Bench grinder
A bench grinder is a benchtop type of grinding machine used to drive abrasive wheels.
The grinder's RPM must be equal or lower; "the maximum operating speeds indicated on the wheel's tag must never be exceeded".
[2] Greatly overspeeding a grinding wheel makes it explode, which can injure or kill the operator.
Some tool and cutter grinders have cup-shaped wheels designed to do grinding on the side.
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 temper, burn the operator's hand, or both.
For medium-carbon or high-carbon workpieces that are already 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 treatment.
Some grinders for knife sharpening duty are of the wet type, in which the bottom of the wheel runs within a pan of water or other coolant.
Bench grinder wheels sometimes need to be restored to roundness and given a fresh grinding face with newly exposed grains.
Correcting the imbalance not only reduces the annoyance of vibration (which rattles the wheel guards and shakes the workbench) but also is important to prevent premature failure of the spindle bearings, as heavy vibration beats them excessively.
"In other words, to remove the nut, it must be turned in the direction that the spindle revolves when the wheel is in operation.
The paper is conventionally held to be absolutely necessary to prevent the steel flange from bearing directly against the wheel and tending to crack it; trained workers are expected to know and obey this rule.
[2] The wheel's inner diameter may meet the arbor precisely or may be larger with a bushing (sleeve) to reduce it.
When the wheel is first started, the operator stands a bit off center, so that if it were to explode, less pathway for injury exists.
