with_joerg

Corner bouts for Guarneri 'Kreisler'

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I took the forma for the Guarneri del Gesu 'Kreisler' from this forum and want to produce a mould from it. However, the forma does not show the exact size of the corner bouts. I then found a very simple method here in the PDF (that is written for a Strad): www.darntonviolins.com%2Fviolinmagazine%2Fbook%2Fcorner%20blocks.pdf

Using this methid I arrice a IMHO very small corner blocks. I have then researched the internet and found a number of other methologies that in the end . . . all delivered the same results than the easy method described in the PDF.

Can this be right? Or do I just m insunderstand everything I read?

20171020_212856.jpg

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Welcome to MN.  You should repost this topic in the peg box and you will get more responses.  If you trace around the form and corner blocks 3.5 mm (1 mm for the rib and 2.5 mm for the over hang) you will get a better idea of the final look.

-Jim

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Yes those look a little skinny. 1 Here's a link to a CT scan of the ribs structure.  2. Here is alternative geometric method that I like by Jordan Hess.        https://static1.squarespace.com/static/52eed7f6e4b018731083e3a2/t/53232ea3e4b08487acaee544/1394814627419/CT+Dissection+of+the+del+Gesu+Kreisler.pdf                                      https://docs.wixstatic.com/ugd/8d22cb_5aa617efc1cd4c07b7d95281dad35e1e.pdf

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It is to my understanding that Guarneri used corner blocks that where square to the tangent of the corner. does that make sense?

 

they look fine to me, you could make them bigger, but you would only cut them down to smaller than this anyway, so why bother.

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There is something bumby and irregular about the curve from the cBout coming into the upper corner.

Remember, to smoothly join circle arcs, their point of joining must lay on the line through their centers.

In the Strad and Bergonzi forms, the radius coming from the cbout into the upper corner is always 1/5th the main arc for the bout, and for the lower bout it's 1/4th.  I haven't had sufficient source material to research if Guarneri forms were any different in this regard.

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Guarneri del Gesù corner blocks dimensions are pretty similar to those of Stradivari, the difference is mainly in the wood used that is usually spruce and not willow.

Here the Armingaud-Blanco 1732

59eb18435b681_IHS1732Armingaud-BlancoRibsandCornerblocks.jpg.8c4e19a9f8595b6128194998a94fa7dd.jpg59eb181c1da2e_IHS1732Armingaud-BlancoCornerblocks.thumb.jpg.0998acdb9e1209fe9a0a7072226dbf80.jpg

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I am not sure I understand your question.

 If you are talking about establishing the template for the corners I have been lucky ( lazy?) enough to get them from original instruments but there are geometric construction methods of varying degrees of  complexity and plausibility that will get you there.

If you are referring to how to draw the finished corner on the plate including the overhanging edge then it's helpful to realize that most makers flare the corners a bit wider at the end than the regular margin. Some makers do this evenly and some more toward the C bout but without the flare they will wind up too narrow and shapeless. It is important to see that the flaring be consistent from where it starts to the very end . That is if the flare is going to result in the two sides of the corner becoming parallel the rate of flaring must change smoothly to that end at which point you have arrived at the tangent point to the parallel lines and the cut off point of the corner . If the goal is to hook the corner then you will have some sort of spiral which continues to tighten all the way to the end at some coherent rate of change. I hope that makes sense because I certainly don't have the maths to say it any other way.

If you are taking your form and block template from a tracing of the plates  or a poster than you have to reduce the edge by the required amount all the way around except for the corners where you have to visualize the ribs inside the flared corner and then reduce that by the rib thickness to get the shape of the block.

Hope that helps

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3 hours ago, Davide Sora said:

Guarneri del Gesù corner blocks dimensions are pretty similar to those of Stradivari, the difference is mainly in the wood used that is usually spruce and not willow.

Thanks David for mentioning the spruce wood. Is this special spruce? I mean, the tonewood sources in my geographics area ;) sell fronts, backs and ribs. So the bouts, -- what quality does that need to be? What are the ribs made of? In my area I can buy 'bosnian' ribs. No idea what that really is.

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Leaving aside the qualities of the outline, I have always thought that if the blocks are wide enough to accommodate a graceful trimming back that minimizes the block's impact on the plate's movement, that is what counts.  Others can speak to the acoustic pros and cons of wider blocks.  It seems to me that should be a consideration, perhaps THE consideration, as long as the width provides any minimum structural support that is required.  Disclaimer: at this stage, much of my making is "informed" by theories rather than extensive experience.

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2 hours ago, nathan slobodkin said:

If you are referring to how to draw the finished corner on the plate including the overhanging edge then it's helpful to realize that most makers flare the corners a bit wider at the end than the regular margin. Some makers do this evenly and some more toward the C bout but without the flare they will wind up too narrow and shapeless. It is important to see that the flaring be consistent from where it starts to the very end .

Thanks for your reply. As a non-native speaker I must admit . . . that I do not know what 'flare' means in this context. Do you mean they make the blocks 2mm or so bigger than indicated by the geometric shape? Would you have a handsketch that you could share?

Edited by with_joerg

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7 hours ago, with_joerg said:

Thanks David for mentioning the spruce wood. Is this special spruce? I mean, the tonewood sources in my geographics area ;) sell fronts, backs and ribs. So the bouts, -- what quality does that need to be? What are the ribs made of? In my area I can buy 'bosnian' ribs. No idea what that really is.

No special spruce is needed, only low density is recommended to minimize weight on corner blocks, tight grain is more recommended for upper and lower blocks to maximize resistance.

But as you see from the photos, del Gesù did not bother too much.

Ribs are made of maple, bosnian is a maple from Balcans, quite typical for violin making.

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11 hours ago, with_joerg said:

Thanks for your reply. As a non-native speaker I must admit . . . that I do not know what 'flare' means in this context. Do you mean they make the blocks 2mm or so bigger than indicated by the geometric shape? Would you have a handsketch that you could share?

Joerg,

I believe I misunderstood  your original question.

I was referring to the shape of the plate corners not the blocks themselves. I agree completely with finnfinnviolin"s comments about the blocks themselves.

As far as drawings I am lucky I can use these infernal machines at all and do not know how to post  pictures or drawing.

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