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There
comes a time when every model builder faces the dilemma of a part that is too small or
detailed to be scratchbuilt, yet cannot be left out for the sake of convenience.
Photo-etching has quickly become the method of choice for duplicating small detail parts
that could not other wise be done. Excellent examples of photoetch parts include screens
and grilles, landing gear and access doors on aircraft, seatbelts and harnesses, ship
railings, and even automobile parts. This article describes a method for producing
photo-etched parts from standard hobby store .005 inch (0.13 mm) thick sheet brass.
There are several methods of developing parts, the most
common is the duplication of an original. One important aspect to remember is that single
side etching will not produce relief details. The results are flat pieces of brass that
have features that cannot be achieved by mechanical means, or by laser cutting. (If anyone
has a lasercutter in his basement, please let me know...) You will need to create a
drawing of the parts you plan to produce in pencil on drafting paper, typically 50% or so
larger than the actual size of the part. The reason for creating the pattern larger is
this: when the pattern is reduced, the detail is carried over and the spaces in the brass
become very small. Draw the pattern in a manner that will allow runners, or connection
points that hold the parts to the frame, like a sprue of plastic parts, with an outside
frame of metal surrounding the desired parts. The runners keep small parts from falling
into the bottom of the etchant pan. When designing the sheet of parts, you should also try
to minimize the amount of brass that must be removed from the sheet . This is important as
the etching solution will work faster and last longer if there is less brass to etch. Once
you have the design for the entire photo-etch sheet mapped out, you should transfer the
pattern to frosted mylar drafting paper (available at art/drafting stores) using a #0
black technical pen. Color in the parts (corresponding to the brass not to be etched)
using a #2 technical pen. Take the mylar artwork to a shop that can make a
"film-positive" from the mylar original. Most shops that make blueprints and
reproductions of architectural drawings can do this . When you have the positive made, you
should specify the amount of reduction you need so that the positive is the actual size
you want the etched parts to be. The article suggests you draw a "scale" on your
original that should map to 1 of your favorite units of length when the reduction is done
- e.g. if you're working at 5x actual size, draw a 5 inch (or cm) line along one edge of
your artwork. You can then double check the reduction by measuring the line on the film
positive - it should be 1 inch (or cm).
Something to consider when producing really small parts:
If you’re seeking super-fine detail, consider using stainless steel instead of brass.
The etching will take longer, but the results are impressive, and the steel etches more
sharply than brass.
Several people I have talked to have used CAD (Computer
Aided Drafting) packages to print directly to a laser or inkjet printer. If you’re
not a computer type, then skip this paragraph. If you are then you’ll need to adjust
your printer to handle the highest resolution it can handle. The higher the resolution,
the better the curves, and the finer the overall detail. Create the drawing, and do your
editing on the pixel level with photo-retouching software (Photo-styer, PaintShop, Lview
Pro 1.6B). Transfer the drawing to a transparency, then continue on to the next step.
The next step is to transfer the artwork from the film
positive onto the brass. The first step is to thoroughly clean the brass sheet as if you
were going to paint it - wash with detergent, rinse and air dry. Spray both sides with a
few coats of photoresist and allow to dry for a minimum of 60 minutes. The drying process
can be assisted with a hairdryer. If you have the luxury, let the raw brass set for 24
hours. Keep the brass away from bright light until you are ready to expose it.
Next step is to expose the photoresist. You want
sandwich the brass and the photo-positive between a piece of glass and corresponding
surface such as a piece of finished lumber. Hardware stores have pre-made shelving boards,
they come in various sizes and are pre-finished. Place the resist coated brass on the
lumber, the the film positive on top of the brass, then cover the whole thing with a sheet
of glass. Use real glass, as Plexi tends to be too flexible. It is very important to make
sure there is no air space between the brass sheet and the photo positive. Any airspace
will result in a ragged etch. Clamp the whole sandwich together. You’ll need a UV
source to expose the photoresist, and the best part of this step is that it’s free.
Place the brass outdoors in bright sunlight for 3-5 minutes, 5-8 for cloudy conditions.
You may to experiment with exposure times, as factors such as temperature and angle of the
sun will vary the effects and exposure times. NOTE: This procedure doesn’t work at
night (sic). After you’ve exposed the brass, you should remove the plate from any
light source until it can be developed. I recommend developing the brass immediately after
exposing. SHORTCUT: If you simply want to duplicate an already existing photoetch part or
tree, simply substitute the part for the photo positive.
Next, you develop the brass - i.e. remove the exposed
parts of the photoresist. Developing is done with a lye (sodium hydroxide) solution
-better electronics shops will carry this. Put the exposed plate in a plastic or glass
tray, and cover it with the developing solution for a few minutes. Rock the container to
agitate the solution. Remove the plate (wear rubber gloves and use forceps or needlenose
pliers) and check the development process - the pattern should appear on the brass, and
then disappear. This occurs within 5-7 minutes of soaking. When the pattern disappears,
the job is finished. Rinse under tap water to halt the development process. If you
overdevelop the plate, the etched image will be fuzzy and unusable. Put the plate back in
the developer solution until all of the resist is gone, and start over.
The etching solution is ferric chloride. Ferric
Chloride, or etching solution, is a red brown liquid available at Radio Shack or from GC
Electronics. A 32 oz. Bottle should run about $5.00. You need a plastic or glass container
that will hold the sheet of brass - a glass cake pan works well. Pour in the ferric
chloride solution about 1/2 deep, and place the brass sheet in face down (so that the
etched brass falls away from the surface of the sheet). It is necessary to keep the
etching solution agitated, new fluid needs to be circulated over the surface of the brass.
A simple method is to use an air source to create a whirlpool effect. TRICK: I use my
airbrush air hose, clamped to the side of the pan at an angle, to keep the fluid
circulating. Remove the plate and check the progress every 15 minutes or so, until the
brass is fully etched. Typical etch times are given as 1.5 hours with new etchant, longer
with used. Rinse with lots of water to stop the etching process. Ferric chloride is then
disposed of by flushing down the toilet. Author’s Note:I questioned the disposal of
the used ferric chloride, but the directions on the bottle clearly state that it can be
flushed.
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