Figure 9-18.—Checking a center’s point with a center gauge.of the pressure of the cut to bear on the work-holdingdevice and the spindle thrust bearings. When you mustfeed the cutting tool toward the tailstock, take lightercuts at reduced feeds. In facing, the general practice isto feed the tool from the center of the workpieceoutward.PRELIMINARY PROCEDURESBefore starting a lathe machining operation, alwaysensure that the machine is set up properly. If the work ismounted between centers, check the alignment of thedead center and the live center and make any necessarychanges. Ensure that the toolholder and cutting tool areset at the proper height and angle. Check thework-holding accessory to ensure that the workpiece isheld securely. Use the center rest or follower rest tosupport long workpieces.PREPARING THE CENTERSThe first step in preparing the centers is to see thatthey are accurately mounted in the headstock andtailstock spindles. The centers and the tapered holes inwhich they are fitted must be perfectly clean. Chips anddirt left on the contact surfaces prevent the bearingsurfaces from fitting perfectly. This will decrease theaccuracy of your work. Make sure that there are no burrsin the spindle hole. If you find burrs, remove them bycarefully scraping and reaming the hole with a Morsetaper reamer. Burrs will produce the same inaccuraciesas chips or dirt.A center’s point must be finished accurately to anangle of 60°. Figure 9-18 shows the method of checkingthis angle with a center gauge. The large notch of thecenter gauge is intended for this purpose. If this testshows that the point is not perfect, you must true it inthe lathe by taking a cut over the point with thecompound rest set at 30°. You must anneal the hardenedtail center before it can be machined in this manner, oryou can grind it if a grinding attachment is available.Figure 9-19.—Aligning lathe centers.Figure 9-20.—Tool overhang.CHECKING ALIGNMENTTo turn a shaft straight and true between centers, besure the centers are aligned in a plane parallel to the waysof the lathe. You can check the approximate alignmentof the centers by moving the tailstockup until the centersalmost touch and observing their relative positions asshown in figure 9-19.To test center alignment for very accurate work, takea light cut over at each end with a micrometer and, ifreadings are found to differ, adjust the tailstockaccordingly. Repeat the procedure until alignment isobtained.SETTING THE TOOLHOLDER AND THECUTTING TOOLThe first requirement for setting the tool is to haveit rigidly mounted on the tool post holder. Be sure thetool sets squarely in the tool post and that the setscrewis tight. Reduce overhang as much as possible to preventthe tool bit from springing during cutting. If the tool hastoo much spring, the point of the tool will catch in thework, causing chatter and damaging both the tool andthe work The distances represented by A and B in figure9-12
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business