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Modelling An Archtop Guitar

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Hi John

You'll be able to this in a couple of months time once you're more familiar with C4D and box modelling. I just started with a plane and selected points then used the scale and move tools to move them around. I then deleted a few polygons for the cutaway area. Then just a matter of extruding with caps enabled and with 1 sub-division. Couple of edge loop knife cuts to sharpen up the edges then a pulled up a few polygons on the top with soft selection enabled. Sounds more complex than really is.

Regards

Nigel / 3DKiwi

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I think the way Nigel suggests is ultimately going to give better results than loft nurbs.

If you already have defined cross sections, then put them altogether on one bitmap and set that as a background image in the viewport. You can use that as a reference when pulling points into position. As you work along the body, you may find you are confused about which points to pull. A method I use when using multiple cross sections is to go to a top view, select the row of points I want to work on then use Hide Unselected. When you switch to a side view, you are sure of moving only the correct points. When you finish, use Unhide All and repeat for the next row.

If you don't need to be exact, then try using the Brush or Magnet tools for pulling up the shape.

As for CAD applications axes, I use Solidworks and that uses Y as up. Applications that use Z as up tend to be CAD apps that started as 2D such as Autocad. Ones that were always 3D such as Inventor, Solidworks, Catia, etc use Y as up. Most 3D CAD systems and C4D are left handed cartesian systems rotated so that Y is up. Autocad is right handed.

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  • great tips, thanks, John

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  • Hello again,

    I was looking for a quick pointer... I'm going with 3Dkiwi's advice and about to try box-modeling. I need the outline of the guitar to be accurate as it will need to conform to an existing body-mould. So I imported the outline, put it as a 'child' under a plane surface, selected all the points and tried to project the points onto the plane. This way I would have a plane with the proper outline which I will hopefully be able to extrude and then manipulate the points. It would be great know how to do that (if it's possible).

    Also, anticipating this potential problem: I have created a template to guage the height at particular points. In an ideal situation I could draw points where all the segments on the bitmap meet the splines on the plane. There will be many points over the template-segments where the the plane's gridlines overlap. i will not know the exact height at these points. Is it possible to delete these and have the hyper-nurbs work out the curvature based on the other points I entered manually?

    Thanks to all for the help,

    John

    post-58759-1225139116_thumb.jpg

    post-58759-1225139234_thumb.jpg

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    I wouldn't bother trying to project the spline. That's possible. Just have the spline in front of an editable plane. Then select all of the spline points, right click and choose the Project too. You'll need to select a plane like XZ depending on the orientation of the spline.

    If you have the plane sub-divided sufficiently you'll be able to model the body reasonably accurately. It may not be 100% but you can get fairly close.

    One thing to be aware of is how hypernurbs works. When you place a mesh under a hypernurbs object the polygons, points and edges are smoothed and projected into new positions. These positions are not their actual position. You can see the actual point position by disabling the hypernurbs object. So you will have to line up and move points by eye and not by entering them in numerically. The higher resolution the mesh the close the smoothed mesh under a hypernurbs object is to the original mesh.

    In the attached image I have enabled the Hypernurbs Cage option (not something I normally do). You can see the actual point positions and their project position.

    Hope this helps.

    3DKiwi

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  • Ok... spent the day trying the box modeling and feel ok about getting a 3d guitar shape using hyper-nurbs. However, I think I need a higher level of accuracy and control over the actual dimensions of the soundboard and arches, since it will be reproduced on cnc and need to match up to other non-cnc parts.

    I did extensive googling and a number of people have created Les Paul models (carved tops, but smaller than the archtop I'm working on). Apparently It's possible to create a very smooth, accurate model using vector-drawings of the arches plus contour patterns (not sure if it's poss. in c4d though). I would assume there's a computer-script out there capable of generating a polygon surface based on the centre-line of the guitar plus the contours. It's logical, I think, that that's the only info you would need: The centre-arch determines the height of the soundboard and the cotours determine how the curvature is distributed around the surface.

    Thanks to everyone's helpful suggestions so far. I'm just not 'nailing it'

    Here's a diagram (created in Illustrator. It shows the height of the arch at different points and how it relates to the contours.

    Does anyone know of a more accurate way of doing this in C4d?

    Thanks,

    John

    post-58759-1225218824_thumb.jpg

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    You could use a method used by a lot of car modellers.

    Using the image you posted as a background to the top view, draw splines following each of the contour bands. The move each spline up in the Y axis by the amount shown. Now use this spline cage as a guide for box modelling the surface. You can switch on snap to spline so the points will align with the spline if you like. Personally I don't bother as the aim is to get the HN surface to pass through the splines, not the control points. When you apply Hypernurbs, the surface will drop back a bit so you will need to move the points again to compensate. The aim is to get the Hypernurbs surface to pass through the spline guides.

    Personally I wouldn't use box modelling at all but build the front polygon by polygon (point to point). This requires less planning than box modelling. Build the first poly, then using 3D snapping, move its points to the splines. When you have completed the first poly, switch to edge mode, then extrude the edge out towrads the next spline by an arbitrary amount. Then snap the new points to the next spline. This way you will get a radial pattern of quads out from the sound hole and will get a better hypernurbs subdivision than a sort of grid pattern. When you finish the front, you can select the boundary edge and extrude it at an angle. Edge extrude down the side, then across the back.

    Heres the first 4 splines set to the correct height with 2 rows of polys built on them:

    post-5909-1225222505_thumb.jpg

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  • Thanks Steve for your last post.

    I've been away from the computer for a few days. So back to the guitar model before my demo runs out!

    Although I'm starting to get to grips with the hypernurbs approach, I still think the polygon approach is interesting. I've been trying to sketch it out on paper to see how the grids will line up. It get very complicated around the edges and towards the cutaway. I found this pic of a violin which was done in c4d. It has the same style arched soundboard as the guitar model I'm building. I think it may be constructed by hand-drawing polys over a template like Steve suggested. Can anyone confirm this? Also I will be putting "f-holes" in the guitar, similar to the violin. I hoped to cut these out of the arched surface (instead of building polys around them). Would this cause problems with the polys? I understand the polygons need to be seamless with a view to converting the model to g-code for a CNC machine. The f-holes are a very particular vector shape and I would like to remain true to the design and exact curvature. Going to try the poly approach now - In the meantime if anyone has any thoughts they would like to share...

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    When you've built the polygon structure as I suggested, you then out the whole lot under a hypernurbs, When you do this you will need edge loops to sharpen up the edges of the sound hole and the outer edges of the body. The vioin you posted uses hypernurbs - you can tell by the way the subdivision is done. How the underlying poly cage is constructed is anybodys guess. The advantages of building it poly by poly are 1) you get the accuracy of the spline cage to snap to and 2) you can avoid triangles and odd shaped polygons that don't subdivide well under hypernurbs. A particular problem with box modelling curved objects is avoiding quads with near collinear edges (they look like a triangle but have 4 points).

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  • Here's where I'm at with the model. This started as a basic plane and I moved the individual points to reference contours on my tracing template. This is similar to what Steve suggested except I'm not snapping to the splines. Perhaps I can try the snapping approach if this doesn't look smooth enough.

    The model looked quite smooth until I started adding more edges. I did this mainly so I can have more control over the edge contours. The highlighted edge is the one that's causing the problem in the render. I drew the new points on the existing grid and then used the bridge tool to connect the points and create edges. Can anyone tell me if this is the right approach or what might be wrong with the render?

    Cheers,

    John

    post-58759-1225644119_thumb.jpg

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