Category Archives: misc

New machine day – Pocket NC

With my efforts to build a gearbox transmission and subsequent plans for a quadruped, there are a lot of parts which just can’t be made effectively from 3d printed plastic.  To date, I’ve sent out a few parts of the gearbox to CNC shops, which while effective, has a relatively slow turn around.  The best you can get without paying an arm and a leg is something like a week turnaround.  One thing I’ve learned from having a 3d printer on site is how transformative it is to be able to have single day turnaround for parts.  Thus, I thought I would experiment with CNC machining on a small scale locally and recently acquired a PocketNC V2-50.



Since this is the V2-50 version, it has a 50,000 rpm spindle, theoretically giving it at least passable material removal rates in aluminum.  Most of my gearbox parts look like they could be machined in an hour or so.

To date, all I’ve done is machine half of a sun gear holder out of the wax stock that ships with the mill.   I took it plenty slow and consider it a success that I managed not to break anything on the first try.

The result is approximately a thousandth off from what I was aiming for on the two critical dimensions I tested, although that probably doesn’t mean much since it was just wax.  It remains to be seen what I can achieve in aluminum.


Now I actually need to get the tools and fixturing that will let me machine the other half.



HT-18 Thermal Imager Macro Mod

While working on the improved actuators for SMMB, I wanted to be able to perform some quantitative experiments to design the thermal transfer of the controller board and enclosure.  I figured that feeling with my fingers probably wasn’t scientific enough to make consistent progress.

Enter an inexpensive Chinese thermal imager, which you can find for under $300 from time to time.  A non-affiliate Amazon link:

HT-18 Thermal Imaging Camera

It has a resolution 220×160, reads up to 300C and being intended for construction inspection has at least a little software support for reading out actual temperatures and capturing images for reports.  The only downside is the focal length.  It really can’t focus on anything less than about a meter away.  That isn’t too great for PCB inspection.

Enter this eevblog thread, describing at least one person who added a lens for a macro mod.  I gave it a try, getting an appropriately specified laser cutter lens from Amazon:  ZnSE w/ approximately 100mm focal length labeled as “Laser Engraver”.  A non-affiliate link for the exact one I got is:

I could have 3d printed a fancy lens mount, but decided I would see how well a quick and dirty hot glue gun job would work:

Macro lens mount
Macro lens mount for HT-18 Thermal Imager

And the answer is pretty good —  I can resolve individual 0603 components on the board just fine.


My First Edit to a Chromium Extension

Feedly just today came out with a Pro version with support for https support! Unfortunately, the one extension I rely on, FeedlyBackgroundTab hard-codes the URL to The required code change is trivial, just updating the list of allowed websites in the manifest file. To install it though, I wasn’t sure what to expect. First I tried just editing the file directly in my “~/.config/chromium” directory. That ended up not being successful. But then I noticed the little “Developer Mode” checkbox in the Chrome extensions page. Lo and behold, it can load unpacked extensions, or pack them for you!

Now if only the Omnibar would learn some awesomeness from the Awesome bar and I would all be set.

3D Printed Cookie Cutters

For my nieces this holiday season, in addition to actual cookies, I printed up some customized cookie cutters on the Artisan’s Asylum 3D printer (A Stratasys uPrint SE Plus)


20121213-emma-inkscapeThe toolchain I used could be applied to a number of 3D projects. First, I either found an image kind of resembling what I had in mind using google images, or drew up a sketch on a piece of paper. Then, I transcribed that image into an inkscape vector drawing, similar to the elf one on the right. The inkscape drawing contained a closed shape for the outer dimensions of the part, the inner dimensions of the part, as well as closed shapes for any surface features that I wanted. I used the “Linked Offsets” feature to force the inner wall boundary to be a precise distance away from the outer wall boundary. Colors were chosen arbitrarily, as the next step ignores the fill colors entirely.


20121213-lilah-freecad.pngNext, I fired up freecad, which can import SVG elements as geometry primitives in the 3D view. Unfortunately, and what was to become the biggest annoyance with this project, is that its import of SVG paths isn’t particularly robust. Notably, for some elements it doesn’t close them properly, and for others it doesn’t even turn them into curves, rather importing them as sets of points. This was done in a hurry, and while I didn’t have enough time to actually fix the problems in freecad, I did dig around in the source enough to figure out that they were not handling paths which ended up on the exact same position as the first point correctly. One problem was that freecad would only count a path as closed if the “z” element was used to close it off. Another was that paths with kinks would just not close with no indication why, even if the kinks were too small to be visible. So, my workaround was to manually edit the .svg files in emacs after inkscape saved them and fiddle around with them afterwords to try and get freecad to import them as closed surfaces. Then for the paths that still didn’t work, I looked extra close in inkscape for any kinked paths. In this project, those largely resulted from inkscape’s linked offset paths being glitchy around regions of high curvature.

With those surfaces imported, I then proceeeded to do a series of extrusions, differences, and unions to get the parts that I was looking for. In some cases, when I ran into limitations of freecad’s boolean operation engine, I had to go back to inkscape to tweak the artwork. This was largely around different objects which were intended to share a border, which didn’t work out so well.


After getting the solid models into good shape in freecad, I exported an .STL file for each model. I pulled this .STL file into netfabb studio basic to verify the volume and to do mesh repair. Sometimes freecad will export .STL files that netfabb doesn’t complain about, but I figure it doesn’t hurt to let it fix up any problems it finds.

uPrint 3D Printer

The final step is printing. This is largely uneventful: feed in the STL files, configure the print job, hit print, and come back in a couple of hours. Usually, when printing a part, you can count on the first iteration to have some problems and this case was no exception. I had designed the cookie cutter wall thickness to be 1.25mm wide, figuring that would be 5 passes of the uPrint. However, the uPrint ended up not actually filling the inside of the wall in many places, resulting in two very thin walls separated by a small void. Given more time, but in this case I was out, so I moved onward with what I had!


So, the final test, using them to cut cookies… Well… They mostly worked. The separated outer walls caused a lot of cookie material to get wedged up inside. I also realized at this point why most cookie cutters have an exposed central area. Without one, extracting the cookies is quite challenging. I painstakingly used chopsticks and a knife, which worked adequately, if with great effort. Certainly, if I were to make a second revision, I would fix both the separated wall problem, and make the cookies easier to eject afterwards.

Below is a picture of the final 3 parts before being gummed up with a season’s worth of cookie making.