Editing Bench grinder (section)

==Operation & Safety==
===Wheel speed===
Wheels come with maximum [[revolutions per minute|RPM]] ratings printed on the label (paper blotter). The grinder's RPM must be equal or lower; "the maximum operating speeds indicated on the wheel's tag must never be exceeded".{{sfnp|Machinery's Handbook|1996|pp=1105–1109}} Greatly overspeeding a grinding wheel makes it explode, which can injure or kill the operator. 

===Workpiece material suited to wheel grade===
The typical wheels on most bench grinders are [[grinding wheel#Wheel bond|vitreous-bond]] wheels. They work best to do their intended task, but they inherently have a risk of cracking. Grinding wheels designed for steel are not to be used for grinding softer metals, like aluminum.  The soft metal gets lodged in the pores of the wheel and later expands with the heat of grinding.  This can dislodge pieces of the grinding wheel, causing injury.

===Sides of wheel versus periphery===
Grinding is prohibited on the side of a typical (disk-shaped) bench grinder wheel, which is designed for grinding on the periphery only. Grinding on the side of a wheel can cause the wheel to explode. Some tool and cutter grinders have cup-shaped wheels designed to do grinding on the side.

===Tool rest and spark arrester placement===
The tool rest needs to be tight and within 2 to 3 mm of the wheel ({{frac|1|16}}" to {{frac|1|8}}"). This prevents the workpiece from slipping down between the wheel and the tool rest. The spark arrestors catch stray sparks.

Grinding is usually done with the workpiece resting on the tool rest. This prevents sudden slips in which the wheel grabs the work momentarily and yanks it out of the operator's hand or pulls the hand toward the wheel.

===Wheel guards===
The wheel guards serve to intercept the fragments of an exploding wheel, keeping them from killing people or damaging surroundings. This is why running a grinder without the guards is prohibited.

===Coolant===
Grinding metal on a power-driven grinding wheel quickly heats up the workpiece. Most bench grinders are of the dry type, in which no [[cutting fluid]] (coolant) is used at the grinding interface, but often the workpiece is recurrently dunked into a pan or pot of water for cooling so as to keep it from getting hot enough to lose its [[tempering (metallurgy)|temper]], burn the operator's hand, or both. Such pots are often mounted just below the grinder for safe and easy reach. For medium-carbon or high-carbon workpieces that are already [[hardening (metallurgy)|hardened]] and tempered (such as tool bits and drill bits), the dipping of the piece into the water must be frequent enough to avoid very high heat followed by substantial [[quenching]], which can easily destroy the existing [[heat treating|heat treatment]].

Some grinders for knife sharpening duty are of the [[wet grinder|wet type]], in which the bottom of the wheel runs within a pan of water or other coolant. A tube may also deliver a stream of coolant near the top of the wheel. These grinders are not always called bench grinders, but they are among the class of benchtop grinding machines.