Dangerous Prototypes

Here's my Bus Pirate case.  I machined it from some scrap black Delrin.  The light pipes were turned from some Lexan sheet I had on hand and superglued into the case before final machining.  It's held together with four #2-56 stainless socket head cap screws.  I made the cable with individual 0.025" square female sockets so I could connect directly to header pins or a set of color-coded E-Z Hooks.  I still need to make a water-slide decal for the top with the logo, pinouts, and LED descriptions.

I did change R2 and R32 to 2k2 and 1k1 respectively to try and balance the LED brightness.

Cheers,

Tom

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Looks good. I don't think it's an issue for a BP, but saw this:

One warning about Delrin:

I work part time in an electronics lab, where we build all kinds of boxes and racks, and frequently use Delrin for custom standoffs, mounting blocks, etc. I'm usually the guy who machines them up. We had always assumed that it was relatively safe in an electrical environment.

Well, we recently had a box catch fire in the field, and it burned up fairly thoroughly. When we got it back and diagnosed it all, we were surprised to find out that the Delrin standoffs played a major role in turing a minor short into a fire. A shorted component heated up a wire that was tie-wrapped to a standoff, which then ignited the Delrin. Because the box was wall-mounted, and the board vertical, there was a vertical row of standoffs, and the fire started on the top one. Sure enough, the drops of burning Delrin fell on the one below, setting it on fire, etc., down the line.

We took some of the standoffs out back and experimented with them. We were surprised at how quickly and easily they caught fire. When they burn, the fire is nearly invisible, like an alcohol fire. One 2" long standoff would burn slowly for several minutes, and every drip from it was itself burning, and would set other things on fire. It was also fairly difficult to put them out. You had to completely smother the oxygen. This was black Delrin, by the way.

This experience sure made us think twice about how and where we use Delrin. We're now using aluminum standoffs in most applications.

In response to a request for the CAD files, attached is the AutoCAD 2010 solid model of the case.  This was all done on a manual Bridgeport mill so there are additional layers in the drawing that are toolpaths for various endmills and cutting depths.

I roughed out the case top to about 0.5mm oversize, and drilled the four lightpipe holes.  I then turned some polycarbonate rods longer than the case top thickness and 0.05mm smaller in diameter than the holes.  These were then inserted into the holes and bonded by wicking cyanoacrylate (Superglue) adhesive around them.  The outside of the case was then milled to the finished size.  I used a sharp flycutter and isopropanol spray to cool the part and ended up with an almost polished finish on the lightpipes that needed no further refining.  Next, the inside pockets were milled.  The final step was to make the cutouts for the USB, probe cable, and aux header.

Cheers,

Tom