Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine Tools 6 th Edition Machining Procedures for Various Workpieces Unit 6

6-2 Objectives Plan the sequence of operations and machine round work mounted between lathe centers Plan the sequence of operations and machine round work mounted in a lathe chuck Plan the sequence of operations to machine flat workpieces

6-3 Machining Procedures for Round Work Most work in machine shop is round –Turned to size on lathe Much of round work held in a chuck Important to follow correct machining sequence of operations –Prevents spoiling work

6-4 General Rules For Round Work Rough-turn all diameters to within.030 in. (0.79 mm)of size required –Machine largest diameter first than progress to smallest If small done first, work might bend when large done Rough-turn all steps and shoulders to within.030 in. (0.79 mm) of length required –Measure all lengths from one end of workpiece or will end up with too much material to finish

6-5 General Rules For Round Work Knurling or grooving done next if required Cool workpiece before starting finishing –Metal expands during machining so when hot measurements will be inaccurate –Metal shrinks when get too cold Finish-turn all diameters and lengths –Finish largest diameter first then work down –Finish shoulder of one step to length then cut diameter to size

6-6 Workpieces Requiring Center Holes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. When machining entire length of a round workpiece, center holes are drilled in each end. Typical part that can be machined between centers on a lathe.

6-7 Workpieces Held in a Chuck Machining external surfaces of round workpieces held in a chuck same as for work held between lathe centers When both external and internal surfaces done –Very important that workpiece be held short for rigidity and to prevent accidents Never let work extend more than three times its diameter

6-8 Machining External And Internal Diameters In A Chuck Square end (minimum removed) Rough-turn external diameters (Large to small) Center-drill work (small to large) Mount boring bar and bore ream hole Tap-drill size = TDS = D – p –D represents diameter –P represents pitch

6-9 Machining External And Internal Diameters In A Chuck Cut groove at end to be threaded Mount threading tool and thread to size Finish-turn external diameters to size and length (large to small) Reverse workpiece in chuck and protect finish diameter with piece of soft metal between chuck jaws Face end surface to proper length

6-10 General Rules for Machining Flat Workpieces Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

6-11 General Rules for Machining Flat Workpieces Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. Select and cut off material a little larger than size required 2. Machine all surfaces to size in milling machine in proper sequence of surfaces 3. Lay out physical contours of part, such as angles, steps, radii

6-12 General Rules for Machining Flat Workpieces Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4. Lightly prick-punch layout lines that indicate surfaces to be cut 5. Remove large sections of workpiece on contour bandsaw within 0.30 in.(0.79 mm) of the layout line 6. Machine all forms, such as steps, angles, radii, and grooves

6-13 General Rules for Machining Flat Workpieces Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7. Lay out all hole locations and, with dividers, scribe reference circle 8. Drill all holes, tap those which require threads 9. Ream holes 10. Surface-grind any surfaces needed