When you use an angle grinder, you must select a correct grinding wheel speed. The grinding wheel speed is an important aspect of using an angle grinder because if the grinding wheel spin too fast, it can shatter and lead to injury. Additionally, if you select a grinding wheel speed that is too low, then the grinding wheel will not effectively remove material and will wear down the grinding wheel quickly.
To prepare for using the angle grinder, you must understand the relationship between the revolutions per minute (RPM) of the grinding wheel and the surface feet per minute (SFPM) of the grinding wheel. The RPM of the angle grinder determine the number of times the grinding wheel will rotate in one minute. Additionally, the SFPM of the grinding wheel is the speed at which the grinding wheel move through the metal.
How to Choose the Right Speed for an Angle Grinder
If the grinding wheel is larger in size than the other grinding wheels, then the grinding wheel will have a more larger circumference. Thus, larger grinding wheels will cover more ground with each rotation of the grinding wheel. Due to the larger grinding wheel covering more ground with each rotation, the larger grinding wheel will require a smaller RPM to maintain the same SFPM as the smaller grinding wheel.
To calculate the required RPM of the grinding wheel, you can utilize the following formula: RPM equals the SFPM multiplied by 12 divided by pi multiplied by the diameter of the grinding wheel in inches. Additionally, you must ensure that the RPM of the grinding wheel is not greater than the maximum RPM that the grinding wheel can handle. The maximum RPM is stamped on the center label of the grinding wheel.
If the RPM of the grinding wheel is too high, then the centrifugal force of the grinding wheel may lead to the grinding wheel break apart. The different types of grinding wheels requires different cutting speeds. For instance, if the grinding wheel is a straight grinding wheel, then it will be used to remove heavy material from carbon steel.
Additionally, if the grinding wheel is a depressed center grinding wheel, the grinding wheel will be used in the corners of the workpiece with an angle grinder. Furthermore, if the grinding wheel is a diamond cup grinding wheel, the grinding wheel will be used to grind concrete with the grinding wheel. However, if you utilize the diamond cup grinding wheel at a speed that is too fast for the material that is being ground with the grinding wheel, the grinding wheel will glaze over.
Each type of grinding wheel will have specific requirement of the cutting speed of the grinding wheel. Additionally, if you do not match the required speed to the type of grinding wheel, then the material will burn or the grinding wheel will dull. Another important aspect of using an angle grinder is knowing at what SFPM the different metals should be ground.
Metal such as carbon steel should be ground at a speed between 5500 and 6500 SFPM with aluminum oxide grinding wheels. Additionally, stainless steel should be ground at a lower speed to prevent the stainless steel from work hardening. Moreover, aluminum should be ground at a higher speed to prevent the aluminum from loading on the grinding wheel.
Cast iron should also be ground at a gentle speed to prevent the metal from glazing. Knowing at what speed the metal should be ground requires knowledge of the thermal properties of the metal. By tailoring the grinding wheel speed to the thermal properties of the metal, heat will be able to dissipate from the metal instead of building up with the grinding wheel.
To determine the correct RPM for the grinding wheel based off its diameter, you can utilize a reference chart for the different sizes of grinding wheels. For example, a small four-inch grinding wheel may require an RPM of over 7000 for cutting application. In contrast, a twelve-inch grinding wheel may require an RPM of less than 3000.
This is due to the fact that larger grinding wheels are more susceptible to breaking if they are rotating at too high of a speed. Additionally, when grinding stainless steel, you should reduce the RPM by 15 percent. This is done to ensure the grinding wheel does not overheat when grinding the metal.
Additionally, when performing handheld work, such as with an angle grinder, you should reduce the RPM by 20 percent when utilizing the grinding wheel. There are some rules that must be adherged to when using an angle grinder and grinding wheels. For example, if the grinding wheel is rotating at 10 percent of the maximum RPM of the grinding wheel, the grinding wheel will experience 21 percent more stress on its bonds.
This additional stress on the grinding wheel could lead to the grinding wheel crack. Additionally, you must inspect every grinding wheel before it is used. If it is a vitrified grinding wheel, it must be tested for crack before use.
The arbor hole of the grinding wheel must also fit perfectly onto the spindle of the angle grinder. If the grinding wheel is too large for the angle grinder, it could break while in use. Finally, the individual must wear a face shield and safety glasses when using an angle grinder.
Additionally, you must run the angle grinder for one minute behind the guard to test the grinding wheel before grinding any metal.
