The two main types of laser cutters (Windows desktop/plotter and CNC/G-Code driven) require different preparation methods.
Desktop/plotter-sized laser cutters work like Windows printers. Examples:
In Rhino 4.0 printing is improved so you can simply print to the machine like you would with a normal paper printer, no special treatment or geometry conversion is necessary.
White Paper on using Rhino 4.0 to drive an Epilog Laser
If the laser cutting is being done in-house, in most cases you will not need arc fitting or other geometry conversion. You can use any normal Rhino geometry.
Industrial G-Code-driven laser or waterjet cutters normally require a CAM product up front, although a few may take DXF files directly. Large industrial laser cutter examples:
Laser and Waterjet cutting may require the geometry from Rhino to be converted to lines and arcs, depending on the age and sophistication of the machine/software being used. Export file formats most commonly used are DXF, DWG and AI (AI, EPS, PDF).
A great many industrial laser/waterjet cutter software/controllers only understand lines and arcs. Thus, in order to cut parts sucessfully, it is necessary to convert any free-form NURBS curves (splines) that might be in your file into arcs and lines. By convert, we mean here that the spline curve is approximated by a polyline or polycurve containing only arc and line segments. The approximation tolerance can be controlled by using the correct settings during the conversion process. Approximating splines by a series of tangent (or nearly tangent) arcs is generally preferable to just polylines, because they allow for a more accurate cut with a smaller file and less possibility of slowdowns along the curves, especially with older machines. Consult your service bureau if in doubt.
You can use the Rhino Convert command for this process, commonly called "Arc Fitting". Set options as follows: Output=Arcs, SimplifyInput=No, AngleTolerance=0, and Tolerance to reasonable number for your model. Run the Convert command on all curves in the file you want to send to the cutter.
Overlaps, gaps, and duplicate curves will cause problems in cutting. The CurveBoolean command may work to clean some of these up, but may not entirely eliminate overlapping sections, and it will not fix gaps. For small gaps, the CloseCrv command in Rhino 4 can be a quick fix for open curves that need to be closed (to be used with caution).
If you need to nest many profiles together onto standard stock sheets, check out Mosaix or RhinoNest , both of which run inside Rhino.
In Rhino 4, once the geometry has been correctly prepared, use the Rhino Export or SaveAs command. Select AutoCAD DWG or DXF file format, name the file and click Save. When the schemes selection box comes up, choose the R12 Natural scheme and hit OK.
To check, open the DWG in AutoCAD or any other product that reads DWG or DXF. There should be only arcs and lines. This is one good way to get the most consistent results.
If you do not need to convert to arcs and lines (if your laser/waterjet supplier can read splines), try the 2004 Natural scheme.
If the results are not what you want, please send a sample. or post the problem to the Rhino newsgroup.