You would find it useful to look at my paper on Violin Arches in the “Violin Society of America/VSA Papers”, 2018, Vol xxvii, No. 1.
I suggest you do not want to put a curve - like the centerline curve - exactly through all the points you measured, but rather choose a nice shape - Bezier curve with a chosen number of control points is the kind of thing I used - and fit it to the data you have.
Hi @davidgolber
Do you have a link to the paper? I would like to have a look…
Thanks,
Abraham
Thanks for posting this link. Reading now…
Thanks for this link, Fred.
https://vsapapers.org/index.php/journal/article/view/7/5
In a message dated 3/30/2019 21:32:35 Eastern Standard Time, mcneel@discoursemail.com writes:
Abraham Wechter
March 31
davidgolber:
Violin Arches in the “Violin Society of America/VSA Papers”, 2018, Vol xxvii, No. 1.
Hi @davidgolber
Do you have a link to the paper? I would like to have a look…
Thanks,
Abraham
Hey gents -
I finally had some time to work on this again. I believe I’ve made some progress using various tips gathered in this thread.
Essentially, I’ve manipulated some of the reference lines. Seeing as my measurements from the actual instrument weren’t perfect, I’ve afforded myself some artistic license.
I found the best result for my intersecting curves was to use @markintheozarks advice with a 3-point curve trimmed to my reference points. I then drew a line to zero out my curve at the perimeter line and used ‘curve > blend curve > arc blend’.
So far so good.
I then joined all the segments of a given curve and rebuilt each curve using 5, 6 point curves as per @Stratosfear.
This is where things went south a bit.
What I noticed is that when I split everything so that I could use the ‘sweep 2 rails’ command, I couldn’t split items. Closer inspection had me realize that after rebuilding the curves, it shifted my intersections slightly, hence not being able to split curves.
I decided to undo the ‘rebuild curves’ command just to see if I could keep going and surface this thing, even if riddled w/ mistakes. That’s the screenshot above. (I wasn’t able to sweep the missing ‘quadrant’ for some reason - not sure why.).
Here are the settings (just used default) to sweep all of these ‘sections’ - if you have tips here on better settings, please advise…
Two suggestions were made on how to surface this model (by @Stratosfear and @abrahamwechter).
I realize I’m likely way off on surfacing (and probably jumping the gun since the 'rebuild curve’s blew out my intersections) but again, I wanted to keep moving / learning even if it’s clumsy. In short, I’m not sure how to go about surfacing this as per either of these two options:
“Then you can build surfaces from Edge curves. You want bezier surfaces that can be easily point edited and matched.” (@Stratosfear)
OR
Sweep 2 Rails with tangency enabled to produce the best result, contour through surface and manipulate lines to get smooth, then, run network surface to finalize. (paraphrased, from my conversation w @abrahamwechter)
I realize that with what I have, there isn’t consistency between the quadrants (for lack of a better word) that I’ve surfaced.
If anyone can offer some guidance on where to go from here, I’d greatly appreciate it.
I’ll upload the recent file in case it’s helpful.
Back_Recurve.3dm (3.4 MB)
Thanks in advance.
UPDATE -
Not sure if this is the right way to do it, but I tried the patch command and selected everything, then trimmed off everything outside my perimeter… seems to look okay. Open to feedback on this.
Patch only on the outer border curve and the middle profile.
Back_Recurve.3dm (381.3 KB)
Thanks, B.
Is it possible to save the file you posted so it will open in Rhino 5 (I’m on a Mac if that matters). OR - is there a way I can open this file / something I can do on this end? If using the patch only on the border and middle curve, what do you recommend for surfacing the rest?
Cheers.
MW
Hi Mike - for what it is worth, I’ve found this surface layout to be pretty good for these designs:
-Pascal
Sure. Here is the Rhino 5 version. For the “Patch” command I used the blue outline and the green curve across the middle. Then I additionally split the patch surface with the red curves to get the shape you were looking for. Note that the border is not perfectly leveled, so there may be some areas that are a fraction of a millimeter raised above the ground level. But that should not be a problem when you combine that shape with the vertical extrusion that will form the thickness of the guitar’s body. 
Cheers,
Bobi
Back_Recurve-1 (Rhino 5).3dm (379.6 KB)
Thanks Bobi!
I’m just trying to get my head around what you’ve done (looks great!). So, you just ignored the intersecting lateral curves (not required?) and patched the perimeter w/ the centre-line? From there, I guess it’s just a matter of an extrusion on the cutaway portion of the curve (red line) and then a split? I tried to do this and notice I had to extend the red line slightly past the perimeter in order for the split tool to work (perhaps you can let me know if that’s the best approach or if there’s a ninja trick to do this differently).
As an aside, in my other thread, I have a new file I’ve been working on (same project). I’m just wondering if that would have been a better reference than the file in this thread - not sure if you have time to take a look:
Back_Recurve-TEST-JAN2020-V2.3dm (3.3 MB)
In the version you sent, I notice you’ve mirrored the perimeter to make a non-cutaway (or maybe I did that - lol - it’s been a while since I worked with that older file). Do you find that to surface this properly, that it’s better to have a non-cutaway version and then subtract it? I assume that is what you meant by “…split the patch surface with the red curves…”, which is what I did in the above screenshot.
Again, my more recent model may be more true to form (or at least have a better shape) as I borrowed the arch lines from a 17" archtop DFX file I found online and scaled / adjusted them to fit my shape.
Thanks a ton!
Mike
