I've done something similar with old instrument knobs. I first give
them a good soap-and-water cleaning with mechanic's hand cleaner
(Go-Jo, Goop, etc) and an old tooth brush. Sometimes, this is all
that's needed to make the witness line visible again. Then I use a
dental pick or large sewing needle to put a few scratches the length
of the witness line - like K2WH said, you need a way to hold the knob
secure and steady during this operation, and working under a magnifier
helps, too. If the paint that forms the line seems to flake off or
show signs of poor adhesion I'll scratch most of it away.
Then I use model airplane enamel to create a new witness line. But I
don't apply the paint with a brush; instead I apply it by dipping a
flat toothpick in the paint and dragging it along the line. On knobs
where the witness line is molded into the plastic, the enamel will
fill the indentation level to the surrounding area and look extremely
precise. In other cases a little practice and a steady hand can
produce results that require very close examination to discern from
"stock" condition.
The preparatory step of scratching the line serves 2 purposes: it
creates a roughened surface for the paint to grab onto, and it defines
a straight "channel" that the paint flows into with a straight,
well-defined edge.
Dale ex-WA8VTN
--- In HallicraftersRadios@..., Bill Gerhold <k2wh@o...>
wrote:
Still working on the SX-117 receiver. . . .
The knobs on the SX-117 and similar series radios, all have a white
reference line running the length of the knob . . .
. . . most of the white line has been worn off.
. . . I then used a bottle of "White Out" to restore the line.
K2WH
