Removing dull grains in order to make grinding wheel sharp is known as

Explanation:

Glazing:

• The sharp cutting points of abrasive grains in a wheel becomes dull after some use which results in the wheel face becoming smooth. Such a wheel instead of biting into the work materials give the rubbing action only. The phenomena are known as glazing and the affected wheel is called the glazed wheel.
• This phenomenon happens more with hard wheels operating at high speeds.
• The face or the cutting edge of the wheel takes a glass-like appearance.

Truing:

• Truing is the operation of changing the shape of the grinding wheel as it becomes worn from an original shape, owing to the breaking away of the abrasive and bond.
• Truing is done to make the periphery of the wheel concentric with its axis and to make its sides true and this way to recover the lost shape of its face.
• Truing is done on Glazed wheel.

​Dressing:

• Dressing of the wheel is done to recover proper cutting action of wheel face by removing the layer of dulled grains or grains clogged with foreign material.
• Dressing removes the loading of the wheel.
• Truing and dressing are done with the same tool but these are done not for the same purpose.

​Buffing:

• Buffing is similar to policing, with the exception that very fine abrasive is used on soft disks made of cloth or hide. The abrasive is supplied externally from the stick of abrasive compound. Polished parts may subsequently by buffed to obtained an even fibre surface finish.