ROTATE SPRING TENSION CORRECTED
I managed to find a solution to the conflict between lights, my eyes and the tools, so that I could see and maneuver the rotate spring and its detent. I relieved tension on the spring and then carefully added it back in until I got to the desired range of rotate tape tension.
The tension is measured by setting up the machine with the type element (ball) on the lower case side, commanding a character with a -5 rotation and hand cranking this until the rotate pulley on the right is just about to hit a stop pad that limits the pulley lever arm travel. With this condition set up, an IBM spring scale pushes against the pulley lever arm and measures the force required to move the arm outwards.
This force is the target spring tension of 1 7/8 to 2 1/2 pounds. I found a setting that produced 2 1/4 pounds of force, right in the desired range. To verify this is good, we also check at +5 rotate character from the upper case side of the ball.
Tripping a solenoid on the side of the machine causes the pulley lever arm to move outwards to the right, which pulls the ball around so that the upper case side faces the platen and paper. The +5 rotate character was triggered and hand cranked to the point where I could again measure the force on the pulley lever arm. We still had 2 1/4 pounds of force, confirming that the rotate tension setting is correct.
TAB SETTING SLIDER CORROSION
The tab setting sliders are discs that fit inside slits on the long tab cylinder, one slit per column that the carrier can reach. The disc rotates so that the two projections which stick outside of the tab cylinder diameter are either rotated backwards to the rear of the typewriter or partly forward. The forward position puts a projection right in line with the escapement mechanism on the carrier. The carrier strikes the projection and releases the latched tab condition allowing the escapement pawl to enter the rack and stop the carrier at this position.
Quite a bit of corrosion has occurred inside the slits and on the faces of the discs, which froze some in place and made them all very hard to rotate. Using my clock oil and patiently moving each one back and forth many times, I got most of them to move freely. I still have a few that are stiff but with time and more manipulation I expect them to all work properly.
I verified the gang clear function, where as the carrier is pulled right to left during a carrier return operation, if the Tab Clear lever is activated simultaneously, a wedge on the front of the carrier will force up any tab discs that are rotated into the 'set' position. This clears all tabs in one operation, instead of requiring the user to repetitively tab to each set position and then move the Tab Clear lever.
ADJUSTING STOPS ON WHIFFLETREE LINKAGES
IBM implemented a mechanism called Whiffletree Linkage to select the amount of movement of the tilt and the rotate tapes required to move the ball to print the intended character The heart of this mechanism is different lengths from pivot points to the activation levers for each 'bit' of selection.
Tilt is easier to explain since it has only four possible positions. A horizontal bar has two levers dangling from its ends. One is twice as far from the horizontal bar pivot as the other lever. Thus, pulling down on the far lever produces one unit of movement, pulling down on the nearer lever creates exactly twice as much movement of the tape, and pulling both down adds together the movement to pull the tape three times as much as the far lever alone.
https://www.youtube.com/watch?v=G_SC7oWL78A
Rotate requires five positions in one direction and five positions in the other plus no rotation, thus eleven possible rotary positions of the ball. The mechanism has a negative rotation link which reverses the direction of the movement plus four levers to select one of the six positions in a direction from no movement to rotating five positions.
As the typewriter sits right now, it rotates the ball less than one character position so that a +5 or -5 character request only produces a movement to the +4 or -4 character on the actual ball. I will be working through the adjustments that must be made, in the proper sequence, to cause the ball to rotate properly.
The first sets of adjustments are setting the rotate spring tension and setting the left side rotate pulley lever to be exactly vertical when the ball is set to the zero rotation position. Immediately afterwards, I had to deal with the failure of the vertically hanging levers from the Whiffletree to restore themselves under the bail that will pull the levers which select the amount of tilt or rotate movement.
I don't know if the improper position of the levers is part of the inadequate rotation of the ball but the adjustment needs to be made so that they do restore. When a lever is selected by the solenoid, it is pulled away from the bail so that that lever is NOT pulled down. It should restore under the bail so that the next request for a character where the solenoid is not driven should have the lever pulled down. Failure to restore may result in mis-selection of print characters at speed, thus this must be corrected.
Metal tabs above the top pivot of the vertical levers are bent downwards until the bottom end of the lever will restore under the bail. These are called stops. There is no direct way to reach and bend those tabs while the Whiffletree mechanism is in place, but I don't want to disassemble everything. I will figure out a method to adjust the stops and do it.
CR DRUM SLIPPING AND RELEASING SOME CORD TENSION
I noticed that at the end of the day today, the transport pulley has moved outwards away from the scribed line, indicating insufficient tab cord tension. It seems obvious that the CR drum screws are not holding the drum on the shaft sufficiently, I was worried about the amount of torque I had to apply last time and it still didn't hold.
My guess is that sludge is in the threads of the drum hole and on the screws. I will try to clean them out thoroughly and reinstall the drum. I may have to use some Loctite Threadlocker to hold them in place so they don't loosen up on their own, but only when I am certain that the screws are holding the drum firmly to the shaft.
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