From the simplest grinding machine to the most complex, grinding machines can be classified as utility grinding machines, cylindrical grinding machines. and surface grinding machines. The average machinist will be concerned mostly with floor-mounted and bench-mounted utility grinding machines, bufting machines. and reciprocating surface grinding machines.
The utility grinding machine is intended for offhand grinding where the workpiece is supported in the hand and brought to bear against the rotating grinding abrasive wheel. The accuracy of this type of grinding machine depends on the operatorís dexterity. skill, and knowledge of the machineís capabilities and the nature of the work. The utility grinding machine consists of a horizontally mounted motor with a grinding abrasive wheel attached to each end of the motor shaft.
The electric-motor-driven machine is simple and common. It may be bench-mounted or floor-mounted. Generally, the condition and design of the shaft bearings as well as the motor rating determine the wheel size capacity of the machine. Suitable wheel guards and tool rests are provided for safety and ease of operation. Grinding machines come in various sizes and shapes as listed below.
The typical floor-mounted utility grinding machine stands waist-high and is secured to the floor by bolts. The floor-mounted utility grinding machine shown in Figure 5-1 mounts two 12-inch-diameter by 2-inch-wide grinding abrasive wheels. The two wheel arrangement permits installing a coarse grain wheel for roughing purposes on one end of the shaft and a fine grain wheel for finishing purposes on the other end this saves the time that would be otherwise consumed in changing wheels.
Figure 5-1. Floor mounted utility grinding machine.
Each grinding abrasive wheel is covered by a wheel guard to increase the safety of the machine. Transparent eyeshields. spark arresters. and adjustable tool rests are provided for each grinding wheel. A tool tray and a water pan are mounted on the side of the base or pedestal. The water pan is used for quenching carbon steel cutting took as they are being ground. Using the 12-inch wheel, the machine provides a maximum cutting speed of approximately 5.500 SFPM. The 2-HP electric motor driving this machine has a maximum speed of 1.750 RPM.
Like the floor mounted utility grinding machine, one coarse grinding wheel and one fine grinding wheel are usually mounted on the machine for convenience of operation (Figure 5-2). Each wheel is provided with an adjustable table tool rest and an eye shield for protection. On this machine, the motor is equipped with a thermal over-load switch to stop the motor if excessive wheel pressure is applied thus preventing the burning out of the motor. The motor revolve at 3.450 RPM maximum to provide a maximum cutting speed for the 7 inch grinding wheels of about 6,300 surface feet per minute (SFPM).
Figure 5-2. Bench-type utility grinding machine.
The bench-type drill grinding machine is intended for drill sharpening . The accuracy of this type of grinder is not dependent on the dexterity and skill of the operator because the drill is placed in a holding device. The holding device places the drill in the correct position for the clearance and included angle.
The bench-type utility grinding and buffing machine is more suitable for miscellaneous grinding, cleaning, and buffing (Figure 5-3). It is not recommended for tool grinding since it contains no tool rests, eyeshields, or wheel guards. This machine normally mounts a 4 inch-diameter wire wheel on one end. The wire wheel is used for cleaning and the abrasive wheel is used for general grinding. One of the two wheels can be removed and a buffing wheel mounted in its place for buffing and polishing. The 1/4-HP electric motor revolves at a maximum of 3,450 RPM. The maximum cutting speed of the 4-inch-diameter wheel is approximately 3,600 SFPM.
Figure 5-3. Bench-type utility grinding and buffing machine.
The bench-type tool and cutter grinder, see Figure 5-4, was designed primarily to grind end mills. It can also grind a large variety of small wood and steel cutters as well as slitting saw cutters up to 12 inches in diameter using the saw grinding attachment.
Figure 5-4. Bench-type tool and cutter grinder.
Capacity of the typical bench-type tool and cutter grinder is as follows:
Non-specialized cylindrical grinding machines include the tool post grinding machine and the Versa-Mil attachment.
The tool post grinding machine, see Figure 5-5, is a machine tool attachment designed to mount to the tool post of engine lathes. As described in a later lesson, it is used for internal and external grinding of cylindrical workplaces.
Figure 5-5. Tool post grinding machine.
Also called a Versa-Mil this attachment is a versatile machine tool attachment that mounts to the carriage of a lathe. As described in a later lesson, it performs internal and external cylindrical grinding among its other functions.
The surface grinding machine is used for grinding flat surfaces. The workpiece is supported on a rectangular table which moves back and forth and reciprocates beneath the grinding wheel. Reciprocating surface grinding machines generally have horizontal wheel spindles and mount straight or cylinder-type grinding abrasive wheels.
he reciprocating surface grinding machine is a horizontal-type surface grinding machine (Figure 5-6). Workpieces are fastened to the table and can be moved beneath the grinding abrasive wheel by hand or power feed. A magnetic chuck maybe used for fastening the workpiece to the table. This grinding machine has an internal pump and piping network for automatic application and recirculation of a coolant to the workpiece and wheel. The grinding abrasive wheel, mounted o the horizontal spindle is straight and cuts on its circumferential surface only. Grinding wheel speeds are adjustable.
Figure 5-6. Reciprocating surface grinding machine.