There is a gear template designer on woodgears.ca, a website dedicated to wooden gears and other wooden mechanical things. The template designer takes various parameters and produces patterns for cutting out gears from plywood or other materials. The output format is HPGL, which uses units of 1/40 mm. So the conversion to Postscript units is (72 / (25.4 * 40)).
The settings I used were two gears, both with 20 teeth, 10mm per gear tooth,
contact angle 25 degrees, 3 spokes, bore diameter 6.35 mm (1/4"). When I asked
for a print, I only got one gear but that's OK because they're identical. The
result is the file gear.plt.
There is some great information in the online material for Carnegie-Mellon's rapid prototyping course. Gear teeth should have a shape described by an involute curve described here. The fact that this information is available online means that I can eventually put it in the Python code and not need to go to the woodgears.ca website. And check out the section on rigid body mechanics. Also, there is info about stepper motor sizes here.
Initially I wanted to put together a little Python library that enables gears to be copied and repositioned, and the center hole replace by a hexagonal cutout for nuts. For my immediate need, the wrench size for the hex cutout is 7/16". This is the beginnings of a library like that. It looks like it may be possible to do something a bit more ambitious.
Download a reasonably recent Jython installer jar file and run the installer. It's convenient to follow the default and put the installation in a subdirectory of your home directory.
Make sure you have a Java JDK and Maven installed, and type
mvn clean packageto build the Java code into a jar file. To run the script, type
java -jar $HOME/jython2.5.2/jython.jar mygears.py [args...]Let's try to borrow from what we learned working on geom3d.py in the proj-driver project. And if possible, unify these two projects.
For starters, geom3d.py has lovely classes for Vector and BBox, which could accomodate 2D geometry with
no trouble at all.
Actually let's just think about what we really need, rather than blindly reproducing everything here.
After some thought, I think unification is eminently practical. You can use OpenSCAD from the
command line
to generate an STL file, and I think a little bit of work can get everything up and running
that way. Rewrite the code that runs underneath mygears.py, and make it generate extruded polygons in
OpenSCAD.
Postscript generation is no longer needed, see below.
We need something that takes a bunch of 2D shapes in a
plane and produces Postscript. The code in proj-driver takes a STL file, which is a bunch of triangle is 3D
space, and computing their intersections with a line in the x-direction.
Let's start to envision another sort of slice operation to generate Postscript. As a plane cuts through a
bunch of triangles, you get a bunch of line segments. You could be stupid and just do moveto lineto for each
of them, but really you want to try to join them to form paths.
In a given Z plane, you compute all those line segments in an XY plane, and then
you partition the plane with a big square grid. Every (x,y) point goes in one square of the grid. You avoid
floating-point ambiguity by using xmin - epsilon <= x < xmax - epsilon as the membership criterion, where
epsilon is tiny.
Now you pick a line segment as random, and you try to grow it at both ends by finding other line segments that connect to it, which is efficient because the partitioning has you looking at only a teeny number of candidates each time. When you have a path, you remove those line segments from the line segment list and add that path to a path list. You keep going until the line segment list is empty. Now you render all those paths in Postscript.
Danger!awesome's website says:
We prefer .eps, .pdf, and .dxf files, though if needed we can work from a range of raster-based file formats for etching/engraving and vector-based file formats for etching/engraving and cutting.
OpenSCAD can generate DXF from a slice of a 3D model.
There is a 2D subsystem in OpenSCAD. Convert the HPGL to primitives. All I need to do is take the output of Gear Generator and convert it to an OpenSCAD polygon, and extrude it to produce a 3D gear.