workshop technology-course material

MIME 2230 Workshop Technology

Chapter 1

Safety in Workshop

(i) Introduction to Safety

Personal Safety

Always wear overalls in the workshop

Always protect the eyes by wearing goggles when using machinery.

Always wear safety boots in the workshop

Wear a suitable respiration when dust and fumes are present

Keep hair shorts or wear a cap.

Don’t wear rings or watches when working on a machine

Gloves should always be worn when handling sharp components.

Never wear gloves when operating machine tools.

Use hand cream to remove oil or grease from the hands.

Safety Precautions in Machines

Don’t start a machine without receiving operating instructions.

You have to know how to stop the machine before start it.

Make sure that all guards are in position.

Isolate the machine before starting repair work on it.

Do not lean on a machine whilst it is working.

Safety Clothing

Overalls Caps Gloves Boots and shoes Respirators Ear protection Goggles

Salalah College of Technology


Proper Clothing’s in Workshop

Mandatory signs

You can recognize these signs as they have a blue background colour. The symbol must be white. Figure shows five typical mandatory signs. These signs indicate things that you must do and precautions that you must take. These signs must be obeyed; you have no option in the matter. To disregard them is an offence in law as, again, you would be putting yourself at considerable risk.



Appearance

Clothing

For general workshop purposes a boiler suit is the most practical and safest form of clothing. However, to be completely effective certain precautions must be taken.

Long hair

Long hair is liable to be caught in moving machinery such as drilling machines and lathes. This can result in the hair and scalp being torn away which is extremely dangerous and painful. Permanent disfigurement will result and brain damage can also occur. Long hair is also a health hazard, as it is almost impossible to keep clean and free from infection in a workshop environment. Either adopts a short and more manageable head style or some sort of head covering that will keep your hair out of harm’s way.

Sharp tools

Sharp tools protruding from the breast pocket can cause severe wounds to the wrist. Such wounds can result in paralysis of the hand and fingers.

Buttons missing and loose cuffs

Since the overalls cannot be fastened properly, it becomes as dangerous as any other loose clothing and is liable to be caught in moving machinery. Loose cuffs are also liable to be caught up like any other loose clothing. They may also prevent you from snatching your hand away from a dangerous situation.

Hole in pocket

Tools placed in a torn pocket can fall through onto the feet of the wearer. Although this may not seem potentially dangerous, it could cause an accident by distracting your attention at a crucial moment.

Overalls too long

These can cause you to trip and fall, particularly when negotiating stairways.

Lightweight shoes



The possible injuries associated with lightweight and unsuitable shoes are: puncture wounds caused by treading on sharp objects; crushed toes caused by falling objects;

Hand protection

Your hands are in constant use and, because of this; they are constantly at risk handling dirty, oily, greasy, rough, sharp, hot and possibly corrosive and toxic materials. Gloves and ‘palms’ of a variety of styles and types of materials are available to protect your hands whatever the nature of the work.

Head and eye protection

As has already been stated, long hair is a serious hazard in a workshop. If it becomes entangled in a machine, the operator can be scalped. If you wish to retain a long hairstyle in the interests of fashion, then your hair must be contained in a close fitting cap. This also helps to keep your hair and scalp clean and healthy. When working on site, or in a heavy engineering erection shop involving the use of overhead cranes, all persons should wear a safety helmet complying with BS 2826. Even small objects such as nuts and bolts can cause serious head injuries when dropped from a height.



The hazard of long hair

(ii) Causes of Electrical shock

An electric shock from a 240 volt single-phase supply (lighting and office equipment) or a 415 volt three-phase supply (most factory machines) can easily kill you. Even if the shock is not sufficiently severe to cause death, it can still cause serious injury. The sudden convulsion caused by the shock can throw you from a ladder or against moving machinery. To reduce the risk of shock, all electrical equipment should be earthed or double insulated.

Further, portable power tools should be fed from a low-voltage transformer at 110 volts. The power tool must be suitable for operating at such a voltage. The transformer itself should be protected by a circuit breaker containing a residual current detector. The fuses and circuit breakers designed to protect the supply circuitry to the transformer react too slowly to protect the user from electric shock.



The electrical supply to a portable power tool should, therefore, be protected by a residual current detector (RCD). Such a device compares the magnitudes of the current flowing in the live and neutral conductors supplying the tool. Any leakage to earth through the body of the user or by any other route will upset the balance between these two currents. This results in the supply being immediately disconnected.

The sensitivity of residual current detectors is such that a difference of only a few mill amperes is sufficient to cut off the supply and the time delay is only a few microseconds. Such a small current applied for such a short time is not dangerous.

(iii) Fire Fighting

Fire fighting is a highly skilled operation and most medium and large firms have properly trained teams who can contain the fire locally until the professional brigade arrives. The best way you can help is to learn the correct fire drill, both how to give the alarm and how to leave the building. It requires only one person to panic and run in the wrong direction to cause a disaster.

Smoke is the main cause of panic. It spreads quickly through a building, reducing visibility and increasing the risk of falls down stairways. It causes choking and even death by asphyxiation. Smoke is less dense near the floor: as a last resort crawl. To reduce the spread of smoke and fire, keep fire doors closed at all times but never locked. The plastic materials used in the finishes and furnishings of modern buildings give off highly toxic fumes. Therefore it is best to leave the building as quickly as possible and leave the fire fighting to the professionals who have breathing apparatus.

Saving human life is more important than saving property.

Fire extinguishersThe normally available fire extinguishers and the types of fire they can be used for are as

follows.

WaterUsed in large quantities water reduces the temperature and puts out the fire. The steam

generated also helps to smother the flames as it displaces the air and therefore the oxygen essential to the burning process. However, for various technical reasons, water should be used only on burning solids such as wood, paper and some plastics. A typical hose point and a typical pressurized water extinguisher are shown in this figure.



Foam extinguishersThese are used for fighting oil and chemical fires. The foam smothers the flames and

prevents the oxygen in the air from reaching the burning materials at the seat of the fire. Water alone cannot be used because oil floats on the water and this spreads the area of the fire. A typical foam extinguisher is shown in Fig. (a).Note: Since both water and foam are electrically conductive, do not use them on fires associated with electrical equipment or the person wielding the hose or the extinguisher will be electrocuted.

Carbon dioxide (CO2) extinguishersThese are used on burning gases and vapours. They can also be used for oil and chemical

fires in confined places. The carbon dioxide gas replaces the air and smothers the fire. It can be used only in confined places, where it cannot be displaced by draughts. Note: If the fire cannot breathe neither can you, so care must be taken to evacuate all living creatures from the vicinity before operating the extinguisher. Back away from the bubble of CO2 gas as you operate the extinguisher, do not advance towards it. Figure (b) shows a typical CO2 extinguisher.

Vaporizing liquid extinguishersThese include CTC, CBM and BCF extinguishers. The heat from the fire causes rapid

vaporization of the liquid sprayed from the extinguisher and this vapour displaces the air and smothers the fire. Since a small amount of liquid produces a very large amount of vapour, this is a very efficient way of producing the blanketing vapour. Any vapour that will smother the fire will also smother all living creatures which must be evacuated before using such extinguishers. As with CO2 extinguishers always back away from the bubble of vapour, never advance into it.



Vaporizing liquid extinguishers are suitable for oil, gas, vapour and chemical fires. Like CO 2

extinguishers, vaporizing liquid extinguishers are safe to use on fires associated with electrical equipment. A typical example of a vaporizing liquid extinguisher is shown in Fig. (c).

Dry powder extinguishersThese are suitable for small fires involving flammable liquids and small quantities of

solids such as paper. They are also useful for fires in electrical equipment, offices and kitchens since the powder is not only non-toxic, it can be easily removed by vacuum cleaning and there is no residual mess. The active ingredient is powdered sodium bicarbonate (baking powder) which gives off carbon dioxide when heated. A typical example of a dry powder extinguisher is shown in Fig. (d).

Various Types of Fire Extinguishers

a) Foam type b) Co2 type c) Vaporizing liquid d) Dry powder



Chapter 2

Measuring Devices

Vernier Caliper

The Vernier Caliper is a precision instrument that can be used to measure internal and external distances extremely accurately. The example shown below is a manual caliper. Measurements are interpreted from the scale by the user. The manual version has both an imperial and metric scale.To measure outer dimensions of an object, the object is placed between the jaws, which are then moved together until they secure the object. The screw clamp may then be tightened to ensure that the reading does not change while the scale is being read.The first significant figures are read immediately to the left of the zero of the vernier scale and the remaining digits are taken as the vernier scale division that lines up with any main scale division.

.



Examples:

Example-1: In the figure, the first significant figures are taken as the main scale reading to the left of the vernier zero, i.e. 37 mm. The remaining two digits are taken from the vernier scale reading that lines up with any main scale reading, i.e. 46 on the vernier scale. Thus the reading is 37.46 mm.

RULE:TOTAL READING = [MAIN SCALE READING + (VERNIER SCALE READING X LEAST COUNT)]

= 37 + (23 X .02) = 37.46 mm

Example-2: In the figure, the first significant figures are taken as the main scale reading to the left of the vernier zero, i.e. 34 mm. The remaining two digits are taken from the vernier scale reading that lines up with any main scale reading, i.e. 60 on the vernier scale. Note that the zero must be included because the scale can differentiate between fiftieths of a millimetre. Therefore the reading is 34.60 mm.




= 34 + (30 X .02) = 34.60 mm

Example:-3: In the figure the zero and the ten on the vernier scale both line up with main scale readings. Hence the reading is 40.00mm.


= 40 + (0 X .02) = 40 mm

Home Work:

The figures shown below refer to some readings taken during the measurement. Find the readings and show them step by step in the form of the rule.

Figure-1:



Figure-2:

Figure-3:

Micrometer Screw Gauge

The micrometer screw gauge is used to measure even smaller dimensions than the vernier calipers. The micrometer screw gauge also uses an auxiliary scale (measuring hundredths of a millimeter) which is marked on a rotary thimble. Basically it is a screw with an accurately constant pitch (the amount by which the thimble moves forward or backward for one complete revolution). The micrometers in our laboratory have a pitch of 0.50 mm (two full turns are required to close the jaws by 1.00 mm). The rotating thimble is subdivided into 50 equal divisions. The thimble passes through a frame that carries a millimeter scale graduated to 0.5 mm. The jaws can be adjusted by rotating the thimble using the small ratchet knob. This includes a friction clutch which prevents too much tension being applied. The thimble must be rotated through two revolutions to open the jaws by 1 mm.



In order to measure an object, the object is placed between the jaws and the thimble is rotated using the ratchet until the object is secured. Note that the ratchet knob must be used to secure the object firmly between the jaws, otherwise the instrument could be damaged or give an inconsistent reading. The manufacturer recommends 3 clicks of the ratchet before taking the reading. The lock may be used to ensure that the thimble does not rotate while you take the reading.

The first significant figure is taken from the last graduation showing on the sleeve directly to the left of the revolving thimble. Note that an additional half scale division (0.5 mm) must be included if the mark below the main scale is visible between the thimble and the main scale division on the sleeve. The remaining two significant figures (hundredths of a millimeter) are taken directly from the thimble opposite the main scale.

Example-1:

The reading is 7.38 mm.



In figure the last graduation visible to the left of the thimble is 7 mm and the thimble lines up with the main scale at 38 hundredths of a millimeter (0.38 mm); therefore the reading is 7.38 mm.

Example-2:

Figure: The reading is 7.72 mm.

In figure the last graduation visible to the left of the thimble is 7.5 mm; therefore the reading is 7.5 mm plus the thimble reading of 0.22 mm, giving 7.72 mm.

Example-3:

The reading is 3.46 mm. In figure the main scale reading is 3 mm while the reading on the drum is 0.46 mm; therefore, the reading is 3.46 mm.



Example-4:

Figure: The reading is 3.56 mm.

Example-5: In the figure, 0.5 mm division is visible below the main scale; therefore the reading is 3.5 mm + 0.06 mm = 3.56 mm.

Home Work:

Find the reading by seeing the figure.

Problem-1:



Chapter 3

Limits, Fits and Tolerance

Limits

This figure explains the terminologies used in defining tolerance and limit. The zero line, shown in the figure, is the basic size or the nominal size. The definition of the terminologies is given below. For the convenience, shaft and hole are chosen to be two mating components.

Tolerance

Tolerance is the difference between maximum and minimum dimensions of a component, i.e., between upper limit and lower limit. Depending on the type of application, the permissible variation of dimension is set as per available standard grades. Tolerance is of two types, bilateral and unilateral. When tolerance is present on both sides of nominal size, it is termed as bilateral; unilateral has tolerance only on one side. The figure shows the types of tolerance. 50 is a typical example of specifying tolerance for a shaft 0xy0 of nominal diameter of 50mm. First two values denote unilateral tolerance and the third value denotes bilateral tolerance. Values of the tolerance are given as x and y respectively.



Allowance

It is the difference of dimension between two mating parts.

Upper deviation

It is the difference of dimension between the maximum possible size of the component and its nominal size.

Lower deviation

Similarly, it is the difference of dimension between the minimum possible size of the component and its nominal size.

Fundamental deviation

It defines the location of the tolerance zone with respect to the nominal size. For that matter, either of the deviations may be considered.

Problem

In a turning operation on a lathe for a job, following details were collected.

Basic size = 40 mm; Upper deviation = 0.3mm; Lower deviation = 0.5 mm; Find the maximum limit, minimum limit and tolerance for the given situation.

Solution:

Basic size=40mm; Upper deviation = 0.3 mm; Lower deviation = 0.5 mm;

Maximum limit = Basic size + Upper deviation =40 +0.3 = 40.3 mm

Minimum limit = Basic size - Lower deviation = 40 – 0.5 = 39.5 mm

Tolerance = 40.3 – 39.5 = 0.8 mm

Fit System

We have learnt above that a machine part when manufactured has a specified tolerance. Therefore, when two mating parts fit with each other, the nature of fit is dependent on the limits of tolerances and fundamental deviations of the mating parts. The nature of assembly of two mating parts is defined by three types of fit system, Clearance Fit, Transition Fit and Interference Fit.

There are two ways of representing a system. One is the hole basis and the other is the shaft basis. In the hole basis system the dimension of the hole is considered to be the datum, whereas, in the shaft basis system dimension of the shaft is considered to be the datum. The holes are normally made by drilling, followed by reaming. Therefore, the dimension of a hole is



fixed due to the nature of the tool used. On the contrary, the dimension of a shaft is easily controllable by standard manufacturing processes. For this reason, the hole basis system is much more popular than the shaft basis system.

Clearance Fit

In this type of fit, the shaft of largest possible diameter can also be fitted easily even in the hole of smallest possible diameter.

Transition Fit

In this case, there will be a clearance between the minimum dimension of the shaft and the minimum dimension of the hole. If we look at the figure carefully, then it is observed that if the shaft dimension is maximum and the hole dimension is minimum then an overlap will result and this creates a certain amount of tightness in the fitting of the shaft inside the hole. Hence, transition fit may have either clearance or overlap in the fit.

Interference Fit

In this case, no matter whatever may be the tolerance level in shaft and the hole, there is always a overlapping of the matting parts. This is known as interference fit. Interference fit is a form of a tight fit.



Chapter 4

Machine tools

Introduction to machining and machine tools

Material removal processes form another most important group of processes. The basic technique in this is to cut away the unwanted portion of the material to get the required shape. Cutting tools made of special materials are used in all these processes.

The special feature of the machining processes is that the required shape is generated by the complex motion of the cutting tool and the work piece. It has to be understood that large forces are required to cut metals. It will not be possible to apply these large forces by hand operations. Therefore, special machines are used to cut metals into different shapes with these tools. They are called machine tools

Machine tools are made to carry out a given set of cutting operations. They have facilities to hold the cutting tool and the work piece. They also provide the necessary motions between the cutting tool and the work piece. Generation of different complex shapes requires different types of movements for the tool and the workpiece. It is impossible to provide all possible motions on one machine tool. Different machine tools are made with different sets of motions between the tool and the workpiece. Therefore, a particular type of operations only can be carried out on a given machine tool. Similarly, the shape and operation of the cutting tools also will be different in different machining operations. The most common machining operations, machine tools used for them, cutting tools and the type of the tools are listed below:

Machining operation

Machine tool Cutting toolType of cutting

tool

Turning Lathe Turning tool Single point

Shaping Shaper Shaping tool Single point

Drilling Drilling machine Drill bit Multi-point

Milling Milling machine Milling cutter Multi-point

GrindingGrinding machine

Grinding wheel Multipoint

Further details about these processes are presented in the following sections



Constructional features of the center lathe

A center lathe is a machine tool designed and manufactured to produce cylindrical, conical (tapered) and plain (flat) surfaces. It produces these surfaces using a single point tool. It can also be used to cut screw threads. Figure 5.1 shows a typical centre lathe and names the more important features. You can see that it is built up from a number of basic units that have to be accurately aligned during manufacture in order that precision turned components may be produced.

Figure 5.1 Centre lathe

The bed

A typical lathe bed is a strong, bridge-like member, made of high grade cast iron and is heavily ribbed to give it rigidity. Since these slideways locate, directly or indirectly, most of the remaining units, they are responsible for the fundamental alignments of the machine. For this reason the bed slideways must be manufactured to high dimensional and geometrical tolerances. Further, the lathe must be installed with care to avoid distortion of the bed.

The headstock

The headstock, or ‘fast-head’ as it is sometimes called, is a box-like casting supporting the spindle and containing a gearbox through which the spindle is driven and its speed adjusted to suit the work being turned. The spindle nose is machined externally to carry various workholding devices such as chucks and faceplates.



The tailstock

The tailstock, or loose head as it is sometimes called, is located at the opposite end of the bed to the headstock. It can be moved back and forth along its slideways on the bed and can be clamped in any convenient position. It consists of a cast iron body in which is located the barrel or poppet. The barrel is hollow and is bored with a morse taper. This taper locates the taper shank of the dead centre and it can also locate the taper shanks of tooling such as drill chuck, taper shank drill, die holders, etc.

The bore is coaxial with the taper bore and nose of the spindle. That is, they have a common axis that is parallel to the bed slideways. This is a basic alignment of a lathe. Figure 5.2 shows a section through a typical tailstock. The barrel is given a longitudinal movement within the tailstock body by means of a screw and hand wheel. The screw also acts as an ejector for any device inserted in the taper of the barrel. The barrel can be locked in any convenient position within its range of movement. The base of the tailstock has adjusting screws that provide lateral movement. This enables the tailstock to be offset for taper turning.

Figure 5.2 Centre lathe tailstock

The carriage

A typical lathe carriage is shown in Fig. 5.3. This consists of a saddle that lies across the bed of the lathe and an apron that hangs down in front of the saddle and carries most of the carriage controls.



Figure 5.3 Carriage

The carriage moves along the bed of the lathe on the bed slideways. Its movement is parallel to the common axis of the headstock spindle and the tailstock barrel. This movement is used when turning cylindrical components.

The cross-slide is situated on top of the saddle and its movement is perpendicular (at right angles) to the common axis of the headstock spindle and tailstock barrel. This movement is used to provide ‘infeed’ for the cutting tool when turning cylindrical components. It is also used to face across the ends (faces) of components to provide plain (flat) surfaces.

The compound slide, which is also called the top-slide, is mounted on top of the cross-slide. It is used to control the ‘in-feed’ of the cutting tool when facing. It also has a swivel base and can be set at an angle when turning short, steep tapers such as chamfers.

The apron carries the controls for engaging and disengaging the power traverse for the carriage and the power cross-feed for the cross-slide. It also carries the control for engaging and disengaging the half-nut when screw cutting from the lead screw.

The tool post

The tool post is mounted on top of the compound slide and carries the cutting tool. Figure 5.4 shows the four types most commonly used. The tool post shown in Fig. 5.4(a) is simple and robust but not much used nowadays other than on small, low-cost lathes. The height of the tool can be adjusted only by adding or removing packing and shims until the tool is at the correct height. The tool post shown in Fig. 5.4(b) is commonly used on light-duty lathes. The tool height is quickly and easily adjusted by rocking the boat-piece in its spherical seating. Unfortunately this type of tool post lacks rigidity due to the overhang of the tool. The four-way turret tool post shown in Fig. 5.4(c) saves time when making a batch of components. The quick release tool post



shown in Fig. 5.4(d) is increasingly used. An unlimited number of tools can be preset in the holders ready for use. Tool height is quickly and easily adjusted by means of a screw.

Figure 5.4 Centre lathe tool posts: (a) English (clamp) type tool post; (b) American (pillar) type tool post; (c) turret (four ways) type tool post; (d) quick release type tool post

Work holding devices (centers)

Holding work between centres is the traditional method of workholding from which the centre lathe gets its name. This method of workholding is shown in Fig. 5.5. The centres locate the work in line with the common axis, and the work is driven by the catch plate on the spindle nose and a carrier on the workpiece. The centres are located in morse tapers to ensure concentricity with the bores of the spindle nose and the tailstock barrel. To ensure true running of the workpiece, the centres and the bores must be carefully cleaned before the centres are inserted. The tailstock centre does not rotate so it is made from hardened steel to prevent wear. It must be suitably lubricated. The headstock centre rotates with the spindle so there should be no wear and a hard centre is not necessary.



Figure 5.5 Workholding between centres

Workholding devices (self-centring chuck)

Figure 5.6 shows the constructional details of a three-jaw, selfcentring chuck, used for holding cylindrical and hexagonal workpieces. You can see that the scroll not only clamps the component in place, it also locates the component as well. Unfortunately, if the scroll becomes

Figure 5.6 The three-jaw, self-centring chuck.

Work holding devices (collets)

Collets of the type as shown in Fig. 5.7 are located in the taper bore of the spindle nose either directly or in a tapered adapter sleeve. The range of movement is very small and a separate collet is required for each bar size. The collets can be either pushed into the taper by a collar



Figure 5.7 The split-collet chuck: (a) split (spring) collet; (b) collet chuck for a simple plain nose spindle (typical of small instrument lathes) tightening the collar forces the collet back into the taper bore of the sleeve which closes the collet down onto the workpiece

5.2.9 Workholding devices (faceplate)

The workholding devices previously described are designed so that a diameter may be machined true to another existing diameter. However, the faceplate enables a component to be mounted so that the workpiece may be turned either parallel or perpendicular to a previously machined flat surface.

Figure 5.8 The faceplate: (a) balanced work; (b) unbalanced work; (c) positioning the balance



Lathe tool profiles

The profile of a lathe tool is the shape of the tool when viewed from above. Figure 5.9 shows a selection of lathe tools and states their typical applications. A lathe tool is selected to suit the job to be done. The rake angle is indicated by the letter R and the direction of the rake is indicated by the associated arrow.

Figure 5.9 Lathe tool profiles: these tools are right handed; left-hand tools cut towards the tailstock; the arrows indicate the rake angle (R) of each tool

Lathe operations

FACING: The tool is fed radially into the rotating work on one end to create a flat surface on the end.

TAPER TURNING: The tool is feed in angle to create a conical shape. CONTOUR TURNING: Instead of feeding the tool along a straight line parallel to the axis

of rotation as in turning the tool follows a contour. FORM TURNING: Forming : The tool has a shape that is imparted to the work by plunging

the tool radially into the work. CHAMFERING: The cutting edge of the tool is used to cut an angle on the corner of the

cylinder. CUTOFF: The tool is fed radially into the rotating work at some location along its length to

cut off the end of the part. (parting) THREADING: A pointed tool is fed linearly across the outside surface of the rotating

workpart in a direction parallel to the axis of rotation at a large effective feed rate. BORING: A single point tool is fed linearly, parallel to the axis of rotation, on the inside

diameter of an existing hole in the part. DRILLING: Can be performed by feeding the drill into the rotating work along its axis. KNURLING: Not a machining operations, but it is a metal forming operation used to

produce a regular cross-hatched pattern into the work surface.



Figure 5.10 Lathe operations

Drilling Machine



Constructional features of the Drilling Machine

Drilling is a process of making holes of different sizes. A special tool called drill bit is used for drilling. The machine tool used for this is known as drilling machine.

The main disadvantage of drilling is that it is not possible to make holes of any odd size. Drill bits are available in standard sizes. The size that is close to the required size of the hole is to be selected for making the hole. In addition, the surface quality is not very good in drilling.

However, drilling is a simple process. The drilling machine also is not very complex. It can be readily used to make holes of different sizes on different jobs. The operator need not be skilled.

5.3.1 Principal cutting motions in drilling

The principal cutting motions involved in the drilling process are shown in Fig. 5.11.

The drill hit is made out of a cylinder, with two grooves spiraling around it. Two cutting edges are formed at the end of the drill bit. The two edges are twisted and joined in an end cutting edge called chisel edge. Therefore, drill bits are multi-point cutting tools.

The main cutting motion in drilling is rotation of the drill bit about its own axis. When it is rotated, the two cutting edges remove small layers of the work material. The cut material comes out in the form of chips. These chips ravel along the groves and finally come out of the hole being drilled.

Fig. 5.11 Principal cutting motions in drilling



The other motion required for drilling is the ability to move the rotating dnll bit into and out of the work piece. This is called the feed motion. This will help in controlling the depth of the drilled hole.

5.3.2 Drilling machine

The construction of the drilling machine can be understood from Fig. 5.12. It can be seen that the drilling machine is made of a base, supporting a column and a drilling head mounted on the column. A motor is mounted at the top of the column. This motor is connected through some driving mechanisms to the main spindle of the machine. This vertical spindle rotates when the motor is switched on. The drill bit can be fixed into the spindle. When the spindle rotates, the drill bit also rotates. This is how the basic cutting motion in drilling is achieved.

A special mechanism is used to provide the feed motion to the rotating drill bit. By using the handle fixed to the drill head, the spindle and along with it, the drill bit can be moved up and down. Further description of the different parts of the drilling machine is given below.

Base: This is a solid block mounted on the floor. This gives support for the machine. Column: This is usually a round column erected vertically on the base. This supports the

drill worktable, c .11 head and other driving mechanisms. Worktable: This is mounted on the column. This can be raised or lowered on the

column. This will help in working with jobs of different sizes. The worktable can also be rotated about the column. This will help in properly locating the drill bit at the place where the required hole is to be made. A vice is fixed on the worktable. The work piece can be fixed in the vice.

Fig. 5.12 Drilling machine



Drill head: This contains the main spindle of the machine. The main spindle is connected through some mechanisms to the driving motor. The control switches are also fixed on the drill head.

Spindle: This is a shaft mounted in the drill head. This rotates about its own axis when the machine is switched on. It can be rotated at different speeds by using the gearbox provided in the drill head. It has a tapered hole at the bottom. This tapered hole can be used to fix the drill bit into the spindle.

Drill bit: This is the cutting tool used for drilling. It is fixed in the tapered hole of the spindle. Some times, a special chuck, called drill chuck is fixed in the spindle. The drill chuck can be used to fix drill bits of different sizes.

Feed handle: This handle can be used to raise or lower the drill bit when it is cutting a hole. This helps in controlling the depth of the hole being machined.

Operations that can be performed on a drilling machine

Fig. 5.13 shows some of the operations that can be performed on a drilling machine.

Drilling: This is the process of making holes. Core drilling: This is the process of enlarging an existing hole. The drill bit used in this

case is flat at the bottom. It does not have any chisel edge. Step drilling: This is the process of making a stepped hole with different diameters.

Special stepped drill bit is used for this purpose. Counter boring: This is the process of enlarging the top portion of an already drilled hole.

Special counter boring tools are used for this purpose. the front portion of the tool goes into the existing hole and guides the counter boring tool.

Counter sinking: This is the process of enlarging the top of. hole j a tapered shape. This tapered enlargement takes the tapered screw head.

Reaming: Reaming is the process of correcting the hole produced by drilling. It is mentioned that drilling produces bad surfaces. The surface quality of the drilled hole is improved by reaming. It will also correct the size of the hole. Special tools called reamers are used for this purpose.

Center drilling: This is the process of marking the center for further operations. Special tools are used for this purpose.

Gun drilling: This is the process of making very deep holes. Special hallow drill bits are used for this purpose.



Fig. 5.13 Drilling operations

MILLING MACHINE

Introduction

Milling is the process of machining flat, curved, or Milling machines are basically irregular surfaces by feeding the workpiece against a rotating horizontal cutter containing a number of cutting edges. Most machines consist basically of a motor driven spindle, mounts and revolves the milling cutter, and a reciprocating adjustable worktable, which mounts and feeds the workpiece.

The milling machine removes metal with a revolving cutting tool called a milling cutter. With various attachments, milling machines can be used for boring, slotting, circular milling dividing, and drilling. This machine can also be used for cutting keyways, racks and gears and for fluting taps and reamers.

Types

Milling machines are basically classified as being horizontal or vertical to indicate the axis of the milling machine spindle. These machines are also classified as knee-type, ram-type, manufacturing or bed type, and planer-type milling machines. Most machines have self-contained electric drive motors, coolant systems, variable spindle speeds, and power operated table feeds.



SAFETY RULES FOR MILLING MACHINE

Do not make contact with the revolving cutter.

Place a wooden pad or suitable cover over the table surface to protect it from possible damage.

Use the buddy system when moving heavy attachments



Milling cutter Nomenclature

Pitch is determined by the number of teeth. The tooth face is the forward facing surface of the tooth that forms the cutting edge.Cutting edge is the angle on each tooth that performs the cutting.Land is the narrow surface behind the cutting edge on each tooth.Rake angle is the angle formed between the face of the tooth and the centerline of the cutter. The rake angle defines the cutting edge and provides a path for chips that are cut from the workpiece.Primary clearance angle is the angle of the land of each tooth measured from a line tangent to the centerline of the cutter at the cutting edge. This angle prevents each tooth from rubbing against the workpiece after it makes its cut. This angle defines the land of each tooth and provides additional clearance for passage of cutting oil and chips.Hole diameter determines the size of the arbor necessary to mount the milling cutter.Plain milling cutters that are more than 3/4 inch in width are usually made with spiral or helical teeth. A plain spiral-tooth milling cutter produces a better and smoother finish and requires less power to operate. A plain helicaltooth milling cutter is especially desirable when milling an uneven surface or one with holes in it.

Types of teeth:



The teeth of milling cutters may be made for right-hand or left-hand rotation, and with either right-hand or left-hand helix. Determine the hand of the cutter by looking at the face of the cutter when mounted on the spindle. A right-hand cutter must rotate counterclockwise; a left-hand cutter must rotate clockwise. The right-hand helix is shown by the flutes leading to the right; a left-hand helix is shown by the flutes leading to the left. The direction of the helix does not affect the cutting ability of the cutter, but take care to see that the direction of rotation is correct for the hand of the cutter.



Saw Teeth

Saw teeth are either straight or helical in the smaller sizes of plain milling cutters, metal slitting saw milling cutters, and end milling cutters. The cutting edge is usually given about 5 degrees primary clearance. Sometimes the teeth are provided with off-set nicks which break up chips and make coarser feeds possible.

Helical Milling Cutters

The helical milling cutter is similar, to the plain milling cutter, but the teeth have a helix angle of 45° to 60°. The steep helix produces a shearing action that results in smooth, vibration-free cuts. They are available for arbor mounting, or with an integral shank with or without a pilot. This type of helical cutter is particularly useful for milling elongated slots and for light cuts on soft metal.

Metal Slitting Saw Milling Cutter

The metal slitting saw milling cutter is essentially a very thin plain milling cutter. It is ground slightly thinner toward the center to provide side clearance. These cutters are used for cutoff operations and for milling deep, narrow slots, and are made in widths from 1/32 to 3/16 inch.

Side Milling Cutter

Side milling cutters are essentially plain milling cutters with the addition of teeth on one or both sides. A plain side milling cutter has teeth on both sides and on the periphery. When teeth are added to one side only, the cutter is called a half-side milling cutter and is identified as being either a right-hand or left-hand cutter. Side milling cutters are generally used for slotting and straddle milling.

Interlocking tooth side milling cutters and staggered tooth side milling cutters are used for cutting relatively wide slots with accuracy. Interlocking tooth side milling cutters can be repeatedly sharpened without changing the width of the slot they will machine.

End Milling Cutter

The end milling cutter, also called an end mill, has teeth on the end as well as the periphery. The smaller end milling cutters have shanks for chuck mounting or direct spindle mounting. End milling cutters may have straight or spiral flutes. Spiral flute end milling cutters are classified as left hand or right-hand cutters depending on the direction of rotation of the flutes. If they are small cutters, they may have either a straight or tapered shank.

T-Slot Milling Cutter

The T-slot milling cutter is used to machine T-slot grooves in worktables, fixtures, and other holding devices. The cutter has a plain or side milling cutter mounted to the end of a



narrow shank. The throat of the T-slot is first milled with a side or end milling cutter and the headspace is then milled with the T-slot milling cutter.

Woodruff key slot Milling Cutter

The Woodruff key slot milling cutter is made in straight, tapered-shank, and arbor-mounted types. The most common cutters of this type, under 1 1/2 inches in 1/2 circle or less. The size of the cutter is specified by the diameter, are provided with a shank. They have teeth on the periphery and slightly concave sides to provide clearance. These cutters are used for milling semi cylindrical keyways in shafts.

Angle Milling Cutter

The angle milling cutter has peripheral teeth which are neither parallel nor perpendicular to the cutter axis. Common operations performed with angle cutters are cutting V-notches and serrations. Angle cutters may be single-angle milling cutters or double-angle milling cutters. The single-angle cutter contains side-cutting teeth on the flat side of the cutter. The angle of the cutter edge is usually 30°, 45°, or 60°, both right and left. Double-angle cutters have included angles of 45, 60, and 90 degrees.

Gear Hob

The gear hob is a formed tooth milling cutter with helical teeth arranged like the thread on a screw. These teeth- are fluted to produce the required cutting edges. Hobs are generally used for such work as finishing spur gears, spiral gears, and worm gears. They may also be used to cut ratchets and spline shafts.

Concave and Convex Milling Cutter

Concave and convex milling cutters are formed tooth cutters shaped to produce concave and convex contours of 1/2 circle or less. The size of the cutter is specified by the diameter of the circular form the cutter produces.

Corner Rounding Milling Cutter

The corner-rounding milling cutter is a formed tooth cutter used for milling rounded corners on workplaces up to and including one-quarter of a circle. The size of the cutter is specified by the radius of the circular form the cutter produces, such as concave and convex cutters generally used for such work as finishing spur gears, spiral gears, and worm wheels. They may also be used to cut ratchets and spline shafts.

Special Shaped-Formed Milling Cutter

Formed milling cutters have the advantage of being adaptable to any specific shape for special operations. The cutter is made especially for each specific job. In the field, a fly cutter is



formed by grinding a single point lathe cutter bit for mounting in a bar, holder, or fly cutter arbor. The cutter can be sharpened many times without destroying its shape.

Indexing

Indexing is the process of evenly dividing the circumference of a circular workpiece into equally spaced divisions, such as in cutting gear teeth, cutting splines, milling grooves in reamers and taps, and spacing holes on a circle. The index head of the indexing fixture is used for this purpose.

Index Head

The index head of the indexing fixture contains an indexing mechanism which is used to control the rotation of the index head spindle to space or divide a workpiece accurately. A simple indexing mechanism consists of a 40-tooth worm wheel fastened to the index head spindle, a single-cut worm, a crank for turning the worm shaft, and an index plate and sector. Since there are 40 teeth in the worm wheel, one turn of the index crank causes the worm, and consequently, the index head spindle to make 1/40 of a turn; so 40 turns of the index crank revolve the spindle one full turn.

Index Plate

The indexing plate is a round plate with a series of six or more circles of equally spaced holes; the index pin on the crank can be inserted in any hole in any circle. With the interchangeable plates regularly furnished with most index heads, the spacing necessary for most gears, bolt heads, milling cutters, splines, and so forth can be obtained. The following sets of plates are standard equipment.



Brown and Sharpe type consists of 3 plates of 6 circles each drilled as follows:

Plate I -15, 16, 17, 18, 19, 20 holes Plate 2-21, 23, 27, 29, 31, 33 holes Plate 3-37, 39, 41, 43,47,49 holes

Cincinnati type consists of one plate drilled on both sides with circles divided as follows

First side -24, 25, 28, 30, 34, 37,38, 39,41,42,43 holes Second side -46, 47, 49, 51, 53, 54, 57, 58, 59, 62, 66 holes.

Sector

The sector indicates the next hole in which the pin is to be inserted and makes it unnecessary to count holes when moving the index crank after each cut. It consists of two radial, beveled arms which can be set at any angle to each other and then moved together around the center of the index plate. Suppose that, it is desired to make a series of cuts, moving the index crank 1 1/4 turns after each cut. Since the circle illustrated has 20 holes, turn the crank one full turn plus five spaces after each cut, Set the sector arms to include the desired fractional part of a turn or five spaces between the beveled edges of its arms, as shown. If the first cut is taken with the index pin against the left-hand arm, to take the next cut, move the pin once against the right-hand arm of the sector. Before taking the second cut, move the arms so that the left-hand arm is again against the pin; this moves the right-hand arm another five spaces ahead of the pin. Then take the second cut, and repeat the operation until all the cuts have been completed.

NOTE: It is good practice always to index clockwise on the plate to eliminate backlash.

Plain Indexing

The following principles apply to basic indexing of work pieces: Suppose it is desired to mill a project with eight equally spaced teeth. Since 40 turns of the index crank will turn the



spindle one full turn, l/8th of 40 or 5 turns of the crank after each cut will space the gear for 8 teeth, If it is desired to space equally for 10 teeth, 1/10 of 40 or 4 turns would produce the correct spacing.

The same principle applies whether or not the divisions required divide equally into 40, For example, if it is desired to index for 6 divisions, 6 divided into 40 equals 6 2/3 turns; similarly, to index for 14 spaces, 14 divided into 40 equals 2 6/7 turns. These examples may be multiplied indefinitely and from them the following rule is derived: to determine the number of turns of the index crank needed to obtain one division of any number of equal divisions on the workpiece, divide 40 by the number of equal divisions desired (provided the worm wheel has 40 teeth, which is standard practice).

Direct Indexing

The construction of some index heads permits the worm to be disengaged from the worm wheel, making possible a quicker method of indexing called direct indexing. The index head is provided with a knob which, when turned through part of a revolution, operates an eccentric and disengages the worm. Direct indexing is accomplished by an additional index plate fastened to the index head spindle. A stationary plunger in the index head fits the holes in this index plate. By moving this plate by hand to index directly, the spindle and the workpiece rotate an equal distance. Direct index plates usually have 24 holes and offer a quick means of milling squares, hexagons, taps, and so forth. Any number of divisions which is a factor of 24 can be indexed quickly and conveniently by the direct indexing method.

Differential Indexing

Sometimes, a number of divisions is required which cannot be obtained by simple indexing with the index plates regularly supplied. To obtain these divisions, a differential index head is used. The index crank is connected to the worm shaft by a train of gears instead of a direct coupling as with simple indexing. The selection of these gears involves calculations similar to those used in calculating change gear ratio for lathe thread cutting.

Indexing in Degrees

Workpieces can be indexed in degrees as well as fractions of a turn with the usual index head. There are 360 degrees in a complete circle and one turn of the index crank revolves the spindle 1/40 or 9 degrees. Therefore, 1/9 turn of the crank rotates the spindle 1 degree. Workpieces can therefore be indexed in degrees by using a circle of holes divisible by 9. For example, moving the crank 2 spaces on an 18-hole circle, 3 spaces on a 27-hole circle, or 4 spaces on a 36-hole circle will rotate the spindle 1 degree, Smaller crank movements further subdivide the circle: moving 1 space on an 18-hole circle turns the spindle 1/2 degree (30 minutes), 1 space on a 27-hole circle turns the spindle 1/3 degree (20 minutes), and so forth.



Indexing Operations

The following examples show how the index plate is used to obtain any desired part of a whole spindle turn by plain indexing, Milling a hexagon. Using the rule previously given, divide 40 by 6 which equals 6 2/3 turns, or six full turns plus 2/3 of a turn or any circle whose number is divisible by 3. Take the denominator which is 3 into which of the available hole circles it can be evenly divided. In this case, 3 can be divided into the available 18-hole circle exactly 6 times. Use this result 6 as a multiplier to generate the proportional fraction required.

Example: 2 x 6=123 x 6=18

Therefore, 6 full turns of the crank plus 12 spaces on an 18-hole circle is the correct indexing for 6 divisions to cut a gear. To cut a gear of 52 teeth, using the rule again, divide 40 by 52. This means that less than one full turn is required for each division, 40/52 of a turn to be exact. Since a 52-hole circle is not available, 40/52 must be reduced to its lowest term which is 10/13. Take the denominator of the lowest term 13, and determine into which of the available hole circles it can be evenly divided. In this case, 13 can be divided into a 39-hole circle exactly 3 times. Use this result 3 as a multiplier to generate the proportional fraction required.

Example:10 x 3=3013 x 3=39

Therefore, 30 holes on a 39-hole circle is the correct indexing for 52 divisions. When counting holes, start with the first hole ahead of the index pin.

DRILLING MACHINE

Drilling is the operation of producing circular hole in the work-piece by using a rotating cutter called DRILL. The machine used for drilling is called drilling machine. The drilling operation can also be accomplished in lathe, in which the drill is held in tailstock and the work is held by the chuck. The most common drill used is the twist drill. It is the simplest and accurate machine used in production shop. The work piece is held stationary ie. Clamped in position and the drill rotates to make a hole.

Types a) Based on construction: Portable, Sensitive, Radial, up-right, Gang, Multi-spindleb)Based on Feed: Hand and Power driven



SENSITIVE DRILLING MACHINE:

Drill holes from 1.5 to 15mm. Operator senses the cutting action so sensitive drilling machine.

UP-RIGHT DRILLING MACHINE

Drill holes up to 50mm. Table can move vertically and radially.

RADIAL DRILLING MACHINE:



• Drill holes up to 50mm. Table can move vertically and radially. It is the largest and most versatile used for drilling medium to large and heavy work pieces.

DRILL MATERIAL:

The two most common types are

1. HSS drill: Low cost

2. Carbide- tipped drills: High cost and used in production and in CNC machines

Other types of drill material:

Solid Carbide drill, TiN coated drills, carbide coated masonry drills, parabolic drills, split point drill.

Types of drills:



Twist drill: Most commonly used drill tool.Step drill: Produces holes of two or more different diameters.Core drill: Used to make an existing hole bigger.

Drilling operations:

Counter boring & countersinking: To produce depressions on the surface to accommodate the heads of screwsCenter drill: Is used to produce the hole at the end of a piece of stockSpot drill: Is used to spot (start) a hole at the desired locationGun Drilling: Is used for drilling gun barrels and deep holesDrilling Practice:Hold the drill bit in drill chucks. The drill should be guided. Use a center drill to start a hole.Drills can be reconditioned. Drill life is measured by the number of holes drilled.

Drilling operations Drilling Centre Hole Drilling Deep Holes Drilling Thin Material Drilling Pilot Hole

TOOL HOLDING DEVICES:



The different methods used for holding drill in a drill spindle are:

By directly fitting in the spindle hole. By using drill sleeve. By using drill socket By using drill chuck

DRILLING OPERATIONS:

Operations that can be performed in a drilling machine are

Drilling, Reaming, Boring, Counter boring, Countersinking, Tapping.

TYPES OF CUTTER:



Reamers :- Multi tooth cutting tool. Accurate way of sizing and finishing the pre-existing hole. Accuracy of ±0.005mm can be achieved

Boring Tool:-Single point cutting tool. Boring tool is held in the boring bar which has the shank. Accuracy of ±0.005mm can be achieved.

Countersinks :-Special angled cone shaped enlargement at the end of the hole. Cutting edges at the end of conical surface. Cone angles of 60°, 82°, 90°, 100°, 110°, 120°.

Counter Bore Tool:- Special cutters uses a pilot to guide the cutting action. Accommodates the heads of bolts.

Combined Countersinks and central drill :-Special drilling tool to start the hole accurately. At the end it makes countersinks in the work piece.

Gun drill :- Machining of lengthy holes with less feed rates. To overcome the heating and short life of the normal drill tool

COUNTER BORE AND SPOT FACING:

TYPES OF CUTTERS:



Tapping:-For cutting internal thread. Multi cutting edge tool. Tapping is performed either by hand or by machine. Minor dia of the thread is drilled and then tapping is done.

WORK HOLDING DEVICES:

Machine Table vice Step Blocks

Clamps V-Blocks Angles Jigs T- Slots Bolt



Definitions:

Cutting Speed (v):-It’s the peripheral speed of the drill

v = P*D*N where

D = dia of the drill in m

N = Speed of rotation in rpm

Feed Rate (f):-It’s the movement of drill along the axis (rpm)

Depth of Cut (d):-The distance from the machined surface to the drill axis

d = D / 2

Material Removal Rate:-It’s the volume of material removed by the drill per unit time



MRR = (P D2 / 4) * f * N mm3 / min

Machining Time (T) :-It depends upon the length (l) of the hole to be drilled , to the Speed (N) and feed (f) of the drill

t = L / f N min

Precautions for drilling machine:

Lubrication is important to remove heat and friction.

Machines should be cleaned after use

Chips should be removed using brush.

T-slots, grooves, spindles sleeves, belts, pulley should be cleaned.

Machines should be lightly oiled to prevent from rusting

Safety Precautions:

Do not support the work piece by hand – use work holding device.

Use brush to clean the chip

No adjustments while the machine is operating

Ensure for the cutting tools running straight before starting the operation.

Never place tools on the drilling table

Avoid loose clothing and protect the eyes.

Ease the feed if drill breaks inside the work piece.

Grinding machine

Grinding Machines are also regarded as machine tools. A distinguishing feature of grinding machines is the rotating abrasive tool. Grinding machine is employed to obtain high accuracy along with very high class of surface finish on the workpiece. It is also possible to machine hard material and ductile material. Conventional grinding machines can be broadly classified as:

(a) Surface grinding machine (b) Cylindrical grinding machine (c) Internal grinding machine (d) Tool and cutter grinding machine



Surface grinding machine:

This machine may be similar to a milling machine used mainly to grind flat surface. However, some types of surface grinders are also capable of producing contour surface with formed grinding wheel. Basically there are four different types of surface grinding machines characterised by the movement of their tables and the orientation of grinding wheel spindles as follows:

• Horizontal spindle and reciprocating table • Vertical spindle and reciprocating table • Horizontal spindle and rotary table • Vertical spindle and rotary table

Horizontal spindle reciprocating table grinder

Figure-1 illustrates this machine with various motions required for grinding action. A disc type grinding wheel performs the grinding action with its peripheral surface. Both traverse and plunge grinding can be carried out in this machine as shown in Fig. 2

A: rotation of grinding wheel B: reciprocation of worktable C: transverse feed D: down feed



Vertical spindle reciprocating table grinder:

This grinding machine with all working motions is shown in Fig. 29.3. The grinding operation is similar to that of face milling on a vertical milling machine. In this machine a cup shaped wheel grinds the workpiece over its full width using end face of the wheel as shown in Fig. 29.4. This brings more grits in action at the same time and consequently a higher material removal rate may be attained than for grinding with a peripheral wheel.

Fig.3 Vertical spindle reciprocating table surface grinder

Fig.4 Surface grinding in vertical spindle reciprocating surface grinder

Horizontal spindle rotary table grinder

Figure 5



Surface grinding in this machine is shown in Fig. 5. In principle the operation is same as that for facing on the lathe. This machine has a limitation in accommodation of workpiece and therefore does not have wide spread use. However, by swiveling the worktable, concave or convex or tapered surface can be produced on individual part.

Vertical spindle rotary table grinder

The principle of grinding in this machine is shown in Fig. 6. The machine is mostly suitable for small work pieces in large quantities. This primarily production type machine often uses two or more grinding heads thus enabling both roughing and finishing in one rotation of the work table.

Figure 6 Surface grinding in vertical spindle rotary table surface grinder

Cylindrical grinding machine

This machine is used to produce external cylindrical surface. The surfaces may be straight, tapered, steps or profiled. Broadly there are three different types of cylindrical grinding machine as follows:

1. Plain centre type cylindrical grinder 2. Universal cylindrical surface grinder 3. Centre less cylindrical surface grinder

Plain centre type cylindrical grinder

Figure 7 illustrates schematically this machine and various motions required for grinding action. The machine is similar to a centre lathe in many respects. The workpiece is held between head stock and tailstock centres. A disc type grinding wheel performs the grinding action with its peripheral surface. Both traverse and plunge grinding can be carried out in this machine as shown in Fig.7.



External center less grinder

This grinding machine is a production machine in which outside diameter of the workpiece is ground. The workpiece is not held between centres but by a work support blade. It is rotated by means of a regulating wheel and ground by the grinding wheel. In through-feed centreless grinding, the regulating wheel revolving at a much lower surface speed than grinding wheel controls the rotation and longitudinal motion of the workpiece. The regulating wheel is kept slightly inclined to the axis of the grinding wheel and the workpiece is fed longitudinally as shown in Fig. 8.

Figure-8 Centreless through feed grinding

Parts with variable diameter can be ground by Centreless infeed grinding as shown in Fig. 9 (a). The operation is similar to plunge grinding with cylindrical grinder. End feed grinding shown in Fig. 9 (b) is used for workpiece with tapered surface.



Figure 9 Centreless (a) infeed and (b) end feed grinding

The grinding wheel or the regulating wheel or both require to be correctly profiled to get the required taper on the workpiece.

Internal grinding machine

This machine is used to produce internal cylindrical surface. The surface may be straight, tapered, grooved or profiled. Broadly there are three different types of internal grinding machine as follows:

1. Chucking type internal grinder 2. Planetary internal grinder 3. Centreless internal grinder

Chucking type internal grinder

Figure 10 illustrates schematically this machine and various motions required for grinding action. The workpiece is usually mounted in a chuck. A magnetic face plate can also be used. A small grinding wheel performs the necessary grinding with its peripheral surface. Both transverse and plunge grinding can be carried out in this machine as shown in Fig11.

Figure 10 Internal Centreless Grinders

Figure11 Internal (a) Transverse grinder (b) Plunge grinding



Planetary internal grinder

Planetary internal grinder is used where the workpiece is of irregular shape and can not be rotated conveniently as shown in Fig. 12. In this machine the workpiece does not rotate. Instead, the grinding wheel orbits the axis of the hole in the workpiece.

Fig 12. Internal grinding in planetary grinder

A: rotation of grinding wheel

B: orbiting motion of grinding

Centreless internal grinder

This machine is used for grinding cylindrical and tapered holes in cylindrical parts (e.g. cylindrical liners, various bushings etc). The workpiece is rotated between supporting roll, pressure roll and regulating wheel and is ground by the grinding wheel as illustrated in Fig. 13.

Figure 13 Internal centreless grinder



EXERCISE

Q1. State the basic advantage of a creep feed grinder over a conventional surface grinder. Q2. State the specific application of a planetary internal grinder. Q3. What are the characteristic features of a universal cylindrical grinder? Q4. State the disadvantages of centreless cylindrical grinding machine?

Q5. Is transverse feed provided in vertical spindle reciprocating table surface grinder?

Answer

Ans. to Q1.

Productivity is enhanced and life of the grinding wheel is extended.

Ans. to Q2.

Planetary internal grinders find application for grinding holes in workpieces of irregular shape or large heavy workpieces.

Ans. to Q3.

Characteristic features of a universal cylindrical grinder not possessed by plain cylindrical grinder are:

• Swivelling wheel head • Swivelling wheel head slide • Swivelling head stock

Ans. to Q4.

Disadvantages of a centreless cylindrical grinder are: • It does not grind concentrically with centres. • Large diameter short workpiece are difficult to control in the process • It may not improve workpiece perpendicularity.

Ans to Q5.

Usually no transverse feed is provided in such machine. The wheel diameter is kept larger than the width of the workpiece surface to be ground.



Chapter 5

Maintenance Engineering

Introduction

Maintenance Engineering is the discipline and profession of applying engineering concepts to the optimization of equipment, procedures, and departmental budgets to achieve better maintainability, reliability, and availability of equipment.

Maintenance, and hence maintenance engineering, is increasing important due to rising amounts of equipment, systems, machineries and infrastructures.

A person practicing Maintenance Engineering is known as a Maintenance Engineer.

Maintenance Engineer's Essential Knowledge

A Maintenance Engineer shall possess significant knowledge of statistics, probability and logistics, and additionally in the fundamentals of the operation of the equipment and machinery he or she is responsible for.

A Maintenance Engineer shall also possess high interpersonal, communication and management skills.

Typical Maintenance Engineering Responsibilities

Assure optimization of the Maintenance Organization structure Analysis of repetitive equipment failures Estimation of maintenance costs and evaluation of alternatives Forecasting of spare parts Assessing the needs for equipment replacements Application of scheduling and project management principles to replacement programs Assessing required maintenance tools and skills required for efficient maintenance of

equipment Assessing required skills required for maintenance personnel Reviewing personnel transfers to and from maintenance organizations Assessing and reporting safety hazards associated with maintenance of equipment



Types of Maintenance

Reactive or breakdown maintenance

Preventive maintenance

Predictive maintenance

Reactive or breakdown maintenance

It is performed after the occurrence of an advanced considered failure for which advanced provision has been made in the form of repair method, spares, materials, labour and equipment. It is basically “run to failure maintenance.

It has advantages of less operating cost and less staff. The disadvantages are increased cost due to unplanned downtime, increased labor cost, cost involved with repair or replacement of equipment etc.

Preventive Maintenance

Preventive maintenance (PM) is currently the most widely accepted approach to maintaining equipment. PM is a calendar based program in which very comprehensive test routines are applied to off-line equipment. A systematic approach to eliminate failure/breakdowns through regular care and attention, early diagnosis and rectification.

The care and servicing by personnel for the purpose of maintaining equipment and facilities in satisfactory operating condition by providing for systematic inspection, detection, and correction of incipient failures either before they occur or before they develop into major defects.

Maintenance, including tests, measurements, adjustments, and parts replacement, performed specifically to prevent faults from occurring.

Preventive maintenance helps to:

Protect assets and prolong the useful life of Production equipment Improve system reliability Decrease cost of replacement Decreases system downtime Reduce injury



Researchers subdivided preventive maintenance into different kinds according to the nature of its activities:

• Routine maintenance which includes those maintenance activities that is repetitive and periodic in nature such as lubrication, cleaning, and small adjustment.

• Running maintenance which includes those maintenance activities that are carried out while the machine or equipment is running and they represent those activities that are performed before the actual preventive maintenance activities take place.

• Window maintenance which is a set of activities that are carried out when a machine or equipment is not required for a definite period of time.

Maintenance of Lathe machine:

Organize Tooling Completely clean the machine. Disassemble the 3- Jaw chuck, but DO NOT pulls the Cam pins. Clean the chuck scroll, jaws and reassemble according to information sheet. Check belts for wear and tension. Check Backlash in end gears. Adjust the cross slide gibs Adjust the tool slide gibs Adjust the tailstock clamp Check and maintain coolant if applicable.



Lubrication chart for Lathe machine:

Grease each week - rack and end train gears (change wheels) Oil each week - Tailstock, Lead screw, End gear, Bushes and Top slide Apron: Check level and top up each week Headstock: Check level and top up each week Gearbox: Check level and top up each week Cutting fluid in the reservoir is done on 4 or 6 weeks frequency.

Predictive Maintenance

Predictive maintenance sometimes called “on-line monitoring,” “condition-based maintenance,” or “risk-based maintenance” From visual inspection, which is the oldest method yet still one of the most powerful and widely used, predictive maintenance has evolved to automated methods that use advanced signal processing techniques based on pattern recognition, including neural networks, fuzzy logic, and data-driven empirical and physical modeling.

As equipment begins to fail it may display signs that can be detected if sharp eyes, ears, and noses are used to sense the failure precursors. Fortunately, sensors are now available to provide the sharp eyes, ears, and noses and identify the onset of equipment degradations and failures. Integrating these sensors with predictive maintenance techniques can avoid unnecessary equipment replacement, save costs, and improve process safety, availability, and efficiency.


workshop technology-course material

Documents

long hair long hair

workshop technology

hazard of long hair

general workshop

workshop environment

workshop mandatory signs

machine tools

hair shorts