Facing center drilling

Facing & Center Drilling MACH 118: Lathe & Mill I Thaddeus Stevens College of Technology Machine Tool Technology FACING AND CENTER DRILLING Introduction  Facing and center drilling the workpiece are often the first steps taken in a turning project to produce a stepped shaft or a sleeve from solid material ◦ Much lathe work is done in a chuck, requiring considerable facing and some center drilling OBJECTIVES After completing this unit, you should be able to…  Correctly set up a workpiece and face the ends  Correctly center drill the ends of a workpiece  Determine the proper feeds and speeds for a workpiece  Explain how to set up to make facing cuts to a given depth and how to measure them FACING AND CENTER DRILLING Setting Up For Facing  Facing is done to obtain a flat surface on the end of cylindrical workpieces or on the face of parts clamped in a chuck or face plate ◦ Work is most often held in a three- or four-jaw chuck FACING AND CENTER DRILLING Setting Up For Facing  Round stock can be set up using a dial indicator Fig I-152 Setting up round stock in an independent chuck with a dial indicator FACING AND CENTER DRILLING Setting Up For Facing  Square or rectangular stock can be set up either with a dial indicator or by using a tool-holder turned backward Fig I-153 Rectangular stock being set up by using a toolholder turned backward The micrometer dial is used to center the workpiece FACING AND CENTER DRILLING Setting Up For Facing Workpieces can be chucked: Normally Internally Externally Fig I-156 Internal chucking position Fig I-155 Normal chucking position Fig I-157 External chucking position FACING AND CENTER DRILLING Facing  Facing from the center out produces a better finish, but it is difficult to cut on a solid face in the center Fig I-158 Facing from the center to the outside of the workpiece FACING AND CENTER DRILLING Facing  Heavier cuts may be taken when facing from the outside, and it is easier to work to the scribed lines on the circumference of the work Fig I-159 Facing from the outside toward the center of the workpiece FACING AND CENTER DRILLING Facing  Machining should not be done on workpieces extending more than three x dia from the chuck face FACING AND CENTER DRILLING Facing  The tool point should be set to dead center Fig I-160 Setting the tool to the center of the workpiece using the tailstock center FACING AND CENTER DRILLING Facing  The tool point should be set to dead center FACING AND CENTER DRILLING Facing  The carriage may be locked when taking facing cuts Fig I-161 Carriage must be locked before taking a facing cut FACING AND CENTER DRILLING Facing  Facing to length may be accomplished by trying a cut and measuring with a hook rule or by facing to a previously made layout line ◦ A more precise method is to use graduations on the micrometer collar of the compound Fig I-162 Facing to length using a hook rule for measuring FACING AND CENTER DRILLING Facing  The compound slide is set parallel to the ways ◦ The carriage is locked in place & a trial cut taken with the micrometer collar set on zero index Fig I-163 The compound set at 90 degrees for facing operations Fig I-164 Close-up of the compound set at 90 degrees FACING AND CENTER DRILLING Facing  The workpiece is measured with a micrometer & the desired length is subtracted from the measurement ◦ The remainder should be removed by facing  A short trial cut (about 1/8”) should again be taken on the finish cut and adjustment made if necessary ◦ Cuts can vary considerably, depending on machine size, horsepower, tooling, and setup FACING AND CENTER DRILLING Facing  Quite often the compound is kept at 30 degrees for threading purposes ◦ At this angle the tool feeds into the face of the work 001 in for every 002 in that the slide is moved Fig I-165 Fig I-166 The compound set at 30 degrees Close-up of the compound set at 30 degrees FACING AND CENTER DRILLING Facing  Both right-hand and left-hand facing tools are used for facing work held on mandrels ◦ Care should be taken when machining pressure is toward the small end of a tapered mandrel ◦ Excessive pressure may loosen the workpiece on the mandrel Fig I-171 Work held between centers on a mandrel can be faced on both sides with right- & left-hand facing tools FACING AND CENTER DRILLING Speeds  Speeds (rpm) for lathe turning are determined in essentially the same as speeds for drilling tools ◦ Work diameter is used instead of drill diameter  In facing operations, outside diameter of the work-piece has greater surface speed than its center ◦ The rpm should vary as the tool is moved in or out ◦ Two or three speed changes may be required to get a uniform surface finish, depending on the size of the work FACING AND CENTER DRILLING Center Drills And Drilling  When work is held and turned between centers, a center hole is required on each end of the work ◦ It must have a 60-degree angle to conform to the center and have a smaller drilled hole to clear the center’s point  Facing the workpiece is almost always necessary before center drilling ◦ An uneven surface can push sideways on the fragile center drill point and break it FACING AND CENTER DRILLING Center Drills And Drilling  Center drills are usually held in a drill chuck in the tailstock ◦ Workpieces are most often supported & turned in a lathe chuck for center drilling Fig I-172 Center drilling a workpiece held in a chuck FACING AND CENTER DRILLING Center Drills And Drilling  Long workpieces are generally faced by chucking one end and supporting the other in a steady rest ◦ The greater the work diameter & the heavier the cut, the larger the center hole should be Fig I-173 Center drilling long material supported in a steady rest FACING AND CENTER DRILLING Center Drills And Drilling  Drilling too deeply causes the center to contact only the sharp outer edge of the hole, a poor bearing surface ◦ It soon becomes loose & out of round, causing chatter and roughness ◦ Center drills often are broken from feeding the drill too fast with the lathe speed too slow or with the tailstock off center Fig I-174 Correct and incorrect depth for center drilling Questions? ... dead center Fig I-160 Setting the tool to the center of the workpiece using the tailstock center FACING AND CENTER DRILLING Facing  The tool point should be set to dead center FACING AND CENTER. .. larger the center hole should be Fig I-173 Center drilling long material supported in a steady rest FACING AND CENTER DRILLING Center Drills And Drilling  Drilling too deeply causes the center. .. position FACING AND CENTER DRILLING Facing  Facing from the center out produces a better finish, but it is difficult to cut on a solid face in the center Fig I-158 Facing from the center to