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I decided to give the NetworkSrf command a go to create the carve tops. I quickly ran into problems though .

There are small little gaps between the surface edges. I've tried the JoinEdge command to stick them together; it works - but the other edge(s) will end up with gaps. Attached are some photos illustrating the little gaps and some of the curves I have used to create the network surfaces.

I will post in the next few hours explaining how I got this surface with plenty of pictures.

Will this surface be ready for machining even with the small gaps?
Are there any dvds/videos/tutorials that could be useful for creating surfaces?

Thanks,
David

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David
Vancouver, BC

It depends on the size of the gaps. Machining software will skip over lots of little gaps, but sometimes they can create problems where the software doesn't handle them quite right and makes 'wiggles' in the toolpath.

If they're little cracks, and the surface is otherwise geometrically correct, there are a few things you can do to patch them up. You can make some planar surfaces to fill the gaps just by duplicating the naked edges and joining them with lines and using edgesrf. It isn't pretty from a surfacing standpoint...but the CAM software doesn't care, and it'll stop the wiggles from happening.

You could also convert the surfaces to meshes in Rhino and then weld the edges that way since meshes are easier to fix. Once again it makes sort of an ugly model from a CAD perspective...but it'll machine just fine in CAM and that's what matters!

You can also experiment with how you make the surfaces. Besides NetworkSrf (which already has a lot of options so far as how edges are followed by the surfaces and which I DO love), you can also mess around with sweep2, edgesrf, and patch.

Another trick is that you dont' necessarily need to make your network surface to the exact edges of your top contour; make a bigger, rectangular surface and then trim it to shape with the top outline. Often the issues with making a surface are caused by trying to make it a certain shape from the get-go instead of making something with the right contours and then trimming it to shape.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

The surface looks pretty smooth, and should machine fine. Along the lines of what Bob was saying....As long as the "gaps" aren't big enough to where the tool tip could conceivably dip into there, CAM shouldn't notice them.

As for avoiding the issue in the first place, I have been using the sweep2 command in conjunction with the network surface command. With parametric software like solidworks, I have had better luck breaking the surface into sections as you have done. With Rhino, I seem to get more seamless results surfacing bigger chunks at a time. Doing a violin carved cutaway top like that though, I don't think you can avoid doing some "patching" up near the horns - regardless of the software.

One other thing to do is to make sure that you have the display controls cranked up to their highest levels - sometimes this stuff appears just due to display issues.

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http://www.PeakeGuitars.com

Bob,

I just tried the technique using Duplicated Edges and EdgeSrf commands you suggested. Unfortunately, the edges are actually the same edges! It appears the render mesh just isn't able to reach up there.

I liked the idea to just create a few planes and trim them to size. I'll definitely make more use of that... I used to try patching and ran into all sorts of problems. I did that to cap off the flat/angled top of the body but that tiny gap was still there.

Would it be just a render mesh issue?

Thanks,
David

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David
Vancouver, BC

Parser,

The gaps are >0.1mm; I hope the CAM won't see that! I'll incorporate some double rail sweeps in my next attempt at this top.

Thanks,
Dave

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David
Vancouver, BC

I don't know what CAM software you use, but some require that the geometry be "watertight" or they just won't create a tool path. But there may not be any gaps in the your actual geometry. What you see isn't real geometry, but the rendering mesh. Check the tolerance on your rendering mesh (Render>Render Properties>Mesh). The Rhino defaults are set pretty high to speed up the display. Another way that I like to use is Analyze>Surface>Environment Map. You can adjust the mesh from the dialog that pops up without affecting the global mesh setings.

You can also show naked edges to see geometry edges that don't touch (Analyze>Edge Tools>Show Edges, then only show naked edges)

I agree with all the comments made so far, and yes, not having a "watertight" model quite often will create problems with tool paths, when bringing the model into a CAM package.

What I have found to be quite useful, and I am not sure if Rhino has this feature (I am a solidworks user) is to try and do the following when modeling:

-Create the top surfaces first (so in your case, the top of the guitar body) and then, extrude the surface below, but with a "tangency" constrain to the extrusion. If done right, this will blend the surface.

Sometimes, do to geometry, this might not work, in which case I do this:

I create the surface, and then, where there are small gaps, I create geometry to DELETE with a spline-cut that part of the surface. I then go and use a "patch" tool, to patch that part in, again with tangency constrains, and quite often that does the trick.

Once I then have the model looking pretty good, I use a "stitch" feature, which will take any remaining gaps, and stitch them together, as to create a watertight model. I also have the option of "filling in" the model, in essence making it a solid.

I am not sure if Rhino has a stitch feature, I imagine it would? as it is a great surface modeler...have not used it much thought, so I am sorry I do not know the answer to this...

Just a couple of more pointers...

There's no 'autostitch' like in MasterCAM or Solidworks (though, in general, one should try to avoid ever using them even if they're available!)

Svandru mentioned ShowEdges which is the way to go in water-tighting a model, it shows all the edges that autostitch would attempt to close up, but you can usually do a better job manually. You'll also learn a lot about how trimming etc. can affect things if you use ShowEdges once in awhile while working.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I've reached the next big wall that I can't seem to get past. I'm using RhinoCam2.0 now and I just can't seem to get this to machine. I have no clue what the problem is. Is anyone willing to take a look at the file?

Thanks,
Dave

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David
Vancouver, BC

I've figured the problem out! It appears one of the lines was snapped to a grid intersection that was a sliver away from the actual line I needed to connect. Now it's time to figure out feed rates!

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David
Vancouver, BC