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3D Arching Exploration


Mike B

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Here are several figures I made today that show the Betts Strad's back arching. These were taken from a video of a CT scan. The plots are in units of "voxels" and I've not converted them to something useful just yet. A photo of the Betts violin's back is included for comparison.

 

 

 

1666535339_bettsback.JPG.07fcb0dc6e2689d7cf1d646b8d20cb49.JPG

Betts with Lighting.jpg

Betts Point Cloud 1.jpg

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The first plot appears to my untrained eye to have a straight line from a point on the center line of the long arch just below the lower corners to a point near the start of the trough that is at the maximum distance from the start point.  Or is my imagination working overtime?  I believe that our famous French contributor shows that also.

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On 10/19/2020 at 12:36 PM, Roger Hill said:

The first plot appears to my untrained eye to have a straight line from a point on the center line of the long arch just below the lower corners to a point near the start of the trough that is at the maximum distance from the start point.  Or is my imagination working overtime?  I believe that our famous French contributor shows that also.

That is a deep scratch of memory serves

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9 hours ago, Mike B said:

The real utility is that the images I provided can (and will) be 3D printed ...

I agree completely, but think there's a fair bit of value in an interactive 3D model - being able to interactively slice in x, y and z is something I find extremely useful. Have you looked at converting your Matlab-generated model to a web-friendly format, and getting it into the browser (and possibly sharing online)?

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  • 7 months later...
On 10/19/2020 at 8:52 AM, David Burgess said:

In my opinion, the first photo shows more of value to a fiddle-maker, than the following images.

Are you serious, or just ben smokin sumthun:rolleyes:

On 10/19/2020 at 10:21 AM, David Beard said:

We agree on something?!

you too***:unsure:

On 10/20/2020 at 6:43 AM, Urban Luthier said:

As for CG visualization - i think what would be very useful as a study aid is the kind of techniques automotive designers use to study the curvature of class A surfaces. In the old days you'd need tools like Alias to do this but now you can do it in any number of tools like Fusion (Free) or Rhino. 

yes

On 10/24/2020 at 5:57 PM, Mike B said:

The real utility is that the images I provided can (and will) be 3D printed. This should be a useful study aid. In addition, corresponding arching templates can be machined, laser cut, or printed.

Thank you for the access to this information.

 

This arching shows a lot of key things, that need to be understood in back arching,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,nuf said,,,

683624132_stradbackbettsrs.thumb.jpg.e676a1be557d6c5c8657daf64eef0e23.jpg

 

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2 hours ago, Evan Smith said:

 

 

This arching shows a lot of key things, that need to be understood in back arching,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,nuf said,,,

683624132_stradbackbettsrs.thumb.jpg.e676a1be557d6c5c8657daf64eef0e23.jpg

 

That is not nuf said.  Say more,  what key things are you seeing?   Seriously,  I'm a noob when it comes to arching.    I do like this.  it makes visualizing the contours much better than just looking at a photo of the instrument.   I would really like to have a 3D printed version of both plates top and back but having a hard time convincing my friend who has a 3D printer to do that for me.    

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On 10/20/2020 at 5:43 AM, Urban Luthier said:

As for CG visualization - i think what would be very useful as a study aid is the kind of techniques automotive designers use to study the curvature of class A surfaces. In the old days you'd need tools like Alias to do this but now you can do it in any number of tools like Fusion (Free) or Rhino. 

I have been using (con)Fusion360 to design my plates lately, and found that the curvature analysis tools are an immense help to get smoothly varying shapes.  But that might not be a good thing if the goal is to imitate the hand-carved plates of the Old Guys, where the gouges and scrapers used may have influenced the shapes to some degree.  It is very easy and convenient to use smooth splines to make arching in CAD and CNC, but those shapes are more difficult to make by hand.

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On 6/18/2021 at 9:25 AM, Don Noon said:

I have been using (con)Fusion360 to design my plates lately, and found that the curvature analysis tools are an immense help to get smoothly varying shapes.  But that might not be a good thing if the goal is to imitate the hand-carved plates of the Old Guys, where the gouges and scrapers used may have influenced the shapes to some degree.  It is very easy and convenient to use smooth splines to make arching in CAD and CNC, but those shapes are more difficult to make by hand.

Regarding imitating old masters, I agree with you Don. Tools for visualizing Class A surfaces can help with the initial shapes but isn't the best solution for visualizing the type surfaces left by hand work. I think this image (Guarneri tenor) says it all. I expect you'll find a way to set up a CNC template to get you 90% of the way there. Pun about Fusion noted ;). I notice the software slows down with each passing release...

504976474_1644AGuarneriViolaTenor(LLib)-ARCHING-top-dimensional-bass-cBout.jpg.d053bea9f237775ea01849e5634b7a7f.jpg

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1 hour ago, Urban Luthier said:

I expect you'll find a way to set up a CNC template to get you 90% of the way there.

There's always hand-finishing needed, at least to get rid of the toolmarks from the CNC bit.  It's not that big of a deal to allow some more stock for hand-carving.  Getting rid of the major volume of wood and establishing some basic geometry without having to diddle with templates are the primary benefits of using CNC for arching.  Cutting the purfling groove and the plate outline also help me immensely.

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On 6/18/2021 at 6:21 AM, MikeC said:

That is not nuf said.  Say more,  what key things are you seeing?   Seriously,  I'm a noob when it comes to arching.  

 

 

40540165_stradbackbettsrs.thumb.jpg.bd07ffcd63ddd1deb135368712d6c75a.jpg

 

This really exemplifies the change from the c-bout cross-arch, through the upper corner and how it spills out across the upper bout, and ends up puddling into a wider channel surrounding it like a trampoline. Whereas going south through the lower corner the arch follows the edge a bit more faithfully, but not crowded. Going north the arch just gives a nod to the edge shape and continues to spill out on to it's destiny.

 

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Thanks for your comments on that.  I've noticed those flatish areas around the perimeter in CT cross sections also.   I would like to see an image like that of a top plate.  

Is that a Guarneri pictured earlier?  That pinch looks like  a ridge leading away from the edge and other smaller ridges can be seen.  probably remnants of gouge marks, the gouge used cross grain.  

 

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