[GreenKeys] TTY model 33 case repair.

[Jones, Douglas W]

I've completed the repair on the cover of our Model 33 ASR.

-- http://.cs.uiowa.edu/~jones/pdp8/UI-8/bugs.shtml#17

As you can see, we replaced the broken window in the cover
with a new one fabricated of plexiglass.  I used a wood plane,
adjusted to take off the finest possible shavings, to plane the
"tear edge" to an angle that matched the original (broken)
window.  Then, I used a "Mr Clean Magic Eraser" scouring
sponges (and elbow grease) to polish the planed surface to
optical quality -- it is now a good match for the original.  The
window was a bit oversize, so also clamped the new window
to the old one (using blocks of 1/4 inch soft wood to protect
the new window from the clamps) and planed the new window
to the outside dimensions of the original.  While clamped, I
also used the old window's holes as templates to drill matching
holes in the new window.

I then used the new window as a template to guide a square
nosed drill as I cleaned up the remains of the broken studs
that had held the old window on.  All stud locations were
drilled as square-bottomed holes about 1/32" into the case
(leaving about 1/16" of plastic shell intact.  I then glued new
studs about 3/16 inch long in place (3 mm diameter ABS rod)
using "Plastruct Bondene" cement to weld the new studs in.

Instead of melting the studs to hold the window in place (I
tried some experiments with a soldering iron and managed
to convince myself that the result would be a mess), I made
up a batch of ABS washers with 1/8 inch holes in them and
then used more "Bondene" cement to glue the washers to
the studs to hold the window in place.  It looks good.

I now face another problem:  The Teletype keys.  I hadn't looked
closely, but now that one of my students has cleaned everything
up, they are a mess.  See the photo here:

-- http://www.cs.uiowa.edu/~jones/pdp8/UI-8/bugs.shtml#27

I've found a photoset on line where a guy has made some
truly beautiful keys out of laser cut acrylic -- for a different
purpose, but I wonder if it would be possible to make up new
keys from grey plexiglass using his methods.  The link is on
the above-cited web page.

                     Doug Jones
                      jones at cs.uiowa.edu