| Engraving Fact Sheet |
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 Click Above to see larger image of burnished plate. |
Burnishing Below is a list of headings. Click on the heading to go to that part of the text, or scroll down through the fact sheet.
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Description
Burnishing is a surface marking technique intended for coated metals - usually
lacquered brass - where the coating is removed to expose the bare metal.
It is a method of rotary engraving on metals that tends to bridge the gap
between diamond drag (scratch engraving) and routing. The biggest advantage
of burnishing is that it enables the engraver to produce wider line widths
than are obtainable with a diamond graver without having to cut deeply into
the metal. Burnishers can be used with single and multiple line fonts, and
are excellent for producing detailed line and logo work on metal. Burnishing
offers the ability to create enhanced effects on both lettering and graphics
and is relatively simple process.
Application
The most common application is on the brass plates on trophies and plaques.
This "trophy brass" is a relatively hard material that yields
excellent burnishing results. It is available in various gold tones with
clear or colored lacquer coatings. When burnishing the gold material, the
lacquer is removed exposing the bare metal. The burnished areas can then
be oxidized or blackened resulting in a gold plate with contrasting black
letters. (See "Color Filling Fact Sheet"). When burnishing the
colored materials, the result is a colored plate with contrasting gold letters
without the need for further treatment.
Burnishing can also be done on materials other than brass. However, much
of the success or failure depends on the hardness of the material. Since
burnishing is a surface marking technique, it is critical that the tip of
the burnishing tool does not penetrate the surface of the material by an
appreciable amount. Hard materials tend to prevent deep penetration of the
burnisher forcing the tool to work on the surface as it was designed. However,
on softer materials the tool is able to penetrate deeper and can produce
ragged edges and unacceptable results. Many of the colored aluminum products
on the market fall into this category and are not ideal choices for burnishing
although some can be burnished effectively using a diamond burnisher. There
are also harder aluminum products available with clear or black anodize
treatments that can be effectively burnished.
It is also possible to burnish metals such as steel and stainless steel.
Since the burnishing tool produces a swirled pattern, the mark is visible
and may be suitable for some marking applications not requiring a sharp,
well defined character. Generally speaking, however, these metals do not
have coatings and therefore, the burnishing can not be blackened to add
contrast.
Burnishing Tools
The tool used for burnishing is called a "burnisher"
which is a rotating tool that is used in a motorized spindle. It is usually
a carbide or carbide-tipped tool that is ground with four facets. Two of
the facets form an angled chisel
edge on the center
of the tool. The other two facets are ground perpendicular to the chisel
edge, equidistant from the center of the tool and determine the width of
the tip. Antares carbide burnishers are available in widths from .005"
up to the full diameter of the tool in increments of .005" (.005",
.010", .015", etc.).
Burnishers can also be made as diamond-tipped tools (diamond burnishers
or rotating diamonds) similar to those used in glass engraving. These tools
produce a more brilliant effect and have a longer life, but are considerably
more expensive. Diamond burnishers are standardly available in tip sizes
of .005", .010", .015", .020" and .030". Larger
sizes are available as special orders.
When selecting a tip size, follow the same guidelines that are used for
standard engraving cutters. For example, if you were to use a .030"
cutter when engraving plastic, you would use a .030" burnisher when
burnishing a brass plate with the same font and letter size. Since burnishing
is generally done with small, multiple-line fonts, the most common tip sizes
are between .005" and .030".
Burnishers are quite durable and are capable of producing thousands of characters.
Like cutters, they do become dull, however, and require periodic resharpening.
As a burnisher dulls, the chisel edge becomes rounded. This produces rough
edges and if allowed to continue, will result in the surface coating being
smeared in to the burnished stroke and can hamper oxidizing.
Process
Since the purpose of burnishing is to remove the coating from the surface
a the material, the key to achieving successful results lies in the amount
of downward pressure that is exerted on the tool. A burnishing tool is not
a cutter and if too much pressure is applied, the tool will be forced into
the material resulting in a rough, ragged stroke. Ideally, the tip of the
tool should "float" over the surface with only enough pressure
to remove the coating without digging into the metal.
To set the machine for burnishing, remove the depth nose and lower the spindle
to its down position. Next, screw the knob into the spindle, slide the burnisher
down through the knob until the tip contacts the plate and then tighten
the set screw in the knob. Raise the spindle and then increase the "depth"
a few thousandths of an inch by either adjusting the down stop on the spindle
or sliding the burnisher further through the knob. Since the bases and tables
of all machines are not perfectly level and material thickness can vary,
it is important to set the tool at the lowest point on the plate. This will
ensure that the tip of the tool will remain in contact with the entire surface
of the plate.
On computerized machines where the Z-axis (up and down) is controlled by
air and spring pressure, both should be set to their lowest setting. The
motor speed should be relatively fast and the engraving speed should be
at about the middle of its range. A slower engraving speed will produce
a smoother finish in the burnished stroke.
The set-up procedure is identical for both pantographs and computerized
engraving machines, however on a pantograph the correct pressure is determined
by the "touch" of the operator. It is a technique that is easy
to develop and the results should be equally as good as those achieved on
a computer. One trick that some pantograph operators use is to remove the
spindle return spring. This allows the spindle to drop on its own and float
over the material. The weight of the spindle alone is sufficient to produce
the desired results, but you must remember to lift the spindle when moving
from character to character.
One way to simplify the burnishing process and achieve consistent results
is through the use of a spring loaded burnishing attachment. These devices
are used in place of the conventional knob and have an internal spring that
applies the correct amount of pressure. These attachments usually require
a burnisher that is longer than normal, so be sure to specify that you are
using one of these attachments when ordering to ensure you get the proper
length tool.
