RESTORING CALCOMP 565 PLOTTER
I was given a Calcomp 565 Plotter, one of the first drum plotters, which is the same mechanism as IBM resold under the model number 1627 for use on their 1620 and 1130 computer systems in the early 1960s. Since I own an IBM 1130 I was given this machine as an eventual restoration project.
The machine had suffered a serious blow on the drum, denting it significantly. It had been disassembled and was in a bin when I received it. In addition to the drum damage, it was missing the pen assembly, a solenoid that pulled a pen up away from the paper or dropped it down to draw on paper fed around the drum.
Recently I found a Calcomp cutter which was the same solenoid and a slightly different top. used to cut films on the same plotter instead of drawing. I bought it and plan to modify it to accept a pen so that this plotter could once again draw graphs under computer control. All that assuming I could repair or find a substitute for the drum.
I recently repaired the circuitry, which had a few bad semiconductors, then began to reassemble it temporarily, with the bad drum, to confirm whether it could be restored once I solved the drum and pen issues. I discovered it was missing a spring as well as some nuts and bolts. The fasteners are no issue at all, but I needed to replace the spring.
CABLING TO MOVE PEN CARRIER LEFT AND RIGHT
A pair of metal rods across the front of the plotter support a moving fixture into which the pen solenoid is mounted. Cables stretch from both sides of the fixture, around pulleys inside the plotter, connect to a stepping motor, and then are joined by the missing spring at the back.
These cables are insulated with a plastic sleeve at the front, since they also carry the current to activate the solenoid when the pen is to be held up off the paper. The rear portions of the cable are not insulated and ride over metal pulleys that are isolated from the machine chassis. These two pulleys make the connection of the 24V solenoid power to the cables.
The routing and winding of the cables around one pulley and around the stepper motor is a bit complex, but the result is that when the stepper moves, the fixture slides left or right. The spring at the back maintains the proper tension on the cables. The two cables have nylon eyelets so that the spring does not make electrical contact, merely providing tension.
What I didn't have was any idea of how long the spring is and how resistant it is to extension. Too, I didn't know the target tension it should be applying to the cabling.
KIND ASSISTANCE FROM COMPUTER MUSEUM OF BASEL
I have had help over the years from the Computer Museum of Basel, in Switzerland, as they have a restored IBM 1130 system. We often cooperate on 1130 issues. Alex and Christoph agreed to measure the spring in their Calcomp 565 plotter so that I could then look for a suitable replacement.
They provide very precise measurements of the rest and extended length of the spring as well as the tension it provided to the cables. That was just what I needed.
FOUND SUITABLE SPRING AND INSTALLED IT ON CABLING
I did locate a spring that had the correct rest and extended length, as well as the force it should exert when stretched to the target length. I wound the cable through the machine and inserted the spring in the rear to hold the cable ends together. It wasn't a final assembly but was sufficient to verify that this will allow the plotter to work properly once I have the pen and drum issues solved.
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| Rough fit test of spring |
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