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There's definitely a difference between a linear copy and an offset, though it'd be small on something like an archtop plate. The only time they'd be the same is if all your surface normals point in the exact same direction (which only happens on one kind of surface )

All my arched top surfaces are either one or two surfaces max (if using two, they'd be symmetrical and I don't think any are like that anymore). I've had to use multiple surfaces on PRS-style instruments as there's far too much going on in the horn areas. The more surfaces you're dealing with, the more issues you need to deal with regarding transitions and continuity, and making changes on 'patchwork' models SUCKS!

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I agree with Bob, that there is definitely a difference between an offset and a copy...but that for a fairly flat carved top (such as an archtop) the amount of error is fairly small.

Patch surfaces can be pretty quick to generate, but I think you can get closer to "perfect" by building a surface with lofts, sweeps, and network surfaces. These features force the surfaces to actually follow those guide curves and not just coincide with them.

As was mentioned before, if you can get good results with fewer surfaces...then that does make everything easier.

There's a million different ways to model something, you just have to figure out what works for what you are doing.

Best,
Trev

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http://www.PeakeGuitars.com

http://www.cnczone.com/forums/showthread.php?t=8814&page=5

The "GCode to DXF Converter.exe" shown in the top message seems to work fairly well.
I was able to convert archtop plate contour GCode into DXF and import it into Rhino.
Had to remove the header info from the program first as it likes to see only cut geometry.
Has an option to remove the G0 rapid moves.
Nelson

Hey Nelson, it sounds like this is backplotting the code. If this is the case, the resulting geometry would not match the finished part geometry although it could be useful in reverse engineering the shape.

Trev

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http://www.PeakeGuitars.com

Trev, I was thinking that the GCode generated geometry would be offset by the amount of cutter radius like when converting a digitized point cloud into a surface?

Pretty close...if you took all the little end points of the lines showing the tool moves, you could treat those points as your point cloud. From this point on it is same process I used on your archtop...you would model up a surface that fits all these points nicely and then do a surface offset (by the radius of the ball mill) to get the actual geometry. You have to do the surfacing though - there's no way to just offset the toolpath unless you do some of that math that Bob and I were chatting about earlier in the thread...

Trev

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http://www.PeakeGuitars.com

I see what you're saying, Trev. I was able to LOFT the resulting tool path and save it as an STL. Just assumed that an offset surface could be made from that.
You know what they same about ASSUME.
Nelson

Hey Nelson,
I'm not too familiar with meshes (an STL is a mesh) but it looks like there is an offset mesh option...that would probably do the trick!

I'm a big fan of keeping things as surfaces - seems to be easier to create them as well as to modify them if needed.

Trev

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http://www.PeakeGuitars.com