NAIT Machinist Program - Lathe Operations PDF

MACHINIST PROGRAM - FIRST PERIOD LATHE OPERATIONS 150102g  OBJECTIVES 1. SET–UP THE CUTTING TOOLS TO PERFORM PARALLEL TURNING AND BORING OPERATIONS 2. OPERATE TO TURN TO A SHOULDER (SHOP TRAINING) 3. DEMONSTRATE CENTER DRILLING, DRILLING AND REAMING OPERATIONS. (SHOP TRAINING)...

MACHINIST PROGRAM - FIRST PERIOD LATHE OPERATIONS 150102g  OBJECTIVES 1. SET–UP THE CUTTING TOOLS TO PERFORM PARALLEL TURNING AND BORING OPERATIONS 2. OPERATE TO TURN TO A SHOULDER (SHOP TRAINING) 3. DEMONSTRATE CENTER DRILLING, DRILLING AND REAMING OPERATIONS. (SHOP TRAINING) 4. DEMONSTRATE SET–UP AND CUTTING A TAPER ON A LATHE (SHOP TRAINING) 5. DEMONSTRATE KNURLING, GROOVING, PARTING OFF, FORMING, AND PROFILING ON THE LATHE (SHOP TRAINING) 6. DEMONSTRATE THE USE OF TAPS, DIES, AND SINGLE POINT THREADING TOOLS 7. DEMONSTRATE SET-UPS FOR DIFFERENT OPERATIONS ON A LATHE (SHOP TRAINING)  OBJECTIVE 1 PARALLEL TURNING AND BORING OPERATIONS Parallel Turning operations  Verifying Parallel Turning Accuracy Verifying that the lathe you are operating turns parallel to the axis (with the tailstock center in place) is very important. Take two trial cuts (or one long cut): -if the diameter is the same on both ends, the tailstock is aligned -if the diameter is smaller at the tailstock, move the tailstock away from you by half the difference -if the diameter is larger at the tailstock, move tailstock towards you by half the difference If diameter is smaller by 0.004” at the tailstock, move tailstock away from you by Figure 3 - Taking a trial cut at each end. 0.002” Parallel Test Bar: -mount between centers -mount dial indicator on cross-slide -check if dial moves as you move carriage along the workpiece. -dial does not change – good -otherwise adjust until bar is parallel to axis. Figure 4 - Using a parallel test bar. Figure 5 - Adjusting the tailstock.  Adjusting the Tailstock The tailstock is adjusted by moving the upper casting away from or towards the operator. If the work is large at the tailstock end it has to move towards the operator. If the work is small at the tailstock end it has to move away from the operator. Example: If the workpiece is 0.004 larger at the tailstock, adjust towards you by ½ that distance, or 0.002  CUTTING ACCURACY Tool Height Adjustments Always lock the carriage when performing heavy facing operations. Tool Height Verification Methods: 1. Turn tool towards the tailstock bearing center and adjusting the height to match the center point. 2. Use a spring steel rule. Bring the tool gently against the rule on the work piece radius and confirm that it is vertical Tool Height Centering Device  Roughing and Finishing When roughing the feed rate should be as high as the machine and the tooling can handle. Feed rate is usually about 0.010” to 0.030” per revolution. Leave about 0.030” for each finishing cut.(2x tool nose radius) Feed rate for finishing depends on the finish required on the part. Figure 10 - Roughing and finishing cuts. ACCURATE DIAMETERS 1. Rough to.100 larger than finished diameter 2. Reduce feed for the required finish 3. Take a.050” cut , do not turn the cross slide dial at the end of the cut, just return to the beginning. 4. Measure the work piece. 5. Take your final cut compensating for the measured diameter and the final diameter. Trial Cut Diameter Verification  Know your Cross Slide If you move a cross-feed dial 0.100” and 0.100” is removed from the diameter of the work you have a direct reading dial. If you move the cross-feed dial 0.100 and 0.200 is removed from the work you have an indirect reading dial. On most lathes each graduation on the cross- feed dial represents 0.001 inches or 0.02 mm. Cross Slide Backlash Backlash on a lathe is created by the clearance between the cross-slide screw and the nut. When setting the depth of cut, if you overshoot your mark, reverse the dial up one full revolution, and reset the graduated dial Verification of a Direct or Indirect Dial Figure 7 - Graduated dial. Using a dial to Verify the Graduated Dial Reading Verses Movement Figure 8 - Use a dial indicator to see if the dial is direct or indirect. Figure 9 - Depth of cut for a direct dial.  INTERNAL CUTTING OPERATIONS Internal Cutting - Boring Boring is the process of machining an internal feature using a single point tool Boring enlarges an existing hole and makes it run true to the axis of the work piece. For best results keep the boring bar as short as possible. For the best result, the Boring Bar should be as large as possible or 2/3 the hole diameter. Figure 11 - Boring, as opposed to turning. Figure 12 - Mounting a boring bar with the least possible overhang. The Boring Operation TURNING TO A SHOULDER Figure 13 - Face and shoulder. Figure 16 - Setting the depth of cut with the compound rest. Using a vernier to establish a shoulder length Figure 18 - Positioning the cutting tool with a vernier caliper. Important to Select the Appropriate tool for Shoulder Turning Figure 19 - Turn down the diameter ahead of the shoulder. Shoulder Turning Measuring Method Figure 21 - Measuring the location of the roughed shoulder. The Importance of Fillets and Work Piece Strength. Figure 22 - Using a filleting tool. Note: Shoulder Machining Techniques Figure 17 - Shoulder types.  CENTER DRILLING, DRILLING, AND REAMING OPERATIONS  Centre Drilling The proper depth of a centre drill is 2/3 of the way up the tapered portion of the centre drill. * Remember to Peck Drill  Center Drill Breakage Speed too slow Feed too high Centers not in line Running in reverse Drilling DRILLING When using HSS drills the chip should be dicoloured. Drilling Operations For all drilling operations, a calculation of the RPM is crucial to the longevity of the machine tools. Break long chips by performing a peck drilling. Pull the drill out of the hole fully after 4 times its diameter. Reaming Machine Reaming Figure 27 - Reaming in a lathe. Reaming Reaming Machining Conditions 1/2 the speed, 2 X the feed Material Allowance Under 1/2 inches leave 1/64th Over 1/2 inches leave 1/32nd.  GROOVING, PARTING, KNURLING, THREADING OPERATIONS Grooving Operations Parting and Grooving Figure 34 - Shapes of grooving tools. Grooving Process Tool set as short as can be but still cut the groove required. Speed = ½ of normal Turning speed. Use Power feed with a goal to get the chip to curl and pop out of the groove when possible. Use plenty of cutting oil or coolant. If chatter is occurring, increase the feed rate. Parting Operations Setting Appropriate Tool Overhang Figure 35 - Setting up a parting tool with as little overhang as possible. Warning!! Never Part a work piece off when it is between centers. Knurling Operations Knurling Knurling process Select the coarseness of the Knurl. Clamp the knurling tool in the tool post securely and at 90 degrees to the surface. Run the lathe at 200 RPM or less. Set the feed Rate to the fastest that the manual lathe will go. Put a significant pressure on the tool against the work piece. Motion the tool back and forth on the work piece , then engage the feed. Reverse the work piece rotation at the end of the knurl and return to the start position. Knurling on the Lathe Displacement Type Knurling Process: 1. Align tool rollers 2. Center the Rollers 3. RPM 100 4. Feed Rate.030 Rev. 5. Press hard onto the Work , and engage feed 6. Use cutting oil Knurling Operations – Cut Type https://youtu.be/Oq1vXbL0zH0 Threading Threading Operations Performing Threading Operations Threading Setup and Pitch Verification The thread center gauge is The screw thread Pitch used to align the threading Gauge is used to verify the tool to the work piece axis. correct pitch is being cut.  Grinding 60˚ HSS Threading Tool Use thread center gauge for checking the angle. Use an aluminum oxide wheel. Grind so tool point is close to the left hand side of the tool bit. Don’t over heat the tool. Use a honing stone to put a small radius on the point. Center height is critical especially when cutting tapered threads such as pipe threads.  Methods of Threading on a lathe Half angle threading The thread is cut using the compound rest set at 29.5 degrees. Depth is calculated using the formula In Feed = 0.750 X Pitch RPM is about 1/4 the normal turning speed when using HSS tooling Figure 38 - Setting the compound rest to 29 1/2 degrees.  Threading on a lathe Plunge cutting Thread is cut using the cross-slide. Thread depth is calculated using the formula Depth = 0.6495 X Pitch Thread depth is used as a reference, thread fit is measured on the pitch diameter.  TAPPING AND DIE CUTTING OPERATIONS Tapping in the Lathe Tapping in the Lathe Using the Spindle face to guide a Die so it remains parallel to the axis of the machine Figure 45 - Using the front of the tailstock spindle to guide the die stock. Using a modified Die Head to thread an external Thread Figure 46 - Using an adapter. STEADY REST AND FOLLOWER REST SET UP Steady Rest - Micro Motion Micro Motion is caused by incorrect setting of the steady Rest. The work piece will walk away from the Lathe jaws causing a dangerous situation. Steady Rest Setting tool This simple device allows the operator to dial in the jaws of a steady rest to very close tolerances – preventing Micro Motion Follower Rest Considerations Too much pressure on the work piece may cause it to walk out of the jaws. Too little pressure will not sufficiently support the work piece under tool pressure causing vibration and inconsistent diameters. Figure 50 - Follower rest. Follower Rests The follower rest bolts on and travels with the saddle. Set up Contact - must only lightly touch the surface. CUTTING TAPERED PARTS  Cutting Tapers With The Compound Rest Set up Compounds are swiveled to a Centerline angle Example: If the included angle is 60˚ then the compound is set to 30˚ For accurate angle( less than 1 degree accuracy), calculate the angle using Trig, then use a dial indicator to inspect the angle. Figure 31 - Cutting a taper with the compound rest. Figure 30 - Compound rest. Figure 29 - Cutting a taper.  Tailstock Offset Rarely used/only if taper attachment is not available. Tapers can be cut over the working length of the machine. Disadvantages… must misalign tailstock and re- align after the taper has been cut. Centers don’t sit properly. Can’t cut internal tapers. Offset is limited. Work must be turned between centers. Figure 32 - Offsetting the tailstock to cut a tapered section.  Taper Calculations – Tail Stock Method TO = (D - d) if the whole shaft is tapered. 2 TO = (D - d) X OL if part of the shaft is parallel. 2 TL Plain Taper Attachment  Telescoping Taper Attachment Figure 1 - Telescoping taper attachment.  Figure 2 - Telescoping taper attachment  Figure 3 - Setting the guide bar.  Setting the Taper Attachment Figure 4 - Test for accuracy. Bluing a Taper for Fit Figure 5 - Check the taper with a taper gauge.  FINISHING OPERATIONS Polishing in the Lathe Hand Polishing In The Lathe 1. Choose Finer grit Emery clothe. 2. Never hold Emery with one hand. 3. Emory polishing is usually held to.001” or less diameter reduction. Belt Sanding Attachment Filing on the Lathe Filing Tips Always hold the file handle with the left hand to keep away from the rotating chuck. Never file more than.001 inches due to causing the work piece from becoming out of round. Use a lathe file or single cut file. Tool Post Grinders Tool Post Grinder Tool Post Grinding hints. Removal is.001 to.002 per rotation of the work Ensure at the point of contact between the lathe and the grinding wheel are turning in opposite directions. Speed: 200 RPM Feed : set to ½ the wheel width per revolution  LATHE MAINTENANCE Lathe Maintenance The engine lathe is a precision machine tool and must be treated with great care.... END