Supermicro rack ear modification

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As I mentioned in my RAIDzilla 2.5 article, one of the few areas where I feel the Supermicro SC836 chassis comes up short is the single mounting hole in the rack ears. Aside from being underneath the handle of the chassis and somewhat hard to access, I don't feel a single mounting point on each side is sufficient.

Supermicro probably expects users to mount the chassis via their slide rails. In that case, the mounting hole is only used to keep the chassis from sliding out of the rack. The rack weight is supported by the slide rails. I prefer a fixed mounting as I don't use cable management arms in the back of the chassis (as shown here). Sliding the server out without disconnecting the cables will likely damage either the cables themselves or the chassis components. Additionally, bouncing 16 spinning 8TB disk drives around is not a good idea.

When I first installed the RAIDzilla 2.5 systems, I used a horizontal bar to provide additional support to the front of the chassis. I always considered that to be a temporary solution while I looked for a better method. Fortunately, the handles are short enough that there is space for an additional mounting hole at the top and bottom (left and right in the following pictures) of the rack ear.

The obvious thing would be to have a machine shop mill out the holes in the rack ears. Unfortunately, this wasn't a workable solution for a number of reasons:

With only a few sets of ears to modify, the price for the actual work would have been dwarfed by setup charges and minimum hour charges.
There is no guarantee that what I got back would be what I wanted. I often think I'm being perfectly clear on something, only to be surprised at the results of miscommunication later on.
With the ears off the servers, they would be loose in the racks for an extended period of time. It would probably take at least a week to ship the ears out, have them modified, and then ship them back to me.

The only other answer was to make the modifications myself. However, as I don't have a machine shop, I needed to use commonly-available tools to do the work. The following pictures show the process from start to finish.

This is what I started out with. As you can see, there is a single oblong slot underneath the handle. The reason it is an oblong shape instead of a circle is the minor variation in rail-to-rail spacing in different racks. The slot accommodates this.

Here is the finished result. As you can see, there are now two additional oblong slots, one at the top and one at the bottom of the rack ear. The need for these openings to be oblong greatly complicated the work required.

There was no way I was going to make anything remotely close to the right shape "freehand", so I needed to use a template. Fortunately, I have a large assortment of 23" to 19" rack reducers. They are made out of steel, much harder than the aluminum of the rack ears. I attached a 3U reducer to the rack ear using the single existing hole.

The first step was to drill a pair of small pilot holes in the rack ear, to keep the larger bit from "walking around" on the rack ear.

Next, I used a larger drill bit (slightly smaller than the minor diameter of the slot in the template) to create the two ends of the slot. There is some minor damage to the template - just because it is harder than aluminum doesn't mean the drill bit won't cut into it if the pilot holes are a little off.

This is how things look at the front of the bracket at this point. The diagonal piece at the top left is another rack reducer - since the rack ears don't have threaded holes, I needed to use the threaded side of a second reducer to serve as a "nut" for the screw on the other side of the ear.

I used a Dremel® rotary tool with a 9901 tungsten carbide cutting bit for the next step. This bit is usable on a variety of metals, ceramic tile, and so on.

Using the rotary tool, I carefully removed the remaining metal in the slot.

This is what the front of the rack ear looks like. It isn't perfect, but most of this will be covered by the screw head anyway.

I proceeded to perform the same steps on the other hole on this rack ear and the two holes on the other rack ear. I then re-installed the ears on the chassis and mounted the chassis back in the rack. As you can see, the screw heads obscure most of each slot and conceal any imperfections. The supporting bar has also been removed as it is no longer needed. [This picture is rotated 90° from its actual orientation so that it fits on the page.]

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