This article looks at describing what a burnisher cutter is
Burnishing 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 rout or cut deeply into the metal. It is a surface marking technique intended for coated metals – usually lacquered brass where the coating is removed thereby exposing the bare metal, Burnishers can be used with single and multiple line fonts, and are an excellent tool 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 easy to master.
The most common application for burnishing is on the brass plates on trophies and plaques. This ‘trophy brass’, as it is commonly known, is a hard material that offers excellent burnishing results. It’s available in various gold tones with a clear lacquer coating or in a variety of colours. When burnishing the gold material, the lacquer is removed exposing the bare metal. The burnished areas can then be oxidized or blackened and the result is a gold plate with
contrasting black letters. When burnishing the coloured materials, the result is a coloured plate with contrasting gold letters and no further treatment of the burnishing is necessary.
Burnishing can also be done on materials other than brass, however much of the success or failure lies in the hardness of the material *. Since burnishing is a surface technique, it is critical that the tip of the burnishing tool does not penetrate the surface of the material by an appreciable amount. Hard metals tend to prevent deep penetration of the burnisher and the tool works on the surface as it was designed. On softer metals, however, the tool is able to penetrate deeper which yields ragged edges on the burnished character and generally unacceptable results. Many of the coloured aluminium products on the market fall into this category and are not optimum choices for burnishing. There are harder aluminium 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 cannot be blackened to add contrast.
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 centre of the tool which is responsible for the actual burnishing or ‘scraping’ action. The other two facets are ground perpendicular to the chisel edge, equidistant from the centre of the tool and determine the width of the tip. Burnishers can also be made as diamond-tipped tools similar to those used in glass engraving. These tools produce a more brilliant mark, but are considerably more expensive. Cesco’s carbide burnishers are available in widths from .005″ up to the full diameter of the tool in increments of .005″, i.e. .005″, .010″, .015″, etc. When selecting tip size, you should follow the some guide lines that are used for other types of 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 using the same font and letter size.
For those just getting started in burnishing, we recommend starting with three basic tip sizes of .015″ .020” and .030”. These will handle the majority of the small, single stroke characters commonly used on trophy plates and many of the multiple line, decorative fonts used on plaques and the like.
Burnishers are quite durable and are capable of producing thousands of characters. 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 progress, will result in the surface colour being smeared into the burnished stroke, The latter condition can severely hamper oxidizing. Resharpening restores the edge to its original condition and costs the same as resharpening a standard engraving cutter.
Since the purpose of burnishing is to remove the coating from the surface of 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 surface of the metal and the result will be 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 your machine for burnishing, remove the depth nose and insert the burnisher into the spindle. If the depth nose on your machine is large enough, you may leave it on and adjust the burnisher so that it extends beyond the bottom of the nose. In any case, the depth nose is not used in the burnishing operation and your set-up should prevent the nose from coming in contact with the surface of the material.
The next step is to lower the spindle to its full down position and set the burnisher. Loosen the set screw in the knob and lower the tool so that its tip firmly contacts the plate and then tighten the screw, Since the bases and tables of all machines are not perfectly level, it is important to set the tool at the lowest point on the plate. This will ensure that the tip of the tool will make contact over the entire surface. On computerized machines where the z-axis (spindle up-down) is controlled by air and or 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 it’s 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. On a pantograph, however, the correct pressure is determined by the ‘touch’ of the operator. It’s 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 or disable the spindle return spring. This allows the spindle to drop on its own and float over the material. The weight of the spindle clone is sufficient to produce the desired results, but you must remember to lift the spindle when going from character to character.
One way to simplify the burnishing operation 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 so that you get the proper length tool.
Compiled from an article by Antares Inc.
* To blacken brass use Brass oxidant. For oxidizing aluminium use aluminium oxidant.
* For burnishing aluminium or glass and even brass we recommend the use of diamond burnishers. These burnishers will give a longer life and provide a better cut.