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Modelling An Archtop Guitar

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Guest archtop
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  • great tips, thanks, John

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    Guest archtop
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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

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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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    Guest archtop
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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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    Guest archtop
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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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    Guest archtop
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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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    If you use the Bridge tool, it is very easy to create polys with reversed normals. Your render suggests that this is what you have done. Select all polys and select align normals to fix.

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    Guest archtop
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  • Hello Again Everyone

    I have been using this program for about two weeks now and although I'm still scratching the surface of what it can do, I now have something that resembles the top plate of an archtop guitar.

    It's built poly by poly, like Steve suggested (cheers Steve!). It was tricky around the tight corners of the waist to avoid 'triangular' polys. Still, I hypernurbed it it it came out good.

    Some of my next tasks include:

    projecting the f-hole splines onto the body and keeping the bezier shape, if possible (I have already made the hypernurbs editable, but can't figure out how to cut the shapes from the surface.

    I will need to give the top plate a thickness, but with a catch... the soundboard needs to be 6mm along the centre line and taper to 5mm at the edge.???

    Finally I will need to create g-code from this, buy a CNC mill and make the darn thing! :) I've already made a bunch of these by hand by the way - if anyone's interested to see what the end result is supposed to look like, see archtop.ie

    Many thanks to everyone who has shown an interest here, helping newbies like me!

    John

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    Guest shawnfoster
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  • Remember, The Iron tool can be your best friend when you need to smooth your model .... Keep that in mind when you are modeling.. Your over all model will thank you for it..

    Back when I was modeling a Chet Atkins Solid Body Acoustic Guitar... I used the IRON tool quite a bit to tighten up my own P2P modeling.

    ~Shawn

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    For the f-holes, you have 2 choices:

    1) Don't make the HN editable, then try to model the f-holes into the mesh. This is harder but can give better results (pariclularly if you need rounded edges to the holes) than

    2) Use a boolean on the HN mesh (either before or after you have made it editable). This will work OK but you will end up with sharp edges to the holes. Using the bevel tool on these edges is nearly impossible.

    Modelling the holes is best if you are rendering but you need to be aware of the mesh topology. To make the holes you will need to make extra loop cuts, and this can upset the general form if you are not careful. If this is for manufacturing, I would go with the boolean.

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