This week, a topic very near to my heart, gears.  Catarina’s helical gears from OpenSCAD are gorgeous, and fully parameterized.  As I said before: OpenSCAD is a game changer.

I felt compelled to make this week’s thing of the week (which is a bit late, yes) a tie between the two unquestionably awesome kit robots that have been built and shared on Thingiverse this week.  Each uses standard boards and gear motors to make sturdy, beautiful kit robots!

On the left we have a single-part chassis that accepts standard servos, battery pack and an arduino board– a lovely expression of the bare bones of robotics which could easily be extended in functionality by stacking a shield on the Arduino.  Neat!

On the right we have a really excellent line-follower that really shows off how beautiful and customized an object can be when digital fabrication is involved.  The creator has a lovely website with lots of beautiful documentation.  This design looks really devastatingly pro with that ribbon cable and obviously-custom plastic parts.  Awesome sauce.

Wrapping up Skeinforge Week we have a feature I wish I’d known about a long time ago: Jitter.  The above cups weren’t actually made with Skeinforge, but they’re the best illustration I could find of a big problem: the print head turning at the same point over and over again, eventually resulting in a thick, heavy seam on one side of the object.  All my dodecahedrons have this.

The Jitter setting in Skeinforge moves the stop point around randomly so the seam doesn’t have a chance to form.  Another handy feature from the BitsFromBytes Wiki article!

Most printers don’t have support material yet, but skeinforge can create a fibrous, comparatively-loose mesh of plastic strands for later (often laborious) removal.  This is usually more trouble than it’s worth, but I’ve had it work out well on one or two builds in the past.  (The above Snorks-inspired tower came out pretty dandy once I’d scraped all those plastic hairs out.)

The BitsFromBytes Skeinforge Wiki links a discussion thread where some examples of the Support Material Crosshatch is used, to give you some idea what it can do.  (Another reason I mention this is that it can be on in default, and for most prints you want it OFF.)

Like yesterday’s post, this one is from the BitsFromBytes Skeinforge Wiki.

Here’s an option I ignored because I didn’t know what it was for, but which could have saved me a TON of frustration if I’d known about it.  Clip is one of those little nudge-items that can make the difference between a trouble-free build and a trouble-fought build.  When the print head makes a loop on the build surface, Skeinforge can tell the head to stop short of completing the loop– this matters because if the head makes the complete loop, plastic will get extruded onto the same point twice, resulting in a blob, which can cool into something for the head to pick across in later traversals or mar the surface.

The Clip option is phrased: Clip Over Extrusion Width (ratio).  A value of 0.5 is a jump of half the extrusion width, 2 is twice that, and so on.  The default value is 0.15, but given my experiences with blobs at this setting, 0.5 or more is probably a better choice.

In my original set of Skeinforge tutorials, I didn’t include anything on installation because in all honesty I had a devil of a time getting it to work and couldn’t remember what the magic words were that finally got it to run.  Mercifully, the tutorials page from BitsfromBytes includes this key bit of wisdom: Skeinforge is not set up to handle file names with spaces in them.  More on that later– for now, let’s overview the pieces you’ll need to get Skeinforge running!

First you’ll need to install Python.  Python is a marvelous open-source programming language which I’ve mentioned before.  One of its key virtues is actually the thing that will be most off-putting to new users who are used to C or Java: curly braces are not used to separate parts of a program.  You can get it here. You’ll also need Tkinter.  Tkinter is a library set that provides the GUI features (windows, drawing capabilities, buttons) of Skeinforge.  Last I looked, it was an option box you could check on Python’s installation procedure, but you can get it separately.

BitsfromBytes also recommends an Imaging library and a math accelerator library, but I haven’t needed them.  (Your setup may vary, of course.)

Once you have the full suite of Python tools installed, you’re ready to download the Skeinforge zip file: This version looks really nice! Pick an installation directory with no spaces.  I put the unpacked files in c:\skeinforge, which has no spaces, unlike c:\Program Files\SkeinForge, which is where my first instinct to put it would be.  My current Windows 7 box seems be able to run it from just double-clicking the skeinforge script itself, but under XP I know I had better luck if I called up the command prompt, CD’d to the skeinforge directory (for this reason I kept all my skeinforge directories at 8 characters or less) and typed:

python skeinforge.py

And that’s it!  I haven’t had a very wide installation experience (my Ubuntu install on Ye Olde Lappy is so flakey I couldn’t get Python working, and as for Macintosh, I just haven’t ever owned one) so look to the MakerBot or Thingiverse google groups for help.

BitsFromBytes, long a friend of the RepRap project, is hosting a great Skeinforge page on their Wiki.  Skeinforge is, as I’ve said, a really, really complex tool designed with more of an eye to getting all the features in there than making it easy to use, and finding the “magic settings” for your machine can be a daunting task.

The work on the BitsFromBytes page is really helpful for a number of reasons, not the least of which is that they use images directly from skeinview to illustrate what a given function does.  This week I’ll be picking some key lessons from the page.

This page has a lot of great stuff on it, maybe even enough to take a few of us to the next level in print quality.  When your slicing software is a manually-operated tool, expertise can make a big difference!

I.materialise has launched. If you’ve seen 3D printed artistic objects in art galleries, these folks very likely printed them. Arriving on the scene, they appear to be a direct competitor with Shapeways. Materialise does really high end work and they’ve just opened up a business that lets you upload your own designs. Also, they’ve joined thingiverse and have promised to upload and share some of their of their own designs! I love that Thingiverse is the place to share designs, but if you want to get them made and don’t have a printer yet, i.materialise offers another option for turning your designs into beautiful objects. Cool!

I want to be clear about one thing: when it comes to 3D, it’s hard to win praise from me.  AOI is probably a pretty good 3D program, given how many people use it successfully to do great things, as is Google Sketchup.  However, the warmest praise I can be recorded giving either of them is “we need lots of different points of view!”  (Okay, there was that one time I admitted Google Sketchup was better for scribing things onto surfaces.  But still.)

I say this so you will understand what I mean when I say: OpenSCAD is a game changer.

The above shape, which in any mesh-based modeler would be a tedious chore of plucking verts around and stitching blocks and deleting and creating faces, is a lark in OpenSCAD.  Seriously, here’s the code for it:

Not only is that practically nothing in terms of file length, it was easy to put together.  And the tear drop?  Permanently available as a library now.  TearDrop() is portable to anything I might want a reprap-style hole in, scalable to fit any blot or rod, translatable to anywhere on a design, replicable to any number of copies.

And OpenSCAD has for loops.

I dragged the above into Blender to get a real close look at the mesh, not sure whether to believe that the mesh could have come out clean, but found no errors.  There are cosmetic issues (mesh cosmetics: lots of thin triangles and a few tiny protrusions, yes, I’m PICKY) but what matters for nearly every possible scenario is that it be manifold, and it was.  I’ve tested a few corner cases like two planes intersecting at exactly their endpoints, and they come through clean.  OpenSCAD marks the beginning of really usable open-source CSG.  Which is a very big deal: there are wide classes of problems that are brutal on a mesher but trivial in CSG.

One of the keen things about digital fabrication is that a lot of the bodge-jobs that makers put together can be reborn as rock-solid commercial-grade construction.  The LED glasses clip recreates what a maker might do with some tape, a paperclip and maybe a rare-earth magnet as something that looks pretty dang sharp.  Not that tape on glasses isn’t a time-honored nerd tradition, but looking like you can command the forces of industry (which arguably you do) to create such a geegaw?

Super cool.