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Work Holding

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					Work Holding Methods

  By Tom Brown, Matt Charlton and
          Andy Faulkes
The Lathe
    Work Holding Methods
The three most commonly used work holding
  devices are:
• Three-jaw chuck
• Four-jaw chuck
• Face plate
• Between centres
 What type of work can be held?

•3 jaw chuck used for easy fitting of circular
components
•4 jaw chuck can be used for non-round
components, or for turning on an eccentric centre
•Long jobs can be suspended and turned between
centres
•Large jobs can be held with jaw attachments on a
faceplate
3 Jaw Chuck

       A chuck with three
       jaws has a
       simultaneous
       movement to centre
       the job as the chuck
       jaws tighten.
Advantages of using 3 jaw chucks
The three-jaw chuck     • Very common.
is used to hold round   • Quick and easy to
work pieces of            use.
various diameters as    • Self centering.
the component is
centered in the chuck
before machining.
  Disadvantages of using 3 jaw
            chucks
Although the operator can set the machine
up quickly, the job will never be perfectly
concentric.
If re-work on a finished component is
needed, it is hard to align the work back to
its original axes in the jaws.
Sometimes can damage job if tightened
without soft jaws.
             4 Jaw Chuck
• The four-jaw chuck is used to hold
  irregular shapes because of its
  independent action on each jaw.
• Heavy to transport.
• Accurate with concentricity when using
  DTI and magnetic base.
• Timely set up.
                  Face Plate
• The work piece is clamped to the faceplate,
  typically using t-nuts in slots in the faceplate, or
  less commonly threaded holes in the faceplate
  itself.
               Face plate
• The face plate is also used for irregular
  shapes that need to be through-bored.
• Used on vertical lathes for holding large
  jobs.
• The job can be clamped concentric when
  using a DTI.
• Timely set up.
  Turning Between Centres
•Initially requires the use of a centre drill, used in both ends of
(a faced) component
•Chuck is removed and a morse taper sleeve with dead
centre is fitted to the head of the lathe
•Faceplate with threaded peg fitted to lathe head
•Dead centre fitted to the tail stock (with lubrication)
•Lathe carrier attached to the job, which is then supported
between the centres
•As the lathe rotates, the threaded peg pushes against the
carrier and rotates the job at normal lathe speed
  Turning Between Centres
 Faceplate
 with threaded
 peg
                            Job




Dead centre /w
                            Lathe
morse sleeve
                            carrier
 Turning Between Centres

Positives:
•Can machine much more of the job in one process –
no real minimum protruding length as with a chuck
•Allows the full length of the job to be machined
without difficulty (although flipping the job and
moving the carrier will be neccesary)
•Job will always be centred when removed and
refitted
 Turning Between Centres
Negatives:
•Lubricant important – can be easy to overheat the
dead centre in tail stock end
•Sometimes hard to achieve good finish due to
vibrations from imbalanced rotating parts
•Heavy duty processes not possible – such as
knurling – normal chuck required
•Precise tail stock alignment needed, or job will end
up tapered
Thank You!

				
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