From: dpettit@javelin.sim.es.com (Daina Pettit)
Subject: Re: Protecting silkscreened playfield lightshields
Organization: Evans & Sutherland Computer Corporation
Date: Mon, 17 Aug 1992 18:19:26 GMT

In article <19540@fritz.filenet.com> ung@fritz.filenet.com (Bill Ung) writes:
>I just ordered (well, ordered and received) a new set of the silkscreened
>playfield lightshields for my HIGH SPEED game.  Several of the ones that
>came with the game were broken and one is missing.  Of the ones that are
>still there, a lot are scratched so that part of the scenery is missing,
>although the physical shield is still intact.  I attribute this to years
>of half-unscrewing the shields to change the light bulbs underneath and
>scraping the paint off the plastic shield in the process.  
>
>Now that I have a new set, I'd like to keep them new.  I'll be as careful
>as possible, but accidents do happen.  What can I do to protect the
>artwork on my new lightshields?  Is there something like Cover-Your-Glass
>for lightshields?  Can you spray them with clear acrylic or something?
>How about re-enforcing them against breakage?  Is there anything that
>helps out in that department?
>
>Thanks in advance,
>
>Bill Ung
>  ung@filenet.com
>
Yow, Bill, I've heard horror stories on how much Williams charges for
replacement plastics sets.  If you don't mind, how much did you pay?

I've never heard anything about preventative substances for plastics.  I've
been led to believe that some plastics break because they're screwed down
*too* tight--the ball, or something else, hits them and they can't give
without breaking, so they do.  If the plastics are just loosely attached
they can shift just enough to keep from breaking.  I get miffed every time
I have to remove plastics to change rubber rings and find that someone
screwed the nuts on the posts so tight that the post screw comes out
instead of the nut.  This is hard on the plastics. 

I have also been led to believe that one of the main culprits of broken
plastics and broken drop targets is the ball falling down the playfield
from the outhole when the machine body is positioned vertical, usually when
moving.  Every broken drop target I have seen is near the center of the
playfield right in the path of a falling ball.  The worst broken plastics
also have been towards the center and back of the playfield.  When moving a
machine it is important to remove the ball(s), or at least move them to the
plunger trough first.

Heat is also hard on plastics.  Transporting a machine in the daylight even
when cool outside can warp the plastics.  The sun beats on the plastics
through the glass like a little greenhouse and gets hot enough to do the
damage.  One technique to prevent this is to put newspaper *under* the
glass, or just throw a blanket over the whole thing.  The warping of
plastics is not serious and can be easily fixed.  An article about a year
or so ago in the Pinball Trader described how to do this.  It was called
"Plastics-a-la-Bill".  The idea is to place the plastics print side up on a
clean cookie sheet in a 200 or 250 degree F. (preheated!) oven until the
warping starts drooping.  I think this takes around 10 minutes.  Remove the
plastics and place them in a large book or something similar to hold flat
until cool.  I've used this technique and have been very pleased.  However,
I am fearful about what might happen if I left the plastics to cook too
long.  
-- 
  Daina Pettit  (801) 582-5847  dpettit@javelin.sim.es.com   
  Evans & Sutherland  600 Komas Drive, SLC, UT  84108