|Grinding of Simple Tools - Course: Technique for Manual Working of Materials. Trainees' Handbook of Lessons|
These are grinding wheels. They are manufactured in different forms and structural compositions.
Straight grinding wheels:
Most used grinding wheel for all kinds of tools; it is used in various widths. Since the grinding operation takes place only at the circumference of the wheel, the result is always hollow grinding.
Special grinding wheel for the pointing of drills.
Grinding wheels with flaring or straight (cylindrical) outer face, which - due to their flat end faces - are especially suited for grinding surfaces that must not be hollow-ground, such as lathe tools and planing tools.
3.2. Structural compositions
Grinding wheels consist of abrasives (natural or synthetic) and binding agents.
Abrasives are produced in grain sizes ranging from very coarse to dust-fine and showing different void spaces between the grains - from very wide to very narrow - in the structure of the grinding wheel.
Binding agents may consist of elastic or inelastic materials, which - by the stability of their coherence with the grains of the abrasive - determine the hardness of the grinding wheel.
- If the abrasive grain shall remain for a long time, because a soft material is to be ground and. therefore, the edges of the abrasive grains are worn out only little, a hard binding agent is used, i.e. a hard wheel.
- Shall a hard material be ground, a soft binding agent is to be used, so that the rapidly dulling abrasive grains can tear loose quickly to make room for the following sharp grains: soft grinding wheel.
Since with off-hand grinding the pressure exerted on the wheel differes greatly and the abrasive grains tear loose more quickly, mostly hard grinding wheels are used.
3.3. Selection of the grinding wheels for off-hand sharpening
Soft to medium hard with medium grain size for tool steel and high-speed steel.
Silicon carbide wheels:
Hard with medium to fine grain size for tools with carbide cutting edges.
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