PDP-11/45

From: William Donzelli <aw288_at_osfn.org>
Date: Tue Dec 7 20:13:49 2004

> One thing specifically I wanted to ask applies to many systems not just my
> /45. What have most of you found to be good for working with scratches or
> gouges in painted metal?

A serious issue, at least to some of us. I have a few machines that have
some serious sheet metal problems. I think thet best we can hope for is to
hide the scars.

> I'm thinking like the side panels of the H960
> cabinet, etc. I'm not into painting really but was considering using an
> airbrush to touch up lots of scratches and perhaps blending the new paint in
> with the old areas. Perhaps this would come out worse? Exactly what kind of
> paint should I get, can I have a paint dealer reliably scan existing
> surfaces with their color cameras to generate the correct hue? Suggestions?

I have had a decent amount of success with "splattercoat" finishes - the
kinds we see on almost all old computer skins. It is actually pretty easy
to do, just don't rush.

I don't use an airbrush. I have one from my model painting days, but I
don't use it. I have found that airbrushing a section may work fine from a
stright on view, but almost invariably at an angle, the patched section
tends to stick out. Unless you are very skilled with an airbrush, getting
a matching finish to the original is really difficult.

I tend to fix scratches in the paint using just the right amount of
paint. Most dings are quite small, so any mismatch in the finish is minor,
and easily overlooked by casual viewing.

Splattercoats can be very effectively patched, if you want to put in the
time. Look at a bit of the original finish - you will see somewhat random
blobs of paint "buried" under the outer surface. Recreating these simply
involves building up matching random bumps of paint. To do this properly,
use some of the sludge found on the bottom of an unmixed jar of paint
(keep in mind to use the same, or similar, color of the finish coat). I
use a toothpick and a metal pin to build them up. You may have to do
several applications to get the bumps the right texture. Remember, most of
the volume of the liquid paint you apply will go away.

After the bumps are satisfactory, wait as long as you can to apply the
finish coats. I tend to like to use rather thin finish coats, so I want
the bumps to be as hard as I can get. Once again, I use a toothpick, or
maybe even a small brush.

I use oil based model paints - specifically the nasty stuff the railroad
geeks use. Some of the other paints have been dumbed down quite a bit, so
I stay away. Testors, in the little bottles, used to be great, but no
longer can be found. I fear that eventually even the good railroad model
paint will go away.

Of course, any halfway decent painter will tell you preparation is %90 of
the game. Still true - be sure to have the wounds in the panels clean and
rust free, and if possible, even roughed up a little. Primer wouldn't hurt
either.

Color matching is a problem. I do it by eye, and can get damn close. If
you do this method, expect to ruin some paint. In fact, you may waste a
huge amount of paint, compared to how much you use. Lots of trila and
error.

So there you have it. Just remember, it takes time to do a good job - it
can take a week to fix a small scratch properly. Each day of work may only
have a few minutes of work in it, but the results will probably suprise
you.

William Donzelli
aw288_at_osfn.org
Received on Tue Dec 07 2004 - 20:13:49 GMT