GEC 218
GEC 218
WORKSHOP TECHNOLOGY
(2 UNITS)
LECTURE NOTE MECHANICAL ENGINEERING PART
PREPARED BY
OKENIYI, JOSHUA OLUSEGUN
LECTURER MECHANICAL ENGINEERING PART
COLLEGE OF SCIENCE AND TECHNOLOGY
OTA
NIGERIA
SEPTEMBER 2007
module three machine TECHNOLOGYAnd he made ten bases of
brass;
And under the borders were four wheels;
And the axletrees of the wheels were joined to the base
And on the borders thereof, he graved cherubims, lions, and palm
trees,
According to the proportion of every one1King 7:27-36
3 machine TechnologyMachines, in general workshop usage, refer
to devices or system of devices with rigid moving parts that
perform or assist in performing some work in the form of
transmitting or modifying a workshop material, the workpiece.
Devices with no rigid moving parts are commonly considered tools,
or simply devices, not machines. Machines normally require some
energy source known as input and always accomplish some sort of
work known as output.3.1 Machining in engineering workshopMachining
in an engineering workshop could take any form of metal removal
processes that may include:i. Cutting offii. Drilling
iii. Turningiv. Planingv. Millingvi. Surface Grinding3.1.1
Cutting offThe step of cutting off is the first step in any given
machining operation in an engineering workshop. This is because
every machining operation will usually begin with a rough cut of a
blank, slug, or other workpiece to dimensions normally somewhat
larger than finish sizes to allow for stock removal. The machine
equipment for the cutting off may be used to create just one piece
or large numbers of blanks to begin the process of making a part,
which may be a turning screw, a gear or other integral part for a
machine, an attachment or fixture for drilling holes, a die for
stamping, an aluminium extrusion or any other workpiece. Though
cutting off operation may be performed on a variety of machines,
including the lathes, automatic screw machines, shears, presses,
flame cutters, and various high-tech systems such as lasers, water
jets and abrasive water jets, electro-discharge and
electro-chemical machines, nevertheless, most cutting off work
especially high production jobs is performed using some type of
mechanically powered sawing instrument. Machines for common cutting
off by sawing can be categorised into three, in accordance to how
they move their saw-teeth past the material being cut, as:
i. Circular blade saws the saw-teeth moves along the perimeter
of a flat, circular blade e.g. circular saw machines, (Figure
3.1(a)), radial cold saw, rotary saw, miter saw concrete saw,
abrasive saw;
ii. Reciprocating blade saws the blade reciprocates up and down
or forward and backward e.g. powered hacksaw (Figure 3.1(b)); iii.
Continuous band saw e.g. band saw (Figure 3.1(c)), chainsaw the
teeth are along one edge of a continuous band, Figure 3.1(d).
(a) (b) (c) (d)
Figure 3.1 Cutting saw machines (a) circular saw machine (b)
powered hacksaw (c) band saw (d) band saw blades3.1.2
DrillingDrilling can be described as the process of making
cylindrical holes in solid materials by the use of a cutting tools
known as drill bits. The drill bit is held gripped by a chuck at
one end of the drill, and is pressed against the target material
and rotated. The tip of the drill bit does the work of cutting into
the target material, slicing off thin shavings, as in twist drills
or auger bits, or grinding off small particles as obtainable in oil
drilling.The drill is a multi-edge cutting tool that cuts on the
point. The drills cutting edges, or lips, are provided with lip
clearance to permit the point to penetrate the workpiece as the
drill revolves. It may be fed into the work manually or
automatically.All drilling machines contain certain basic parts,
Figure 3.2, depending on the model of the drilling machine. The
main parts on the bench and floor models are the base, column or
pillar, table, and drilling head.
Figure 3.2 Basic parts of a drilling machinei. Base usually made
of cast iron, it provides stability for the machine and rigid
mounting for the column. The base is usually provided with holes so
that it may be bolted to a table or bench. The slots or ribs in the
base allow the work holding device or the workpiece to be fastened
to the base.ii. Column also known as pillar, it is an accurate
cylindrical post that fits into the base. The table, which is
fitted to the column, may be adjusted to any point between the base
and head. The drill press head is mounted near the top of the
column.
iii. Table or worktable, either round or rectangular in shape,
is used to support the workpiece to be machined. The table, whose
surface is at 90 to the column, may be raised, lowered, and
swiveled around the column. On some models, it is possible to tilt
the table in either direction for drilling holes on an angle. Slots
are provided in most tables to allow jigs, fixtures, or large
workpieces to be clamped directly to the table.
iv. Drilling Head The head, mounted close to the top of the
column, contains the motor, pulley and gear system and the
mechanism used to revolve the cutting tool and advance it into the
workpiece. These mechanisms include:
(a) The spindle, which is a round shaft that locates, holds and
drives the cutting tool, is housed in spindle sleeve, or quill the
end of the spindle may have a tapered hole to hold taper shank
tools or may be threaded or tapered for attaching a drill chuck;(b)
The spindle sleeve (also known as quill) does not revolve but
slides up and down inside the head to provide a downward feed for
the cutting tool; (c) The hand feed lever is used to control the
vertical movement of the spindle sleeve and the cutting tool;(d) A
depth stop attached to the spindle sleeve can be set to control the
depth that a cutting tool enters the workpiece.3.1.3 TurningTurning
is the machining process used to produce cylindrical components in
a lathe, whose basic parts are shown in Figure 3.3(a). Turning can
be done manually, or using a CNC (Computer Numerically Controlled)
machine.
When turning, the workpiece is held securely in a chuck or
between lathe centers. A turning tool, mounted on a holder and set
to a given depth of cut, is fed parallel to the axis of the work to
reduce the diameter of the workpiece. As the workpiece revolves and
the cutting tool is fed along the axis, material is separated by
the edge of the cutting tool, Figure 3.3(b), to produce precise
diameters and depths. Turning can be either on the outside of the
workpiece or on the inside (also known as boring) to produce
tubular components. Figure 3.3(c) shows a typical turning set-up of
a cylindrical workpiece, with multiple cross-sections, on a centre
lathe machine.
(a) (b)
(c)
Figure 3.3 Turning by the lathe (a) Basic parts of the centre
lathe machine (b) diagrammatic representation of material machining
by turning (c) typical turning set-up on the centre latheA typical
centre lathe has, as main machine elements shown in Figure 3.3(a)
the lathe bed, headstock assembly, the tailstock, the saddle, the
cross slide, the top slide and the apron.i. Bed the lathe bed is
the foundation of the complete machine. It is made from cast iron,
designed with thick sections to ensure complete rigidity and
freedom from vibration. On the top surface, two sets of guide ways
are provided, each set consisting of an inverted vee and a flat.
The outer guide ways guide the saddle, and the inner guide ways
guide the tailstock and keep it in line with the machine spindle.
The guide ways are hardened and accurately ground.
ii. Headstock the complete headstock assembly consists of a
box-shaped casting rigidly clamped to the guide ways of the bed and
contains the spindle, gears to provide a range of spindle speeds,
and levers for speed selection. The drive is obtained from the main
motor through vee belts and pulleys and a series of gears to the
spindle.iii. Tailstock the function of the tailstock is to hold a
centre when turning between centres or to act as a support at the
end of long workpieces or to hold drills and reamers when producing
holes. The tailstock can be moved on its guide ways along the
length of the bed and locked in any position. The tailstock quill
contains a Morse-taper bore to accommodate centres, chucks, drills
and reamers and is graduated on its outer top surface for use when
drilling to depth. It can be fed in or out by means of the
handwheel at the rear.iv. Saddle the saddle rests on top of the bed
and is guided by two guide ways which, for stability, are the two
furthest apart. Accurate movement is thus maintained relative to
the centre line of the spindle and tailstock for the complete
length of the bed. The top surface contains the dovetail slideway
into which the cross-slide is located and the cross-slide lead
screw, complete with hand wheel and graduated dial.
v. Cross-slide mounted in the dovetail slideway on the top
surface of the saddle, the cross-slide moves at right angles to the
centreline of the machine spindle. Adjustment for wear is provided
by a tapered gib strip, which can be pushed further into the slide
and slideway by the screw as wear takes place. Attached to the
underside of the cross-slide is the leadscrew nut through which
movement is transmitted from the leadscrew. Power feed is available
to the cross-slide.
vi. Top slide the top slide often referred to as the compound
slide, fits on its slideway and can be adjusted for wear by means
of a gib strip and adjusting screws. Movement is transmitted by the
leadscrew through a nut on the slideway. A toolpost, usually
four-way hand-indexing, is located on the top surface and can be
locked in the desired position by the locking handle. Movement of
this slide is usually quite short, however when used in conjunction
with the swivel base, it is used to turn short tapers.
vii. Apron the apron is attached to the underside of the saddle
at the front of the machine and contains the gears for transmission
of movement from the leadscrew and feed shaft. On the front are the
handles to engage and disengage the leadscrew and feed shaft. Also
mounted on the front is the handwheel for longitudinal traverse of
the carriage along the bed, this movement being transmitted through
gears to a rack fixed on the underside of the bed. The complete
assembly of apron, saddle and slides is known as the carriage.3.1.4
Planing
The cutting tool used in the planning machine or simply the
planer, Figure 3.4(a), is basically the same shape as the lathe
tool for machining similar materials. It should have the proper
rake and clearance angles ground on it to machine the workpiece
efficiently. The cutting action of a planer is illustrated in
Figure 3.4(b). The workpiece is moved back and forth under a
cutting tool, which is fed sideways a set amount at the end of each
table reversal.
The basic elements of the planing machine include the base, the
column, the reciprocating table and the head on which the planing
tool is mounted.
(a) (b)
Figure 3.4 Machining by planing (a) Planing machine (b) material
machining by planing3.1.5 MillingMilling is a machining operation
during which the workpiece is moved into the cutter on any of the x
or y or z-axis for material removal. A milling cutter is a
multi-tooth tool having several equally spaced cutting edges
(teeth) around its periphery. Each tooth may be considered to be a
single-point cutting tool and must have proper rake and clearance
angles to cut effectively.While being machined by milling, the
workpiece, held in a vise or fastened to the table, is fed into the
horizontal revolving cutter by hand or by automatic table feed. As
the work is fed into the cutter, each tooth makes successive cuts,
which produce a smooth flat or profiled surface depending on the
shape of the cutter used. There are four standard types of milling
machines. They are i. The bed type; ii. Column and knee; iii.
Horizontal; and iv. Vertical milling machines, Figure 3.5. The
controls on the vertical milling machine used in materials
processing consist of the following:
i. A magnetic power switch this must be reset if the main power
is interrupted.
ii. A spindle break to enable loosening of the spindle nut in
order to take the collet out of the chuck.
iii. A quill feed handle for manually feeding the cutter into
the stock.iv. A quill lock for locking the cutter in place.
Figure 3.5 The vertical milling machinev. A longitudinal feed
screw handle for moving the workpiece into the cutter on an
x-axis.
vi. A cross feed screw handle for moving the workpiece into the
cutter on a y-axis.
vii. A knee height adjustment screw for positioning the depth of
the cut.
viii. A high and low speed clutch knob.
ix. A back gear control knob.
x. A power feed engagement knob.
xi. A manual feed knob.
xii. A feed control knob.
xiii. A quill feed selector knob.
xiv. A draw bar knob.
3.1.6 Surface Grinding
Surface grinding is used to produce flat accurate surfaces and
can be carried out on all materials, hard or soft. There may be no
other way of removing metal from a hardened workpiece. It is
normally considered a finishing operation, but large machines are
used in place of milling and shaping machines to remove large
amounts of material.A typical surface grinder (Figure 3.6(a)) uses
a reciprocating table (Figure 3.6(b)) a grinding wheel (Figure
3.6(c)) and a cross-slide whose movements could be manually
operated by hand or through a provided automatic system of
operation e.g. hydraulic or electric system.
(a) (b) (c)
Figure 3.6 Machining by surface grinding (a) Surface grinding
machine (b) basic machine operation (c) grinding wheel operationThe
basic element of the surface grinding machine include
i. Base the base is a heavily ribbed box-section casting to
ensure rigidity and complete freedom from vibration. The bottom of
the base houses the hydraulic pump and fluid reservoir. At the rear
of the base is a vertical dovetail slideway which guides the
column. Two vee slideways on top of the base guide the saddle and
are widely spaced to maintain accuracy and rigidity.ii. Column the
column, guided on a dovetail slide, carries the wheelhead at its
top end and contains the motor and belt drive to the wheel spindle.
The column and wheelhead are raised and lowered through a screw and
nut from a handwheel on the front of the machine.
iii. Wheelhead the wheelhead carries the wheel spindle, which is
mounted in precision bearings. The complete grinding-wheel collet
assembly is fitted on a taper on the end of the spindle. Drive to
the spindle is by vee belt and pulley from the motor mounted in the
bottom of the column.
iv. Table The table is guided by the vee-and-flat slideway on
the saddle and can be manually operated with a handwheel. Automatic
reciprocation of the table is transmitted through a hydraulic
cylinder at variable speeds. Reversal of the table movement could
be set to give the required length of table stroke and position of
reversal.3.2 Practice questions 31. What do you understand by the
following terms in the workshop usage?i. Machine
ii. Drilling
iii. Turning
iv. Milling
2. Givei. Five machining processes in the workshop;
ii. Four standard types of milling machines;
iii. Three categories of cutting machines, with an example
each;
iv. Seven controls on the vertical milling machine
3. Describe brieflyi. Five basic parts of the drilling
machineii. Four mechanisms that are contained in the drilling head
of a drilling machine;
iii. Seven main machine elements of the lathe machine;iv. Four
basic elements of the planing machine;
v. Four basic elements of the surface grinding machine.4. What
is meant by CNC?
