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I hope this isn't a terribly stupid question. I've spent the last year and a half learning Rhino on my own. I can do pretty much what I want but I seem to lack some knowledge with separating a polysurface from a solid. For example, I was modeling a strat the other day. I dug up a DXF of a strat, turned it into a planer surface, and extruded it to what I'd call a solid ( maybe it isn't a solid since I didn't start with a solid?) that is 1.75 thick. I extruded all the cavities and was left to do the contours...here is what I seem to have issues with. I constructed the tummy contour by drawing curves and adding surfaces. It wouldn't split from the body??? I finally made it larger so that it was sticking out of the top and back, and it split. Question.... what are the rules for splitting? Boolean never seems to work that much either using a similar construction process. Are there some fundemental rules to all this that I am not aware of? Thanks for your responses.

Marty I have found that you either have to have surfaces touching or slightly larger (like you did) to make the split. I don't use boolean often, but when I have, there had to be really good surfaces or solids.

Mike

Kind of the same thing with trim function. Extending all surfaces and trimming to get model that does not have naked edges.

The guys pretty much covered it. A surface can look like it's coincident with another, but it might not be. You can check the exact intersection by using the intersect command. The best way to get around this is to extend the surface, trim with it, and then use the newly formed edge to trim the original surface.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

OK thanks for the replies. I thought maybe there was something more to it. I guess I figured it out like everything else by trial and error. Mostly error...LOL.

Marty,
"Bullying and spitting" are strongly discouraged on this forum!

Nelson (just trying to get in the last word here)

OK I'll be good............. While we are still on this topic, does anybody have any idea of what is the best way to isolate the contour body surfaces on a strat so I can just generate g code of the two particular contours for the arm and belly? I want to add that gcode to existing files I already have made.
I'm using Meshcam for 3D and generating the drawings in Rhino. Thanks!

Marty if the body is joned surfaces, select the body, and hit the explode button right next to the join button. This will seperate the body into seperate surfaces, including any fillets you have. If you decide to rejoin, make sure you select everything at once, are you may end up with a model with holes in it that don't appear to be holes.

Mike

Boolean's act differently depending on the surface normal direction. It's good practice to have the surface normal direction pointing out of the part you want to trim.

Sheldon,
How would one check the direction of the surface and change it if need be.

Mike,
I'll see what happens as I have already isolated them by themselves. I just didn't try to create code with them.
Thanks.
Marty

Use the Dir command to show the normals, and then hit 'flip' to flip them if need be. You can also select a particular surface and run the Flip command to flip it.

Using Dir lets you see the normals, so it's a better way to go unless you're in a rush.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

OK, I have the two separate surfaces floating in space. Is there a way to just have the cutter drop down from zero ( the top of the body)and machine out that contour area until it reaches that surface without machining the whole body area? I'm sure it can be done in meshcam, but I'm not that experienced with it. I have all the strat routs turned into gcode,and what I would like to do is rout out the pickup, neck and control cavities via 2d and then machine the body contours after that, one side first and then flipping it over and doing the spring cavity routs and the other contour. I hope that makes sense. It's faster in my opinion to do that instead of covering the entire surface area of a body blank in 3D. Thanks for the help again.

First off, realize that I don't have a machine yet (hopefully in two weeks!) and have generated exactly 0 lines of G-code. But, if your coordinates are matched up with the ones of your strat and the surfaces are located in the correct location in space, why couldn't you just generate g-code for those surfaces and run them as necessary? You'd basically just make sure that your zero is in the right spot.

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http://www.birkonium.com CNC Products for Luthiers
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You are correct and that is the approach I would take. The problem is that I have 2 alternatives to g code generation. I have an older version of BobCad which does 2D nicely and a copy ofMeshCam which does 3D nicely. My meshcam experience is limited to necks at this point where a whole blank is being machined. My problem is I don't know if just a 3d surface is machinable by itself in Meshcam, or if I would have to extrude it into a solid first then try and machine it... I was hoping there was a quick and easy approach that I was overlooking . I guess I'll extrude it and see what happens.