Dressing and Truing Grinding Wheels :

The perfect grinding wheel operating under ideal conditions will be self-sharpening. i.e. as the abrasive grains become dull they will tend to fracture and be dislodged from the wheel by the grinding forces, thereby exposing new sharp abrasive grains. While in precision machine grinding this ideal may be partially attained in some instances, it is almost never attained completely. Usually the grinding wheel must be dressed and trued after mounting on the precision grinding machine spindle and periodically thereafter.

Dressing may be defined as any operation preformed on the face of a grinding wheel that improves its cutting action. Truing is a dressing operation but is more precise, i.e., the face of a wheel may be made parallel to the spindle or made into a radius or special shape. Regularly applied truing is also needed for the accurate size control of the work particularly in automatic grinding.

Guidelines for Truing and Dressing with Single Point Diamond :

The Diamond point should be set at an angle of 10 to 15 degrees in the direction of the wheel rotation and also, if possible, by the same amount in the direction of the cross feed traverse during the truing. The dragging effect resulting from this angling, combined with the occasional rotation of the diamond point in its holder, will prolong the diamond life by limiting the extent of wear facets and will also tend to produce a pyramid shape to the Diamond tip. The Diamond should also be set to contact the wheel 0.12 to 0.25 mm below its centerline.

Diamond Cross feed rate :

This value may be varied to some extent depending on the required wheel surface: faster cross feed for free cutting, and slower cross feed for producing fine finishes. Such variations, however, must always stay within the limits set by the grain size of the wheel. Thus the advance rate of the truing diamond per wheel revolution should not exceed the diameter of a grain or be less than half of that rate. Consequently, the diamond cross feed must be slower for a large wheel than a smaller wheel having the same grain size number.

Coolant should be applied before the Diamond comes into contact with the wheel and must be continued in generous supply while truing.

The Speed of the grinding wheel should be at the regular grinding rate, or not much lower.

The initial approach of the Diamond to the wheel surface must be carried out carefully to prevent sudden contact with the Diamond, resulting in penetration in excess of the selected depth of cut. It should be noted that the highest point of a worn wheel is often its center portion and not at the edge from which the cross feed of the Diamond starts.

The General Conditions of a truing device are important for the best truing results and for assuring extended diamond life. A rigid truing spindle, well seated diamond nib, and firmly set Diamond point are mandatory. Sensitive in feed and smooth traverse movement at uniform speed also must be maintained.

Resetting of the Diamond point :

Never let the Diamond point wear to a degree where the grinding wheel is in contact with the steel. Such contact will damage the diamond and the setting of the diamond and result in its loss. Expert resetting of a worn Diamond can repeatedly add to its useful life, even when applied to lighter work because of reduced size.

Selecting the type of tools to use :

Straight dressing - Single point dressers are most commonlyused as well as multi-point and impregnated tools.

Step Dressing - Form tools are most commonly used (including blade style tools) to form one or more diameters or shoulders (steps) on straight wheels.

Form Dressing - Conical or cone tools are most commonly used for higher accuracy special forms as well as a specific radius on chisel type tools.