Voilin curves in Rhino 5

polysurface
rhino5
unhandled

#1

Hello!

I’m trying to draw a 3d surface reflecting the negative shape of a violin. It will be lated machined with CNC on wood.
I have the violin contour, and 5 depth curves. What would be the smoothest method to do this? Below are some images. Thanks in advance!




(IVELIN PEYCHEV) #2

Hi,

can you get 2-3 curves in direction perpendicular to the one you have?
If so, you can use surface from network of curves command. But you’ll need to explode the closed curves shown on the pictures and use only the curve that defines the shape of the surface.

Question:
Do you want the surface to go through these curves, or they will act as controls?

Could you upload the file with the curves or similar. With the contour of the violin (or similar). This way we can try and give you a solution approach.


#3

Hi!
Yes, the closed red curves can be exploded and use only the top curved part.
The surface has to go through those curves and the black contour.

So Surface from network of curves would be the best approach?
If I get the chance I’ll upload the file later

thanks


(IVELIN PEYCHEV) #4

Not the best approach. You’ll have to try.
Loose loft could also be a possible solution. However you’ll need to make adjustments if you want your surface to pass exactly through these curves.

Sorry, I’m not familiar with interior structure of a violin, are these sections you have contours of the internal framing? Maybe they are temlpates for the shape. You did mention negative shape.

This is using the command Patch surface
I also create one spline in the perpendicular direction.

You can adjust the stiffness to change how the surface behaves around the curves.


#5

Thanks Ivelin! I’ll try with the patch, it seems like a good choice


#6

Because the outer boundary has sharp curvature deviations (corners) you should not use it for generating the surface because those discontinuities will adversely affect the surface curvature.

The general approach would be to model the surface bigger than you need based on your cross sections, then trim the surface with your boundary.


(IVELIN PEYCHEV) #7

You can’t really do that if you don’t have more curves.
If you rely only on the curves provided, in the middle area where the sharp edges are you’ll get gaps. I think Patch does the job pretty well. If only there were more curves at the critical locations especially.


(Abraham Wechter) #8

I model similar shapes often and find that while patch through 4 or 5 cross sections will give me a smooth shape with no creases it will often deviate more than i want from a co planar perimeter, and not follow my design intent sufficiently even if the surface is modeled larger and trimmed back to your final outside shape afterwards. Networksrf and even a series of adjacent sweep2 surfaces with tangent continuity can follow your design intent more closely but i often need to smooth out the surface afterwards to get rid of little creases, ripples and dips that can show up when your cross sections are followed too closely. So i often model for accuracy first then run the contour command to generate a relatively dense series of cross section wires in both x and y axis-maybe 5 mm spacing. Then i run the patch command through this denser network of wires to “relax” the surface a little but still not deviate too far from my original design intent. You can play around with contour and patch wire density to get the balance you want between accuracy and smoothness.


#9

I’d handle it like this.


(Abraham Wechter) #10

This looks quite nice. Would you be willing to post the 3dm file and share your modeling method?


#11

Don’t expect to generate viable violin top plates from that little information you have. If you understand german, you may try look into the Institut für Musikinstrumentenbau in Zwota (www.ifm-zwota.de) they did some research in CNC machining back in 2006. They even used Rhino to reverse engineer the surfaces.

The actual plate geometry is way more complicated. And the geometry defines the sound so you may want do get it right.


#12

as it was explained to me by the customer, those depth curves are the ones used as templates for handmade violin. The mould i’m trying to make here is an negative mould of the back plates so she can place the plate and carve the inner side, so it doesn’t have to be perfect. Great data though! i’m not fluent on german but I’ll check it


#13

You can explode the curves, then use extend to get needed amount of curve and do a loose loft command.
Then trim or split using the outline of the violin.


#14

Yeah, this is not enough info.

On the tops of instruments in the violin family, the mandolin family and on archtop guitars, there is, for lack of a better word, a recurve all around the edges.

To see that accurately, you need contours perpendicular to the Z axis.

I’m struggling for the right words here, but I think the recurve, a short distance where the plate is slightly convex, moves perpendicular to the outside edge of the instrument.

Iike, you could model it roughly by offsetting the outside edge by 1/2" and 1" inwards, gumballing the middle curve down 1/8" or so, and lofting.

I’d do the whole thing in Clayoo if it was me, but it’d be a multi step process and it’s not a cheap plug in.


#15

As a template for further manual tuning, you don’t need a lot of detail. In fact it’s probably better to leave room for the work.

Precision should not really be an issue, as you can expect the whole surface to be retouched. I think @Stratosfear’s approach is probably the best. It gives you a simple and good quality surface and closely resembles the original process.