Building a rack-mounted card cage

From SecretLab

Secret lab has a small board farm for the various eval boards that we've worked with. Originally, eval boards were just placed on a desk or a lab bench and used from there. Unfortunately, It didn't take long before the tabletops were no longer visible amongst the various boards, cables and power supplies.

Ideally, all the boards should be mounted into one of the server racks and they should be accessible remotely. On the physical side, this requires some form of chassis to mount the boards onto. The goal is to have at least 1 board per rack unit of space and boards need to be easy to remove so they can still be used on the bench. For control, the minimum requirement is the ability to control power, reset and serial ports over the Ethernet network.

Chassis

Searching for case vendors online did not come up with many good options for board chassis. The most feasible option seems to be to use 1U server cases which cost about $150 each and are readily available. Another option would be to try and find an OEM blade server chassis; but those seem to be quite a bit more expensive and not nearly as easy to find.

However, there are a number downsides to using standard 1U cases:

• They are much bigger that is typically needed for an eval board. A 1U case takes up a lot of room on the bench and it imposes a limit of only 1 eval board per rack unit.
• 1U cases don't slide in and out easily without installing separate sider rails for each case.
• Eval boards don't always conform to server motherboard form factors. Eval boards require flexibility, but server cases already have a lot of standard mounting points for other equipment which can get in the way.
• Not a lot of bare metal front panel space to cut custom holes into.
• $150/case is not unreasonable, but it can add up in a hurry.

As an alternative, I started looking at possible ways to build a chassis instead of buying one. Here is what I decided:

Materials: 6U of space available in a 19" equipment rack 12" deep rack shelf (x2) 12x17.5" 3/4" MDF (x2) 9.75x16" 32 gauge aluminum sheets (x9)

Tools: drill rubber mallet C-clamps table saw (or hand saw with guide fence) Triangular metal file large square

• Starting 1/4 inch from the short edge of the MDF, cut 1/2" deep grooves into the MDF at 1.75" intervals. 1.75" also happens to be the size of 1 rack unit. This will give you 10 groves along the edge of the board. Repeat for 2nd MDF board.
• Mount the MDF panels onto the rack shelves. The shelves will be mounted one above the other in the rack with the MDF sheets facing inward. Make sure that the panels are mounted so that the groves are directly above each other when the shelves are mounted into the rack
• Mount the shelves into the rack. Place the shelves 6U apart.
• Measure 1.5" from the short edge of an aluminum sheet and use the square to draw a straight line across the board.
• Place the aluminum sheet on a workbench and line up the straight line with the edge of the bench. The aluminum will now be hanging over 1.5" from the edge of the bench.
• Place a 2x4 on top of the aluminum and line it up with the marked line. Clamp the bench, aluminum and 2x4 together.
• Use the rubber mallet to bend the aluminum over the edge of the bench. This will give you a 90 degree bend. Repeat for all 9 aluminum sheets.
• Fit the aluminum sheets into the slots in the MDF.

This will give you a basic card cage chassis. To actually make use of it, use the drill and metal file to cut whatever holes are needed by an eval board into one of the aluminum sheets and mount it to the sheet. Make sure to leave at least 1/2" free on each side of the aluminum so that it still fits in the slot.