the metal being cut; the quality, shape, and sharpness ofthe cutting tool; the depth of the cut; the tendency of thework to spring away from the tool; and the strength andpower of the lathe. Since conditions vary, it is goodpractice to find out what the tool and work will standand then select the most practical and efficient speed andfeed for the finish desired.When ROUGHING parts down to size, use thegreatest depth of cut and feed per revolution that thework, the machine, and the tool will stand at the highestpractical speed. On many pieces where tool failure is thelimiting factor in the size of the roughing cut, you maybe able to reduce the speed slightly and increase the feedto 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 feedto about 0.040 inch per revolution without having tooltrouble. The speed is therefore reduced 25 percent, butthe feed is increased 100 percent. Thus the actual timerequired to complete the work is less with the secondsetup.For the FINISH TURNING OPERATION, take avery light cut, since you removed most of the stockduring the roughing cut. Use a fine feed to run at a highsurface speed. Try a 50 percent increase in speed overthe roughing speed. In some cases, the finishing speedmay be twice the roughing speed. In any event, run thework as fast as the tool will withstand to obtain themaximum speed during this operation. Be sure to use asharp tool when you are finish turning.COOLANTSA cutting lubricant serves two main purposes: (1) Itcools the tool by absorbing a portion of the heat andreducing the friction between the tool and the metalbeing cut. (2) It also keeps the cutting edge of the toolflushed clean.The best lubricants to use for cutting metal mustoften be determined by experiment. Water-soluble oilis acceptable for most common metals. Specialcutting compounds containing such ingredients astallow, graphite, and lard, marketed under variousnames, are also used. But these are expensive and usedmainly in manufacturing where high cutting speedsare the rule.Some common materials and their cuttinglubricants are as follows:MetalCast ironLubricantUsually worked dryMild steelOil or soluble oilHard steelMineral lard oilMonel metalBronzeDry (or soluble oil)Dry (or soluble oil)BrassDry (or soluble oil)CopperDry (or soluble oil)BabbittDry (or soluble oil)AluminumDry (or soluble oil)A lubricant is more important for threading than forstraight turning. Mineral lard oil is recommended forthreading the majority of metals that are used by theNavy.CHATTERChatter is vibration in either the tool or the workThe finished work surface appears to have a grooved orlined finish instead of a smooth surface. The vibrationis set up by a weakness in the work, work support, tool,or tool support and is probably the most elusive thingyou will find in the entire field of machine work As ageneral rule, strengthening the various parts of the toolsupport train will help. It is also advisable to support thework by a center rest or follower rest.The fault may be in the machine adjustments. Gibsmay be too loose; hearings may, after a long period ofheavy service, be worn; the tool may be sharpenedimproperly, and so on. If the machine is in excellentcondition, the fault may be in the tool or tool setup.Grind the tool with a point or as near a point as the finishspecified will permit; avoid a wide, round leading edgeon the tool. Reduce the overhang of the tool as much aspossible. Be sure all the gib and bearing adjustments areproperly made. See that the work receives propersupport for the cut and, above all, do not try to turn at asurface speed that is too high. Excessive speed isprobably the greatest cause of chatter. The first thing youshould do when chatter occurs is reduce the speed.Direction of FeedRegardless of how the work is held in the lathe, thetool should feed toward the headstock. This causes most9-11
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business