Curtate Cycloids. Again

[David Burgess]

4 minutes ago, carl stross said:

 

By the process of paying attention.  You're not against "more thinking" by the way ?

"More thinking" can sometimes lead to better outcomes, or to fooling oneself, or delusions. Did you ever see the movie, "A Beautiful Mind"?

[Carl Stross]

1 minute ago, David Burgess said:

"More thinking" can sometimes lead to better outcomes, or to fooling oneself, or delusions. Did you ever see the movie, "A Beautiful Mind"?

Absolutely. And I've seen the movie.

[Janito]

4 hours ago, Roger Hill said:

If you follow the arch shape line from any interior point along the line, you will at some point come to the edge, i.e. the point at which the top plate is glued to the lining.  This is the end of the arch.  as you approach the end of the arch,the angle between the rib and the arch shape line (extended) is very close to a right angle.

 

Now I am confused.

What do you mean by "from any interior point along the line"?  I agree that the interior line appears the intersect with the rib at right angles, but the curtate cycloid shape is on the outside surface.  What has curtate cycloid shape on the outside to do with right angle on the inside?

What am I missing?

[Frank Nichols]

2 minutes ago, Janito said:

Now I am confused.

What do you mean by "from any interior point along the line"?  I agree that the interior line appears the intersect with the rib at right angles, but the curtate cycloid shape is on the outside surface.  What has curtate cycloid shape on the outside to do with right angle on the inside?

What am I missing?

My interpretation of that is that at any point on the arch, the tangent to the line points to the edge. As you get closer to the edge the arch becomes steeper.

But then, I know nothing, and that is probably wrong.

 

[Roger Hill]

"What do you mean by "from any interior point along the line"?" 

A point on the arch shape curve that is not at either end.  If you carve a perfect CC on the outside and use a uniform thickness for the top, both the arch shape curve and the parallel line along the inside surface of the plate will also be curtate cycloids to a close approximation.  You will find a lot of clarification if you simply print out a transverse ct scan picture and draw the middle line of the top and look at what I am saying.  If you are a windows user, open Windows accessories and find "snipping tool" to make this easy.

"But then, I know nothing, and that is probably wrong."

yup, its wrong.  As you get closer to the end, the tangent becomes horizontal and not steeper.

[Frank Nichols]

2 hours ago, Roger Hill said:

"But then, I know nothing, and that is probably wrong."

yup, its wrong.  As you get closer to the end, the tangent becomes horizontal and not steeper.

Told you so -
 

[Don Noon]

2 hours ago, Roger Hill said:

 As you get closer to the end, the tangent becomes horizontal and not steeper.

To continue nitpicking, a cycloid has no end... only where you decide to cut it off.

[Roger Hill]

Don:

I know what a cycloid looks like.   You know what a cycloid looks like.  We both know what a cycloid approximation to a violin arch looks like, with the low point at the minimum of the trough.  I guess no nit is too fine to be left unpicked.  You are not contributing to the understanding of the point I made for those who do not have the knowledge of mathematics that you and I have.  You know very well from what I said that I meant the end of the arch shape curve as I defined it.  You don't have to prove to me that you are smart, I know that. I've made my point, no good deed goes unpunished.  I'll bow out now and move on to other things where I don't have to be harangued with pedantic bullshit.

Roger Hill

 

[Torbjörn Zethelius]

I don't get it either. 

[Conor Russell]

If I do understand  what Roger is saying, the feature so common  in these old violins, often missed, is this. 

The inside  of the plate is hollowed out, and the hollowing approaches the rib gluing  surfaces  in a smooth curve, not with a ridge or an angle. The recurve that we see on the outside of the plate is fully reflected on the inside, at least to its lowest point. Obviously, rather than rising again to form the edge, it flattens out to form the rib gluing surfaces. Even in strongly arched plates whose  arching rises quickly from the edge, this is true. 

I found it hard to get my head around this, because carving the plates as I learned to do at school, unless I hollowed the inside right to the edge, I had a really  thick margin that the edge fluting  (as I knew it) couldn't fix. 

In order to achieve this, one must start from a much  thinner edge, or carve the fluting  very deep, or move the fluting inward. In fact, some combination  of  all three, depending on the arching. I don't use templates, but 'draw' the arching  shape on the wood with my gouge, always  with  this in mind.

I'm sure  many of you spotted this , or were told about it from day one, but it took me  years to get it, and to pluck up the courage to carve boldly enough  to make my violins that way.

[Torbjörn Zethelius]

Ok, so he's talking about the inside? Well, I solved that problem 11 years ago.  

 

[ezh]

On 5/26/2017 at 12:40 PM, Roger Hill said:

If you spend some time looking at the various CAT scans of the violins of the old masters....

Can you point us to any publically available CT  scans of Strads and Guarneris?

[MikeC]

35 minutes ago, ezh said:

Can you point us to any publically available CT  scans of Strads and Guarneris?

 

 

[MikeC]

Here's the Strad 3d site.  

https://strad3d.org/

 

 

[Dr. Mark]

It's interesting that the claim in this discussion seems to be that correlation equals causality.  Who is the modern 'discoverer' of the use of such a device, and was/is there any evidence for its intentional use by classical makers other than post-mortem fitting to violins?  Anyone find a drawing on Amati or Strad mould or a curtate cycloid template in Cozio's collection?  Curtate cycloids are certainly not simpler than STDs, but the latter don't seem to have caught on much as intentional design elements.  Does anyone think that perhaps classical arching aesthetic matches a particular curve simply because the curve is pretty close to the aesthetic?

Without other evidence for it's use classically, arguing that curtate cycloids are the reason for the classical violin arching seems to be like arguing that the ancient Greek tonal system was developed by mathematics rather than by ear.

[LCF]

42 minutes ago, Dr. Mark said:

....  Does anyone think that perhaps classical arching aesthetic matches a particular curve simply because the curve is pretty close to the aesthetic?

 

I think many people have thoughts along those lines. 

 

It is a nice curve with good smoothnesses, easy to generate, changes from convex to concave in a proper fashion and probably is a useful metric to use to judge archings. Possibly it is also a big red herring. 

 

 

[LCF]

I like this comparison pic that was posted by Fiddle Doug.  The Stainer and the Strad resemble CCs but thet have inflection points at the same location with different heights so that doesn't work. The Guarnerius has similar height to the Strad but a radically different arch style.  

 

Arching comes in all different flavors. 
 
https://maestronet.com/forum/index.php?/topic/359462-is-this-arching-wrong/&do=findComment&comment=1016222

 

 

[bick]

I was reading on this recently... but if I understand this paper correctly the CC is not matching the profiles of most instruments. Not sure if this is a trusted source or not, but at least a data point.

 

https://www.savartjournal.org/articles/12/article.pdf

[MikeC]

Some are quite far off, others are remarkably close,  considering the variability in hand wood working.  

Anyway, just carve what looks good. 

 

[Dennis J]

What looks good is right and that looks about right. Trying to categorise the curvature is pointless. I make templates having fixed heights and inflection points using French curves to draw a compound curve on to anodised aluminium and then cut and file them to a smooth compound curve. But those inflection points have be located pretty accurately on the horizontal and vertical axis at each cross arch location. The upper and lower bout arches are fairly straightforward because the inflection points have to be at edge height level and about the right distance from the plate edge.

The middle bout arch at the narrowest cross arch position is critical. It needs to be just about as full as practical. So a template there should be pretty important. A good arch profile there should be close to circular.

[MikeC]

While I did use the usual five cross templates on this one, I find they are not necessary.  A good arch forms naturally from the carving process.  

[Dennis J]

I know that is the case but it can be a bit of a guessing game. Establishing exact profiles at the usual cross arch locations  any wood removal between them can be completed quite smoothly using that principle. It is very easy to take too much away around the edges without templates, especially at the centre bout. And going in too far, especially at the lower bout, can result in very thinly graduated plates there. There are plenty of examples of that which I think is a carving problem, not deliberate.

[David Alex T.]

On 7/20/2024 at 4:00 PM, Dr. Mark said:

It's interesting that the claim in this discussion seems to be that correlation equals causality.  Who is the modern 'discoverer' of the use of such a device, and was/is there any evidence for its intentional use by classical makers other than post-mortem fitting to violins?  Anyone find a drawing on Amati or Strad mould or a curtate cycloid template in Cozio's collection?  Curtate cycloids are certainly not simpler than STDs, but the latter don't seem to have caught on much as intentional design elements.  Does anyone think that perhaps classical arching aesthetic matches a particular curve simply because the curve is pretty close to the aesthetic?

Without other evidence for it's use classically, arguing that curtate cycloids are the reason for the classical violin arching seems to be like arguing that the ancient Greek tonal system was developed by mathematics rather than by ear.

 

On 7/22/2024 at 3:32 AM, Dennis J said:

What looks good is right and that looks about right. Trying to categorise the curvature is pointless. I make templates having fixed heights and inflection points using French curves to draw a compound curve on to anodised aluminium and then cut and file them to a smooth compound curve. But those inflection points have be located pretty accurately on the horizontal and vertical axis at each cross arch location. The upper and lower bout arches are fairly straightforward because the inflection points have to be at edge height level and about the right distance from the plate edge.

The middle bout arch at the narrowest cross arch position is critical. It needs to be just about as full as practical. So a template there should be pretty important. A good arch profile there should be close to circular.

On 7/20/2024 at 4:52 PM, LCF said:

 

I think many people have thoughts along those lines. 

 

It is a nice curve with good smoothnesses, easy to generate, changes from convex to concave in a proper fashion and probably is a useful metric to use to judge archings. Possibly it is also a big red herring. 

 

 

I made a test comparing Cycloid and 2 Cello Template. in both case there is an issue with the shape. Inflexion  point is not good.

The Cycloid are interesting to connect to top and to the channel, but a parameter is lacking to adjust the inflexion poiint

 

 

 

[LCF]

9 hours ago, David Alex T. said:

 

 

I made a test comparing Cycloid and 2 Cello Template. in both case there is an issue with the shape. Inflexion  point is not good.

The Cycloid are interesting to connect to top and to the channel, but a parameter is lacking to adjust the inflexion poiint

 

 

 

The location where you are likely to find  arching profiles closer to a cycloid shape is across at the  upper and the lower corners. Everywhere else, not so much. 

[Christian Pedersen]