Figure 9-26.—Facing a cylindrical piece.Figure 9-27.—Facing a shoulder.MACHINING OPERATIONSUp to this point, you have studied the preliminarysteps leading to the performance of machine work in thelathe. You have learned how to mount the work and thetool and which tools are used for various purposes. Now,you need to consider how to use the proper tools incombination with the lathe to perform variousmachining operations.FACINGFacing is the machining of the end surfaces andshoulders of a workpiece. In addition to squaring theends of the work, facing provides a way to cut work tolength accurately. Generally, only light cuts are requiredsince the work will have been cut to approximate lengthor rough machined to the shoulder.Figure 9-26 shows the facing of a cylindrical piece.The work is placed between centers and driven by a dog.A right-hand side tool is used as shown. Take a light cuton the end of the work, feeding the tool (by handcrossfeed) from the center toward the outside. Take oneor two light cuts to remove enough stock to true thework Then reverse the workpiece, install the dog on thejust finished end, and face the other end to make thework the proper length. To provide an accurate basefrom which to measure, hold another rule orstraightedge on the end you faced first. Be sure there isno burr on the edge to keep the straightedge frombearing accurately on the finished end. Use a sharpscribe to mark off the dimension desired.Figure 9-27 shows the use of a turning tool infinishing a shouldered job having a fillet corner. Take afinish cut on the small diameter. Machine the fillet witha light cut. Then use the tool to face the work from thefillet to the outside of the work.In facing large surfaces, lock the carriage in position,since only crossfeed is required to traverse the tool acrossthe work. With the compound rest set at 90° (parallel to theaxis of the lathe), you can use the micrometer collar to feedthe tool to the proper depth of cut.TURNINGTurning is the machining of excess stock from theperiphery of the workpiece to reduce the diameter. Inmost lathe machining operations requiring removal oflarge amounts of stock, a series of roughing cuts is takento remove most of the excess stock Then a finishing cutis taken to accurately “size” the workpiece.Rough TurningWhen a great deal of stock is to be removed, youshould take heavy cuts to complete the job in the leastpossible time. This is called rough turning.Select the proper tool for taking a heavy chip. Thespeed of the work and the amount of feed of the toolshould be as great as the tool will stand.When you take a roughing cut on steel, cast iron, orany other metal that has a scale on its surface, be sure toset the tool deep enough to get under the scale in the firstcut. Unless you do, the scale on the metal will dull orbreak the point of the tool.Rough machine the work to almost the finished size;then take careful measurements.Bear in mind that the diameter of the work beingturned is reduced by an amount equal to twice the depthof the cuts; thus, if you desire to reduce the diameter ofa piece by 1/4 inch, you must remove 1/8 inch of metalfrom the surface.Figure 9-28 shows the position of the tool for takinga heavy cut on large work. Set the tool so that if anythingFigure 9-28.—Position of the tool for a heavy cut.9-17
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