Re: broken plastic parts - reasonable thickness?


Schuyler Larrabee
 

-----Original Message-----
From: Brian Chapman
[mailto:cornbeltroute@...]
Sent: Friday, July 09, 2004 10:15 AM
To: STMFC@...
Subject: [STMFC] Re: broken plastic parts -
reasonable thickness?

Once, Quality Craft (tells you how long ago
this was, doesn't it?)
offered etched brass roofwalks, which were .025"
thick. They looked
right<. They had a rectangular hole, and I've
always wondered if the
x by y of the holes was right or not, but they
did look good,
and better than Plano because of the thickness.
<

Schuyler,

Highly interesting. I have built a power-spray
chemical
etching unit, and it works well. I'm having
trouble, though,
finding high- resolution clear film output with
which masking
is made (direct-to- press apparently has
significantly
changed the printing industry). I intend to
experiment with
running boards.

However, as I understand it, widths of features
to be etched
should be no less than the thickness of the
material because
of undercutting. So, if the depth of the walkway
is .025, the "bars"
or "strips" forming the walkway should be .025
wide, which is
a tash over 2 inches in HO. Did QC's rectangular
holes appear
as though they were formed this wide?

Perhaps QC fudged the "bar" width.

I have CAD drawn a running board for a project,
and I used a "bar"
width of .004 . . . I'm expecting trouble. <g

Thanks much for the information,

Brian Chapman
Cedar Rapids, Iowa
Brian, sorry for a delay. I meant to go grab a
car with that roofwalk material and measure it.
Now I have

The "rim" bar on that material measures roughly
.018" The interior bars measure .010" The
overall roofwalk is .250" wide, and has six
openings across. Lengthwise, the openings are ~
.070" long. Well, eight openings, including cross
bars on either end, = .570" Like I said before,
it was .025" thick.

Having said that, this material was obviously
etched from both sides, with good registration
between them, so the etch depth was .0125" The
edge of the bars might be less than the width I
measured (this is on a finished model, one of my
better efforts, so I'm not getting too aggressive
about measuring it.) like down to .007" or .008"
But it's see through, and looks right to me as to
thickness.

So, experts, does that correspond to any known
prototype roofwalk material?

SGL

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