To keep hand tools in the best usable condition, cutting edges must be sharpened frequently and certain other tools trued or shaped for special purposes. Chisels, punches, drills, tin snips, screwdrivers, and other hand tools are shaped or sharpened on an abrasive grinding wheel.
Grinding may be defined as the act of shaping or wearing down a surface or sharpening an edge by means of the cutting action of thousands of abrasive grains on the surface of the grinding wheel. Excessive grinding shortens the useful life of a tool. A variety of grinding machines are in use in the Navy. Many of them are special machines used in tool and die making or machines used for other special purposes. Nearly all mechanical shops in shore installations or aboard the ship will have a bench grinder.
The grinding wheel is a fragile cutting tool which operates at high speeds. Great emphasis must be given, therefore, to the safe operation of bench and pedestal grinders. Observance of safety precautions, posted on or near all grinders used in the Navy, is mandatory for the safety of the operator and the safety of personnel in the nearby vicinity.
What are the most common sources of injury during grinding operation? Hazards leading to an eye injury caused by grit generated by the grinding process are the most common and the most serious. Abrasions caused by bodily contact with the wheel are quite painful and can be serious. Cuts and bruises caused by segments of an exploded wheel, or a tool “kicked” away from the wheel are other sources of injury. Cuts and abrasions can become infected if not protected from grit and dust from grinding. Want to know more see the link.
Safety in using bench and pedestal grinders is primarily a matter of using common sense and concentrating on the job at hand. Each time you start to grind a tool, stop briefly to consider how observance of safety precautions and the use of safeguards protect you from injury. Consider the complications that could be caused by your loss of sight, or loss or mutilation of an arm or hand.
A grinding wheel is composed of two basic elements:
The abrasive grains may be Compared to many single point tools embedded in a tool holder of bonding agent. Each of these grains extracts a very small chip from the material as it makes contact on each revolution of the grinding wheel. An ideal cutting tool is one that will sharpen itself when it becomes dull. This, in effect, is what happens to the abrasive grains. As the individual grains become dull, the pressure that is generated on them causes them to fracture and present new sharp cutting edges to the work. When the grains can fracture no more, the pressure becomes too great and they are released from the bond, allowing new sharp grains to be presented to the work.
SIZES AND SHAPES
Grinding wheel come in various sizes and shapes. The size of a grinding wheel is given in terms of its diameter in inches, the diameter of the spindle hole, and the width of the face of the wheel. The shapes of all grinding wheels are too numerous to list in this manual, but figure 5-1 shows most of the more frequently used wheel shapes. The type numbers are standard and are used by all manufacturers. The shapes are shown in cross-sectional views. The specific job will dictate the shape of the wheel to be used.
Grinding wheel markings are comprised of six sections. Figure 5-2 illustrates the standard marking and possible variations. The following information breaks the marking down and explains each section. This information should be studied carefully as it will be invaluable in marking the proper wheel selection for each grinding job you will attempt.
The first section on the wheel marking (reading from left to right) shows the abrasive type. There are two types of abrasives: natural and manufactured. Natural abrasives, such as emery, corundum, and diamond, are used only in honing stones and in special types of grinding wheels. The commonly manufactured abrasives are aluminum oxide and silicon carbide. They have superior qualities and are more economical than natural abrasives.
Aluminum oxide is used for grinding steel and steel alloys, and for heavy-duty work such as cleaning up steel castings. Silicon carbide, which is harder than but not as tough as aluminum oxide, is used mostly for grinding nonferrous metals and carbide tools. The abrasive in a grinding wheel comprises about 40 percent of the wheel.