Burrs or burs (sometimes called rotary files) are small cutting tools; not to be confused with small pieces of metal formed from cutting metal, used in die grinders,

rotary tool Die grinders and rotary tools are handheld power tools used for grinding, sanding, honing, polishing, or machining material (typically metal, but also plastic or wood). All such tools are conceptually similar, with no bright dividing line ...

s, or dental drills. The name may be considered appropriate when their small-sized head (3 mm diameter shaft) is compared to a bur (fruit seed with hooks) or their teeth are compared to a metal burr.

Description

Burrs are a rotary analog to files that cut

linearly Linearity is the property of a mathematical relationship (''function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear re ...

(hence their alternate name, rotary files). They are also in many ways comparable to

endmill An end mill is a type of milling cutter, a cutting tool used in industrial milling applications. It is distinguished from the drill bit in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, most m ...

s and to

router bit The router is a power tool with a flat base and a rotating blade extending past the base. The spindle may be driven by an electric motor or by a pneumatic motor. It routs (hollows out) an area in hard material, such as wood or plastic. Router ...

s; a distinction is that the latter usually have their toolpath controlled by the machine, whereas burrs are often used freehand. However, there is substantial overlap in the use and toolpath control of these various classes of cutters, and in the outcomes accomplished with them. For example, endmills can be used in routers, and burrs can be used like endmills in milling by CNC or manual

machine tool A machine tool is a machine for handling or machining metal or other rigid materials, usually by cutting, boring, grinding, shearing, or other forms of deformations. Machine tools employ some sort of tool that does the cutting or shaping. Al ...

s. In fact, burrs (the tools) are often used in CNC machining centers for removing burrs (the small flakes of metal) after a machining process. To maintain the correct surface speed and cutting conditions, burrs are rotated at high speed (thousands or tens of thousands of RPM; often the top speed available on a given spindle). The cutters shown in the image are made from tungsten carbide, which allows them to operate at higher speeds than similar HSS cutters, yet still maintain their cutting edges. Because the cutting edges of burrs are so small, they can often be touched when spinning by a finger without cutting the skin, which flexes out of the way, although it would not be safe to pinch or grip them from two sides. Hard metal or ceramic workpieces cannot flex beyond the cutting edges, so the tools remove material from them. This characteristic makes burrs suitable for dentistry, as the tool will grind the hard enamel of teeth, yet leaves soft mouth tissues unharmed if the tool should unintentionally touch them.

References

Metalworking cutting tools {{Tool-stub