420.6 A power-driven buffing machine (grinding wheel) is appropriate for buffing irregularities from the samples from which die-cut specimens are to be prepared. The abrasive wheel is to be of about No. 36 grit (particle size of 0.019 inch or 0.486 mm). The wheel is to run true and is not to vibrate. The diameter of the wheel is not specified; however, 4-3/4 – 6-1/4 inch or 0.12 – 0.16 m has been found appropriate. The rotary velocity of the wheel is to be 2500 – 3500 r/min. The diameter and rotary velocity of the wheel are to be selected to give the wheel a peripheral speed (rpm×p×wheel diameter) of 3000 – 5000 ft/min or 15 – 25 m/s. CAUTION – The maximum wheel diameter stated in this paragraph and the maximum wheel rpm stated in this paragraph shall not be used together as this combination will result in a peripheral speed above 5000 ft/min or 25 m/s. This applies even for wheels that are marked as being intended for a peripheral speed above 5000 ft/min or 25 m/s. The machine is to have a slow feed that applies light pressure and removes very little material atShielding="http://www.chemm.cn/Images/TempImage/1015310741.JPG">
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