1. Mounting, Removing, and Aligning Lathe Centers
Unit 49

2. Objectives Mount and/or remove lathe centers properly
Align lathe centers by visual, trial-cut, and dial-indicator methods

3. Lathe Centers
Work machined between centers turned for some portion of length, then reversed, and other end finished
Critical when machining work between centers that live center be absolutely true
Concentric work

4. To Mount Lathe Centers
Remove any burrs from lathe spindle, centers, or spindle sleeves
Clean tapers on lathe centers and in headstock and tailstock spindles
Partially insert cleaned center in lathe spindle
Force center into spindle
Follow same procedure when mounting tailstock center
Check trueness of center

5. To Remove Lathe Centers
Live center
Use knockout bar pushed through headstock spindle (slight tap)
Use cloth over center and hold to prevent damage
Dead center
Turn tailstock handwheel to draw spindle back into tailstock
End of screw contacts end of dead center, forcing it out of spindle

6. Alignment of Lathe Centers
Parallel diameter produced when lathe center aligned
Three common methods used to align
Aligning centerlines on back of tailstock with each other
Only a visual check and not too accurate
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

7. Alignment of Lathe Centers
Using the trial-cut method where small cut taken from each end of work and diameters measured with a micrometer
Using parallel test bar and dial indicator
Fastest and most accurate method
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8. To Align Centers by Adjusting the Tailstock
Loosen tailstock clamp nut or level
Loosen on of the adjusting screws, depending on direction tailstock must be moved and tighten other until line on top aligns with line on bottom half
Tighten screw to lock both halves in place
Make sure tailstock lines still aligned
Lock tailstock clamp nut or lever

9. To Align Centers by Trial-Cut Method
Take a light cut (~.005 in.) to true diameter from section A at tailstock end for .250 in. long
Stop feed and note reading on graduated collar of crossfeed handle
Move cutting tool away from work with crossfeed handle
Bring cutting tool close to headstock end

10. To Align Centers by Trial-Cut Method
Return cutting tool to same graduated collar setting as at section A
Cut a .500-in (13 mm) length at section B and stop lathe
Measure both diameters with micrometer

11. To Align Centers by Trial-Cut Method
If both diameters not same size, adjust tailstock either toward or away from cutting tool ½ difference of two readings
Take another light cut at A and B at same crossfeed graduated collar setting. Measure diameters and adjust tailstock.

12. To Align Centers Using Dial Indicator and Test Bar
Clean lathe and work center, mount test bar
Adjust test bar snugly between centers and tighten tailstock spindle clamp
Mount dial indicator on toolpost or lathe carriage
Indicator plunger should be parallel to lathe bed and contact point set on center

13. To Align Centers Using Dial Indicator and Test Bar
Adjust cross-slide
Indicator registers approximately .025 in at tailstock, indicator bezel to 0
Move carriage by hand so indicator registers on diameter at headstock end and not indicator reading
If both indicator readings not same, adjust tailstock with adjusting screws until indicator registers same at both ends

14. To Align Centers Using Dial Indicator and Test Bar
Tighten adjusting screw that was loosened
Tighten tailstock clamp nut
Adjust tailstock spindle until test bar snug between lathe centers
Recheck indicator readings at both ends and adjust tailstock, if necessary