Julian Cossmann Cooke

Conforming f-hole templates to arching between c-bouts

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Working from a "live" instrument as a source of data for making creates the opportunity to make f-hole templates that follow the arching between the c-bouts in a way that working from a photograph does not.  

Has anyone developed a way of doing this from a poster --- capture the three-dimensional?

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I don't know what I am talking about here, but the first thing that came to my mind was to use something like a slide projector and to project the f-hole template down onto a top that had the arching completed. Then you could mark out landmarks on the projected image on the top.  Just a thought - is that what you were meaning?

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10 minutes ago, Frank Nichols said:

I don't know what I am talking about here, but the first thing that came to my mind was to use something like a slide projector and to project the f-hole template down onto a top that had the arching completed. Then you could mark out landmarks on the projected image on the top.  Just a thought - is that what you were meaning?

Interesting idea, Frank.  That is the kind of thing i meant.  I may even have a projector -- it's an old 1960's model...but I might have to have a slide made...I clearly need to noodle around with this some more!

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I'm not sure if something like this is what you mean, but Andrew dipper showed me this quick and easy way to make a 3D copy of f-holes. 

Basically you put a piece of aluminum foil over the part you want to copy and rub it with a soft old toothbrush to create a depression in the foil. You can then photocopy the foil and make a template from the photocopy. You can also cast the foil in plaster  for a more permanent copy. 

I'll try to upload a photo later

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13 minutes ago, Mason said:

I'm not sure if something like this is what you mean, but Andrew dipper showed me this quick and easy way to make a 3D copy of f-holes. 

Basically you put a piece of aluminum foil over the part you want to copy and rub it with a soft old toothbrush to create a depression in the foil. You can then photocopy the foil and make a template from the photocopy. You can also cast the foil in plaster  for a more permanent copy. 

I'll try to upload a photo later

I was getting at the challenge of using a one-dimensional photo of a 3-dimensional subject -- so getting from the photo to 3-D rather than the other way around.  But maybe I am not understanding your suggestion, Mason.

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1 hour ago, Julian Cossmann Cooke said:

Interesting idea, Frank.  That is the kind of thing i meant.  I may even have a projector -- it's an old 1960's model...but I might have to have a slide made...I clearly need to noodle around with this some more!

What "might" be easier to get together. Back in the 50's or 60's there was a device used to learn to draw things. It was basically a periscope that you looked through and you would see the thing you are wanting to draw, appear to be on the paper (maybe a half silver mirror?). Then you would draw on the paper by tracing the object - a person or flower or whatever. I expect half silver mirrors are easy to come by on the internet and then use hang the template in front and the top plate below and trace the apparent image...

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You can construct something similar to pin router but with pencil instead of router bit . Make flat template from the poster- photo or 2D drawing out of thin plastic sheet (you can use clear over the poster and just trace outlines), cut out the f holes and place the top on the template with sticky tape or such. You can just use soft pencil in your drillpress and thin pin in the flat table and put a dot every few mm around the f hole and then trace it by hand. Or make some device that will allow the pencil slide up-down with minimal force (round pencil in a matching tube held in chuck of drillpress) and you can go all around in one move.

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Not from the poster, but you can always email certain luminaries in the field who are sure to have the highest quality violin porn available: you know who they are. And so do I. Seeing how the light hits that area where the fluting is makes such a difference. It's not really possible with posters,  at least, you have to guess a lot. I have been surprised before that I was looking at photos of the same instrument as a poster showed.  Some of those people are pretty generous with photos and information. You know every time someone gets a very interesting item they are talking about it, getting measurements, taking photos. Some say they don't, but they do. 

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My first post - I'm excited to be able to add a small drop of suggestion to the ocean of wisdom I find here.

A camera lucida is a good direction.  My wife, a painter, sometimes uses an App on her iPad called Camera Lucida to duplicate portions of photographs.  I tried it once on a non-violin project and was able to "project" a 2D image onto a contoured surface.  It was a bit fiddly, but worked OK.   If you can position the standoff distance to get the dimensions and alignment on the plate correct, it might work for an ff hole.  Not sure it's better than a trusty template cutout.  But might be worth a try.  I included a link to a YouTube demo.

If someone tries it, let us know how it works.

 

Edited by AZFiddle

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Julian

If the photo is taken straight on by a good professional photographer then the inner edge of the FF will be pretty close to right while the outer line will be distorted and will look narrower than it should, increasingly so as it gets to the lower wing.  if you make  the template from the photo you will have to widen the FF slightly as it goes toward the lower hole. The best bet is to familiarize yourself with that makers work and finish  the FF by eye to give the right look. If you really want to make an exact copy then certainly best to take a rubbing from an original instrument. 

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I made a template of an F that I liked from a Strad poster. I knew going in that the photo was not going to be entirely true to the complex 3d shape of the F. But, I had a decent enough guide with the template to allow me to freeform compensate as I cut them to get a better match. 

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On 11/14/2017 at 2:25 AM, carl1961 said:

you could just buy or print a template and draw it on the violin, or if you have a violin with a nice f-hole you trace it.

 

 

7e299674fb0d8b209e65195b0d683ddc.jpg

 

I have lots of f-hole template resources, Carl, but applying them to the surface of the plate does not compensate for the distortion created by head-on photography.  I have a book of templates similar to the one you posted, but I suspect they were not done by doing a rubbing of the original f-holes -- the only way I know to get a true template when the instrument is in hand.  Short of the camera lucida, I may be left to do the adjustment by eye.  Not the worst thing in the world.

Given the role the area of the f-holes appears to play, it is interesting (disheartening?) to contemplate what instruments might sound like if made with f-holes conforming to something closer to the 3D reality of the original -- assuming of course that we got the arching right.  ;)

 

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9 hours ago, Martin McClean said:

sounds interesting all the same.... Could you post tge photos anyway?  Thanks 

It isn't exactly a good 3D model, but it's just as quick to make a foil rubbing as a pencil rubbing, but you get more information. You can make a pretty accurate template photocopying the foil, and a more permanent reference by casting it in plaster.

This is from a Testore cello that I only had about 10 minutes to take measurements. In this case I was mostly interested in the f-s, but I did get partial c-bout and corner with it, which also shows the purfling and edge details. 

IMG_3369.JPG

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10 hours ago, Mason said:

It isn't exactly a good 3D model, but it's just as quick to make a foil rubbing as a pencil rubbing, but you get more information. You can make a pretty accurate template photocopying the foil, and a more permanent reference by casting it in plaster.

This is from a Testore cello that I only had about 10 minutes to take measurements. In this case I was mostly interested in the f-s, but I did get partial c-bout and corner with it, which also shows the purfling and edge details. 

IMG_3369.JPG

Is the issue the difference between caliper length of the f-hole vs. following the arch length?  If so, in addition to Nate's advise (always good), you could drill the eyes based on the measurements given then make Strad style templates (sans eyes) to draw the rest.  I wish I had a cast like the Bett's cast we saw at the LOC.  Feeling the fluting and edge of the f-hole from the lower wing up across the eye brow are details that pictures really can't convey.

-Jim

Edit: Betts F-hole picture taken in 2013

Betts_Bass_ff_in_sun.thumb.JPG.725564e6f55d520c7a5998dc5b853b23.JPG

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I like the camera lucida idea, but with a 3D drawing app, such as any CAD program,  you can take your 2D f-hole drawing and project it onto a 3D contour representing your arch. Then, print this out and use this projected shape as your template. I do this.

You will need to evaluate 3D packages that have this feature and see if they fit your budget. Google around for 3D drawing features and prices. My old CAD package is no longer available.

Back to the camera lucida: put your iPad on a lab jack to adjust the height. I bought a used one on eBay and use it for lots of shop setups. It is an indispensable tool. They come in various sizes.

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21 hours ago, Julian Cossmann Cooke said:

>

>

Given the role the area of the f-holes appears to play, it is interesting (disheartening?) to contemplate what instruments might sound like if made with f-holes conforming to something closer to the 3D reality of the original -- assuming of course that we got the arching right.  ;)

 

The A0 frequency is proportional to the f hole area A to about the one fourth power  A^.25.  

The width distortion reduction might be around ten percent from a 3d projection to 2d so 0.9^.25 = 0.974 so your A0 frequency would be only 97.4%

If your A0 goal was 280Hz you would end up with only 273Hz.  I doubt any body could notice this difference.

I've found you have to make a massive change in f hole widths to notice anything changing.

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15 minutes ago, Marty Kasprzyk said:

The A0 frequency is proportional to the f hole area A to about the one fourth power  A^.25.  

.

approximately proportional to the square root of the area, surely?

Subjectively, the influence of f-hole size on high frequency performance seems to me to be more important than what goes on in the signature mode range.

 

 

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6 minutes ago, JohnCockburn said:

approximately proportional to the square root of the area, surely?

 

A ridged cavity would indeed have a square root proportion.  But the violin body is flexible and compliant so tests have shown the exponent is closer to one fourth power.

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1 minute ago, Marty Kasprzyk said:

A ridged cavity would indeed have a square root proportion.  But the violin body is flexible and compliant so tests have shown the exponent is closer to one fourth power.

fair point, although I did some basic measurements a while back and found the square root dependence held pretty well.

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At the VSA, Joseph Curtin, Fan Tao, and Marilyn Wallin  (I don't have my notes in front of me) gave a lecture on a viola study with 25 violas made from identical outlines (cnc forms).  Part of Oberlin acoustics lab I believe.  One thing they noted from the mountain of data that they are still wading through is that a trend is surfacing from the preliminary data that the area between the f-holes (f-hole length and distance apart) has a major affect on tone.  Smaller area = brighter more focused; vs. larger area = darker less focused tone. 

Also that AO depends on length of f-hole, body of instrument (internal volume?), and stiffness of top.

Again, this is from memory not my notes.  

-Jim

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