Machining. Module 5: Lathe Setup and Operations. (Part 1) Curriculum Development Unit PREPARED BY. August 2013

Transcription

1 Machining Module 5: Lathe Setup and Operations (Part 1) PREPARED BY Curriculum Development Unit August 2013 Applied Technology High Schools, 2013

2 Module 5: Lathe Setup and Operations (Part 1) Module Objectives Upon the completion of this module, the student will be able to: Identify the main machining operations using a lathe machine. Describe the logical sequence of the main machining operations. Set the cutting tool to the center of the machine. Set the cutting depth using graduated collars. Describe and Implement the main check list before starting a lathe machine. Perform a facing operation using a lathe machine Perform a center drilling operation using a lathe machine Module Contents Topic Page No. Introduction 3 1 Practical project Machining procedure 4 2 Machine Setup 8 3 Hints on chuck work 11 4 Lathe machine safety 12 5 Lathe machine check list 15 6 Lathe operations 16 References 27 2 Module 5: Lathe Setup and Operations (Part 1)

3 Introduction Lathe could be used for many operations to produce different shapes to the required size. In this course the machine operations will be covered through an on going practical project. 1. Practical Project The practical project is to use the lathe machine tool to make the part shown below. Fig. 5.1 Fig. 5.1 Module 5: Lathe Setup and Operations (Part 1) 3

4 1.1 Machining Procedure To machine the part shown in Fig. 5.1, the following sequence of operations is suggested: A piece of Aluminum ϕ 25 x 80 mm will be provided. Step 1: Cut the two ends of the workpiece to make it flat, straight and to reduce the workpiece length to the required size. This operation is called Facing. Fig. 5.2 Facing operation Step 2: Drill a center hole on one end of the workpiece. Center holes are used either to be used as a seat for the tailstock centers which may support the workpiece or as start and guide for drilling operation. This operation of making small conical spot on the end of the workpiece is called center drilling. Fig.5.3 Fig. 5.3 Center drilling 4 Module 5: Lathe Setup and Operations (Part 1)

5 Step 3: Reduce the diameter from 25 to 12 mm to a length = 18 mm as shown. This is called Parallel Turning. Fig. 5.4 Fig. 5.4 Parallel turning Step 4: Cut the tapered shape as shown. The operation of increase or decrease of diameters is called taper turning. Fig. 5.5 Fig. 5.5 Taper turning Module 5: Lathe Setup and Operations (Part 1) 5

6 Step 5: Cut the groove shown, in its correct position (see the drawing) and to the required size. This operation is called external groove or external recessing. Fig. 5.6 Fig. 5.6 Recessing (grooving operation) Step 6: Cut the thread shown. Thread is the process of cutting spiral or helical shapes. Fig. 5.7 Fig. 5.7 Threading operation 6 Module 5: Lathe Setup and Operations (Part 1)

7 Step 7: Drill at the center of the workpiece to the dimensions shown. Fig. 5.8 Step 8: Fig. 5.8 Drilling operation Use a piece of sand paper (abrasive) to polish the work. Note: This sequence of operations is just a suggestion. Some operations must be done in a certain sequence but some other operations don t need to be in sequence. Examples: You shouldn t start a taper turning before reducing the diameters to the required size by parallel turning. You should not do polishing before finishing the work. You can t do drilling before center drilling. Module 5: Lathe Setup and Operations (Part 1) 7

8 2. Machine Setup There are many setup procedures that must be done beforee starting the lathe such as: Checking the machine for readiness. Mounting the cutting tools. Mounting the appropriate workpiece s holding device on machine spindle Mounting drill chucks and centers in the tailstock and setup the tailstock Setting the cutting tool to the center of the machine. Required settings for all lathe operations (Facing, turning, etc) 2.1 Setting the cutting tool to the center of the machine Before any turning takes place it is common practice to check that the point of the lathe tool is centered (Fig. 5.9). This means that the lathe tool point should be the same height as the tip of the tailstock centre. If this is not done and the tool point is either above or below the centre point - usually the finish to the steel will be poor. Also, a significant amount of vibration could take place during turning. Fig. 5.9: Setting the cutting tool to the center of the machine 8 Module 5: Lathe Setup and Operations (Part 1)

9 ATM 412 Machining 2.2 Use graduatedd collars Graduated micromete er collars are sleeves or bushingss that are mounted on the compound rest and cross slide screws, (Fig. 5.10). They assist the lathe operator in setting the cutting tool accurately to remove the required amount of material from the workpiece. The cross slide graduated collars may indicate the distance that the cutting tool has moved toward the work, or the amount thatt will be removed from the work diameter. The circumference of the screw collars on some lathe machines is divided into 0.05 mm divisions. Therefore, if the cross slide screw is turned clockwise 10 graduations, the diameter will be reduced by 0.5 mm (10 x 0.05), i.e. an amount equal to the reading on the collar. The cutting tool will move only 0.25 mm which is the cutting depth, seee Fig However on some other machines the reading on the collar is the cutting depth. Fig. 5.10: Graduated collar Fig. 5.11: Depth of cut Hints on graduated collar use: 1. Move the cutting tool by compound or cross slide until you slightly touch the surface thatt you want to remove metal from. Fig Fig. 5.12: The tool touches the surface zero positioning Module 5: Lathe Setup and Operations (Part 1) 9

10 Fix the handwheel by one hand and rotate the collar by the other hand to adjust the zero on the graduation collar to the fixed line on the compound or cross slide (Fig. 5.13). Set zero on the graduated collar means touching the surface from which you are going to take the correct value for depth of cut. 2. All depths of cut must be made by feeding the cutting tool toward the workpiece while the collar is released. Fig. 5.13: Setting the graduated collar to zero 3. If the graduated collar is turned past the desired setting, it must be turned backward a half-turn and then fed into the proper setting to remove the backlash (the play between the feed screw and the nut). 4. Never hold a graduated collar when setting a depth of cut. Graduated collars with friction devices can be moved easily if held when a depth of cut is being set. 10 Module 5: Lathe Setup and Operations (Part 1)

11 3. Hints on chuck work: If possible, all diameters should be machined on a workpiece in one setup before it is removed from a three or four jaw chuck. If the work is removed and then replaced in the chuck for further machining, it will probably not run true, or it will take some time to bring it back to the original trueness. Since we need to remove and mount the workpiece several times in our course, so a step of making a center hole on the face of the workpiece is done at the beginning to help in mounting the workpiece properly every time we need to work on it. Tighten the chuck jaws around the most rigid part of the work to prevent distortion of the workpiece If the work projects more than three times the diameter of the stock, it should be supported by a revolving tailstock center or steady rest. Never grip the work on a diameter smaller than the diameter to be machined unless absolutely necessary. Tighten the chuck securely so that the workpiece is not moved into the chuck by the pressure of the cut. Always set the toolbit point on center. If the toolbit is set too low, the work may be bent. Position the toolpost on the left side of the compound rest. Move the carriage until the toolbit is at the extreme left end of travel and the toolbit is off the work surface. Rotate the chuck one turn by hand to see that the jaws do not strike the compound rest. Never use an air hose to clean a chuck Never leave a chuck wrench in a chuck. Module 5: Lathe Setup and Operations (Part 1) 11

12 4. Lathe Safety In addition to the general safety rules in machine shop described in module 2, the following points should be considered during the lathe operation: Do not attempt to operate a lathe until you know the proper procedures and have been checked out on its safe operation by your instructor. Never attempt to operate a lathe while your senses are impaired by medication. Fig Dress appropriately; Remove any necklaces, other jewelry, wristwatch, or rings. Secure any loose-fitting clothing and roll up long sleeves. Wear an apron or a properly fitted shop coat, safety glasses are a must. Fig Fig. 5.26: Medication Always be sure that the cutting tool and the workpiece are properly mounted before starting the machine. Turn the chuck by hand to be sure there is no binding or danger of the work striking any part of the lathe. Fig. 3.27: Safety overall. Metal chips are sharp and can cause severe cuts. Do not try to remove them with your hands. When they become stringy and build up on the tool post, stop the machine and remove them with pliers. 12 Module 5: Lathe Setup and Operations (Part 1)

13 Do not permit small-diameter work to project too far from the chuck without support from the tailstock. The work will be tapered or worse, spring up over the cutting tool and /or break. Fig Fig. 5.28: Small diameter work should not project too far from the chuck Do not run the cutting tool into the chuck. Check any readjustment of the work or tool to make sure there is ample clearance when the cutter has been moved leftward to the farthest point that will be machined. Fig Fig. 5.29: Ample clearance between the chuck and the cutting tool Before repositioning or removing work from the lathe, move the cutting tool clear of the work area. This will prevent accidental cuts on your hands and arms from the cutter bit. Fig Fig. 5.30: move the cutting tool clear of the work area Module 5: Lathe Setup and Operations (Part 1) 13

14 Always remove the key from the chuck. Make it a habit to never let go of the key until it is out of the chuck and clear of the work area. Fig When doing filing on the lathe, make sure the file has a securely fitting handle. Fig. 5.31: Always remove the key from the chuck Tools must not be placed on the lathe ways. Use a tool board or place them on the lathe tray. Fig If any odd sounding noise or vibration develops during lathe operation, stop the machine immediately. Get help from your instructor. Fig. 5.32: Tools must not be placed on the lathe ways. 14 Module 5: Lathe Setup and Operations (Part 1)

15 5. Lathe Machine Check List: The checkout procedure for the lathe should include the following actions: Clean and lubricate the machine. Fig.5.33 Be sure all guards are in position and locked in place before start the machine. Fig.5.34 Turn the spindle over by hand to be sure it is not locked. Move the carriage along the ways. Therefore should be no binding. Check cross-slide movement. If there is too much play, adjust gibs, (Adjusting screws are used to adjust the movement of the slides of the machine). This is applicable for most of machine s slides Fig 5.35 Adjust the drive mechanism for the desired speed and feed. If the tailstock is used, check it for proper alignment. Fig Clamp the cutter bit in the appropriate tool-holder and mount it in the tool post. Do not permit excessive compound rest overhang, since this often causes tool chatter and results in a poorly machined surface. Mount the work. Check for adequate Fig. 5:33: Clean and lubricate the machine. Fig. 5.34: Machine guards are in place. Fig. 5.35: Adjusting screws s are used to tighten and release the movement of the cross slide. clearance between the work and the Fig. 5.36: The tailstock must be various machine parts. aligned to zero. Module 5: Lathe Setup and Operations (Part 1) 15

16 6. Lathe operations 6.1 Facing Facing is to remove a small amount of material (around 1 2 mm) from the end of the workpiece to produce smooth and true face and also to bring the workpiece to the desired length. The facing operation and the cutting tool is shown below in fig Fig. 5.37: Facing operation and the cutting tool Fig. 5.38: The facing tool must be placed on the centerline of the workpiece and the tip of the tool should meet the end of the work piece at a slight angle 16 Module 5: Lathe Setup and Operations (Part 1)

17 6.1.1 Practical Task 1: a) To do facing on the free end of the workpiece. b) To reverse the work and do facing on the other end of the workpiece to bring the final length to 78 mm. Blank part dimensions: Ф 25 X 80 mm. Fig (a) Finished Part: as shown in Fig (b) Tool: Right hand tool. Material: Aluminum Fig (a): Before facing Fig (b): After facing ( length is reduced) No. Setup and production steps description 1. Read, understand fully and follow all the safety regulations. As always, wear safety glasses and keep your face well away from the work. Make sure the power feed lever is disengaged, the compound rest is set at zero angle and the carriage s lock is Fig. 5.40: Carriage lock not tightened down. Fig Module 5: Lathe Setup and Operations (Part 1) 17

18 2. Mount the workpiece securely in a chuck and make sure to remove the chuck key. Use a three jaw universal chuck to avoid the effort to true up the work in the chuck. To get the work properly centered, close the jaws until they just touch the surface of the work, then twist the work piece in the jaws to seat it; then tighten the jaws. It's good practice to tighten the jaws from all 3 chuck key positions to ensure even gripping by the jaws. Fig Fig. 5.41: Workpiece mounted in three jaw chuck 3. Set the work in the chuck so that no more than three times its diameter extends beyond the chuck jaws. Fig Fig Module 5: Lathe Setup and Operations (Part 1)

19 4. Clamp the cutting tool in the tool post. Set up the facing cutting tool to the height of the dead center (on the tailstock) and turn the tool post so that the tip of the cutting tool will meet the end of the work piece at a slight angle. Fig The tool bit should be clamped in the tool holder with minimum overhang. Otherwise, tool chatter and a poor surface finish may result. Fig Advance the carriage toward the chuck until the tool is about even with the end of the workpiece. Fig. 5.44, Make sure that the compound rest is not all the way at the end of its travel towards the chuck. The carriage is then locked in position. 6. Set the rotational speed relative to the diameter of the workpiece. Fig Rotate the chuck by hand to be sure it is not locked then return the chip guard (cover) over the chuck. 8. Start the machine Module 5: Lathe Setup and Operations (Part 1) 19

20 9. The usual practice is to start from the center and feed outward (both directions are correct). Rotate the cross slide handwheel clockwise until the cutting tip reaches the center of the workpiece. Use the compound rest handwheel to advance the tip of the tool until it just touches the end of the work piece (Fig. 5.45). Use the cross slide handwheel to back off the tool until it is beyond the diameter of the work piece. A rounded nubbin (remaining piece of unmachined material) will result if the tool is slightly above center. Fig A square-shoulder nubbin indicates that the cutting tool is below center. Fig With the cutting tool on center a smooth face will result from the cut. This cutting sequence is repeated until the part has been leveled (faced off). Fig Fig Fig Stop the machine 20 Module 5: Lathe Setup and Operations (Part 1)

21 11. Release the carriage and move it away to the right. 12. Measure the total length of the workpiece. 13. Reverse the workpiece in the chuck. 14. Subtract the finished length from the measured length this is equal to the amount you want to remove by the second facing operation. Fig Reverse the compound rest to its permissible length then bring the carriage back in front of the workpiece and lock it. 16. Move the compound rest handwheel until the cutting tip just touches the surface of the free end at the center of the workpiece (Fig. 5.48). Adjust the compound rest graduated collar (fig. 5.49) to zero and then start the machine. Fig Module 5: Lathe Setup and Operations (Part 1) 21

22 17. Set the depth of cut by using the graduated collar on the compound rest. 0.5 mm could be removed every cut. 18. Crank the cross slide backside until the tool clears the work. 19 Reverse the cross slide movement to bring the cutting tool to the center of the workpiece again. 20 This sequence of cutting mentioned in steps 17 to 19 is repeated until you reduce the length of the workpiece to 78 mm Fig (Stop the machine at intervals to take measurements) Fig Stop the machine, release and move the carriage to the right side of the machine, near the tailstock. Check the length by the vernier caliper. 22. Use a hand file to break the sharp edge as shown in fig Fig Remove the workpiece. 22 Module 5: Lathe Setup and Operations (Part 1)

23 6.2 Center drilling Center hole is a short combined hole of both straight and tapered shape, drilled into the ends of the part to allow the conical points of the lathe centers to fit snugly into it. Lathe center is mounted on the tailstock to support long workpiece on its free end when the part is held on the lathe chuck. Center drills are also used to set a true center point as a guide and start point for drilling operation. Fig Note: This operation should not be done before facing. Fig. 5.52: Center drill The tool used is called a center drill (combination of drill and countersink). Regular center drills are made with a 60 degree angle on the pointed end. Center drill s are available in different sizes (0,1,2,3,.. etc) to suit different diameters of work. Table 5.1 Center drill Size and over Workpiece diameter in (mm) Table 5.1 Center Drill Sizes Module 5: Lathe Setup and Operations (Part 1) 23

24 6.2.2 Practical Task 2: Objective: To drill a center hole on the free end of the workpiece provided. Blank part dimensions: Ф 25 X 78 mm Finished Part: as shown in Fig Tool: Center drill. Size 4. Material: Aluminum Fig. 5.53: Before center drilling Fig. 5.54: Finished part No. Setup and production steps description 1. Read, understand fully and follow all the safety regulations. As always, wear safety glasses and keep your face well away from the work since this operation will throw off hot chips and/or sharp spirals of metal. Check the lines on the back of the tailstock to see that they are aligned. Correct if necessary. Fig Module 5: Lathe Setup and Operations (Part 1)

25 2. Mount the workpiece in a three jaw chuck. No more than three times the diameter should extend beyond the chuck jaws. 3. Mount a drill chuck on the tailstock spindle. Mount the correct center drill, in the drill chuck. A center drill BS 4 is suitable for 25 mm diameter workpiece. Fig Fig The tailstock has two lock arms. Long one is to hold the tailstock to the bed of the machine and the other short one is to stop the movement of the tailstock spindle. Fig and Release the tailstock lock and advance the tailstock until it reaches near the workpiece and in front of the work free end. Lock the tailstock at this position. Make sure the tool post is far enough from the chuck. Fig Fig Set the rotational speed to approximately 1200 to 1500 RPM, then start the machine. Fig Module 5: Lathe Setup and Operations (Part 1) 25

26 6. 7. Advance the tailstock spindle slowly by rotating the handwheel clockwise to feed the tool into the work (fig. 5.58), (make sure the lock of the spindle is released). The suitable depth is to feed the tool to approximately more than half of the countersink (tapered part) of the tool head. Fig Reverse the headstock handwheel until the cutting tool is free from the workpiece, then stop the machine. Fig Fig Release the lock of the tailstock and draw it back to it s position on the right side of the machine. Fig Module 5: Lathe Setup and Operations (Part 1)

27 References 1. Technology of Machine Tools. Seventh Edition, McGraw-Hill Companies, 2. Machine shop operations and setups, 4 th edition, Lascoe nelson Porter. 3. Machine tool and Manufacturing technology, Steve F. Krar, Mario Rapisarda, Albert F. Check., Delmar Publishers. 4. en.wikipedia.org/wiki/machining 5. Module 5: Lathe Setup and Operations (Part 1) 27

28 Student s notes 28 Module 5: Lathe Setup and Operations (Part 1)

29 Worksheet 1. List the main lathe machine operations required to make the part shown below: No. Name of the part Module 5: Lathe Setup and Operations (Part 1) 29

30 2. Define the term facing operation? For what purposes do we need to do center drilling? What is the function of the graduated collars? Mention one method used to bring the cutting tool tip to the center of the machine? Module 5: Lathe Setup and Operations (Part 1)