Summary: Tips and techniques for using Rhino to prepare files for laser and waterjet cutting
There are two main styles of laser cutters: Desktop/plotter and CNC/G-Code driven industrial machines. The two different types require different preparation methods.
Desktop/plotter type laser cutters are generally more lightweight than their industrial counterparts and are intended for cutting non-metal materials in an office, sign, or model shop environment. They work a lot like computer printers – A printer driver is installed and you can simply print to the machine like you would with a normal paper printer, via the Print dialog box.
In most cases, if the laser cutting is done in-house on one of these types of machines, you don't need arc fitting or other geometry conversion. You can use any normal Rhino geometry.
Industrial laser or waterjet cutters normally need CAM (Computer Aided Manufacturing) software to drive them. Geometry from the design software (Rhino) is transferred to the CAM software, which in turn translates it into a language (G-Code) that the cutting machine can understand. Large industrial laser/waterjet cutter examples include:
Working with industrial laser and waterjet cutters require exporting a transfer file with the 2D geometry to be cut, as these machines do not work like printers and virtually none will accept native Rhino files. They may also require the geometry from Rhino to be converted to lines and arcs before exporting. This depends on the age and sophistication of the machine/software used.
The most commonly used export format in industry is an AutoCAD DXF. Others include AutoCAD native DWG and Adobe Illustrator (AI, EPS). PDF files containing vector info are also becoming quite commonly used. All the above formats except PDF can be natively exported by Rhino. To export PDF files from Rhino, it is necessary to print to a PDF printer program. (Many are available.)
A great many industrial cutting machines and software only understand lines and arcs. So, to cut parts sucessfully, it is necessary to convert any free-form NURBS curves (splines) in your file into a series of arcs and lines. By convert, we mean that the spline curve is approximated by a polyline or polycurve containing only arc and line segments. Control the approximation tolerance 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 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 to: Output=Arcs, SimplifyInput=No, AngleTolerance=0, and Tolerance to a reasonable number for your model. Run the Convert command on all curves in the file you want to send to the cutter.
Note: Before running Convert, Explode any collection of NURBS curves that are joined into a set of curves. Run convert on the set of curves. If they are not joined, the convert will work as expected and the exported arcs and lines will match the original curves.
Overlaps, gaps, and duplicate curves 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 can be a quick fix for open curves that need to be closed. (Use this with caution.)
In Rhino, once the geometry has been correctly prepared, use the Export or SaveAs command. Select AutoCAD DXF or DWG file format, name the file, and click Save. When the schemes selection box comes up, choose the R12 Natural scheme and click OK.
To check, reopen your exported file in Rhino or any other software that reads DXF or DWG. There should be only arcs and lines in the file. 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 NURBS splines), try the 2004 Natural scheme.
Comment: Laser cutting work wells for cutting patterns into a fabric materials that will be used as a tablecloth. Check out this site for a better idea of what can be done: http://www.synrad.com/search_apps/materials/Plastics.htm . It's simple enough to do a sample, so once you find someone local take a series of sample materials. Note: Typically this would be done with a low power laser under 100 watts (30 would probably do it). With this sort of power range be sure there is no metallic materials in the material because it won't be able to cut the metal element. One other thing to note: With the right setting you'll do better with a polyester type material rather than a cotton as the laser will cut the polyester and seal the edge at the same time. [Ken Miller - 2005-11-10]
Comment: With the new V4 print modes laser cutting directly, Rhino works wonderfully. No converting to line, polyline, and arcs . Snappier too.
Comment: I think 30 watts is too much. We had prototypes made of .004“ PET film done on a 35W CO2 laser and the edges were a bit singed. This is okay for initial prototypes but not for presentation. Even at 10 or 15 watts on a .003” beam, the operator probably still has to be careful with the power settings of the beam and travel speed of the head. [Jensen Didulo - 2005-11-10]