[GreenKeys] [External] Model TT-45/FG Not Punching Through

[Jones, Douglas W]

From: Chris DeMuro [kn4obk at gmail.com] -- Monday, August 2, 2021 5:21 PM

> It does punch and feed tape, but it does not punch all the way through the tape. It just seems to create bumps in the tape when trying to punch, or only partially detach the bit from the paper. Now, I suppose this could be normal behavior, but I can't find a manual for this machine, and all photos and videos I have seen of other reperfs have shown the tape being completely punched through.

There were chadless punches, punches specifically designed to not detatch the chad.  Each piece of chad ends up being on a hinge so it hangs loose and does not make a mess -- chad being the chief complaint of anyone who has ever been in charge of cleaning up around teletypes.

The die in a normal (non-chadless) punch has round punch pins that punch into round holes.  In contrast, the die on a chadless punch has pins that punch into a hole that started out round but has a rectangular notch cut into about 1/3 of the perimeter on the downstream side of the hole (that is, the side toward which tape is moving).  This prevents the punch from cutting through the tape on that side of the hole, forming the hinge that retains the chad.

Chadless tape is readable on essentially all mechanical paper tape readers, but utterly incompatible with high-speed photoelectric readers.  Mechanical fingers to sense holes in the tape push open the "trap doors" formed by the hinged bits of chad, but they stay shut and block attempts to read the holes by shining light through them.

               Doug Jones
               jones at cs.uiowa.edu