Introduction: Retro Mainframe Computer Digital to Analog Shelf

Kinda where it all started or evolved from, mainframe computers were huge. Tiny in storage capacity but enormous in physical size, let's apply the inverse concept to make a small shelf with a relatively large storage capacity. It is scalable by design.

This shelf is based on the venerable IBM 729 Magnetic Tape Unit which was just one part of the massive IBM mainframe computer system. It would probably be cool to make a whole wall full of shelves or cabinets that resembled the entire computer system.

For the truly geeky, you can also make this Star Trek Enterprise Composite Shelf.

And for real retro funk, maybe you can do something with this Giant Vacuum Tube.

Step 1: Get Wound Up...

I already had my Adafruit Circuit Playground Express board wired up with a strip of Neopixel LEDs and a servo from a previous project so I thought about what else could I incorporate that in. Lights are always fun to watch and you can animate something with the servo motor to make it move.

So I said to myself, "Self, you should make something that looks like spinning old time movie projector, DJ console, a reel to reel tape drive or something."

And so I researched and found a few videos on the IBM 729 Magnetic Tape Unit. Technology has made computer storage so much faster, cost effective and efficient that these units are obsolete. You see them used as TV/movie props all the time for computer room settings. There were probably a few tucked in the back of the computer room when I was in college. Ahem, I did learn FORTRAN programming by using punchcards. If you bent the cards on a certain column, you could launch them out of the card reader...

The IBM 729 would make a great look for a set of shelves.

I didn't have anything to model the magnetic tape reels so I just used 2 blank DVD disks. I had some spare wood toy parts so I built up the cassette tape hubs with some wood model car wheels/axles. I used piece of wood popsicle stick to give it some more detail.

I had a pair of continuous rotation servos to use and they would be great to to make a set of "reels" to spin around.

Once everything was wired up, it was relatively easy to code up everything in Circuit Python to drive the Neopixels for blinkenlights and move the servos to simulate the tape drive in operation.

On the real IBM 729 there are two vacuum columns that contain a length of the tape that it is spooled out to be read or has passed through the reader head. This allows some slack as there since there was not precise motor control back in the day and you could damage the tape as it was pulled. This was the physical "data buffer". So it was fun coding in the randomness to simulate the realistic movement as the two reels may move in sync, in opposite directions or independently.

Step 2: Getting Started With Basic...

This shelving unit is simply made with simple woodworking.

Keep it simple. You can go all out and design/make some 3-D printed parts, use fancy joinery or expensive power tools but this was something I literally made in my kitchen. What...doesn't everyone use their dining room table as a workbench? Mostly handtools, a portable drill/driver and glue. Make it so.

This is a good project to use up scraps of wood and other spare stock that you may have in the shed. 1/2"x 6" cabinet/craft wood strips were used for the sides and 3/8th inch square stock for the inside panel frames with a 1/4" thick blue panel insert. For a bigger and stronger shelf you can go with the usual 1x stock which is really 3/4" thick.

I had a piece of masonite/hardboard that forms the back of the shelving unit.

This is not really a scale reproduction of the IBM 729 so nothing is really measured out. Arrange and lay out pieces to get the look.

To add detail to the tape drive mechanism and capstand rollers, I used bits from the wood cutoffs, some craft wood punched circles, bamboo skewers, and whatever. This is classic modelling technique to use miscellaneous parts (greebles) to add texture and shapes to a piece.

The tape mechanism is built on a small raised platform that fits in the upper section of the shelf unit. Servos are mounted in cutouts in the panel. I glued some positioning blocks on the shelf so that when the electronics need to be worked on, the panel can be lifted off and then put back in place.

The control panel is a strip of wood that has holes drilled out for the Neopixels to shine through. Stop and positioning blocks are glued on to fix it in place. A printout of the control lights and switches is covered with clear packing tape and double-sided taped on as the bezel faceplate.

The nameplate is printed out and double-sided taped on to a small piece of wood glued on to the bottom of the top shelf.

I could have added on some trim to be the metal frame that goes around the edges of the cabinet. I just scribed a line around the edges with an awl to demark the frame and will paint that section silver. I don't know where I put my marking gauge, I think I have one.

The bottom cavity was large enough for another shelf so I made that out of a piece of clear acrylic since a solid wood shelf would look out of place. If cutting acrylic sheet to size, score the cut line with a scoring tool or knife. You can then clamp it in place and bend the piece to snap apart along the scored line. The clear shelf would slide in and be supported by the strips glued to the sides and back piece which form a slot. You could probably cut or route a channel to mount the shelf or just use some shelf pins on the sides.

Step 3: Assembly Language...

Everything was sanded to ease the sharp edges and sanding dust removed with a barely damp rag.

I first sealed the pebbly surfaced back of the hardboard pieces with clear polyurethane. It reduces the dust that comes off when you handle that kind of particle board.

I guess the proper way to paint is to mask off the sections and go along. I prefer to live dangerously and besides, good masking tape is not cheap.

I used up a bit of that Big Blue TARDIS stain that I still have a lot of. I also used silver, black and cream color acrylic paint.

The stain takes several coats to develop a consistent deep color. Acrylic paints tend to crackle when they dry on glossy areas like the glue fillets I made so touchup or a second coat of paint is needed. Ideally everything should to be primed to accept paint easily.

I used a silver paint marker to outline the detail on the tape reader mechanism part and double-sided taped on some reel cutout shapes on the DVD disks to better simulate the tape reels.

Time to attach all the parts together and stuff the electronics in.

And there you have it.


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