing off a back and have been following the advice of a well known maker to head for a weight of about 110grams. I have got to 125 but am feeling I'm getting as thin as I dare - and possibly a bit too thin. It ranges from about 2.7 to 4.2mm.

So my question - which is more important?

Or is this the wrong question entirely?

Thanks,

Tim

PS - I should have said this is a violin back I'm talking about. Full size, after the Allard Amati (very much after :) )

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Both :) !

But for some advice about plate weight loss, I find paying attention to the area around the purfling channel, and the edge work to pay off. And the area where the blocks sit.

Basically the glueing area around the plates. This ties in to the long arch shape. All arches, actually.

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Flexibility and rigidity in specific places, and to some extent inertia (which vaguely relates to weight "in specific places") are more important than either weight or thickness, I think. Adjusting weight and thickness are means to arrive at a specific degree of flexibility or rigidity in a specific area. Since flexibility is affected much quicker at a certain stage in graduation than weight by the removal of wood, I think adjusting either weight or thickness without considering the effect on flexibility can easily produce undesirable results.

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Darren said: " I find paying attention to the area around the purfling channel, and the edge work to pay off."

Darren, could you be more specific? Do you mean you make the area thinner there if the top is too heavy, or is it something else? Thanks!!

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There are three basic determinants of vibrations in a violin plate, mass/density, stiffness and damping.

Damping is determined mostly by properties of the wood and the coating. (sealer and varnish)

Mass is also a property of the wood. Before you start to carve it is helpful to know what to expect. If you are starting with a dense/heavy piece of wood then it should not surprise you when the plate ends up heavy. To determine the specific gravity of a piece of wood you dip the end of the board into a bucket of water until it floats, make a mark, then divide the total length by the mark. for Maple this should give you a figure less than 1.0 usually around .55-.65 for Spruce it's .45-.35. You could take a cut off from your maple back and test it, although wood can have some variations in density, this should give you a good 'ball park' figure .

Stiffness is also an inherent property of the wood but on a violin plate is also determined by the arching.

Higher arching results in a stiffer plate, provided that the archings are properly done.

If the arching on your Amati copy are fairly high I would think you could go thinner. But I would follow the advice above and look for any way you can to shave off some weight. When looking to loose weight on a plate I start at the perimeter and work my way to the center.

Oded Kishony

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Hi,

The shape of the fluting at the f's and similarly on the back, will produce a difference.

For a brighter more powerful sound leave the arch flatter and for a darker sweeter Amati sound scoop a little more.

I have accurate drawings by John Pringle, made in 1978 for Hill & Sons, of the Allard Amati.

He shows the archings of the Allard, the back is a high arch and VERY scooped at the C bouts.

I am making a loose copy of the Allard, and I did not use the archings that Amaiti used.

If you like, I can photocopy the drawing by John Pringle, and send it to you.

Regarding thickness of the Allard back, it's odd, just like the belly.

The max thickness is between the lower corners, and it's 5mm !

There are areas down to 2mm near the edges, and generally, I didn't copy those thicknesses.

The front is similarly weird, the max thickness is between the upper corners..... 4mm !

As said above, the ratio of stifness/density to weight is a major factor, but the arching is the most important.

How the maker finds that equilibrium is interesting, but just like everything man made, a violin is not perfect or brittle in the sense that it cannot be changed or bettered somehow. So we evolve to change and make new violins.

Good luck, and I look forward to your results.

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To determine the specific gravity of a piece of wood you dip the end of the board into a bucket of water until it floats, make a mark, then divide the total length by the mark. for Maple this should give you a figure less than 1.0 usually around .55-.65 for Spruce it's .45-.35. You could take a cut off from your maple back and test it, although wood can have some variations in density, this should give you a good 'ball park' figure .

Oded, did you mean divide the mark by the total length instead? If you divide the other way, the result will always be greater than 1.

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Oded, did you mean divide the mark by the total length instead? If you divide the other way, the result will always be greater than 1.

Yes, thanks for the correction. For maple and spruce the number will be less than one, othewise the wood will sink.

BTW my mentor Oliver Rodgers had a simple computer program where you could test for density, stiffness, along, across and transverse to the grain. Oliver has passed away so I don't know what will happen to his program. It only took a few minutes to analyze a joined plate. Perhpas the VSA could purchase the rights from his estate and make it availalbe for free. As I recall he only charged about $10 for it.

Oded Kishony

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Oded,

If your are referring to the Excel program, it can be found at Tom King's website -- http://www.fiddleheadstrings.com/fiddlehea...b_mar06_007.htm Click on the link at the end of the paragraph "Testing the quality of violin wood."

I have used it and still use it. You need to prepare the two sides of the top or back to the same dimensions (roughly). And then joint them and finally take the measurements.

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I'm finishing off a back and have been following the advice of a well known maker to head for a weight of about 110grams. I have got to 125 but am feeling I'm getting as thin as I dare - and possibly a bit too thin. It ranges from about 2.7 to 4.2mm.

So my question - which is more important?

Or is this the wrong question entirely?

Thanks,

Tim

PS - I should have said this is a violin back I'm talking about. Full size, after the Allard Amati (very much after :) )

Thickness, thickness, thickness.

I've never wieghed my plates or the finished violin.

Maybe I'm missing something, and maybe I'll start.

But maybe not.

The arching and the graduations are what matter, IMO.

As with people, the weight of a violin is not a good measure of character.

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Maybe I'm missing something,

You are, you are, you are! You're sitting on a one legged stool. The weights of classic Cremonese instruments are move consistent than the graduations!

Oded

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As with people, the weight of a violin is not a good measure of character.

So... heavy people are not necessarily dark, dense, and hard to hold, and light people are not necessarily bright, airy, and easy to play.

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You are, you are, you are! You're sitting on a one legged stool. The weights of classic Cremonese instruments are move consistent than the graduations!

Oded

Perhaps I am. And I mean that sincerly.

However, I also do not fuss around much with tap tones and eigenmodes.

I do not do my arching from the inside out.

I use willow for my blocks and linings.

I don't seal the inside of my instruments.

Indeed, there are many, many stools that I may be on the verge of falling off of.

I make instruments through an amalgam of all the techniques all the teachers/makers I have worked for or with or under. Not one of them ever weighed any part of the instrument while I was there, or asked me to weigh any part. Maybe I just missed out?

One admonition that stays with me to this day, as I was taking my time with a particular job, "Come on, just get it done, we're not making watches here."

Pehaps my instruments suffer because of the methods I do and do not use. Time will tell.

If you find success with how you work, more power to you.

Now excuse me while I go find a scale. :)

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To determine the specific gravity of a piece of wood you dip the end of the board into a bucket of water until it floats, make a mark, then divide the mark by the total length. for Maple this should give you a figure less than 1.0 usually around .55-.65 for Spruce it's .45-.35.

Oded Kishony

Chris Germain told us about this test when he was here and it is very interesting to do. He said he wouldn't use any belly wood that was over 0.40. One word of caution though... we tested our wood and found it was almost all below 0.40. But we later tested some other pieces and also redid some of the ones we had tested and got quite different results. We realised that the humidity in the workshop was different (very high) and this would change the specific gravity. So you need to either use controlled conditions, or do all your wood at once and just use the figures as a relative measure.

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Good point Alan! I also check both ends because wood can have variation in density. I've even measured two halves of a flitch before joining them and found one less dense than the other!

Oded Kishony

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Good point Alan! I also check both ends because wood can have variation in density. I've even measured two halves of a flitch before joining them and found one less dense than the other!

Oded Kishony

Dear All,

Please accept my apologies for my tardiness in thanking you for the responses. I thought I had replied but my pc clearly ate it. As I had pretty much finished the arching (and I did the outside first - let's not go there again for a while) I'll just have to suck it and see.

We live an learn (hopefully).

The next one I'll measure specific gravity on first.

Regards,

Tim

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Hi Tim,

Not too late, you can still measure the specific gravity of your plate by taking a cut off, like the C bout, and measuring it's SG. This should give you some sense of what your current plate should weigh. And a head start on compiling this information.

Oded

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I think in an other forum, a well known maker, mentioned varying thicknesses depending on density. My personal interpretation is that there should be an optimum weight for every single component and so the overall violin body. I think this coincides with the idea that weight of old master pieces stay in a certain range.

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Hi Selim,

...there should be an optimum weight for every single component.

Yes, an optimum weight depending on it's density. If you take a plate with high density and reduce it to some theoretical optimum weight you will be very dissapointed.

If a light weight violin is what you're after then yu must choose low density materials. Stiffness shuld also be in the equation.

It's like making a glider out of lead (an extreme example to make the point) you could probably thin lead out so that it doesn't weigh very much but it will not hold it's shape.

I've seen examples of violins and plates that were too light and not stiff enough. The result was an instrument that was almost unplayable it was so wolfy and hard to control.

Oded

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Since about 1970, I have kept track of my plate weights and tap tone frequencies. A uniform trend came out that works well for me.

If you google "simple harmonic oscillator" you will find the formula for the frequency in terms of stiffness of a spring connected to a mass (whose mass is "m").

In analogy with this, I define an effective stiffness for a plate using the ring mode frequency. This mode couples the stiffness in both directions and is the main one you hear if you simply hold the plate in the upper bout and tap with a hammer.

For example, if you get 105 grams for a back with a frequency of 365 Hz, frequency squared times mass will give about 14 million. I keep the 1.4 for my records and ignore ten million and a couple of factors of 1/2pi.

For me, 1.2 to 1.4 gives a good violin if the top is right. I aim for this and also a top with .7-.8. My very best violins have had .8 and 1.4. Much over these makes for too much stiffness. Two low, and the violin sounds "flabby." Recently, I find that maple backs are more soft and pulpy in many cases. It is more difficult to keep the stiffness up when trying to reduce graduations. If you want to change graduations, I find it best to do them in proportion to your standard.

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..and reduce it to some theoretical optimum weight you will be very dissapointed.

This is true.

I never advice such thing either. I am trying to connect thicknes==volume to the weight==density.

If a dense wood is in consideration it will be on thin side comparing to lower density wood does.

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According to reliable drawings, the back of the Allard Amati is 5mm between the lower corners.

The front of the same violin is 4mm between the upper corners.

By most people working methods, I'd say that's weird !

Has anyone ever tested the modes on such plates to see if they respond to the testing procedures outline above ?

Cheers.

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Has anyone ever tested the modes on such plates to see if they respond to the testing procedures outline above ?

For every 'violin rule' if you can't find a couple of dozen exceptions, you're not trying :)

Oded

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