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Care of Chucks
Machining Operations

Engineman 2 - Intermediate engine mechanics training manual
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Figure 9-24.—Work clamped to an angle plate. angle, as shown in figure 9-24. Note the counterweight added for balance. For work to be mounted accurately on a faceplate, the surface of the work in contact with the faceplate must be accurately faced. It is good practice to place a piece of paper between the work and the faceplate to prevent slipping. Before you clamp the work securely, move it about on  the  surface  of  the  faceplate  until  the  point  to  be machined  is  centered  accurately  with  the  axis  of  the lathe.  Suppose  you  wish  to  bore  a  hole,  the  center  of which has been laid out and marked with a prick punch. First, clamp the work to the approximate position on the faceplate. Slide the tailstock up until the dead center just touches the work. (NOTE: The dead center should have a  sharp,  true  point.)  Now  revolve  the  work  slowly;  if the work is off center, the point will scribe a circle on the work. If the work is on center, the point of the dead center will coincide with the prick punch mark. Using the Center Rest and Follower Rest Place the center rest on the ways where it will give the greatest support to the workpiece. This is usually at about the middle of its length. Figure 9-25.—Work mounted in a chuck and center rest. Ensure that the jaws of the center rest are adjusted to  support  the  work  while  allowing  it  to  turn  freely. Figure 9-25 shows how a chuck and center rest are used for machining the end of a workpiece. The follower rest differs from the center rest in that it  moves  with  the  carriage  and  provides  support  against the forces of the cut only. Set the tool to the diameter selected, and turn a “spot” about 5/8 to 3/4 inch wide. Then  adjust  the  follower  rest  jaws  to  the  finished diameter to follow the tool along the entire length to be turned. Use a thick oil on the center rest and follower rest to  prevent  “seizing”  and  scoring  of  the  workpiece. Check the jaws frequently to see that they do not become hot.  The  jaws  may  expand  slightly  if  they  get  hot, pushing  the  work  out  of  alignment  (when  using  the follower rest) or binding (when using the center rest). Holding Work in a Draw-In Collet Chuck The  draw-in  collet  chuck  is  used  for  very  fine, accurate  work  of  small  diameter.  Long  work  can  be passed through the hollow drawbar. Short work can be placed directly into the collet from the front. The collet is tightened on the work by rotating the drawbar to the right;  this  draws  the  collet  into  the  tapered  closing sleeve. The opposite operation releases the collet. Accurate results are obtained when the diameter of the  work  is  exactly  the  same  size  as  the  dimension stamped on the collet. In some cases, the diameter may vary as much as 0.002 inch; that is, the work may be 0.001 inch smaller or larger than the collet size. If the work diameter varies more than this, it will impair the accuracy  and  efficiency  of  the  collet.  That  is  why  a separate collet should be used for each small variation or work diameter, especially if precision is desired. 9-16







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