PDP-11/03 to H960 rack angle rail drilling jig

Description

I have been modifying modern server rack slides for DEC PDP-11 equipment for some time now, and recently hit a problem when it came to racking up a 3-1/2" (2RU) high PDP-11/03. The computer chassis width only has a clearance of about 3.5mm on each side when placed in the H960 rack frame. I have no idea how they made rack slides thin enough for the PDP-11/03 to slide out, and have not been able to find any references in drawings or photos of them. So, rather than just hang the weight of the computer off the front mounting screws I decided to place the computer on alminium angle rails. This allows the machine to be slid in and out without placing weight on the screws. The front screws can be used when the computer has been slid on the rails completely into the rack. Using 1" x 1" x 1/8" angle makes for a good snug fit for the PDP-11/03 cabinet. From the local hardware store I bought a 3m length of 25mm x 25mm x 3mm thick aluminium angle, and cut it into 635mm lengths. This length is the distance between the front and rear verticals of the H960 rack. The jig is designed to accommodate both 25mm and 1" angle. Now, how to get the rails at the correct rack spacing and height. This is where this jig comes in. Two are required, the shape is rotationally symmetrical so only one model is needed, and printed twice. The jig is 2RU (3-1/2") high which is the same as the smaller PDP-11/03 chassis height. To use, simply push the jig into the rack from the outside. The positioning accuracy of the pins and angle spacing is "baked in" to the jig so you only need to look to see that the "close pair" of holes is going to position directly between the middle of the pins. Once pressed in firmly, slide the ends of your pre-cut length of angle from underneath the jig and upwards so the inner horizontal surface of the metal angle contacts the lower outer (bottom) face of the jig "L". Place a clamp on the jig and angle as shown in the pictures. Before final clamping, check for forward-backward horizontal alignment of the front and rear edges of the angle is flush with the H960 vertical's front surface (or just inside). After both ends are clamped, use a 6mm drill bit and drill through the aluminium angle using the most suitable rack hole on the H960's side set of holes. A 1/4" drillbit is TOO LARGE and will ream out the rack hole - don't use it. If you only have imperial drills use a 15/64" bit instead. The rails will be mounted using these holes. After drilling, check the clamps are still accurately in place and using a screwdriver or small socket spanner a 1/4-20 screw (or what have you) can be neatly self-tapped into the angle. Cut and fit the screws to suit and use a nyloc locking nut to secure. Don't forget to scrupulously sweep up all the metal shavings before you start racking your equipment. I have also used this jig for positioning angle rails for other height PDP-11 equipment that I don't have slides for, or have not modified modern slides yet. If you decide to use this, assure yourself whether this is fit for your purpose, and if so double-check everything before drilling and make sure the screws are capable of bearing the required weight.

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