Restoring Nylon parts (like the card guides in a PDP-8a chassis)

[Doug Ingraham]

A friend mentioned that there was a thread about the card guides in an 8a
or 8e chassis but I was unable to locate it so I am posting this as a new
thread as it has more relevance than just specifically those card guides.

Nylon is hygroscopic. Hygroscopic means it has the ability to absorbs
water.  As nylon ages it drys out.  When nylon dries out it shrinks and it
becomes brittle.  If a nylon part has not yet cracked or been damaged by UV
it can be restored to almost like new simply by boiling it in water for 15
to 20 minutes.  Boiling will force water back into the material and it will
expand and soften.

Do not use a pan with a ceramic type of non stick coating.  I almost ruined
a 10" skillet because it imparted a flavor to the coating which then
transferred to the food cooked in the skillet.  I don't know what effect
microwaves would have on the Nylon matrix so I suggest you just use
something like a Corning Ware ceramic glass pan on your range.

I was able to restore almost all the unbroken card guides on my 8a.  A
couple of them had taken on a permanent bend due to excessive shrinkage.
Some had broken pins.  A few of the pieces expanded too much and you could
plug them into the chassis but they bowed away from the edge because they
had lengthened beyond original length.  Waiting a few weeks allowed them to
dry out a little and shrink and restored them to original size.

Unfortunately there are no adhesives that will adhere to nylon long term so
it is not possible to repair broken nylon parts in a usable manner.  Nylon
while cheap and easy to injection mold was probably not the best choice for
card guides.  But then who would ever have expected these machines to still
be coveted 40 years after manufacture.

-- 
Doug Ingraham
PDP-8 SN 1175