Sunday, December 14, 2014

SAC interface work and 1053 typewriter repair progress


I found the part that must move to adjust the backlash and began adjustments. I can get it well engaged but the backlash of the print shaft to the idler gear is still more than the .001 to .005" that is recommended even with the idler stop as far as I can move it.

I will look at some other machines I have to check the backlash they experience - if it is consistent then I can move on to adjusting the cycle clutch latch holder height, otherwise back to fiddling with the idler gear position.

There are about seven more adjustments to make, some of which I know are quick and easy (e.g. the cycle clutch latch holder height). I continued with the work, getting the backlash into a good range. I then did the height of the cycle clutch holder, using the Hooverometer, a special tool to use with Selectrics.

Next up came a check of the cycle clutch spring and overshoot adjustments, which were within the proper range. As well, I verified the bite of the clutch latch lever was in tolerance.

The next two adjustments are the timing of the filter and print shafts relative to the cycle clutch mechanism. These must move in synchronization which is accomplished by the gear train, once their relative position is set properly.

I loosened setscrews in the gear at the end of the filter shaft and rotated the shaft while the cycle clutch was in its 'rest' position, putting the escapement and shift interlock cams at the proper rotational position.

Before I touched the print shaft, I decided to adjust the motor tension because the belt was skipping cogs on the motor pulley, producing a little 'jump' on each turn. The usual cause of this is that the belt is too loose, plus I thought that the spare belt still had a slight deformation from the way it was stored over the years which would ease out with use.

However, even tightening the belt (by loosening the mounting screws then  pulling the motor) didn't help. I removed the belt from the motor pulley and looked closely, finding a chunk of old belt rubber wedged into one of the slots of the pulley. That caused the slip on each rotation. I removed the pulley and scraped the old rubber out of the slot.

Rubber wedged in slots of the motor pulley
I could see that the bad slot and the two adjacent ones had some corrosion, so they didn't clean up as well as I wished even with a lot of scraping. In spite of having amassed several cubic feet of Selectric parts, for almost every model including Composers and other such rare ones, I had no spare pulley.

Corrosion of pulley after as much scraping and cleaning as possible
I reassembled it and tightened up the tension, happy to feel it rotating smoothly and without any hitches. I believe the wedged up slot and resultant skipping was what caused the failure of my previous replacement belt.

I will finish the adjustments tomorrow with the last step, the print shaft timing. I can then test the printer, reassemble the covers and put it back in place.


I found the pin-out for the wiring of the micro and standard USB connectors, allowing me to attempt to solder the cable from the front panel USB connector to the fpga board. As I typed this, I realized that I would be permanently tethering the FPGA board to the enclosure if I just soldered the connections directly, so I will look for a suitable set of connectors to put in the middle of the cable for disconnection when the board must be removed.

The pads are so small that I have to use 30 gauge wire wrap for the connection on the board then make a joint to larger, more durable wire for the connector I chose. I began soldering these onto the fpga board but the spacing is very close and I found that my soldering iron would release the adjacent wire when I tried to solder a wire on another pad. I need a method of securing all four wires at precisely the right separation, and a means of holding them in position, such that I can solder all of them simultaneously.  This is fussy work and will take some time to figure out a suitable set of jigs.

In the meantime I reinforced the connector plate for the power cable, as the steel is fairly thin and flexed too much with the heavy cable connected. I improved it quite a bit although the receptacle itself does some flexing which I can't avoid given the current thin plate to which it is secured.

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