Surface grinding is an abrasive machining process that involves securing an object to a holding device known as a chuck, then slowly moving the surface of the object across a fast-spinning grinding wheel. The chuck is part of a table that moves back and forth on the machine. The table raises the object slightly deeper into the wheel at set intervals, such as 0.001 inches (0.0254 mm) with each pass, for example. The grinding wheel's rotation, combined with the abrasive particles on the wheel, removes small amounts of material from the object with each pass and creates a flat surface. Usually, surface grinding acts as a finishing step, designed to bring aspects of an object within certain tolerances, although the procedure is followed by a polishing step during a grinding-and-lapping process.
The surface grinding process inherently generates a flat plane where the wheel comes into contact with the object. The machined surface isn't just flat; the process also gives the object a relatively even surface roughness or finish. Increasing the length of time that the wheel spends at the final cutting depth and using grinding wheels with higher grit counts will improve the surface finish even further. The slow increase in the depth of cut allows machine operators to achieve tight thickness tolerances.
Surface grinder chucks secure objects in one of three ways: magnetically, using a suctioning vacuum or holding the object with a mechanical restraint. Properly securing the object to the chuck is a critical factor to surface grinding. Misaligned setups result in an incorrect cut at best. At worst, loose objects can break free from the chuck when they come into contact with the rapidly spinning grinding wheel and can shoot out of the machine at high speed.
Grinding wheels feature a doughnut-like design; the hole in the center slides over a metal rod known as a spindle. Surface grinders come in a variety of models from dozens of manufacturers. All surface grinding machinery, however, uses one of two basic structures: a vertical spindle design or a horizontal spindle design.
Vertical spindle designs look exactly how the name implies — the spindle points straight up and down. The grinding wheel lays flat on its face at the bottom of the spindle, allowing the full width of the wheel to be used to grind an object. Typically, vertical spindle designs are used while surface grinding larger panels or sheets of materials or when a large amount of material needs to be ground away quickly.
Horizontal spindle designs suspend the wheels over the table. With a horizontal spindle design, only the flat outer edge of the wheel comes into contact with the object secured by the chuck. The smaller grinding surface allows for cuts with greater precision. As such, horizontal spindle surface grinders tend to be used when smaller features such as angles or profiles are needed.