Figure 9-29.—Machining to a shoulder. occurs  during  machining  to  change  the  position  of  the tool,  it  will  not  dig  into  the  work,  but  rather  will  move in  the  direction  of  the  arrow-away  from  the  work Finish Turning When  you  have  rough  turned  the  work  to  within about 1/32 inch of the finished size, take a finishing cut. A   fine   feed,   the   proper   lubricant,   and,   above   all,   a keen-edged   tool   are   necessary   to   produce   a   smooth finish.  Measure  carefully  to  be  sure  you  are  machining the  work  to  the  proper  dimension.  Stop  the  lathe  when you  take  measurements. If  you  must  finish  the  work  to  close  tolerances,  be sure the work is not hot when you take the finish cut. If you  turn  the  workpiece  to  exact  size  when  it  is  hot,  it will be undersize when it has cooled. Perhaps  the  most  difficult  operation  for  a  beginner in machine work is to make accurate measurements. So much  depends  on  the  accuracy  of  the  work  that  you should make every effort to become proficient in the use of  measuring  instruments.  You  will  develop  a  certain “feel”   in   the   application   of   micrometers   through experience  alone;  do  not  be  discouraged  if  your  first efforts  do  not  produce  perfect  results.  Practice  taking micrometer   measurements   on   pieces   of   known dimensions. You will acquire skill if you are persistent. Turning to a Shoulder Machining  to  a  shoulder  is  often  done  by  locating the  shoulder  with  a  parting  tool.  Insert  the  parting  tool about 1/32 inch from the shoulder line toward the small diameter end of the work Cut to a depth 1/32 inch larger than the small diameter of the work. Then machine the stock  by  taking  heavy  chips  up  to  the  shoulder.  This procedure  eliminates  detailed  measuring  and  speeds  up production. Figure  9-29  illustrates  this  method  of  shouldering. A parting tool has been used at P and the turning tool is taking  a  chip.  It  will  be  unnecessary  to  waste  any  time in  taking  measurements.  You  can  devote  your  time  to rough  machining  until  the  necessary  stock  is  removed. Then   you   can   take   a   finishing   cut   to   accurate measurement. Boring Boring  is  the  machining  of  holes  or  any  interior cylindrical  surface.  The  piece  to  be  bored  must  have  a drilled or cored hole, and the hole must be large enough to  insert  the  tool.  The  boring  process  merely  enlarges  the hole   to   the   desired   size   or   shape.   The   advantage   of boring is that a true round hole is obtained, and two or more  holes  of  the  same  or  different  diameters  may  be bored  at  one  setting,  thus  ensuring  absolute  alignment of the axis of the holes. Work to be bored may be held in a chuck, bolted to the faceplate, or bolted to the carriage. Long pieces must be supported at the free end in a center rest. When  the  boring  tool  is  fed  into  the  hole  of  work being  rotated  on  a  chuck  or  faceplate,  the  process  is called   single   point   boring.   It   is   the   same   as   turning except that the cutting chip is taken from the inside. The cutting   edge   of   the   boring   tool   resembles   that   of   a turning tool. Boring tools may be the solid forged type or the inserted cutter bit type. When the work to be bored is clamped to the top of the  carriage,  a  boring  bar  is  held  between  centers  and driven  by  a  dog.  The  work  is  fed  to  the  tool  by  the automatic longitudinal feed of the carriage. Three types of boring bars are shown in figure 9-30. Note the center holes at the ends to fit the lathe centers. Figure 9-30, view A, shows a boring bar fitted with a   fly   cutter   held   by   a   headless   setscrew.   The   other setscrew, bearing on the end of the cutter, is for adjusting the  cutter  to  the  work Figure 9-30, view B, shows a boring bar fitted with a two-edged cutter held by a taper key. This is more of a finishing or sizing cutter, as it cuts on both sides and is used for production work. The  boring  bar  shown  in  figure  9-30,  view  C,  is fitted with a cast-iron head to adapt it for boring work 9-18