Facing Center Drilling MACH 118 Lathe Mill I

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 The compound set at 30 degrees. Fig. I-166 Close-up of the compound set at 30 degrees.

FACING AND CENTER DRILLING Facing � Both right-hand 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.

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