Iron Grindstone
<Iron Grindstone>
A grinding wheel with a reservoir holds water as a lubricant and coolant.
Grindstone is one of the most used abrasives for grinding scissors. A Bonded abrasive is the most commonly used.
A bonded abrasive is composed of an abrasive material contained within a matrix, although very fine aluminum oxide abrasive may comprise sintered material. This matrix is called a binder and is often clay, resin, glass, or rubber. This mixture of binder and abrasive is typically shaped into blocks, sticks, or wheels.
A bonded abrasive is made of abrasive grains, bonded material, and pores.
The most common abrasive used is aluminum oxide—also, silicon carbide, tungsten carbide, and garnet. Artificial sharpening stones are often bonded abrasive and are readily available as a two-sided block, each side being a different grade of grit.
Grinding wheels are cylinders that are rotated at high speed. While once worked with a foot pedal or hand crank, the introduction of electric motors has made it necessary to construct the wheel to withstand tremendous radial stress to prevent the wheel from flying apart as it spins. Similar issues arise with cutting wheels often structurally reinforced with impregnated fibers. The high relative speed between abrasive and workpiece often makes necessary the use of a lubricant of some kind. Traditionally they were called coolants as they were used to prevent frictional heat build-up, which could damage the workpiece (such as ruining the blade's temper).
It is easy to understand the grinder operating mechanism through the figure.
Some research suggests that the heat transport property is less important when dealing with metals as the metal will quickly conduct heat from the work surface. More important are their effects upon lessening tensile stresses while increasing some compressive stresses and reducing "thermal and mechanical stresses during chip formation."
Various shapes are also used as heads on rotary tools used in precision work, such as scale modeling.
Bonded abrasives need to be trued and dressed after they are used. The dressing cleans the surface's waste material (swarf and loose abrasive) and exposes fresh grit. Depending upon the abrasive and how it was used, the dressing may involve the abrasive being placed under running water and brushed with a stiff brush for a soft stone or the abrasive being ground against another abrasive as aluminum oxide used to dress a grinding wheel.
Truing is restoring the abrasive to its original surface shape. Wheels and stones tend to wear unevenly, leaving the cutting surface no longer flat (said to be "dished out" if it is meant to be a flat stone) or no longer the same diameter across the cutting face. This will lead to uneven abrasion and other difficulties.
