Editing Bench grinder (section)

==Wheel replacement==
Wheels sometimes need replacing. The grinder is unplugged, and then the outer guard is removed. Typically a large nut holds the wheel on the arbor. The [[screw thread#Handedness|handedness]] (sense) of each nut is assigned to avoid any loosening tendency during grinder use.{{sfnp|Machinery's Handbook|1996|pp=1105–1109}} Thus on a typical grinder the nut is left-handed on the left side of the grinder from the operator's viewpoint, with wheel rotation "toward" the operator (if the wheel could travel), whereas on the other side the nut is right-handed. "In other words, to remove the nut, it must be turned in the direction that the spindle revolves when the wheel is in operation."{{sfnp|Machinery's Handbook|1996|pp=1105–1109}} Holding the wheel against the wrench's turning action is difficult, but usually the wrench is gently tapped with a hammer instead, which neatly taps the nut loose. A large steel flange is on either side of the wheel, then a paper washer (blotter), then the wheel. 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. <!-- I don't know whether this has been *proven* in controlled experiments, but it is widely held to be true among skilled workers. --> Thus the entire contact area between flange and wheel is covered, either with paper or with compressible coating (rubber or gasket) on the flange.{{sfnp|Machinery's Handbook|1996|pp=1105–1109}} The wheel's inner diameter may meet the arbor precisely or may be larger with a bushing (sleeve) to reduce it.{{sfnp|Machinery's Handbook|1996|pp=1105–1109}} Before the new wheel is mounted it is ring tested,{{sfnp|Machinery's Handbook|1996|pp=1105–1109}} which involves ''gently'' tapping it with a fingernail or tool handle (wood or plastic) to hear its high-pitched ring (comparable to a [[bell]]'s ring, although not loud), indicating that it is not cracked.{{sfnp|Machinery's Handbook|1996|pp=1105–1109}} It is rung in various spots to be sure. A "flat" or "hoarse" sound (failing to "sing") indicates a crack.{{sfnp|Machinery's Handbook|1996|pp=1105–1109}} With the wheel having passed the ring test, the bushing (if any), wheel, paper blotters, steel flanges, and nut are assembled, and the nut is tightened, not as hard as possible, but enough to be firmly fastened in place. The guard is reinstalled, and then the grinder can be plugged in again. Dressing may be needed afterward. 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.