Week ending June 30 - progress on physical construction of 1130 and on card reader adapter


The logo bar on an 1130 is a bit of aluminum, 10" wide by 1 1/4" high by 3/8" deep, standing on two cylindrical posts atop the display light pedestal. I milled a bar of aluminum to these dimensions, drilled and tapped holes in the bottom for the posts, and began to make the front and back images.

The front and rear faces of the aluminum are painted, the edges remain bare. The image is built up by applying an 'etching' primer coat and a white base coat on top. A vinyl mask is applied to cover the portions that will remain white, the edges are covered, and a black coat is sprayed through the mask to complete the image.

The posts were made from 1/4" diameter stainless steel rod, threaded at 10-24 with a die to match the hole I tapped in the aluminum bar. These posts mount at the bottom into holes at the top of the pedestal display unit I am also building this week.

It was not possible to get the fonts exactly the same as on the IBM manufactured 1130 logo, but I produced a design that I think will be good enough. At the time of the 1130 (and the 360 series as well), IBM had not yet moved to the striped letters so familiar today. The company logo was similar, but solid. The designer, Paul Rand, created it in 1956 by modifying the City Medium font (for example, the middle of the M reaches to the bottom on the IBM logo but the font had it stop about mid height).

 I am not sure what outline font was used for the number 1130, as well. I picked fonts that were evocative and similar, but it won't stand up to a side by side comparison. Notice that the numerals are more geometric and linear in the IBM example, while mine are more curved. The centers of the letter B in the company logo are rectangular but my font has semicircular centers instead.

My design file for the logo plate, used to cut a vinyl paint mask

IBM made logo plate for comparison

My machined aluminum bar was completed Friday, with holes drilled and tapped on the bottom, ready for printing of the design and attachment to the pedestal display box.

Bottom of logo aluminum blank with tapped holes

Saturday I intended to spray the primer on both faces and let it dry before I cut the vinyl logo mask at the Techshop. The paint room was continually busy, I concentrated instead on welding. On Sunday I shot one face with the primer and the white coat, as well as cut the vinyl paint mask for the logo plate. The text "Computing System" actually came out okay - I have only lost the interior of the letter 'e' but the rest came out clean. I think I can cut the letter separately and repair the mask.

The big problem was the large "1130", because the special outline font I used was not installed on the machine that drives the vinyl cutter. I need an alternate method, as I currently have the numerals as single thin characters, with no whitespace inside. This might need to be a decal, or I may need a replacement font, or perhaps I can find a way to scan the actual IBM letters and convert them to vectors for the cutter.


The lights that report the contents of major machine registers and other status information are installed in a box that is suspended above the console typewriter, with a rotary mode switch on one side and the cylindrical "emergency pull" handle on the other side. This box sits on posts which are shaped like rectangular solids, They are 1 7/16" wide, a bit less than 8" high and 1 15/16" deep, rising behind the console typewriter and about 3 1/4" inwards from the left and right sides of the pedestal box. The display box is almost 28" wide, 5" high and 3 5/8" deep. 
IBM made pedestal box and logo plate
I formed the box and the stands from 22 gauge mild steel sheets, cut and bent them to shape, then welded them together. The stands are hollow inside, allowing signal and power wiring to be routed to the box from the base of the 1130 below. The box was made in two halves - an upper and a lower portion, welded together at the sides. A flat plate is attached to the rear with screws, allowing for access to the wiring and various electronics on boards that sit inside the box.

Above is the top half of the pedestal box
Parts after initial fab, before welding or other operations

Above is the bottom half of the pedestal box

Pedestal stands above

The front of the box has two metal plates on the face, with a 20" wide plexiglas panel in the center between the metal plates. The plexiglas panel has the markings, outlines and separators for the various lights which are displayed during machine operation. The right plate has the mode switch and the left plate holds the emergency pull handle. Both plates are painted an off white color on the IBM built machine and are off white powder coated on my replica. 

The mode switch plate contains a knob which is a rotary switch, selecting one of seven 'modes' for the 1130 - allowing the operator to run in single step, single memory cycle and single instruction modes for hand debugging, loading registers/memory, displaying memory locations, and allowing the processor to run normally or with a software debugger program (interrupt run mode that generates an interrupt after every instruction except those issued within interrupt handling routines). 

The left plate has a cylindrical pull handle which dropped power quickly in the event of an emergency - fire or electrocution risk to someone - in a manner that might damage circuitry. It has a red disk in the center labeled "Emergency Pull". The handle is machined, has a red circular insert with appropriate labeling, but is simply bolted onto the plate - nonfunctional - as their are no high amperage power supplies in my 1130 replica. The insert was painted with an 'acid etching' primer and a color coat of reddish-orange paint. The wording was made as a dry transfer decal and applied atop the red paint. The rest of the knob is bare "chromed" metal. A knob was milled by a friend who is building a 360/30 replica system, but it is awaiting some final machining operations before it is ready for painting - as a fallback I can mill the handle at the Techshop. 

The mode switch has a black circle atop the off-white plate, centered under the knob, with lettering marking the seven modes which can be selected. I built the black circle with a vinyl cutter and attached dry-transfer decals for the lettering. A knob from a 360 mainframe was used to provide realism, attached to a rotary switch on the inner face of the plate. The rotary switch offers the seven positions but at slightly different rotary angles than on the IBM built system, which can be detected if you look closely at the knob pointer when it is set to any of the positions except the normal "run" mode with is at the 12 o'clock position on the circle. 
Vinyl paint mask for mode switch circle
I have already described in earlier posts the process of applying the markings and legends and separators to the inside face of the plexiglas panel. I cut plexiglas to size - 20" wide by 5" high - and began creating the dry transfer lettering decals which are used in the first step of the panel fabrication process. These are mirror image, since they are affixed to the inside face of the panel but viewed from the front, through the plastic.

I cut the vinyl masks for painting the plexiglas panel and the mode switch plate - these came out perfectly but for one minor issue. I forgot to mirror (flip) the image for the plexiglas masks, since the paint layers are sprayed on the inside face of the panel, not the front. They need to be reversed like an image in a mirror, allowing them to appear normal when viewed from the front through the plastic. The fix to the design files was trivial to apply, but I had to wait for another opening on the vinyl cutter machine. In the meantime, I realized that it only has to adhere long enough and well enough to block paint, so I will just spray the top of the mask with a light adhesive spray, stick it on to make the pattern correct, spray, then remove. No need to recut the vinyl.

Vinyl Paint Masks for display light panel

I am having problems welding the seam for the stands that hold up the pedestal display box. The thin metal burns through too easily - mostly due to my exceedingly poor welding skills. I switched from the MIG system to the TIG welder, hoping to have more control, but the same burnthrough occured. 

At this point, I think I may need to put a backing plate and solder, to get a filled in surface, grind it flat, instead of attempting welding.

I believe I have worked out the process to make my dry transfer (rub on) decals for the text lettered on the plastic pedestal panel. I have begun the fabrication - producing the toner image, mirrored to apply to the inside face of the panel, using the special printer paper. Soon I will apply a white mylar film over each section of that image, mount it to a carrier board and run it through a laminator machine to fuse the mylar atop all the black portions of the paper - my text characters. The remaining mylar film is peeled off, leaving paper with white mylar lettering. 

This will be combined with a clear mylar, to which a static electric charge has been given, again put on a carrier board and run through the laminator. This yields a sandwich of the paper with its mylar lettering and a thin mylar top film. A water bath causes the paper to curl and separate from the mylar, both the clear film and the lettering in white. This is our decal, whcih is dried and given a thin coat of spray on adhesive to cause the back of the mylar letters to stick to the target (plexiglas panel) as I rub. The clear top film of mylar is peeled off, leaving the white lettering in place. 

The most tricky part that I anticipate will be lining up the lettering so that it touches the plexiglas in the correct location and can be rubbed on firmly. I probably need some kind of jig to ensure proper alignment - thus I will wait a couple of days until I work out and build the alignment jig. 


The console keyboard as well as a number of operational buttons and indicator lamps sit in a black metal plate inset into the white formica desktop of the 1130. I have designed the layout for this plate, to be made of 16 gauge mild steel, about 1/8" thick and quite rigid. It is about 21" wide and 9" high, with precise cutouts for the buttons, lights and keyboard keys.

This will be manufactured using a CNC waterjet tool at Techshop, using high pressure water and garnet sand to cut the openings to exact shape, size and position, driven by the design file I created in Autodesk Inventor Pro. Once the plate is cut and all the parts successfully fit, I will powder coat it a semi-gloss black. It will be installed into an inset on the underside of the formica desktop.

Here is a preliminary version as I was laying out the plate, with lots of visible dimensions to allow me to control placement precisely. The buttons and lamps are correct, but the keyboard is not yet done in this version. I have roughed in the space bar and three keys in the top row, but the final design was based on the actual keyboard mechanism and spacing that I will install.

Designing the plate holding my buttons, lamps and keyboard

IBM made 1130 plate
My keyboard with planned key deletions and changes


The 1130 replica will be built with a steel framework, much like the IBM made computer. I bought some 1/8" think square steel tubing and began welding together the frame of the system on Saturday. I began with a few test pieces to figure out an acceptable technique, after which I blocked out the rear frame sections, tack welded them, then finished the welds on each joint.

I have used a handheld grinder to remove the large ugly blogs of excess metal I left on the joints, producing an acceptable looking and adequately strong frame segment. This unit is the rear of the machine, 58" long top and bottom bars with 27" upright bars between them at each end.

Rear frame segment - 58" wide by 29" high
IBM 1130, 60" wide and 30" high and 30" deep - with covers added
The system frame is 29" high, 29" deep and 58" wide. I bought too much tubing; once I saw how strong they were, I skipped some of the rods as they are unnecessary to support the weight of the system and will make it far too heavy. The frame will be covered with sheet metal faux doors, powder coated with a hammertone finish in a realistic IBM color - Garnet Red for example or the Classic Blue shown above, which also has back and lower panels in a third color, Pebble Gray. While the official 360 colors also included Willow Green, Sunrise Yellow and Charcoal Brown, I have never seen units in any of those colors and believe they were not ordered in any significant quantity.

My frame design has a front and mid segment, plus tubes connecting the rear, mid and front segments. I intend to attach casters to the bottom tubes at the left, midpoint and right, making this easily movable (although heavy and bulky).

The front segment has a 58" long tube at the top, but only a 29" tube at the bottom justified to the right edge. 27" uprights from each end of the 29" bottom tube are attached to the right end and midpoint of the longer upper tube. The section that extends to the left is a cantilever for the desk recess, under which the operator will place their legs while seated and typing at the keyboard that sits above the cantilever.

The mid segment has a 28" top and 29" bottom tube, with 27" uprights on the left and right. It forms the back wall of the leg recess under the keyboard. A 28" long tube runs from back to front along the left edge, sitting atop the mid segment left upright tube and forming the other half of the cantilever for the desk. A 13.5" segment runs from the right side of the mid segment forward to join the upper tube of the front segment (and its upright tube). A 12.5" segment runs from the bottom of the right mid segment upright tube, forward to the bottom tube of the front segment.

Along the right side of the machine, 27" segments at top and bottom join the right side of the front and rear segments.

I intend to work on the welding during the next week, completing the physical frame. I can then begin installing the platforms for the keyboard and controls, for the console printer (typewriter, and for the pedestal stands. The DEC RK-05 disk drive mechanism will be installed in the right side of the machine, roughly where the IBM made 1130's have an internal disk drive.


My startup routine for the console printer (typewriter) adapter moves the carriage to the left until it stops moving, which I detect by the cessation of emitter pulses. This means it has reached the left side, position zero. I step it forward one character position and establish this as the initial left margin. To do this, I had to fire the print cycle trigger but it was not active long enough to trigger the typewriter mechanism. I wasn't sure why this was happening, but I finally tracked it down with the help of the logic analyzer.

The physical switches on the typewriter need 'debouncers' to deliver a single transition from one state to the other, rather than a sequence of rapid oscillations such as occur with physical switches; these instabilities extend from microseconds to sometimes milliseconds depending on the particular mechanism and usage. My debouncer logic reaches a known state during system reset (and power on reset) but was establishing a logic level 0 as the initial state.

 For some switches, that is an acceptable decision, but the print feedback switch that is critical to print cycle timing begins at level '1', dipping to '0' only during part of the print cycle. Having it begin as '0' caused the state machine to switch off the trigger prematurely, believing the mechanism was already moving when it hadn't started yet.

I enhanced my debouncer circuits to be configured in one of three ways - intitially '0', intially '1', and initially the instantaneous value of the switch as we come out of a reset condition. Each is useful in certain situations - the print feedback should start as a '1' to generate a reliable startup movement. The switch detecting whether the typeball is in the upper case or lower case rotational position has to start out with the correct status, based on the real ball, otherwise we might mistype the first character in the wrong case. Other switches need to begin as a '0' to avoid triggering unwanted operations as we come out of reset. 

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