Tuesday, September 3, 2013

Prototype #3: First Machining

Our last two prototypes (#1 and #2) were made by myself to simply reduce the cost and time involved. Now that our design is more refined we can make our next prototype from a machine shop (i.e., from someone who actually knows how to machine metal correctly) hopefully in preparation for an actual production run. 

For manufacturing I used a local CNC machine shop in Mississauga that I regularly used at my previous job which does great work although it is typically a little more expensive than other shops. For a material we will use Aluminum 7075-T6 which has a yield strength of around 65,000 psi. We will make two units of the same design: one for destructive testing and one we can keep. The price for making just two units was very high at around $250 per unit for just the machining costs although this is reduced to around $50/unit if the quantity is increased to 100. For the USB flash drive I just purchased some off-the-shelf consumer models and removed the plastic case. At around $350 total per unit these are definitely one of the more expensive USB drives out there.

The end result can be seen in the pictures below and it looks great! Note that the following pictures were taken after the drive spent a year in my pocket so it is a bit scratched up. The most notable design change from the previous prototypes is the addition of the engraved logo and serial number which turned out well. Our previous issue of a crooked cap on the first two prototypes has disappeared: the cap fits perfectly indicating that the issue was indeed the manual tapping process or my machining inexperience. The only notable issue was the knurling (the diamond grid pattern for grip) was a bit coarser than what I wanted at 0.08" pitch instead of 0.05".

For now only pressure testing has been performed and we again achieved success the first time at 3000 psi for one hour. A variety of destructive testing including temperature, shock, and force will be performed on one of the units later on.

This prototype was made in the fall of 2012 and one of the units has been in my pocket ever since then and has seen a lot of use. Much like the second prototype there were no usability issues noted and it looks and works like a charm.

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