All grinding wheels are breakable, and some are extremely fragile. Great care should be taken in handling grinding wheels. New wheels should be closely inspected immediately after receipt to make sure they were not damaged during transit. Grinding wheels should also be inspected prior to being mounted on a machine.

 

To test for damage, suspend the wheel with a finger and gently tap the side with a screwdriver handle for small wheels, and a wooden mallet for larger wheels. An undamaged wheel will produce a clear ringing sound; a cracked wheel will not ring at all.

 

Wheel balancing

 

It is important to balance wheels over 10 inches before they are mounted on a machine. The larger the grinding wheel, the more critical balancing becomes. Balance also becomes more critical as speed is increased. Out-of-balance wheels cause excessive vibration, produce faster wheel wear, chatter, poor finishes, damage to spindle bearings, and can be dangerous.

 

The proper procedure for balancing wheels is to first statically balance the wheel. Next, mount the wheel on the grinding machine and dress. Then remove the wheel and rebalance it. Remount the wheel and dress slightly a second time.

 

Shifting weights on the wheel mount will balance the wheels. The wheel is installed on a balancing arbor and placed on a balancing fixture. Then, the weights are shifted in a position to remove all heavy points on the wheel assembly.

 

Wheel dressing and truing

 

Dressing is a process used to clean and restore a dulled or loaded grinding wheel-cutting surface to its original sharpness. In dressing, swarf is removed, as well as dulled abrasive grains and excess bonding material. In addition, dressing is used to customize a wheel face so that it will give desired grinding results.

 

Truing is the process of removing material from the face of the wheel so that the resultant cutting surface runs absolutely true. This is very important in precision grinding because an out-of-true wheel will produce objectionable chatter marks on the work piece. A new wheel should always be trued before being put to work. Also, it is a good idea to true the wheel if it’s being remounted on a machine.

 

Dressing and truing conventional grinding wheels are two separate and distinct operations, although they may sometimes be done with the same tool. The tools used for conventional grinding wheel dressing include:

 

Mechanical dressers, commonly called star dressers, are held against the wheel while it is running. The picking action of the points of the star-shaped wheels in the tool remove dull grains, bond, and other bits of swarf. Star dressers are used for relatively coarse-grained conventional wheels, generally in off-hand grinding jobs where grinding accuracy is not the main consideration.

 

Dressing sticks are used for off-hand dressing of smaller conventional wheels, especially cup and saucer shapes. Some of these sticks are made of an extremely hard abrasive called boron carbide. In use, a boron carbide stick is held against the wheel face to sear the dull abrasive grains and remove excess bond. Other stressing sticks contain coarse Crystolon or Alundum grains in a hard vitrified bond.

 

Diamond dressing tools utilize the unsurpassed hardness of a diamond point to clean and restore the wheel grinding face. Although single-point diamond tools were once the only products available for this kind of dressing, the increasing scarcity of diamonds has led to the development of multi-point diamond tools.

 

Multi-point diamond dressing tools use a number of small diamonds held in a matrix. In use, the tool is held securely in the tool holder and held flat against the face of the running wheel. As it dresses, the tool is traversed across the wheel face until the job is done. As diamonds on the surface of the tool wear away, fresh new diamond points are exposed to offer extended life and use. This type of tool produces a very consistent wheel face from dress to dress.

 

Multi-point diamond dressing tools are available in a wide range of shank diameters and face shapes to meet the requirements of a broad variety of grinding machines.