1. Machining Between Centers
Unit 52

2. Objectives Set up the cutting tool for turning operations
Turn parallel diameters to within ±.002-in. (0.05-mm) accuracy for size
Produce a good surface finish by filing and polishing
Machine square, filleted, and beveled shoulders to within .015-in. (0.3-mm) accuracy

3. 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

4. Setting Up a Cutting Tool
Move toolpost to the left-hand side of the T-slot in the compound rest
Mount tool- holder in toolpost so setscrew in toolholder 1 in. beyond toolpost
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5. Heavy Cuts: Set toolholder at right angles to work
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6. Setting Up a Cutting Tool: cont.
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

7. Mounting Work Between Lathe Centers
Procedure same as for facing
Unit 51 listed proper procedure for mounting work between centers

8. Parallel Turning
Used when work must be cut to size and have same diameter along entire length
Many factors determine amount of material that can be removed on lathe at one time
Cut to size in two cuts: roughing and finishing
Lathe centers must be in line
Trial cut taken off diameter before setting depth of cut on crossfeed micrometer graduated collar

9. Purposes 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

10. Procedure to Take 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

11. 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 in.
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

12. Stop the lathe
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

13. Take another trial cut .250 in. 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

14. 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.

15. Procedure for Rough Turning
Set lathe to correct speed for type and size of material being cut
Adjust quick-change gearbox for a to .030-in. 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

16. Take light trial cut at right-hand end of work for a .250 in. length
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
Cut along for .250 in., stop lathe, and check diameter for size
Diameter .030 in. 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. 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
Set depth of cut for half amount of material to be removed
Cut along for .250 in., stop lathe, check
Readjust depth of cut and finish-turn

20. 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 in. 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

21. 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
Select 10- or 12-in. mill file or long-angle lathe file

22. Start lathe
Grasp file handle in left hand and support file point with fingers of right hand
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23. Apply light pressure and push file forward to its full length; release pressure on return stroke
Move file about half width of file for each stroke and continue filing until finished
Use 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

24. Procedure for Polishing in a Lathe
Select correct type and grade of abrasive cloth for finish desired
Piece about 6 – 8 in. long and 1 in. 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
Disengage feed rod and lead screw

25. Remove toolpost and toolholder
Lubricate and adjust dead center
Roll sleeves up above elbows and tuck in any loose clothing
Start 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

26. 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
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27. Three Types of Shoulders
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28. Procedure to Turn 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

29. With turning tool, rough- and finish-turn work to within. 060 in
With turning tool, rough- and finish-turn work to within .060 in. 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
Face (square) shoulder, cutting to line using hand feed
Return crossfeed handle to same graduated collar setting for more cuts

30. 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

31. 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

32. 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 to correct length

33. 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
Most common is 45º

34. 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

35. 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
Apply cutting fluid to assist cutting action
Machine beveled shoulder until it is required size

36. Procedure to Cut Beveled Shoulder 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.
Set compound rest to desired angle
Adjust toolbit so only point does the cutting
Machine the bevel by feeding the compound rest by hand