What’s That?: Extruded Aluminum Drive Housing

I was over at the NC State College of Design (my alma mater) participating in a final crit for a Junior Industrial Design studio, and someone brought me a part to ask me about it. It was the housing from a Maxtor OneTouch portable drive (the first series)…

Maxtor is now owned by Seagate now, but judging from the sizes these things were available in (80GB, 160GB, etc.), these were probably sold around 2003 (wow, that seems so long ago…). They brought it to me because they were digging how the Maxtor logo was applied to this extruded aluminum housing…

The logo is recessed about .010″ and has nice crisp features, so it couldn’t have been machined or you’d see the radii from the cutter. Also, despite all the bead blasting, you’d still probably see cutter marks, which you don’t…

And more notable is that the same graphic is raised inside the housing which indicates that these extrusions are stamped with a matched die…

Why a matched die? Because think about it… If you’re stamping the outside of this aluminum housing, you’re going to need to support it inside (think of the cut extrusion being slipped over a steel tongue or mandrel and clamped in place). When the male die (the one that creates the recessed graphic on the outside of the housing) comes down and presses on to the housing, not only do you need support from the wicked pressure, you need to have somewhere for the displaced material to go. Don’t forget that in stamping, the material actually flows just like plastic does. So there’s a recess in the steel mandrel inside that matches the males features on the outside (offset by the wall thickness of the extrusion, of course). Cool, huh?

Of course I couldn’t help but geek out on the other features in this extruded housing. Take, for example, the bosses and ribs:

These extruded features have several functions in this product. The ribs at the top, side and bottom (without the hole) are guide ribs that align the internal components and hold them in place. The internal chassis (which hold the drive itself) has flanges that slip down the small channel on the sides.

The ribs on the top and bottom support the components as well, but also serve an additional purpose. The front and rear face plates are installed flush to the product so the install into the housing. Those ribs are machined to a set depth to give the face plate a “stop” when the screws pull it into place. The machined hole on the side is the screw boss. It’s drilled (but not tapped) as the screws used for these drives are self-tapping screws. This saves the cost of tapping the housing and it’s unlikely that anyone will need to go back in the housing more than a few times (if at all), so self-tapping screws will work fine.

They even added a little undercut (produced using a cutter wheel) to give the face plate something to snap into. I don’t have the other parts, but I bet there’s a little tab of material that snaps into this when assembled…  Less rattling…  Nice.

Also check out the little cut in the side of the screw boss (probably using the same cutter wheel mentioned above). At first I was thinking that these is where the tailings from the tapping would come out, but that would mean you’d have little pieces of aluminum floating around in the housing and that didn’t sound like a good idea…. My guess it is that this is a stress relief to controll the hoop stress generated by the self-tapping screw.

Lastly, the who thing is bead-blasted to give it a uniform finish without having to paint it–afterall, why paint that beautiful aluminum? This part is a fine example of what you can do with extrusion and a bit of machining. Obviously for Maxtor, it made more sense than trying to create a rugged-cost effective housing out of injection-molded plastic. In the next generation, the OneTouch II used almost the same housing and generated several variations just by changing the plastic endcaps:

So I hope you enjoyed my little gee-out. Let me know what you think: What kinds of projects have you done using extrusions?


3 Responses to “What’s That?: Extruded Aluminum Drive Housing”

  1. 1 Slag January 20, 2010 at 4:49 pm

    Long-time listener, first-time caller:

    I love the way this blog makes me think more about everyday objects that I usually wouldn’t even notice.

    Thanks, and please continue.

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