Tech Talk
When "Internal Grinding", what diameter wheel should be used relative to the bore size?
The internal grinding machine has the difficult task of the grinding wheel having to go inside the bore of the workpiece. The grinding wheel is generally very small. The grinding wheels should be chosen carefully. The wheel diameter should be 2/3 to 3/4 the diameter of the bore being ground. This will allow sufficient room in the bore for the cutting fluid to penetrate and for chip clearance. The wheel width should be no greater than the diameter of the bore being ground. Larger diameter and wider wheels will block the way for the cutting fluid and load with grinding detritus. Also, because of the large area of contact, the forces on the spindle quill will be large and may cause bellmouthing of the bore.
It is important to select the correct grade of grinding wheel, nominally 80 grain and finer, as well as the correct peripheral speed of the wheel and workpiece. ID grinding spindles are high rpm spindles, and may be as high as 200,000 rpm in order to reach the desired cutting speed for the abrasive being used. The grinding wheel must be oscillated axially through the bore of the workpiece to ensure cylindricity. The workpiece should rotate in the opposite direction to the grinding wheel.
