Thursday, May 19, 2016

Nearly done restoring the broken grit wheel for the punch unit in the 1442 reader/punch, while waiting for plotter restoration answers


I worked with my Dremel tool to shape the UV hardened plastic I am using on the broken wheel. I sanded it down on the sides and evened the top, but decided I had to make the diameter of my new section slightly higher so I could sand it down to the exact size I wanted.

This afternoon I got it closer to round. It rolls nicely on a flat surface other than one high spot, but doesn't yet have the grit applied that will ensure it grips and pulls the card one column at a time during punching. In my next session, I will drop the high point and get it very close to perfect before I mix up some grit in the glue and carefully hand apply it to the surface.

By early evening, the wheel was within 1/128" of the diameter of the rest of the wheel. Since this wheel meets a spring loaded rubber roller (with a card pinched in between), I should have less than 2% variation in column spacing at worst case which should be within the margin of any card reader.

The remaining step is to select an appropriate grit which I can mix with the UV curing resin to form a slurry. If I can apply it very thinly and carefully along the replaced arc on the wheel, hardening as I go, it should restore the wheel to usable condition.

Then I have to reassemble the punch unit with this wheel, put the punch unit back and reassemble the rest of the 1442, then continue to clean up bad lubricants and adjust operation until it is reading and punching properly. That will take a few weeks of work, I suspect.


I am still waiting to hear back from the metalworker on whether they can built the replacement cylinder and a ballpark cost. I suppose I should be looking for a backup craftsman in case I don't here from them or they aren't interested in a small but exacting project.

I am also waiting to receive some more detailed drawings that another hobbyist produced to manufacture his own pen assemblies for the plotter. It has been a while, but he may still be searching for them. If not, I have to complete the design and make all the drawings to allow a shop to build this to my spec.

If I design my own, I think I will start with an existing solenoid coil that closely matches the specs of the original Calcomp part. It has to have a hollow center at least large enough for a reasonable pen holding 'slug', ideally the same as the Calcomp barrel diameter. Then, knowing the exact size, I can design the holder and other parts to fit. If I proceed from the Calcomp or hobbyist recreation sizes, then I need to locate a solenoid to fit the outer diameter and length of the original.

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