CNC Ground vs. Hand Ground

Until the mid-1980's, most manufacturers fluted their burs by hand. As CNC machine technology improved, machines became available that could flute any shape bur, as well as section the ends for proper cutting action. Today, the best performing burs are CNC machine ground. Some manufacturers still hand grind their burs, but the flutes of these tools are irregular, causing chatter, chipped edges, premature wear, and operator fatigue. CNC ground burs offer consistent tolerances for flute depth, flute spacing, rake angle, helix angle and flute concentricity. As a result, the bur cuts better, runs smoother, and is easier on the operator. All of these factors produce a more efficient finishing operation.

Operating Data

Carbide burs are chucked into die grinders and used in hand operations. Therefore, feedrates and pressure depend upon the working conditions and experience of the operator. Experienced operators adjust feed and pressure to achieve desired results. However, there are a few guidelines to remember. Avoid using so much pressure that grinder speed is reduced. This will cause the bur to overheat and prematurely dull. Maximize the area of contact with the work-piece, as finish improves when more length of the cutting edge engages the work. Avoid contactinf the workpiece with the shank of a bur, as this can cause the tool to overheat and weaken or even destroy the brazed joint.

Dull burs should be replaced with a new or resharpened tool before it becomes damaged. Dull burs cut slowly, requiring the operator to apply more pressure to the grinder. This can cause damage to the bur and/or grinder that can be far more costly than the cost of a resharp or new bur.

Lubricants can be used with carbide burs to improve lubricity and prevent chip loading. A liquid wax or synthetic lubricant is effective. A common method is to periodically dip the bur in a wax or lubricant.

Speed and Die Grinders

High speeds are essential for efficient and economical use of a carbide bur. At high speeds there will be less tendency for chips to build up in the flute. Also, the bur will cut more freely in the corners or pockets, and reduce the chances of jamming or wedging. These last two factors are biggest reason for shank breakage.

Carbide burs should operate between 1,500 and 3,000 surface feet per minute. Using these guidelines, a grinder can be selected that will efficiently work with a fairly broad range of bur sizes. For example, a 30,000-RPM grinder can be used with a 3/16" to 3/8" diameter bur. A 22,000-RPM grinder will be satisfactory for burs ranging from a 1/4" to 1/2" diameter bur. However, for most efficient operations, the grinder should be specified with consideration given to the diameter that will be most often used. Also, proper maintenance of air and grinding systems is vital. If a 22,000-RPM grinder bogs down too often, your usable RPM is actually much less. Therefore we recommend checking air pressure often, as well as the seals in the die grinder.

Indeed, correct speeds are important to achieving desired removal rates and work-piece finish. Increased speeds will improve finished and tool life. Lower speeds may remove material more rapidly, but may also cause overheating, bouncing, and premature failure. Different cuts are available to slow or speed removal rates. Below are the number of flutes for standard, fine and course cut burs.

see also:
Bur Shapes and Cuts
Carbide Bur Usage Data