Jump to content
Maestronet Forums

Long Arch Drawing


Dennis J
 Share

Recommended Posts

I've marked up a set of cross-arch templates based on the long arch design posted here. I've shown the front arch here. The back arch is .5 mm lower so calculations will be much the same.

All calculations are based on an edge thickness/height of 4.3 mm. And inflection point positions are as per my arching layout based on an arc. But one thing that has worried me about inflection point height calculations in the past is that the two central cross arches (middle and bridge) are a little high to comfortably complete the arching profile.

So I've decided to average the four central cross-arch inflection point heights as calculated and make the lower corner arch height the highest, the upper corner the lowest and the middle two a little lower (about 1 mm). It is not of much significance in the scheme of things but is in making templates. It works much better that way. You might be able to see how I've taken the curve below the horizontal and vertical lines at the waist.

So the arching point heights calculated at a fairly high 7 degrees are 3.4 mm lower corner, 2.7 mm the two central, and 2.4 mm upper corner. Measured from the bottom of the plate that works out at 7.7 7.0 7.0 and 6.7 mm.

I realise that probably not many members are getting into all of this but It is just a matter of dotting the I's and crossing the T's.

DSC_0002 3.jpg

Link to comment
Share on other sites

  • Replies 383
  • Created
  • Last Reply

Top Posters In This Topic

I get confused easily so please humor me.  Is the top arch height measurement the distance from the gluing bottom surface of the plate edge to the highest top plate surface?

So if I make my plate perfectly flat with a thickness of 3mm.  Is the arch height 3mm?

 

Link to comment
Share on other sites

1 minute ago, Marty Kasprzyk said:

I get confused easily so please humor me.  Is the top arch height measurement the distance from the gluing bottom surface of the plate edge to the highest top plate surface?

So if I make my plate perfectly flat with a thickness of 3mm.  Is the arch height 3mm?

 

A flat tire is only flat on one side . 

Link to comment
Share on other sites

26 minutes ago, Dennis J said:

I've marked up a set of cross-arch templates based on the long arch design posted here. I've shown the front arch here. The back arch is .5 mm lower so calculations will be much the same.

All calculations are based on an edge thickness/height of 4.3 mm. And inflection point positions are as per my arching layout based on an arc. But one thing that has worried me about inflection point height calculations in the past is that the two central cross arches (middle and bridge) are a little high to comfortably complete the arching profile.

So I've decided to average the four central cross-arch inflection point heights as calculated and make the lower corner arch height the highest, the upper corner the lowest and the middle two a little lower (about 1 mm). It is not of much significance in the scheme of things but is in making templates. It works much better that way. You might be able to see how I've taken the curve below the horizontal and vertical lines at the waist.

So the arching point heights calculated at a fairly high 7 degrees are 3.4 mm lower corner, 2.7 mm the two central, and 2.4 mm upper corner. Measured from the bottom of the plate that works out at 7.7 7.0 7.0 and 6.7 mm.

I realise that probably not many members are getting into all of this but It is just a matter of dotting the I's and crossing the T's.

DSC_0002 3.jpg

I’m curious, when you say calculate… what formula are you using to decide height of the transition? And how are you generating the cross arches ?
 Personally I never bothered with the distance off the rib surface height other than long arch heights and edge thicknesses, but not for transition from concave to convex.  , but rather  distance from edge , usually about 15 20 mm or so  varied by exact position, with the cc. Bouts, substantially less ,with language akin to a broad vs narrow scoop . And peaked vs rounded arch . Or pinched vs flat … 

Another convenience I found especially handy was to only use half templates for the cross arches, this allows for a certain freedom to adjust things as work progress's .  

Link to comment
Share on other sites

57 minutes ago, Marty Kasprzyk said:

I get confused easily so please humor me.  Is the top arch height measurement the distance from the gluing bottom surface of the plate edge to the highest top plate surface?

So if I make my plate perfectly flat with a thickness of 3mm.  Is the arch height 3mm?

 

As far as I know arching heights are usually measured from the bottom of the plate to the apex of the arch.

When planning arching templates I use a default edge height of 4.3 mm marked from the bottom of the aluminium blank with the actual arching profile on top of that. So, to be specific the highest arch is marked at 14.9 and that is made up by adding the thickness of the edge (4.3 mm) to the actual arch height above edge level at that position.

When I cut the profile out I leave a tab at each end which fits over the edges.

Link to comment
Share on other sites

58 minutes ago, James M. Jones said:

I’m curious, when you say calculate… what formula are you using to decide height of the transition? And how are you generating the cross arches ?
 Personally I never bothered with the distance off the rib surface height other than long arch heights and edge thicknesses, but not for transition from concave to convex.  , but rather  distance from edge , usually about 15 20 mm or so  varied by exact position, with the cc. Bouts, substantially less ,with language akin to a broad vs narrow scoop . And peaked vs rounded arch . Or pinched vs flat … 

Another convenience I found especially handy was to only use half templates for the cross arches, this allows for a certain freedom to adjust things as work progress's .  

Well James I've posted quite a lot of arching geometry stuff which explains how I set the vertical (height above edge level) and horizontal (distance from centre/edge) position of inflection points above edge level for the 4 central cross arches. The inflection point for the upper and lower bout cross arches is at edge level. All heights are taken from a long arch template.

On the blanks you can see the edge height line, the termination point of the arch, the vertical and horizontal location of the inflection point and the apex of the arch.

I use french curves to complete the upper convex and lower concave (including the scoop below edge level) parts of the arch profile. If the inflection points are in the right spot it is easily drawn as you can see in my posted pic. The height and horizontal position of the inflection point is crucial. That is why the calculation of that is important.

Link to comment
Share on other sites

11 minutes ago, Dennis J said:

Yeah. Fifteen pages of mostly waffle and argument.

 

Welcome to Maestronet! That's what this place is about. 

 

Ok Dennis, I'm sorry to single you out in particular, but please show us some woodwork. I'm genuine when I say I admire the time, energy, and effort you've dedicated to your study of the instrument, and I'd like to see what all that work can being to the table. 

Link to comment
Share on other sites

9 minutes ago, Dennis J said:

OK, I'll admit I'm a bit short on the practical stuff. To tell the truth I've said just about enough on the subject. I'm ready to move on.

No worries. I think your ideas deserve to be explored, and I would be glad to make a violin using your designs, and use wood chosen to your specifications. It's unfair to discount your ideas until they've left paper. Please let me know if you'd like to proceed. No gimmicks, just the spirit of experimentation. Let's do it!

Link to comment
Share on other sites

8 hours ago, Dennis J said:

I was referring only to the old photograph. To my eye it is a lot closer to circular than most early instruments. Can't see any sudden downturns there.

The newer photograph is quite different, hard to believe it is the same instrument.

 

Notice that the old photo is grainy low res, and low contrast brown on brown. These comings make it easier to imagine whatever shape you wish.   Notice also that the better contrasted bridge foot os clearly sticking out below the drawning in circle line.

I'm sure you could just as easily make a red trace of the non circle arch on the higher res and better contrasted newer photo and transfer that non circle shape on to the indistinct old photo whithout difficulty.

It's not that the old photo is showing a change in arch, it's just a bad and indistinct photo.  Like photos of the Loch Ness monster.

Cremona top long arches typically show a flatish area, then down turns as you get toward the ends.

Some of the backs also clearly show similar concept, but with shorter flattish areas.   

If you indulge in creative vision, as you all have to impose circles, then you can understand and see (if you will it) the nearly circular backs as just having very minimal flattish areas near the bridge.

At least if you take that approach it allows a consistent interptetation of all the examples, not just a select few.

 

It's also very interest to look at Fench long arches from say 1820 to 1870.  These are the people who actually did start making long arches with a circle or at least a through curve concept.

The curious thing is that some of them made the new ciircle arches, and some made the old Italian shapes with flattish areas and then breaks downward.  And some, like Vuillaume, made a mix of these arch type.

What's very interesting is that who made an instrument is more relevant to which arching is seen than how old the example is.  In other words, the mix of arch types is not about aging, but about who made them.

That actuakly applies to Cremona makers also, but more subtly.  So makers were more likely to make a very exaggerated example than others: Ruggieri, A Amati, Montagnana, Guadagnini.  Again, correlation is more to maker than to aginig.

Anyway, a good number of modern makers somehow ended up receiving and using the later French notion of circular, or at least through curved long arching.  And some of these folks are very entrenched in believing the old Cremona makers bulit that way too. They want to explain every non circular aspect of the long arch as distortion. They are attached and motivated toward that interpretation.

Buy use your own eyes folks.  In clean photos, some French arches that are nearlly 200 years old show truely circular long arcs, because they were made that way.  And some rather younger Fremch arcs show the 'flat with breaks' type long arcs, because those examples were made that way.

Likewise, with the Old Cremona making we see a great range of long arch choices for tops and backs.   All of them can be easily and naturally understood under the 'flattish then curved' concept.

But, for those so motivated, some examples do look close to circular, mostly backs.   And, if you squint hard at bad photos, more examples fall under the 'it almost looks circular in some.photos' category.   But if we're going to squint, we can just as easily understand these examples as simply having very minimal flattish areas just around in front of the bridge.

Look with your own eyes.  Look for what is actually there rather than for what you'd like to see.

Link to comment
Share on other sites

25 minutes ago, David Beard said:

Cremona top long arches typically show a flatish area, then down turns as you get toward the ends.

Yes, as is typical of normal long-term distortion from string load, when an instrument has been exposed to high humidity or repeated humidity cycling.

25 minutes ago, David Beard said:

It's also very interest to look at Fench long arches from say 1820 to 1870.  These are the people who actually did start making long arches with a circle or at least a through curve concept.

We don't know how these instruments started out. Perhaps, with 400 years of previous violin distortion to observe, and with restorations already taking place, they started out with the top more peaky, anticipating that this would settle into something more round, rather than going double-humped.

Link to comment
Share on other sites

I have no horse in this race. I'm building mandolins and spent a couple (thousand) hours measuring and drawing the "holy grail" of archtop mandolin - vintage GIbson F-5 models signed by L.Loar. Those mandolins were carved upon exact mould with machines so they all started basically the same but now, 100 years later the arches are all over the map, especially long arches. I was working with variety of tracings, CT scans and photos of instruments so I have little experience in working with these and finding edges of objects etc.

The pictures I posted are simple screenshots as MN limits file size, if you adjust quality, the original pictures are not great, but certainly sufficient to show the curve. I actually found the Biddulph pictures worse because of bad choce of background and lighting direction that creates almost pure white reflection in the bridge area that possibly got cropped during his editing making the arch look even flatter than it is (the areas under tailpiece and fingerboard are in shade and dark so they appear more bulged).

I would refer to concept of how scientists research history of universe. If you reverse the time, the expanding universe collapses into singularity somewhere at its beginning. Simple observation of plate creep in violin shows where they are moving, if you reverse the time they converge from "camelback" or flat towards the circular arch.  Of course we cannot be sure where the arch started but wherever you look at the violin (or architecture of the time) you see circular arcs so why there's this categorical "no way" for the circular long arch as the original idea?

I've built a number of longbows (archery) and traditional working method is checking the curvature of bent bow and thinning areas so you get very even radiused curve (approaching circle). None of bowyers I know uses templates for this and just steps back tolook for uneven bend. Eyes have the capability to see even the slightest deviations from even curve and the brain even tends to exagerrate those. Just like you can feel even slight bumps in arching with bare fingers and your eyes closed. With some practice they feel like mountains.

 

 

Link to comment
Share on other sites

10 hours ago, Dennis J said:

Well James I've posted quite a lot of arching geometry stuff which explains how I set the vertical (height above edge level) and horizontal (distance from centre/edge) position of inflection points above edge level for the 4 central cross arches. The inflection point for the upper and lower bout cross arches is at edge level. All heights are taken from a long arch template.

On the blanks you can see the edge height line, the termination point of the arch, the vertical and horizontal location of the inflection point and the apex of the arch.

I use french curves to complete the upper convex and lower concave (including the scoop below edge level) parts of the arch profile. If the inflection points are in the right spot it is easily drawn as you can see in my posted pic. The height and horizontal position of the inflection point is crucial. That is why the calculation of that is important.

I’m still wondering what that calculated position is , and how you arrive at the “crucial .” Do all great violins share this inflection point location? Is there some ratio of width to height? Any numerical relationships of width to height? Or are you “calculating “ with guess work and French curves then ? There’s so many possible curves that can blend nicely. 
 Years ago , I think it was R Hargrave wrote some stuff about his theory of arching, he didn’t (as I recall) talk much of the long arch form specifically,  rather the idea that the arch was made and more or less finished down to a platform edge of approx 5mm thick .that plate was then glued to the neck and rib assembly, for final profile edge work and purfling inlaid, only then was the scoop … scooped . This final scoop seems to have often been hastily carried out leaving a somewhat less than perfect juncture between the two efforts. I’ve never personally observed this detail nor have I ever had the courage to scoop the edge while the box is closed, however, I see no reason to doubt R’s integrity, if this is true it rather throws out any idea of the need for a critical location (within say a mm or three . )of the inflection point . 

Link to comment
Share on other sites

Roger H also mentioned in the Biddulph del Gesu exhibition books that he believed that del Gesu used the same cross arching template set for his violins, as half templates variously placed in or outward for different effects, and I agree with that as being a fundamental fact in Cremonese making for all of the Cremonese makers.

Needless to say, curtate cycloids as full templates predetermine the inflection point AND the shape of the curves involved--no guessing needed. From there you have the choice of how to use them and how closely to follow them. Some makers followed them very closely, others were more careless, and there's always the problem of how to blend them where they intersect in the center, but I think most of Cremonese violin making could be done with the same basic set of halfs.

Link to comment
Share on other sites

On 5/2/2022 at 5:51 PM, Andreas Preuss said:

May I ask what this demonstrates? If this is the stress under tension I would expect anything but a symmetric pattern. 

3D imagniary visualization, does that count?

Link to comment
Share on other sites

14 hours ago, David Burgess said:

don't know how these instruments started out. Perhaps, with 400 years of previous violin distortion to observe, and with restorations already taking place, they started out with the top more peaky, anticipating that this would settle into something more round, rather than going double-humped.

You don't know because you don't want to reach the most obvious conclusion. They were made with substantially the long arcs seen today.    Except in the caes were there is localized collapse near the bridge, the long arches haven't change so dramatically.

Absent your strong desire to evade such conclusion, the vast array of differing choices seen in different makers and at different times make it plain that these shapes didn't all start as simple circle arcs with only the one variable of plate height and then magically deform into the specific diverse array of maker dependant choices now seen in the historical examples.  No.  The examples started with those maker dependant diverse choices built in from the begining.

But you're sure it has to be the way you expect. So you see the historical examples as you wish to.

Link to comment
Share on other sites

12 minutes ago, David Beard said:

You don't know because you don't want to reach the most obvious conclusion. They were made with substantially the long arcs seen today.    Except in the caes were there is localized collapse near the bridge, the long arches haven't change so dramatically.

Absent your strong desire to evade such conclusion, the vast array of differing choices seen in different makers and at different times make it plain that these shapes didn't all start as simple circle arcs with only the one variable of plate height and then magically deform into the specific diverse array of maker dependant choices now seen in the historical examples.  No.  The examples started with those maker dependant diverse choices built in from the begining.

But you're sure it has to be the way you expect. So you see the historical examples as you wish to.

Put this way, I’ve seen two hundred yr old beams joists  set to solid curves over the course of time , solid wood moves on a molecular level similar to tar . Under stress. I just went through my copy of violin varnish (the big book of…).where they show many of the side profiles of classical Strad violins viola and cello as well as an Amati and delgesu ,and asked the question, would a circular arch deform under pressure this way …. Over time? And the resounding answer in my mind was… yes . Of course humans made them and humans are flawed , but on the hole it seems to my eye they started out , at least sort of circular. Definitely within reason, in addition the backs all seem a little peaked through the long arch , not exactly pointed but moving in that direction as if the whole body has followed to some extant the strings . I don’t doubt that many makers have elongated the arch into a flattened curve , everyone is searching for the grail, but can’t simply dismiss the idea of a pure radius as a sort of starting point , a pure radius would definitely fit within any design ideas Of the day.

Link to comment
Share on other sites

1 hour ago, James M. Jones said:

Put this way, I’ve seen two hundred yr old beams joists  set to solid curves over the course of time , solid wood moves on a molecular level similar to tar . Under stress. I just went through my copy of violin varnish (the big book of…).where they show many of the side profiles of classical Strad violins viola and cello as well as an Amati and delgesu ,and asked the question, would a circular arch deform under pressure this way …. Over time? And the resounding answer in my mind was… yes . Of course humans made them and humans are flawed , but on the hole it seems to my eye they started out , at least sort of circular. Definitely within reason, in addition the backs all seem a little peaked through the long arch , not exactly pointed but moving in that direction as if the whole body has followed to some extant the strings . I don’t doubt that many makers have elongated the arch into a flattened curve , everyone is searching for the grail, but can’t simply dismiss the idea of a pure radius as a sort of starting point , a pure radius would definitely fit within any design ideas Of the day.

As a concept proposal, it is rational.  And I tend see circles in most every aspect of Cremona making I examine.  If I have a bias, it is to interpret Cremona design through the lens of circle arcs.

But, after examining a very broad range of the available examples/evidence I came to believe a circle interpretation of the long arc is not sustainable against the evidence.

Link to comment
Share on other sites

11 hours ago, David Beard said:

You don't know....

What I wrote is that we don't know, and that includes you. All either of us have are hypotheses. Mine is based on many experiments and a lot of experience with wood creep and distortion on violins, spanning about 50 years, including violins from way before my time which had gone horribly swaybacked (unless you believe that these too were made that way :o).

We've gone around and around about this before. Did you ever do the experiments I suggested so you could witness this creep yourself? No? I didn't think so!

Yesterday, Joseph Curtin gave a presentation titled "Deformation & Creep: The long-term effects of string tension" as part of the Oberlin Acoustics online seminar series. Did you watch it? No? I didn't think so! :)

Could some of the older instruments have been made with a more plateaued long arch on the top than on the back? Possibly. After all, some of those makers may have taken some of their cues from older instruments which were already distorted, just as many do today.

The bottom line is that we just don't know (yet).

There are lots of papers and studies of wood creep, should you be interested. Here is just one: https://jwoodscience.springeropen.com/track/pdf/10.1007/BF01192327.pdf

Link to comment
Share on other sites

1 hour ago, David Burgess said:

What I wrote is that we don't know, and that includes you. All either of us have are hypotheses. Mine is based on many experiments and a lot of experience with wood creep and distortion on violins, spanning about 50 years, including violins from way before my time which had gone horribly swaybacked (unless you believe that these too were made that way :o).

We've gone around and around about this before. Did you ever do the experiments I suggested so you could witness this creep yourself? No? I didn't think so!

Yesterday, Joseph Curtin gave a presentation titled "Deformation & Creep: The long-term effects of string tension" as part of the Oberlin Acoustics online seminar series. Did you watch it? No? I didn't think so! :)

Could some of the older instruments have been made with a more plateaued long arch on the top than on the back? Possibly. After all, some of those makers may have taken some of their cues from older instruments which were already distorted, just as many do today.

The bottom line is that we just don't know (yet).

 can't find but you could gave us the link

Link to comment
Share on other sites

3 hours ago, David Burgess said:

The bottom line is that we just don't know (yet).

It shouldn't be too hard to find out... just slice a plate down the middle, examine the grain with a microscope, and de-convolve the existing arch with the (valid) assumption that the grain was originally straight.  Anyone want to donate their Strad?  (this idea falls apart if you think they bent their plates)

I know nothing about CT scan capabilities, but it might be more feasible if you could do this kind of analysis non-destructively.

Link to comment
Share on other sites

4 hours ago, Don Noon said:

It shouldn't be too hard to find out... just slice a plate down the middle, examine the grain with a microscope, and de-convolve the existing arch with the (valid) assumption that the grain was originally straight.  Anyone want to donate their Strad?  (this idea falls apart if you think they bent their plates)

I know nothing about CT scan capabilities, but it might be more feasible if you could do this kind of analysis non-destructively.

CT scans can show this today.   This is the non speculativr resolution I am also waiting for.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.



×
×
  • Create New...