the metal being cut; the quality, shape, and sharpness of the cutting tool; the depth of the cut; the tendency of the work to spring away from the tool; and the strength and power  of  the  lathe.  Since  conditions  vary,  it  is  good practice to find out what the tool and work will stand and then select the most practical and efficient speed and feed for the finish desired. When  ROUGHING  parts  down  to  size,  use  the greatest  depth  of  cut  and  feed  per  revolution  that  the work, the machine, and the tool will stand at the highest practical speed. On many pieces where tool failure is the limiting factor in the size of the roughing cut, you may be able to reduce the speed slightly and increase the feed to  remove  more  metal.  This  will  prolong  tool  life. Consider an example where the depth of cut is 1/4 inch, the feed 0.020 inch per revolution, and the speed 80 fpm. If the tool will not permit additional feed at this speed, you can drop the speed to 60 fpm and increase the feed to about 0.040 inch per revolution without having tool trouble. The speed is therefore reduced 25 percent, but the feed is increased 100 percent. Thus the actual time required to complete the work is less with the second setup. For the FINISH TURNING OPERATION, take a very  light  cut,  since  you  removed  most  of  the  stock during the roughing cut. Use a fine feed to run at a high surface speed. Try a 50 percent increase in speed over the roughing speed. In some cases, the finishing speed may be twice the roughing speed. In any event, run the work  as  fast  as  the  tool  will  withstand  to  obtain  the maximum speed during this operation. Be sure to use a sharp tool when you are finish turning. COOLANTS A  cutting  lubricant  serves  two  main  purposes:  (1)  It cools  the  tool  by  absorbing  a  portion  of  the  heat  and reducing  the  friction  between  the  tool  and  the  metal being cut. (2) It also keeps the cutting edge of the tool flushed  clean. The  best  lubricants  to  use  for  cutting  metal  must often be determined by experiment. Water-soluble oil is  acceptable  for  most  common  metals.  Special cutting   compounds   containing   such   ingredients   as tallow,   graphite,   and   lard,   marketed   under   various names, are also used. But these are expensive and used mainly  in  manufacturing  where  high  cutting  speeds are the rule. Some   common   materials   and   their   cutting lubricants are as follows: Metal Cast iron Lubricant Usually worked dry Mild  steel Oil or soluble oil Hard steel Mineral  lard  oil Monel metal Bronze Dry (or soluble oil) Dry  (or  soluble  oil) Brass Dry (or soluble oil) Copper Dry (or soluble oil) Babbitt Dry (or soluble oil) Aluminum Dry (or soluble oil) A lubricant is more important for threading than for straight  turning.  Mineral  lard  oil  is  recommended  for threading  the  majority  of  metals  that  are  used  by  the Navy. CHATTER Chatter is vibration in either the tool or the work The finished work surface appears to have a grooved or lined finish instead of a smooth surface. The vibration is set up by a weakness in the work, work support, tool, or tool support and is probably the most elusive thing you will find in the entire field of machine work As a general rule, strengthening the various parts of the tool support train will help. It is also advisable to support the work by a center rest or follower rest. The fault may be in the machine adjustments. Gibs may be too loose; hearings may, after a long period of heavy  service,  be  worn;  the  tool  may  be  sharpened improperly,  and  so  on.  If  the  machine  is  in  excellent condition,  the  fault  may  be  in  the  tool  or  tool  setup. Grind the tool with a point or as near a point as the finish specified will permit; avoid a wide, round leading edge on the tool. Reduce the overhang of the tool as much as possible. Be sure all the gib and bearing adjustments are properly   made.   See   that   the   work   receives   proper support for the cut and, above all, do not try to turn at a surface  speed  that  is  too  high.  Excessive  speed  is probably the greatest cause of chatter. The first thing you should do when chatter occurs is reduce the speed. Direction of Feed Regardless of how the work is held in the lathe, the tool should feed toward the headstock. This causes most 9-11