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Identify and explain function, and safely machine components while using a
milling machine and lathe

SUBJECT OUTCOME 4.1 Use a centre lathe to produce a component  
 * Explain the purpose of using a centre lathe.
   􀂃 with the aid of sketches the parts and components that make up the lathe.
   􀂃 the different turning operations that can be performed on a lathe and
   where relevant the advantages and disadvantages.
 * Identify and explain
   􀂃 the function of the centre lathe with respect to energy flow.
   􀂃 the function and operation of the components that make up a centre lathe.
 * List
   􀂃 the advantages and disadvantages of work pieces being held between
   centres.
   􀂃 safety measures that are to be considered when operating a lathe.
   􀂃 four different type of lathe centres.
 * Plan for work activity.
 * Read and interpret machine engineering drawings and instruction.
 * Prepare machine for operation (pre-operational checks).
 * Ensure that tooling and materials are on hand.
 * Set up lathe for work activity.
 * Perform turning operations.
 * Check that machined components meets specifications and document conformance.
 * Report any discrepancies, problems, malfunctions whilst working.
 * Maintain a clean and tidy work area.
 * Apply safety considerations whilst working.

Explain the purpose of using a centre lathe
 * With the aid of sketches the parts and components that make up the lathe.
 * The different turning operations that can be performed on a lathe and where
   relevant the advantages and disadvantages.

The Centre Lathe. The Centre Lathe is used to manufacture cylindrical shapes
from a range of materials including; steels and plastics. Many of the components
that go together to make an engine work have been manufactured using lathes.

A lathe is a machine tool that carries out many machine shop tasks. ... The
lathe holds and rotates the work piece about the centre line of these two parts.
It can also machine a part between its headstock and tailstock centres. This is
why we call it a centre lathe. Video Additional website 1   Additional website 2

 * Parallel turning
 * Facing
 * Drilling and reaming
 * Boring
 * Taper turning
 * Internal and external thread cutting
 * Knurling
 * Grooving
 * Parting
 * Profile (contouring) cutting
 * Chamfering



  Centre lathe parts   There are many types of lathe machine but each machine
consist some basic part which are essential for its proper working. These parts
are bed, tool post, Chuck, head stock, tell stock, legs, Gear chain, lead screw,
carriage, cross slide, split nut, apron, chip pan, guide ways etc.  



  Headstock

Head Stock The main function of headstock is to transmit power to the different
parts of a lathe. It comprises of the headstock casting to accommodate all the
parts within it including gear train arrangement. The main spindle is adjusted
in it, which possesses live centre to which the work can be attached.

Different clamping components can be attached to the spindle to hold work.

 * It can adjust the spindle speed
 * Adjustment for feed screw for thread cutting
 * Feed adjustment for automatic feed
 * Emergency stop button
 * Cutting fluid pump switch

 

Headstock spindle   The spindle is the hart of the centre lathe.  It is rotating
by means of the headstock motor through the gearbox.  It can rotate in both
directions.  It can accommodate various clamping devices such as:
 * Three jaw chuck
 * Four jaw chuck
 * Faceplate
 * Dead centre for turning between centres
 * Collet



Thee jaw chuck



Four jaw chuck



    Tailstock   It is usually used to apply support to the longitudinal rotary
axis of a work piece being machined. A lathe centre is mounted in the tailstock,
and inserted against the sides of a hole in the centre of the work piece.

It can also accommodate the following:

 * Drill bits for drilling
 * Reamers for reaming
 * Taps for cutting thread





    Lathe bed and gap bed   The lathe bed is made from cast iron and form a
large part of the lathe.  The lathe size are express as the length of the bed. 
To be more precise the maximum distance between the tailstock and headstock.

The bed supports he carriage as well as the tailstock.

Gap bed is a piece of bed that can be removed close to the headstock to
accommodate work with large diameter.

The bed can come in the following guides:

 * Flat bed
 * V-flat bed
 * V-V bed



 

 

 

 

 

V-V bed

V-flat bed

 



    Carriage   The carriage houses the saddle, the cross slide, and the apron.
The main function of the carriage is to position the tool along the lathe bed.
This lever controls the spindle's rotation and direction.

The following components make up the carriage:

Saddle - Fit on top of the bed and is accurately guided by the v-shaped guides
in the bed.

Cross slide is fitted to the saddle and accommodates movement at right angels to
the bed of the lathe.

Compound slide (or top slide) is usually where the tool post is mounted. It
provides a smaller amount of movement (less than the cross-slide) along its axis
via another feed screw. The compound rest axis can be adjusted independently of
the carriage or cross-slide. It can be set to angels to accommodate internal and
external tapers to be cut.  It also facilitate for the cutting of V-thread.

Tool post is used to hold tools for turning and facing, boring, and knurling.
Quick change tool posts are specifically designed for the mini lathe and may
include a tool post and tool holders.

Apron is the front face of the carriage. It is where the feed controls are
located on most manual lathes. The apron is also a housing for the gears and
associated mechanisms related to power feeding of the carriage and cross slide



 

  Feed shaft   The feed shaft (rod) is a power transmission mechanism used for
precise linear movement of the carriage along the longitudinal axis of the
lathe.  This is used to for automatic feed.  The engagement levers is situated
on the apron

Lead screw

The lead screw of a lathe is used to advance the carriage of the lathe in time
with the rotation of the spindle. It is used to make threads by having different
gearing between the spindle and the drive for the lead screw. The half nut on
the apron is used to engage the lead screw.





    Foot brake (emergency brake)   All lathes should be fitted with emergency
stop, foot or knee switches.

In case of an emergency even if hands are tied up, all you need to do is to step
on the foot brake.

The foot brake will cut the power and a disk brake on the motor shaft will stop
the rotation of the spindle.

NOTE: This brake is only for emergency and not to be used for normal operation
as this will put unnecessary strain on the drive train of the lathe.



Graduated hand wheels  

There are four feed handles:
 * Longitudinal feed on the apron
 * Cross feed on cross slide
 * Compound feed on compound slide
 * Tailstock spindle feed handle

Each of this handles have a graduated sleeve where each line will represent a
fraction of a mm.  Be aware that they differed from sleeve to sleeve on a lathe,
and that different make lathes are also different.

Note:  Always take up slack in feed by moving the feed towards the work.  When
touching work, sleeves can then be zeroed.

Some centre lathes is fitted with digital readout on the X and Y axis.  This
means on the carriage feed and the cross feed.

Centre lathes can also be retrofitted with digital readout.  This is extremely
useful as it eliminated backlash and play.  This result in increase in
production and accurate work to be produced.







  The different turning operations that can be performed on a lathe `

        Parallel turning Video Additional website   Face turning Video  
Parallel turning is done along the length of work.  A single-point turning tool
moves axially, along the side of the work piece, removing material to form
different features, including steps, tapers, chamfers, and contours. These
features are typically machined at a small radial depth of cut and multiple
passes are made until the end diameter is reached.

 

 



A single-point turning tool moves radially, along the end of the work piece,
removing a thin layer of material to provide a smooth flat surface. The depth of
the face, typically very small, may be machined in a single pass or may be
reached by machining at a smaller axial depth of cut and making multiple passes.

 

 

 

        Taper turning external Video Additional website   Taper turning internal
  A taper is a conical shape. Tapers can be cut with lathes quite easily. There
are some common methods for turning tapers on an centre lathe,

Using a form tool: This type of tool is specifically designed for one cut, at a
certain taper angle. The tool is plunged at one location, and never moved along
the lathe slides. v Compound Slide

Method: The compound slide is set to travel at half of the taper angle. The tool
is then fed across the work by hand, cutting the taper as it goes. v Off-Set
Tail Stock: In this method the normal rotating part of the lathe still drives
the work piece (mounted between centres), but the centre at the tailstock is
offset towards/away from the cutting tool. Then, as the cutting tool passes
over, the part is cut in a conical shape. This method is limited to small tapers
over long lengths. The tailstock offset h is defined by


h = Lxsinα, where L is the length of work piece, and α is the half of the taper
angle.

 

 

 



Internal tapes can also be machined on a centre lathe. You are limited to only
using the compound slide method or the taper turning attachment method.

Taper Turning Attachment is very much popular and fits on all lathe machine. In
ordinary straight turning, the cutting tool moves along a line parallel to the
axis of the work, causing the finished job to be the same diameter throughout.



 

 

 

 



 

Screw cutting Video   Parting off and Grooving Video   A turning operation in
which a single-point tool, typically with a 60 degree pointed nose, moves
axially, along the side of the work piece, cutting threads into the outer
surface. The threads can be cut to a specified length and pitch and may require
multiple passes to be formed.

Square, ACME and buttress thread can also be cut.

Internal as well as external thread can be cut.

 

 

A turning operation, also known as parting, in which a single-point cut-off tool
moves radially, into the side of the work piece, and continues until the centre
or inner diameter of the work piece is reached, thus parting or cutting off a
section of the work piece. A part catcher is often used to catch the removed
part.

A turning operation in which a single-point tool moves radially, into the side
of the work piece, cutting a groove equal in width to the cutting tool. If the
desired groove width is larger than the tool width, multiple adjacent grooves
will be cut. A profiling cut can be performed to smooth the surface of multiple
grooves. Special form tools can also be used to create grooves of varying
geometries.

        Profile turning Video   Drilling Video   Profile turning is normally
done with a cutting tool that has been shaped according to the profile.

The cutting tool is difficult to make and is time consuming. 

 

The tailstock of a lathe can be used for drilling, with the aid of a drill chuck
or directly in the tailstock spindle.

 If a long piece of material has to be turned on a lathe then a centre drill is
used to produce the hole at one end. This allows the drilled end to be supported
by the tailstock centre.

Boring Video   Knurling Video   Boring is the process of enlarging a hole that
has already been drilled (or cast) by means of a single-point cutting tool (or
of a boring head containing several such tools), such as in boring a gun barrel
or an engine cylinder.



A knurling tool is used to press a pattern onto a round section. The pattern is
normally used as a grip for a handle. Apprentice engineers often manufacture
screwdrivers. These have patterned handles, to provide a grip and this achieved
through the technique called knurling.



Chamfering Video     Machinists use chamfers to "ease" otherwise sharp edges,
both for safety and to prevent damage to the edges. A "chamfer" may sometimes be
regarded as a type of "bevel", and the terms are often used interchangeably.

It is also useful for a leading edge when fitting bearings, or other parts.