A heavy hollow steel pedestal usually forms the bottom portion of the grinder. Pedestals may be bolted firmly to the floor of the shop. Without adequate support, vibration during operation could cause the machine to shift. Small versions called bench grinders bolt directly to a work bench or shelf. Heavy industrial grinders may enclose the motor within the pedestal and drive the wheel arbor with a belt and pulley system.
The armature of the heavy duty electrical motor mounted on the pedestal top usually serves as both left and right arbor of the grinder. The arbor ends are threaded in opposite directions--a clockwise turn tightens the right arbor fittings while a counter clockwise turn tightens the arbor on the left. With this type of thread, the fittings of both wheels tighten during use. If both arbor ends were threaded the same, forward rotation would loosen one wheel.
Left and right grindstones of different abrasive grits provide the actual working surfaces. Most pedestal grinders rotate at high speed--3600 rpm is common. If stones shatter, the pieces become dangerous high speed projectiles. Large washers and backing plates place uniform pressure on the stone's sides, while a large nut holds the stone on the arbor. Metal safety shields cover the back and top of the stones and movable transparent shields deflect sparks and grit away from the operator. Most injuries happen during startup--operators are advised to stand away from the wheels while the grinder builds up to working speed.
The adjustable rest at the front of the wheel supports the metal piece being ground. Forward rotation of the wheels directs force downward through the tool rest. Fine control of the work results from shifting the free end of the workpiece--a large motion of the free end causes a small change at the grinder's surface. Changing the height of the rest also changes the angle at which the tool or metal stock contacts the stone. Pedestal grinders work well with steel and other hard metals, but stones load quickly with softer metals like aluminum and brass. As stones wear, the surfaces degrades and the stones become unbalanced. Wheel dressing tools restore the stones but also reduce the diameter of the wheel.
Buffing wheels of heavy cloth saturated with very fine abrasives in a wax base may substitute for stone wheels when polishing metal. Stones quickly and accurately shape metal but leave scoring on the metal which matches the grade of the wheel. Working from coarse to fine grits refines the metal surface, but polishing wheels create a flawless finish without visible wheel marks.