Offhand Grinding

Introduction to Grinding Grinding machines cut metal with abrasives and pressure Abrasive wheel, disc, or belt “Offhand”: ground materials held in hand Pedestal and bench grinders Sharpening and deburring ferrous metals Tool grinder Sharpening lathe cutting tools (ferrous)‏

FIGURE 3.5.1 (A) A pedestal grinder and (B) a bench grinder. (A) © Cengage Learning 2012 (B) Courtesy of Baldor Electric Company

FIGURE 3.5.2 A tool grinder has adjustable tool rests and is commonly used to grind lathe cutting tools. It can be bench or pedestal mounted. Courtesy of Baldor Electric Company

Abrasive Belt and Disc Machines Slower than pedestal grinders Often used for light deburring Can grind both ferrous and nonferrous metals A B FIGURE 3.5.3 (A) A light-duty abrasive belt machine. Courtesy of Baldor Electric Company (B) A heavier-duty belt and disc machine. Courtesy of Jet-Wilton

Grinding Wheels Vary based on abrasive type, abrasive grain size (wheel grits), wheel size, and maximum wheel speed Characteristics printed on blotter FIGURE 3.5.4 A grinding wheel blotter shows wheel information such as abrasive type, grain size, wheel size, and maximum wheel RPM. © Cengage Learning 2012

FIGURE 3.5.5 An aluminum oxide wheel. © Cengage Learning 2012 FIGURE 3.5.6 A green silicon carbide wheel. © Cengage Learning 2012

FIGURE 3.5.7 A diamond-impregnated wheel. © Cengage Learning 2012 FIGURE 3.5.8 A grinding wheel manufacturer may allow use of a reducing bushing to mount a wheel on a slightly smaller machine arbor. © Cengage Learning 2012

Pedestal Grinder Setup Perform “ring test” before mounting wheel Mounting: seat wheel flanges against blotters Set tool rest to desired angle; check spark breaker Dress wheel before use FIGURE 3.5.9 The major parts of a typical pedestal grinder. © Cengage Learning 2012

FIGURE 3.5.10 Suspend a grinding wheel and lightly tap with a non-metallic object to perform a ring test. A clear ring indicates that the wheel is “sound.” A dull sound means a wheel is damaged and should not be mounted on a grinder. © Cengage Learning 2012

FIGURE 3.5.11 The wheel flanges of a pedestal grinder distribute the clamping pressure evenly on the wheel. Always use a blotter on each side of the wheel between the flange and the wheel. © Cengage Learning 2012

FIGURE 3.5.12 A piece of wood may be needed to keep wheels from spinning when loosening or tightening the nuts that secure the wheel flanges. © Cengage Learning 2012

FIGURE 3.5.13 Keep the clearance between the tool rest and the wheel within 1/16". Always wait until the wheel has completely stopped before making adjustments. © Cengage Learning 2012

FIGURE 3.5.14 The spark breaker should also be adjusted within 1/16" of the grinding wheel. Always wait until the wheel has completely stopped before making adjustments. © Cengage Learning 2012

FIGURE 3.5.15 To dress a grinding wheel, place the wheel dresser on the tool rest and lift the handle upward to make contact with the wheel. Then slide the dresser from side to side on the tool rest to dress the periphery of the wheel. Always wear a face shield when dressing grinding wheels. © Cengage Learning 2012

FIGURE 3. 5. 16 A loaded wheel results from grinding soft metals FIGURE 3.5.16 A loaded wheel results from grinding soft metals. Note the pieces of material embedded in the wheel. © Cengage Learning 2012

FIGURE 3.5.17 A glazed wheel results from grinding very hard materials. Note the shiny appearance of the wheel compared to a sharp wheel. © Cengage Learning 2012

Grinding Procedures Check tool rest and spark breaker Stand to the side Use moderate speed and cool part if needed Grind only on wheel face FIGURE 3.5.18 The proper method for performing grinding on a pedestal grinder. Stand to the side of the wheel, keep fingers and hands away from the wheel, and use the tool rest to help support the work. © Cengage Learning 2012