ADJUSTING THE MACHINE TO CORRECTLY SELECT CHARACTERS FOR PRINTING
There are two aspects to adjusting the Selectric mechanism correctly for printing characters - tension on the two metal tapes and timing. The metal tape bands pull on components inside the carrier to twist the typeball to a specific column and to tilt the ball up or down to a specific row. The ball is locked into position at a defined time as it is pivoted forward to strike the ribbon, which must be related to when the tape tension is changed and when it must hold steady.
A print cycle is the process that begins by moving the selection levers and ends when the typeball returns back to rest position after having struck a character on the paper. The selection levers are pulled down at the early part of the print cycle, which apply differing amounts of tilt to the levers that the metal tape bands run around. Tilting the lever further from the side of the frame will add tension to to the tape band that runs over the pulley, while tilting it inward will release tension.
Thus, the lever and pulley that the rotate tape runs over will move up to five steps outward and five steps inward to select among eleven levels of tension on the rotate metal tape. The coil spring under the typeball resists the rotate tape tension, so that relieving a bit of tension will allow the spring to turn the ball one way, while adding tension turns the ball the other direction.
The lever and pulley that the tilt tape runs over can move up to three steps outward from the frame, selecting among four levels of tension. A spring resists the tension of the tilt metal tape, but when the tension increases the cam that the spring pulls on will turn stretching the spring. This is transmitted to a gear that tilts the typeball to its row (tilt) positions.
It takes a bit of time in the print cycle for the selection levers to be fully set and thus the tension on the two metal tape bands is changing during that time. Once the levers have settled to their full positions, the tape tensions should be static. At this point, a detent lever is lowered into the notches on the bottom of the typeball. This forces the ball to a more exact alignment of the column of type above and holds the ball steady while it is striking the ribbon to produce a character.
The lever must NOT detent until the two tapes have stopped moving, otherwise the change in tension of the tape no longer produces movement of the ball, instead putting stress on the metal. They can fatigue and eventually break if the tape tension changes when the ball cannot move. Similarly, if the typeball is twisted by hand when the tapes are not changing tension, it can put stress on the tape and lead to fatigue failure.
As well, after the ball has struck the ribbon but before it returns to rest position, the selection levers begin to restore to their idle position and the two metal bands change tension back to their rest states. The detent lever MUST be removed from the typeball before the tape tension changes, otherwise we again can strain the tapes leading to failure.
The adjustments for timing must ensure that the detent lever is in the notches of the typeball only when the tape tension is not changing. It must enter before the ball hits the ribbon and it must disengage before the selection levers begin restoring.
The adjustments for selecting the correct character must ensure that when the selection levers pick among the 11 column and 4 row positions, the ball turns to the intended row and column. Detents in the typeball notch (and underneath on the tilt mechanism) will adjust for minor misalignments and hold the ball steady during that midpoint of the print cycle.
Ideally the ball is perfectly aligned for all of the tilt and rotate targets, but real world variations exist in the parts. Thus, the detent levers make fine adjustments - the more they have to adjust, the more strain on the tapes so we want to be as close as we can to perfect.
One addition factor complicates things. The shift mechanism selects from one of two hemispheres of the typeball. On a typewriter, these are upper and lower case characters, but on the typeball with the IBM 1130 there are only upper case letters. Instead, it is numerals and special characters that exist only one one side or the other.
The shift mechanism has its own lever and pulley on the right frame of the typewriter. It can pull the rotate metal tape band to add enough tension to spin the typeball 180 degrees. This is in addition to the tension adjustments performed by the rotate lever on the left frame. Ideally this is exactly 180 degrees but in the real world it is not. Thus, we have to check for the alignment of the typeball for the eleven rotate columns on both sides of the typeball.
A given column might be exactly right on the 'lower case' side but off a bit on the 'upper case' side, due to variations. We want to find the best adjustments of everything to minimize the error in positioning for all 88 characters, two hemispheres by four rows by eleven columns of shift, tile and rotate.
These adjustments are interrelated and take quite a bit of time to dial in to a suitable accuracy. This involves hand cycling the print cycle, adjusting gear positions to time the detent lever movements, and changing lever points and rod lengths until the row and column positioning of the typeball JUST BEFORE detent engagement are as spot on as possible.
LOOPING THROUGH ADJUSTMENTS - EACH ONE AFFECTS THE OTHERS!
The adjustment instructions give a sequence of parts to check and adjust, as if it were a linear process that results in a perfectly working machine when you finish the last step. If only that were true, I would have been done several hours ago.
Instead, each adjustment may shift the parts involved in prior adjustments, so that they are no longer set to the desired position. One needs to iterate through the adjustments, hopefully so that the deviations shrink over time and the results are 'good enough' when you hit the last step once again.
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