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.
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.