In this article we will discuss about wheel truing and dressing of a grinding wheel in the industries.
Wheel truing is defined as act of restoring the cutting face of a grinding wheel by removing the abrasive material from the cutting face and sides of the wheel, so that it will run true with respect to the axis of rotation and produce perfect round or flat work.
It also includes the altering of the cutting face shape to produce special contours. As soon as a fresh wheel is fitted, it becomes necessary to true its face. It also produces concentricity or parallelism of faces. It prepares the wheel to perform a forming operation.
Wheel dressing is defined as the act of improving the cutting action. It can also be described as sharpening operation. It becomes necessary from time to time during the course of working to correct uneven wear and to open up the face of the wheel so as to obtain efficient cutting conditions.
Dressing a wheel does not necessarily true it. The wheel may be out of round or parallel even after dressing as it only removes the outside layer of dulled abrasive grains and the foreign material.
Dressing may be accomplished by using metal crushers, abrasive sticks, abrasive wheels, single-point diamonds, single set and matrix diamond dressers, rotary and stationary diamond rolls, and crushing rolls.
Metal crushers are used to dress wheels meant for roughing operations. Abrasive sticks are used to dress the wheels and to remove loading or glazing from diamond wheels. Crushers are used for profile dressing.
A star dresser consists of pointed discs loosely revolving on a pin and held to the wheel with a handle. Abrasive sticks and wheel are also used. Truing is carried out with diamond which has a shearing action on the abrasive grains and the bond, and so removes the dulled or irregular groups of grains.
It is able to do this because it is harder than abrasive grain, although not much harder than SiC, which wears it more than Al2O3. The diamond is held in a holder. This is done by peening, brazing or securing the diamond by casting a low melting point metal round it leaving sufficient of the stone protruding for it to act as a cutting edge.
Defect with single diamond tool is that:
(i) If traverse feed is not more than grain size then dressing will cause lot of wear;
(ii) Angle at which dresser is held to wheel is dependent upon the cutting edge of diamond;
(iii) Truing can be done in one direction only. The six diamonds dresser as shown in Fig. 20.11 (b) overcomes all these troubles and has long life as compared to single diamond dresser. In it, the middle diamond acts as roughing tool and the other two do finishing. When above three diamonds wear out then three at bottom start working.