A Toishi - A Toishi

...In the use of a grinding wheel, it is necessary to perform shaping (the operation of finishing the circumference of the wheel to the correct geometric shape with a suitable tool), dressing or sharpening (the operation of producing a sharp cutting edge on the wheel surface with a suitable tool).
[Application]
Classified by abrasive grain, A wheels have a high tensile strength (30kgf/mm2 or more) and are used for rough cutting of tough, relatively sticky work materials, while WA wheels have an extremely high tensile strength (50kgf/mm2 or more) and are used for precision grinding of work materials that are tough, dense, and often generate heat during grinding. C wheels are used for hard, relatively brittle work materials, processing non-ferrous metals with high ductility, and non-metallic materials that tend to clog, such as stone, rubber, wood, bamboo, and plastic, while GC wheels have a relatively low tensile strength and are used for grinding extremely hard, dense, and brittle work materials.

*Some of the terminology explanations that mention "A Stone" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…研削といしの使用にあたっては，形直し(適当な工具でといし外周を正しい幾何学的形状に仕上げる操作)，目直しまたは目立て(適当な工具でといし表面に鋭い切れ刃を出現させること)を行う。
［用途］
　砥粒によって分けると，Aといしは引張強さが高くて(30kgf/mm2以上)強靱な比較的粘りのある被削材とか粗加工に，WAといしは引張強さがすこぶる高くて(50kgf/mm2以上)強靱堅密で研削熱を発生することの多い被削材とか精密研削に用いられる。Cといしは，堅硬で比較的もろい被削材，延性の大きい非鉄金属の加工とか，石材，ゴム，木竹，プラスチックなど目づまりしやすい非金属材料に使われ，GCといしは，引張強さが比較的低くてすこぶる堅硬緻密（ちみつ）でもろい被削材の研削に用いられる。…

※「Ａ といし」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報