Buying a Grinding Machine
You need a grinding machine with the right capabilities for your application. Major categories of grinders include surface grinders, cylindrical grinders (OD grinders), centerless grinders, internal grinders (ID grinders) and specialty grinders such as jig grinders.
Surface Grinders: This kind of grinder has an abrasive wheel, a chuck for holding the workpiece and a reciprocating or rotary table. The chuck can hold the material in many ways, from the magnetic force, to vacuum holding and of course, mechanical means. The grinding wheel can be a myriad of shapes depending on the desired geometry of the workpiece. Surface grinders are machine tools that can produce very precise surface finishes. +/-.0001” is achievable on most surface grinders.
Horizontal-Spindle Surface Grinders (Peripheral Surface Grinders): The flat edge or periphery of the wheel contacts the workpiece.
Vertical-Spindle Grinders (Wheel Face Grinders): The face of the grinding wheel is used on the flat surface of the workpiece. The workpiece usually held on a table (reciprocating or rotary).
Cylindrical Grinders: This type of grinding machine is used for shaping the outside of a workpiece. Both the workpiece and the grinding wheel are simultaneously rotated. The grinding wheel is fed towards and away from the work and either the workpiece or grinding wheel is traversed. There are different types of cylindrical grinders including OD grinders, ID grinders, plunge grinders, and centerless grinders.
Outside Diameter (OD) Grinders: The workpiece is mounted between centers (endpoints that hold the piece). The grinding wheel rotates and touches the outside diameter of the workpiece.
Inside Diameter (ID) Grinders: The grinding wheel is smaller the width of the workpiece. The workpiece is held in place by a collet which rotates it. The grinding wheel rotates and creates or touches the inside diameter of the workpiece.
Plunge Grinders: Similar to OD grinders, but the grinding wheel makes continuous contact with a single point on the workpiece instead of traversing it.
Centerless Grinders: This type of grinder used two wheels to hold the workpiece in place. The wheels with the abrasive surface rotate and rotate the piece. The speed of the rotation determines the rate of material removal. Very tight tolerances are possible without a need to hold the workpiece between centers. Thru-feed centerless grinding allows the entire workpiece to move between the wheels and out the other side, in-feed centerless grinding is when a workpiece is partially inserted between the wheels for grinding on a specified length of the part.
Specialty grinders like jig grinders are built to incorporate multiple grinding styles, optimized for specific types of parts. Some used grinders are better at ID and plunge grinding, others do both ID and OD grinding, some have only one spindle and four spindles. Every used grinding machine for sale should list the maximum workpiece weight, distance between centers and maximum grinding wheel diameter. The grinding machine price should reflect the number of spindles, machine size, age and options for that machine.