TM 9-243 USING ELECTRIC BENCH GRINDERS The  electric  powered  bench  mounted  grinder  is  used  to sharpen   tools,   dress   screwdrivers,   and   to   shape   and smooth   metal   stock.      Avoid   grinding   of   non-ferrous metals   (brass,   copper,   aluminum,   etc.)   on   the   grinder supplied:  special  grinding  wheels  are  required  for  this purpose. BENCH GRINDER The bench grinder available at the sites is equipped with two  different  types  of  grinding  wheels.    One  wheel  is coarse and is used for rough grinding.  The other is fine and   is   used   for   tool   sharpening   and   finish   grinding. These   grinders   are   also   equipped   with   safety   shields and  tool  rests.    The  tool  rest  should  be  adjusted  so  that the  space  between  the  grinding  wheel  and  the  tool  rest is approximately 1116 inch, but never over 1/8 inch. MOUNTING GRINDING WHEELS ON SPINDLES Use the following procedure when grinding wheels are to be mounted on the spindle. 1. Inspect  the  wheel  for flaws   and   make   the "ring test." 2. Clean the bearing surfaces of the wheel,     flanges     and spindle  so  that  the  clamping  pressure  will  be  evenly distributed. 3. Check  the  speed  of  the  spindle  to  make  sure  that  it is not running too fast for the type and size of wheel. 4. Make sure the hole in the wheel bushing is the right size for the spindle.  (neither too small nor too large.) 5. Use flanges that are recessed and large enough to clamp the wheel well toward its circumferences. 6. Tighten the spindle end nuts just enough to keep the wheel   from   moving   out   of   position   between   the flanges. WARNING 7. Before  turning  on  power,  make  sure  that  the  wheel runs true and will strike no obstructions GRINDING WHEEL "RING" TEST New grinding wheels should be promptly unpacked upon receipt and given the "ring" test for damage suffered. Also, give this test immediately before mounting either a new or used wheel on the spindle, especially if the wheel has been in storage for a long time. The"   ring   "   test   readily   discloses   defects   in   grinding wheels,  including  flaws  and  cracks,  even  though  most defects are invisible to the naked eye. Make  the  test  by  suspending  the  wheel  free  and  clear and  tapping  it  gently  with  a  light  wooden  implement.    A wooden  screwdriver  handle  would  be  appropriate  for  a light wheel.  A wooden mallet would be good for a heavy wheel. Sound  and  undamaged  wheels  will  emit  a  clear  metallic tone when tapped.  If the wheel is defective there will be no ring. Wheels  bonded  with  organic  material  do  not  emit  the same   clear   metallic   sound   as   do   verified   and   silicate wheels. Any  wheel  should  be  dry  and  free  of  sawdust  when  the "ring"    test    is    given;    otherwise    the    sound    will    be deadened. GRINDING SUGGESTIONS Listed  below  are  several  suggestions  that,  if  followed, will   eliminate   machine   abuse   and   provide   maximum protection for the operator: Wear  safety  glasses  at  all  times  when  working near the grinder, including the period of adjusting  guards  and  tool  rest.    Do  not  remove the  glasses  until  the  job  is  completed  and  the machine shut off. 52-14  Change 3