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Stradivari scroll compass method


Wood Butcher
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5 minutes ago, MikeC said:

Hi TZ,  I read that article.  I have a question,  how do you determine the first turn on the back?  See the circled area.  The rest of the scroll is easy but that part I just kind of eyeball it.  

scroll.PNG

This part is commonly made fairly straight. Its development follow from the angled template (first turn) to the width at point B. 

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Continuing...

 

The sideview geometry of the heads and scrolls does get rather complicated.   And the pattern that consistently organize the arcs and shapes are rather arcane at face.    Only by looking across many examples, and examining all as carefully as possible, only then do the consistent organizing patterns begin to emerge.   But, short of retracing years and years of step by step observation, we're going to have to open this book in the middle, and go from there.

I want to look here at just two examples to show the main themes of the geometry first arcs the shape the head.

Because the notion of Cremona making developing from older roots is interesting, all start with the Zanetto example we've already touched on.

1521058046_Zanettoouterarcs.thumb.jpg.b762bfc8de7a1d42e48015fbca170d22.jpg

 

First, notice that the under turn beneath the box consists of two joined arcs.  The shorter radius arc continues through the heal.

And also, the turn running below the volute consists of two arcs.

Joining between these two curved sections is a flat connecting segment of tangent line.

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Now, in the aspects noted so far, this Zanetto scroll is also perfectly representative of Cremona head work.

However, quite a bit of variation is common in the Cremona use of these basics.

For example, in this example, the two arcs running under the volute join on the same vertical line.  But, the two arcs under the box off set their join.    Generally, we see both types of joins used in either spot.   

Also, it isn't so unusual to sometimes find an additional flattening longer joined in as they two turns aim to meeting up.

Further, in a very few examples, the two curves meet directly without needing a tangent joining line.  But this is much less common than not.

Lastly, we will observe a range of ideas and ratios for actually placing and sizing the actual arcs used in a specific example.   All these choices end up following certain principles, and falling into just a handful of common patterns.   But we will need to look across many examples to sort that out.

 

Now, let's look at the single arc shown in yellow giving the main top curve of the box.   These is typical through Cremona work.    Notice how the center of this arc (yellow cross) is in some arcane way related to the centers of the box's underturn.   That there is some such relation between these centers is consistent in Cremona work.  But the specific relationships instruments by instrument vary along just a few patterns.

Now, take note of the 1:1 'key rectangle' shown in red.   Notice how the centers for both arcs under the volute have a relationship to this 'key rectangle'.   Also notice how the 'key rectangle' provides a necessary reference point for setting the top arc for the box.   Similar 'key rectangles' play the same role consistently in Cremona work.  However, they are generally 3by4 rectangles, and set their size from the volute frame.

Indeed, while the Zanetto example uses a 1:1 square key instead of the common Cremona 3:4 rectangular key, nevertheless a quick check shows it is sized in relation to the volute frame as 1/2 the volute length.

 

1970620263_Zanettohalf.thumb.jpg.65e027885ebd03db0267b1bb429d5f49.jpg

 

Let's note some of the things that make this old Brescian style different than standard Cremona work.

* The 1:1 key puts a larger spacing from the front of the volute to the main top arc of the box.

* The fewer and different turns of the volute.

* The centering of the turn under the volute under the line in front of the volute.

 

This isn't meant to be an exhaustive list.  But these are the big things.   And, otherwise, this Zanetto old style Brescian scroll is more the same as Cremona work than not.

 

Now let's look at the 1615 Brothers Amati 'Staufer' viola as an example of the same things in Cremona work.

1774880044_BrosAmatiStaufervla1615.thumb.jpg.5f834b8ed480f02d9ec7e037e4d71c9a.jpg

More same than not.   The arcs passing beneath the volute are centered on a line in set from the front of the volute.   (For convenience, we'll start referring to this line as the volute stop, marked here with a heavy orange line.)    The 'key rectangle' is 3 by 4, with its width set as 1/3 the volute length.   Since both volute frame and key rectangle are 3 by 4, the height of the rectangle is also 1/3 the volute height.   Notice that all the arc centers relate to this 'key rectangle'.   1/2 its height gives the inset for the volute arcs and their centers.    And a copy of the rectangle relates the centers of the box arcs to a reference line running below the head and volute.

 

Digging further will require looking across more examples.

 

 

 

 

 

 

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