Cylindrical grinding and surface grinding typically utilize a single rotating “grinding” wheel; therefore, these two methods tend to be less critical than centerless grinding. Unacceptable finishes are more a symptom of the machine condition or set-up. As long as the plastic is properly held or fixtured in place, the grinder will make sure the rotating wheel does its job.
With a centerless grinder, set up is extremely important. This type of grinder uses two rotating wheels…a grinding wheel and a “regulating” wheel. The regulating wheel is non-abrasive and is strictly used to feed the rod or tube and apply force pushing it against the grinding wheel as it passes through. Proper set-up of the centerless grinder helps to ensure proper tolerance control and consistent circularity of the finished rod or tube. In this dual wheel grinder, the wheels are located in parallel, side-by-side. The spacing between these two wheels is adjustable and determines how much material is removed per pass. The position of the rod or tube being ground, as it passes between the wheels, is critical. This position is determined by the height of the “work-rest-blade”. This blade sits under and between the wheels and should be set such that the position of the material passing between the rotating wheels falls directly on-center with the wheels to no more than one sixteenth inch above center. When centerless grinding, as the rod or tube is ground and the outside diameter (OD) is reduced, you may need to continue adjusting the work-rest-blade to keep the center of the material positive versus the rotating wheels.
For most grinders the size and speeds of the rotating wheels are not adjustable and run at a consistent RPM. The type and style of the machine determines the size and configuration of the grinding wheel. In a centerless grinder, the regulating wheel is adjustable. The angle position and speed of the regulating wheel determines the feed-rate of the rod. A typical set-up angle for the regulating wheel is three degrees.
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