Measurements for DIY Rackmount / Relay Rails: Networking and Servers in the Same Rack

Posted on September 23rd, 2007 by Dennis Little

A while back I had occasion to mount both networking and server equipment in the same Compaq 4-post server rack. This presented some problems because the rails in the rack needed to be spaced as close to the front and rear doors as possible to accomodate the depth of the servers I was mounting in the rack. At the same time, the rails were too close to the front and back doors and did not allow them to close when the networking equipment was loaded in the rack. To remedy this problem, I needed to have an additional set of vertical mounting ears in the rack, but recessed from the front and rear.

While APC offers what appears to be a solution to this problem in their AR8010BLK and AR7508 products, the solution is expensive and I was not completely convinced that these rails would work with my Compaq rack. If I did buy the kit and it didn’t work, I would have to fabricate my own solution anyway, so I decided to fabricate my own rails instead. Using angled steel and drilling/tapping 10/32″ U mounting holes to make an inner relay rack with round mounting holes inside my Compaq rack would solve the problem.

I needed the following supplies:

  • (2) pieces of angled steel from Home Depot, I used the 1/2″ type - about $8 each
  • (1) 10/32″ metal tap - I used the Irwin 80221 drill bit and tap set - $3
  • (1) bottle of metal tap lubricant - you will definitely need this to ease the metal tapping process - $2
  • (1) tap bit handle to turn the tap - I used Irwin 12088, but there cheaper models available - $12
  • (1) bottle black spray paint - $5
  • Several packs of 10/32″ bolts - $5
  • Total supplies total: ~ $43
  • Time to complete project: ~4 hours

I will not get in to the particulars of cutting the angled steel to length, tapping the metal and painting it, but will say that there are a few things that made this project much easier to execute:

  • Dremel with metal cutting wheels to cut the steel to length
  • A digital caliper - Harbor Freight has decent calipers for really cheap 
  • A drill press - You will never get the holes straight drilling them free hand
  • A jig for the hole spacing - Save yourself a lot of time and use a scrap piece of flat steel the same width as the angle steel for your jig; you can get this at Home Depot for about $3. Precisely measure and drill this jig for about 3-4U of mounting spaces, then just clamp it on to the real rails with vice grips and use the drill press. Once that set of holes is drilled, move the jig and line up 1U of holes on the jig with the holes on the angled steel, then drill the next set and so on.
  • Tap the metal both before AND after painting to make fitting the bolts easier

Believe it or not, finding the proper hole spacing specs online was kind of difficult. If I would have had the rack near me, I could have used my caliper to measure the square holes in the rack, but the rack was in Pennsylvania and I was in Virginia. Luckily, I found that IBM has the specs for EIA-310-D online here. These specs describe exactly how big the openings of a rack should be and how far apart the center of the mounting holes should be.

Here are a few photos of the finished rails installed in the rack with equipment mounted (look for the black vertical rails with round holes):

Filed under: Technology

« OtR: SANS Institute Free Security Whitepapers A LifeLock (TM) Alternative: Free DIY Identity Theft Protection »

Leave a Reply