I have been trying to mill violin plates with EMC for longer than I care to admit, but am not dead yet. I am working from Carleen Hutchins "New Violin Family" drawings. I scanned them on a really big HP scanner, digitized them, and imported them into Mathematica, and then fit curves through them. These and most other violin plans do not have enough cross sections to uniquely define the offsets (as they would be called in boat building) or the thickness distribution everywhere. You are forced to extrapolate the complete surface from very limited data.
As other replies to your post have suggested, I used BSplines to describe the edge curves, with the surface of the violin top or back given by a bilinear Coon's patch, and the arching defined by the Curtate Cycloid. The results are still not good enough, because the surfaces do not have well behaved normals everywhere. Since these surfaces need to be done with a ball mill, you need a reliable normal vector to generate the tool path. The key issue is the Coon's patch, which is not really up to the task of describing the violin plates. To indicate how far afield I have been looking (to replace the Coon's patch) - the latest attempt is to pretend the violin top (or back) is a square sheet of rubber that is being stretched until it matches the outline of the violin. I solve a finite element problem for the deformation of the rubber sheet. The deformation defines the surface in the interior of the bounding curves. As elegantly nerdy as this is, there are still places where the normal vectors misbehave - so the milling operation fails in spectacular ways (think swiss cheese). Next step - replace the virtual rubber with a virtual soap film (membrane), hoping it will be better behaved than rubber. I don't have a membrane element in my finite element code, so am stuck until that is ready. It's not all doom and gloom around here - I have violin fingerboards beat. [email protected] > From: Kirk Wallace <[email protected]> > Subject: [Emc-users] OT: 3D Surface Generation > Date: 12September, 2011 5:18:40 PM ADT > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Reply-To: "Enhanced Machine Controller \(EMC\)" > <[email protected]> > > I would like to mill some 3D surfaces (violin plates) but I need a means > to go from a paper plan to g-code. I have Synergy with 3D, but I would > prefer to use a free and open solution. Heeks looks promising but > doesn't look like it is ready for general consumption yet. It looks to > me like I should be able to use a few key points such as a set of 2D > curve end and center points plus some sort of curve fitting algorithm to > come up with the intermediate points on the curve. I looked at Bezier > and NURBS curves, but from my brief look at them, it looks like the > curves only go through the known end points and not through known way > points. Is there a curve type I should look at? Or, even better, is some > one machining 3D curves appropriate for instrument making or boat hulls > and would like to share how it is generally done? > > Kirk Wallace ------------------------------------------------------------------------------ BlackBerry® DevCon Americas, Oct. 18-20, San Francisco, CA Learn about the latest advances in developing for the BlackBerry® mobile platform with sessions, labs & more. See new tools and technologies. Register for BlackBerry® DevCon today! http://p.sf.net/sfu/rim-devcon-copy1 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
