| Engraving Fact Sheet |
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| Engraving Fact Sheet |
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Description
Some of the most attractive signs are those which are reverse
engraved in acrylic and color filled. The effect is a rich looking sign
with colorful, sub-surface graphics that have more dimension than surface
engraved products.
One common method of reverse engraving in acrylic is to use a cutter
with a wide included angle (90°) which produces a broad, "V"
shaped groove. Due to the angle of the side of the cut, light entering the
edges of the sign reflects off the surface of the cut, instead of passing
through it, and causes the letters to stand out.
One of the problems with this method is that due to the shape of
the cutter, the width of the cut increases significantly with increased
depth. As a result, the bases of the letters can run together when engraving
to any significant depth.
To eliminate this problem and further enhance the effect of reverse
engraved acrylic, Antares introduced the "3-D cutter." This cutter
is sharpened to a narrow included angle, which allows for engraving at considerable
depth without significantly broadening the stroke. After the letters are
filled, the resulting effect is that the lettering appears to have been
"cast" into the acrylic plate.
Technique
The 3-D effect becomes more pronounced as both the material thickness
and the engraving depth are increased. The best effects come from engraving
to a depth of 1/2 to 3/4 of the material thickness. As a guide, 1/8' material
should be engraved at a depth from .060" to .090" and 1/4"
material to a minimum depth of .125".
When you consider that most engraving is done to a depth of .010"
or .015' in soft materials like flexible engraving stock, engraving deeply
in a hard material such as acrylic requires more time. Engraving to a depth
of .125", for example, would require four to five passes of about .030"
depth per pass.
One problem inherent to acrylic engraving is melting of the material
due to the heat generated by the cutter. If the heat is excessive, the chips
that are not ejected by the cutter will "weld" themselves to the
walls of the cut and to the cutter itself. When the latter condition occurs,
the cutting action is severely reduced and the melting problem is magnified.
To help minimize the problem, the initial roughing cuts should be
made at a reduced spindle speed (cutter speed) and a reduced feed rate (engraving
speed). The slower cutter speed prevents heat build-up and the slower feed
rate allows the chips to be cleared from the cut. It is strongly recommended
that the final pass be a "clean-up pass" cut .002" to .003"
deep. This pass, done at the same engraving speed but a higher cutter speed,
will clean out any chips left in the cut and produce a smoother finish which
enhances the appearance of the paint fill.
Using a cutting fluid virtually eliminates the melting problems and
speed up the engraving process. A water-soluble oil keeps the heat below
the melting point of the acrylic, provides lubrication of the cutter, and
can be washed off with soap and water.
If the sign is to have a background color, the plate can be spray
painted on one side before engraving. After the paint has dried sufficiently,
the plate is engraved through the painted surface and then filled with a
contrasting color. If you are not required to match a specific color, you
can eliminate the hassle of surface painting by using a reverse engravable
material such as Rowmark Slickers.
The Slickers are a multi-layered acrylic material with a clear face
and a colored back. The engraving is done through the colored layer and
then filled with an acrylic-based paint. Since the colored layer is very
durable, the material can be engraved using a nose cone without the worry
of scratching through the surface as is possible on painted surfaces. The
Slickers are available in a wide range of colors and in thicknesses of 1/16",
1/8", and 1/4".
