Machining Between Centers

1. Machining Between Centers Session 9

2. Machining Between Centers • Training programs (schools) • Remove and replace work in lathe many times before completed • Need assurance that machined diameter will run true with other diameters • Machining between centers saves time in setting up • Common operations • Facing, rough and finish-turning, shoulder turning, filing and polishing

3. Setting Up a Cutting Tool • Move toolpost to the left-hand side of the T-slot in the compoundrest • Mount tool-holder intoolpost sosetscrew intoolholder 1 in.beyond toolpost

4. Setting Up a Cutting Tool For heavy cuts, set toolholder at right angles to work

5. Setting Up a Cutting Tool • Insert proper cutting tool into toolholder, having tool extend .500 in. beyond toolholder and never more than twice its thickness • Set cutting-tool point to center height • Check it against lathe center point • Tighten toolpost securely to prevent it from moving during a cut

6. Parallel Turning • Used when work must be cut to size and have same diameter along entire length • Lathe centers must be in line • Trial cut taken off diameter before setting depth of cut on crossfeed micrometer graduated collar

7. Purpose of a Trial Cut • Produce accurate turned diameter • Measured with micrometer • Set cutting-tool point to the diameter • Set crossfeed micrometer collar to the diameter

8. Taking a Trial Cut • Set up workpiece and cutting tool as for turning • Set proper speeds and feed to suit material • Start lathe and position toolbit over work approximately .125 in. from end • Turn compound rest handle clockwise ¼ of a turn to remove any backlash

9. Taking a Trial Cut • Feed toolbit into work by turning crossfeed handle clockwise until light ring appears around entire circumference of work • Do NOT move crossfeed handle setting • Turn carriage handwheel until toolbit clears end of workpiece by about .060 inch

10. Taking a Trial Cut • Turn crossfeed handle clockwise about .010 in. and take trial cut .250 in. along length of work • Disengage automatic feed and clear toolbit past end of work with carriage handwheel • Stop the lathe

11. Taking a Trial Cut • Test accuracy of micrometer by cleaning and closing measuring faces and then measure trial-cut diameter • Calculate how much material must still be removed from diameter of work • Turn crossfeed handle clockwise ½ amount of material to be removed

12. Taking a Trial Cut • Take another trial cut .250 inch long and stop the lathe • Clear toolbit over end of work with carriage handwheel • Measure diameter and readjust crossfeed handle until diameter is correct • Machine diameter to length

13. Rough Turning • Removes as much metal as possible in shortest length of time • Accuracy and surface finish are not important in this operation • .020- to .030-in. feed recommended • Work rough-turned to • Within .030 in. of finished size when removing up to .500 in. diameter • Within .060 in. when removing > .500 in.

14. Rough Turning • Set lathe to correct speed for type and size of material being cut • Adjust quick-change gearbox for a .010 to .030 inch feed • Depends on depth of cut and condition of machine • Move toolholder to left-hand side of compound rest and set toolbit height to center

15. Rough Turning • Tighten toolpost securely to prevent toolholder from moving during machining • Take light trial cut at right-hand end of work for a .250 in. length • Measure work and adjust toolbit for proper depth of cut

16. Rough Turning • Cut along for .250 in., stop lathe, and check diameter for size • Diameter .030 inch over finish size • Readjust depth of cut, if necessary

17. Finish Turning • Follows rough turning • Produces smooth surface finish and cuts work to an accurate size • Factors affecting type of surface finish • Condition of cutting tool • Rigidity of machine and work • Lathe speeds and feeds

18. Procedure For Finish Turning • Make sure cutting edge of toolbit free from nicks, burrs, etc. • Set toolbit on center; check it against lathe center point • Set lathe to recommended speed and feed

19. Procedure For Finish Turning • Take light trial cut .250 in. long at right-hand end of work • Produce true diameter • Set cutting tool to diameter • Set graduated collar to diameter • Stop lathe and measure diameter

20. Procedure For Finish Turning • Set depth of cut for half amount of material to be removed • Cut along for .250 inch, stop lathe, check • Readjust depth of cut and finish-turn

21. Filing in a Lathe • Only to remove small amount of stock, remove burrs, or round off sharp corners • Work should be turned to within .002 to .003 inch of size • For safety, file with left hand so arms and hands kept clear of revolving chuck • Remove toolbit from toolholder before filing • Cover lathe bed with paper before filing

22. Procedure to File in a Lathe • Set spindle speed to twice that for turning • Mount work between centers, lubricate, and carefully adjust dead center in work • Move carriage as far to right as possible and remove toolpost • Disengage lead screw and feed rod

23. Procedure to File in a Lathe • Select 10 inch or 12 inch mill file or long-angle lathe file • Start lathe • Grasp file handle in left hand and support file point with fingers of right hand • Apply light pressure and push file forward to its full length; release pressure on return stroke

24. Procedure to File in a Lathe • Move file about half width of file for each stroke and continue filing until finished • Use 30-40 strokes per minute • Safety precautions • Roll sleeves above elbow • Remove watches and rings • Never use file without properly fitted handle • Never apply too much pressure • Clean file frequently with file brush

25. Procedure for Polishing in a Lathe • Select correct type and grade of abrasive cloth for finish desired • Piece about 6 – 8 inch long and 1 inch wide • Use aluminum oxide abrasive cloth for ferrous metals • Use silicon carbide abrasive cloth should be used for nonferrous metals • Set lathe to run at high speed

26. Procedure for Polishing in a Lathe • Disengage feed rod and lead screw • Remove toolpost and toolholder • Lubricate and adjust dead center • Roll sleeves up above elbows and tuck in any loose clothing • Start lathe

27. Procedure for Polishing in a Lathe • Hold abrasive cloth on work • With right hand, press cloth firmly on work while tightly holding other end of abrasive cloth with left hand • Move cloth slowly back and forth • Continue until desired surface finish has been produced

28. Shoulder • Shoulder: the change in diameters, or step, when turning more than one diameter on a piece of work • Three common types of shoulders • Square • Filleted • Angular or Tapered

29. Three Types of Shoulders

30. Turning a Square Shoulder • With work mounted in lathe, lay out shoulder position from finished end of work • For filleted shoulders, allow sufficient length to permit proper radius to be formed • Place point of toolbit at this mark and cut a small groove around circumference to mark off length

31. Turning a Square Shoulder • With turning tool, rough- and finish-turn work to within .060 inch of required length • Set up end-facing tool, chalk small diameter of work, and bring cutting tool up until it just removes chalk mark • Note reading on graduated crossfeed handle

32. Turning a Square Shoulder • Face (square) shoulder, cutting to line using hand feed • Return crossfeed handle to same graduated collar setting for more cuts

33. Fillets • Used at a shoulder • To overcome sharpness of corner • To strengthen part at this point • Toolbit having same radius used to finish shoulder if filleted corner required

34. Procedure to Machine a Filleted Shoulder • Lay out length of shoulder with center-punch mark or by cutting light groove • Rough- and finish-turn small diameter to correct length minus the radius to be cut • Mount correct radius toolbit and set it to center

35. Procedure to Machine a Filleted Shoulder • Set lathe for one-half turning speed • Coat small diameter near shoulder with chalk or layout dye • Start lathe and feed cutting tool in until it lightly marks small diameter near shoulder • Slowly feed cutting tool sideways with carriage handwheel until shoulder cut

36. Beveled (Angular) Shoulder • Used to • Eliminate sharp corners and edges • Make parts easier to handle • Improve the appearance of the part • Sometimes used to strengthen part by eliminating sharp corner of square shoulder • Beveled at angles ranging from 30º to 60º

37. Procedure For Creating Beveled Shoulders • Turn large diameter to size • Lay out position of shoulder along length of workpiece • Rough- and finish-turn small diameter to size • Mount side cutting tool in toolholder and set it to center • Use protractor and set side cutting edge of toolbit to desired angle

38. Procedure For Creating Beveled Shoulders • Apply chalk or layout dye to small diameter close to shoulder location • Set lathe spindle to ½ turning speed • Bring point of toolbit in until it just removes chalk or layout dye • Turn carriage handwheel by hand to feed cutting tool into shoulder

39. Procedure For Creating Beveled Shoulders • Apply cutting fluid to assist cutting action • Machine beveled shoulder until it is required size

40. Beveled Shoulders Using the Compound Rest If size of shoulder large and chatter occurs during cutting with the side of the toolbit, may be necessary to use the compound rest.

41. Beveled Shoulders Using the Compound Rest • Set compound rest to desired angle • Adjust toolbit so only point does the cutting • Machine the bevel by feeding the compound rest by hand