Free Tools for Fabrication

Here are my notes on free tools which can be used to drive the fabrication machines. I've split the list into functional groups of applications, and have notes on what an ambitious hacker could do to make each of these programs even better for our use.

2D drawing

Needed: a 2D drafting program that has object snap facilities, allows specification of exact dimensions, boolean shape/path operations, exports to useful formats (DXF/AI), and ideally allows parametric specification of dimensions so that, for example, you can globally specify a new fit tolerance and have all the parts updated accordingly. The non-free tool here is CorelDraw 10; Corel has a version of CorelDraw 9 for Linux. CorelDraw doesn't do parametric dimensioning (as far as I can tell); it has all the other desired capabilities, though.

Free software alternatives:

Inkscape (C/C++). I just discovered this program (Apr 2004) but it seems very nice. Exact dimensioning and boolean operations are supported. Parametric specification of dimensions doesn't seem to be supported (yet?). It reads and writes SVG; but I've got tools for converting SVG to DXF. I think this is the "way of the future", and if I were to hack on something, I'd spend my effort adding parametric dimensioning to Inkscape and writing more SVG conversion tools.
OpenOffice (C). This is a functional equivalent of CorelDraw -- it's even nicer in some respects: when you type in a new dimension for a shape, you can specify which point you want anchored for the resize (I had a part ruined on the laser cutter when I resized my axle hole and CorelDraw decided to anchor the top left corner, not the center). The output formats are a little limited: there are lots of raster formats, but the only vector formats supported are EMF, EPS, MET, PCT, RAS, SVG, and WMF. I'd like to see DXF or Adobe Illustrator formats. I'll update this item after I've had a shot at making an OpenOffice document play nicely with the laser cutter. (Thanks to Bryce Harrington for the pointer!)
QCad (C++/Qt3). A basic DXF-in/out 2D cad package. Very easy to use. All the desired features, but the parametric dimensioning is very limited: you can create shapes which are stretched by a specified amount on import. It can create arcs and circles but not ellipses or beziers, which may or may not be a severe limitation for you.
Sketch (Python and C/GTK). This is a fairly complete vector drawing program with a nice UI. It allows object snap and exports to a variety of formats; it is also based on Python with a plugin interface so extension and mathematical shape description should be easy. It does not seem to have UI for specifying exact dimensions of shapes; this seems like it would be a simple hacker project. Boolean shape operations are currently implemented incompletely as an extension called PathUtils; implementing this within sketch completely (and correctly?) is included in the TODO file for version 1.0. Finishing the details to make this a useful CAD tool seems like a good project for a motivated Python hacker.
Kontour (formerly known as "KIllustrator") (C++/KDE). Another drawing program with a nice UI. It is missing boolean shape/path operations, object snap, and parametric dimensioning. Its set of export formats is quite limited as well.
Xfig (C/X). This is the stable grand-daddy of Unix drawing programs. Its native file format is simple and well-documented, which makes it very easy to write programs to mathematically generate fig drawings. It is easy to specify exact dimensions, but object snap, boolean path operations, and parametric dimensioning are all missing. Adding these features would again be a good hacker project.
Sodipodi (C/GNOME). Uses SVG as its native format; I'm not sure if this is well-supported by other tools as an input format. It also has a very eccentric user interface. Its features and missing features are otherwise the same as xfig.
Dia (C/GTK+). This is a diagramming tool like the Windows program "Visio". It has very good export support, but seems to be missing exact dimensioning, object snap, and boolean shape operations.

Other useful tools for 2-d drafting:

AutoTrace (C). This program converts bitmaps to vector graphics. This is great for taking scanned or found artwork and converting it into paths for the laser cutter or waterjet. Helpful hint: make sure your input graphics are black-and-white only --- no grayscales! Grayscales look smoother on the screen, but autotrace tries to create a separate contour for each color in the shading, leading to screwed-up results.
Here's a typical session with AutoTrace:

This image was pulled from the web.

I scaled it up by a factor of two, converted to black-and-white and touched up a few pixels to get this image.

I then opened up all the closed areas in the image (the bits that would become unsupported if I cut along the edges of the black areas).

Running AutoTrace on the above then gave me this beautiful smooth and scalable version of the graphic. If your browser can handle SVG, you might be able to scale this version up and down. Smoothness that just won't quit!
A similar tools is potrace, which I actually like even better. There's a paper by Peter Selinger describing the principles upon which it is based; I used this for my stained glass project.

3D parametric modelling

Art of Illusion (Java). This seems the most promising, with a very nice UI, but I haven't gotten enough experience with it to determine if the underlying representations are suitable for engineering/fabrication work.
Sced (C/X). "Constraint-based scene design." The underlying parametric engine looks sound, but it doesn't look like exact dimensioning is exposed by the GUI. The export formats are limited to rendering engine input formats and VRML, which is likely insufficient for driving fabrication tools. Constructive Solid Geometry is supported. All arcs are converted to lines at a rather coarse granularity; it is hard to determine if this is part of the underlying representation (bad) or just an artifact of the on-screen renderer. The GUI as a whole is rather poor.
BRL-CAD (C/Tk). Looks capable, but you have to sign a rather evil license agreement with the US Military before you can see source or binaries.
Graphite is a "research platform for computer graphics, 3D modeling and numerical geometry". It is licensed under the GPL. I haven't tried this yet, but it may well be useful.

You may also be interested in ViewSTL, an open-source program for Linux/IRIX/Windows to let you view STL files (such as those for the Modela or the 3-D printer).

Schematic capture and PCB design tools

I use XCircuit for schematic capture and PCB for PCB layout. The current alpha version of PCB has an auto-router I wrote which Works For Me. XCircuit stores schematics in Postscript; PCB exports to Gerber files. You can send the gerber files directly to Alberta Printed Circuits to have them fabricated, or use my Gerber tools to drive the Roland CAMM-1 (at present) or milling machine (eventually).

Some schematics I drew with XCircuit

Corresponding circuit boards created with PCB

The gEDA project has what look like very nice schematic capture/netlist generation applications; there are also circuit and verilog simulators, waveform viewers, and gerber previewers in the project. In particular, the Icarus Verilog compiler seems to be undergoing very active development at the moment. I'd be very interested in hearing the experiences of anyone who's done a complex schematic in gschem and used it to create a PCB design.

You could conceivably use Dia (see above) to do the schematic capture, but Dia doesn't seem to export netlists, which means your schematics may be pretty, but they're useless for making printed circuit boards from.

Other schematic capture tools include: Oregano (officially abandoned, but talks to SPICE well), and Gael (as of this writing woefully incomplete).

Programming libraries and file formats

OMAX File formats (RTF). Details the DXF and ORD file formats used by the OMAX waterjet.
OpenCascade (C++). This is not an application, it's a set of application development libraries for 3D modelling, including file import/export and all the complicated NURBS, etc, functionality. However, OpenCascade has its own peculiar license. It seems to be a GPL-alike, but I'm not a lawyer. Your milage may vary. It also seems to be a very large body of code, perhaps unmanagable for casual hacking --- but there is an existence proof that this is possible.
DIME (C++). DIME is a DXF file format support library. It does not contain any rendering methods; it is designed for input/output processing.
OpenDWG. This web site contains the official format spec and promises tools, utilities. No libraries unless you're a member of the "alliance", though.
Information on other file formats: Gerber, HPGL, and DXF.