CARRIER RETURN AND TAB CORDS POWER LEFT AND RIGHT MOVEMENT
There are two string like cords in a Selectric typewriter mechanism. One hooks to the left side of the carrier, able to pull the carrier to the left. The other cord hooks to the right side of the carrier and pulls it towards the right. Teeth fitting into racks hold the carrier in position against the rightward pull, allowing it to move one step during a space or to move freely during a tab until it strikes a tab stop that is set at some column.
COUNTERROTATING DRUMS TAKING UP AND RELEASING THE CORDS
The carrier return cord is routed leftwards from the carrier and over a pair of pulleys on the left which reverse the direction of the cord and direct it behind the racks. It is wound around a drum at the rear of the machine - that drum is on a common shaft with a mainspring and a drum that sits forward of the spring. The rear drum winds up the carrier return cord as the carrier is moved to the left, feeding the cord out when the carrier is pulled to the left so that the return cord remains under steady tension.
The tab cord is routed to the right side of the machine, changes direction over a special spring loaded pulley and is then wound around the drum in front of the mainspring. The mainspring will be wound up by the process of a carrier return, storing up energy necessary to pull the carrier rightward. The drum winds up the cord as the carrier is pulled rightward during spacing and tab operations, feeding out the cord during leftward (backspace and carrier return) operations.
MAINSPRING POWERING RIGHTWARD MOVEMENT - SPACE AND TAB
The source of power to move the carrier to the right is the release of energy stored by winding up the mainspring. This winds as the common shaft rotates in one direction and seeks to rotate the shaft in the other direction unless the carrier is held in position, for example with a tooth in the escapement rack. The spring gains energy while the carrier is pulled leftwards during a return and gives it up to move the carrier rightward. IBM refers to this as negative energy for some reason but it is just the potential energy in the wound up spring that powers rightward movement.
MOTOR POWERS LEFTWARD MOVEMENT - CARRIER RETURN AND BACKSPACE
The motor of a Selectric is always running, spinning the operational shaft but that shaft isn't coupled to anything else unless a clutch is activated. This is what IBM refers to as positive power in their training and documentation. In order to pull the carrier left in a return operation, the clutch connects the operational shaft to the common shaft with the cord drums and mainspring, turning it to simultaneously feed out tab cord, pull in carrier return cord, and wind up the spring. The power comes from the motor to make the movement and to restore energy into the mainspring.
SPRING LOADED PULLEY MAINTAINS CORD TENSION
Since the cords can stretch over time, a spring loaded pulley is built into the right side of the Selectric. The pulley can move left or right but has strong spring tension rightward. This holds the cords in the proper tension and automatically adjusts to stretching, within the limits of its range of motion.
INSTALLATION THEORY
The simple sounding theory for installing the cords is much more challenging to put into practice, the issue being getting the cords to be the right length and on the drums correctly, in addition to which setting the mainspring at its proper tension.
The carrier return cord is hooked to the rear drum, threaded around the pulleys and attached to the left side of the carrier, while the carrier is sitting in its rightmost position.
The carrier return mechanism is activated so that as you turn the operational shaft manually the rear drum takes up the cord and pulls the carrier leftward. Proceeding carefully so as to keep the cord winding on the correct spiral grooves of the drum, you move the carrier all the way to the left.
Next one should attach the tab cord to the front drum, thread it around the spring loaded pulley and attach it to the right side of the carrier. Here there are challenges in real life. The drum is usually turned so that the attachment point is downward and away, not convenient to hook up a cord. The spring tension of the pulley will make it almost impossible to hook the cord on, so you really leave the cord off that pulley, hook to the carrier and then force the pulley leftward while pulling the cord over it. Alas, the cord may be too long so that the spring loaded pulley can't move rightward enough to put on tension.
If the cord is hooked to the front drum and engaged in the spring loaded pulley with proper tension, one then has to wind up the mainspring to appropriate tension. If you do all this, the carrier is ready to move left and right, handling the carrier return, space, backspace and tab operations properly.
When I have the carrier full left but the front drum mount point is inaccessible, I need to move the carrier a bit to the right until the drum rotates. Unless you are very careful looking both at the front and back of the machine, you can loosen the carrier return cord making a jumble on the rear drum.
I had to tie several knots in the cord next to the hook that connects to the right side of the carrier, to shorten the cord appropriately. I must then tension the mainspring by winding it nine or ten turns. If all went well, I should be able to space the carrier all the way to the right. During this movement I have to watch that the tab cord winds properly around the front drum.
I have failed multiple times just as I am moving the carrier a bit to the right or trying to connect the tab cord to the front drum. This is very tricky, as moving the shaft the wrong way loosens cords which then scramble up on a drum.
ROTATE SPRING TENSION IS TOO HIGH, BUT RELIEVING IT IS HARD
Inside the carrier there is a vertical rotating shaft that the type ball spins on. It has a spring underneath that provides power so that when the metal rotate cord is loosened, the rotate spring takes up that length by crisply turning the shaft. It has to move fast enough to get into position during typing. However, if it is too tight, then it restricts the range of rotation. This is the cause, I believe, of the failure of this typewriter to rotate to either the +5 or the -5 positions.
This is checked using an IBM spring scale that pushes against the rotate tape pulley on the right side. One sets up a +5 character, hand cycles the machine halfway through a print operation so the rotate tape is appropriately tensioned, then push on the pulley and see 2 to 2.5 pounds of force. My spring is offscale beyond 3 pounds right now
Adding tension to the rotation spring is easy - there are notches around its perimeter that you can see and reach from the top of the machine. Pushing it one way will turn it to click into the next notch, adding tension. However, releasing some pressure requires simultaneously holding it steady by the notch and also pulling on a detent spring to let it rotate the other way. I can't even see this detent, much less figure out a way to get a tool in to move it.
Assuming I find a way that I can pull on the detent while also having another tool control a slow rotation of the spring to release some energy, I can remove tension until the scale shows me the target force of 2 to 2.5 pounds. This is challenging which is why I have spent quite a few hours on the 1053 just trying to deal with the rotate spring; then there is the time fighting to get the tab and carrier return cords properly attached.
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