Die grinders and rotary tools are handheld power tools used for grinding, sanding, honing, polishing, or machining material. All such tools are conceptually similar, with no bright dividing line between die grinders and rotary tools, although the die grinder name tends to be used for pneumatically driven heavy-duty versions whereas the rotary tool name tends to be used for electric lighter-duty versions. Flexible shaft drive versions also exist. The die grinder name comes from one of their earliest and archetypal applications, tool and die work, where they were used to create the precise contours of dies or molds. Especially before the advent of widespread CNC usage, they were heavily relied upon for contouring via manual skill comparable to a sculptor's. CNC now provides much of the contouring for die and mold interior surfaces, but die grinders are still very useful for hundreds of cutting needs, from sculpture-like contouring in the absence of CNC, to cut-off of bar stock, to any of the cutting and grinding needs of fabrication, such as in the work of welders, boilermakers, millwrights, ironworkers, sheet metal workers, to woodworking, hacking, and other hobby or business pursuits. Die grinders are often used for engraving, cylinder head porting, and general shaping of a part.
Methods of cutting action
The cutting may be done in various ways, including:
Small abrasive cut-off wheels, which work like saw blades except via abrasive cutting rather than sawing per se
Small sanding drums
Small sanding flap wheels
Small cloth or fiber wheels, drums, and flap wheels
Mounted laps
Methods of holding the cutter
The cutter is usually held in a collet, which is a convenient means of chucking in this application and provides the concentricity needed for high-RPM use. It also allows for quick changes in cutters. In some applications, other quick-change indexable chucking systems can be used, similar to the indexable chucking types now commonly found on consumer pistol-grip drills.
The most universal safety precaution in die grinder use is to protect one's eyes by wearing safety glasses. Other common PPE in die grinder use includes:
Other eye and face protection, such as safety goggles or a face shield, which is simply a polycarbonate window, hanging from a headband, between one's face and the work. All eye protectors come in clear versions as well as various levels of shading.
Protection for the respiratory and alimentary tracts, such as simple paper masks or, in special applications, a respirator. Masks may be trivial in many applications but important in others. Any abrasive cutting generates dust, from both the abrasive itself and from the workpiece. Depending on the materials and amounts, masks may be needed.
Safety features built into the tool
Most pneumatic die grinder throttles feature a spring-loaded "kickstand" mechanism between the throttle lever and the body of the grinder. This prevents the throttle from opening without operator intervention and inhibits accidental activation. It is similar in principle to the safety catches used on many handguns. Tools with electric motors often have electrical safety features such as grounded cases or double insulation. Some may have both, but this is uncommon, because regulatory requirements require only one or the other.
