Module 1

Introduction to Machining

Module objectives

• Recognize the function and importance of machine tools.

• Differentiate between the basic categories of machine tools.

• Read and understand the main technical drawings’ symbols.

• Take precise measurement using Vernier Caliper and Micrometer.

The importance of tools

• machine tools are used directly in the manufacture of products

• machine tools are required to produce the machinery and the equipment necessary for product processing

What is a Machine Tool?

• A machine tool is a power-driven machine not portable by hand, used to shape or form metals or materials by cutting, impacting, forming, eroding, or a combination of these processes.

CNC milling is a machine tool

The main categories of machine tools:

• Non-chip producing machine tools.• Conventional chip producing machine tools.• New Generation of machine tools

Non-chip producing machine tools

• This type of machines shapes metals by shearing, pressing, and drawing to a desired shape.

Non-chip producing machine tool

Conventional chip producing machine tools• They shape metal to a size and

contour by cutting away the unwanted portions in the form of metal chips

• The collection of material-working processes used is called conventional machining.

Process of Chip removal

Conventional chip producing machine tools• The operator uses machine

handwheels to manually control the machine to produce the part

• The accuracy of the part produced depends upon the skills of the operator or machinist.

Hand wheels of conventional machine tool

Examples of chip producing machine tools

Conventional milling machineConventional lathe machine

New Generation of machine tools

• Computerized Numerical Control (CNC) machines• Electric Discharge Machines (EDM)• Electrochemical Machines • Their purpose:

– To increase the production rate– To increase the preciseness of machined parts

• The programmer programs the machine control unit (MCU), through the use of symbols, letters, and numbers (coded instructions) which automatically control the machine tool movements to produce the desired part

New Generation of machine tools

Computerized Numerical Control machine tool

CNC lathe machine

CNC milling machine

Skills required to use Conventional machine tools• Drafting, • Read drawings and • Taking precise measurements.

Engineering drawing

• It is a common language between drafts persons, tool designers, engineers machinist and toolmakers.

• Drawings are made up of a variety of lines, which represent surfaces, edges, and contours of a workpiece.

• By adding symbols, dimension lines, sizes, and word notes, the draftsperson can indicate the exact specifications of each individual part

Example of engineering drawings

Orthographic Projection• Is a way of drawing a 3D object from different

directions• They are useful especially when a design is almost

ready to manufacture

Three standard views in orthographic drawings

Sectional Views

• They are used to clarify interior or hidden details on a multi-view drawing of an object.

• They are located by creating a Cutting Plane Line in one view.

• "Section Lining" or "Hatching" is added to the Section view mainly to distinguish the solid portions from the hollow areas of an object. Sectional Views

Isometric drawings

• They consist of two-dimensional drawings that are tilted at some angle to expose other views and give the viewer the feeling that what he or she is viewing is a three-dimensional drawing.

Isometric drawing

Tolerance

• It is the permissible variation of specified size of a part

• The basic dimensions plus or minus the variation allowed is given on a drawing

• Example:– The largest permissible dimension = 70.1 mm (70 + 0.1 = 70.1 mm)– The smallest permissible dimension = 69.7 mm (70 – 0.3 = 69.7 mm)– The tolerance = 0.4 mm (70.1 – 69.7 = 0.4 mm)

Allowance• It is the intentional difference in the sizes

of mating parts• On a shop drawing, both the shaft and

the hole would be indicated with maximum and minimum sizes to produce the best fit.

Fit• Fit is the range of tightness

between two mating parts.• There are two general classes of

fits:– Clearance fits, whereby a part may

revolve or move in relation to a mating part.

– Interference fits, whereby two parts are forced together to act as a single piece

Common Symbols and abbreviations

• R: Radius of a circle. Fig. 1• Ø: Dia. = Diameter. Fig. 2• TYP: Typical dimensions. Fig. 2• P: Pitch of the thread Fig. 3• mm: the unit of measurement is millimeter• M: Metric Thread

Fig. 3Fig. 2Fig. 1

M: Metric Thread

• Example: M10 X 1.5: • M = metric thread (Screw) • 10 = diameter• 1.5 = Thread pitch

Measurement

• There are two measuring systems:– International system of measurements (SI) (SI from System International)– Imperial system (Old system using Yard as basic unit

of length) 1 yard = 36 inch

I inch = 25.4 mm

Using Measuring Tools• Care must be taken when using measuring tools. • Most of tools have very sharp edges that may result in

severe injuries. • Tools could be damaged easily if bended, twisted or

screwed with extra force.• When using the graduated measuring tools, you must

look at 90 degrees for accurate measurement.

Steel Rule

• Metric steel rules, are usually graduated in millimeters and half-millimeters,

• They are used for making linear metric measurements that do not require great accuracy.

Metric Vernier• There are three basic types of Vernier caliper.

Digital Vernier

Dial VernierStandard Vernier

Metric Vernier

• The Vernier caliper is used to measure outside, inside and depth measurement

• The accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual (true) value.

Outside Measurements Inside Measurements Depth Measurements

Vernier Measurements

http://www.upscale.utoronto.ca/PVB/Harrison/Vernier/Vernier.html

http://www.stefanelli.eng.br/en/en-vernier-caliper-pachymeter-calliper-simulator-millimeter-05-mm.html

Metric Vernier

• The Vernier caliper with 10 divisions in Vernier scale (Vernier scale is the bottom scale on the Vernier) is accurate to (1/10) ±0.1 mm.

reading = 15.8 mm

Metric Vernier

• The Vernier caliper with 20 divisions in Vernier scale is accurate to (1/20) ±0.05 mm. Fig. 1.25 (b) .

Metric Vernier

• The Vernier caliper with 50 divisions in Vernier scale is accurate to (1/50) ±0.02 mm. Fig. 1.25 (c).

Metric Micrometer

• It is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades.

Basic types of micrometers

• Outside micrometer. For external measurement.

• Inside micrometer, used to measure the diameters

of holes.

• Depth micrometer measures depths of slots and

steps.

Reading the micrometer• Each division on the upper scale on

the sleeve equal 1 mm. • Each line appears after the upper

scale reading is equal to 0.5 mm. • The micrometer screw gauge also

uses an auxiliary scale (measuring hundredths of a millimeter) which is marked on a rotary thimble.

• The micrometers in our laboratory have a pitch of 0.50 mm

Example 1

5.00+ 0.50+

0.28_______

5.78 mm

Example 2

5.00+ 0.28_____

5.28 mm

Digital micrometers

• Digital micrometers are also available to give direct reading.

Prepare the blank part

• Power hacksaw is used to cut the blank part from a long bar.

• Cutting fluids must be used when cutting hard materials (steel).

End Of Module ONE

Module Two

Safety in the Machine shop

Module Objectives

• Recognize safe and unsafe work practices in a shop.

• Identify and correct hazards in the shop area.• Perform his job in a manner that is safe for

him and others in the machine shop.

Safety is everyone’s business and responsibility

Safety

• It is everyone’s business and responsibility

• Accidents don’t just happen; they are caused.

• The machinist must first develop safe work habits

Safe Work HabitsA safe worker should:• Be neat, tidy, and safely dressed for the job.• Develop responsibility for personal safety and

the safety of fellow workers.• Think safely and work safely at all times.

Categories of safety in a machine shop

• Practices that will prevent injury to workers.• practices that will prevent damage to

machines and tools.

Personal Grooming (Preparations)

1. Always wear approved safety glasses in any area of the machine shop. – The most common are plain

safety glasses with side shields. The lenses are made of shatterproof glass.

– Plastic safety goggles. They are generally worn by anyone wearing prescription eyeglasses.

Personal Grooming (Preparations)

2. Never wear loose clothing when operating any machine:– Always roll up your sleeves or

wear short sleeves. – Clothing should be made of hard,

smooth material that will not catch easily in a machine.

– Remove your necktie before starting a machine.

Personal Grooming (Preparations)

2. Never wear loose clothing when operating any machine:– When wearing a shop apron,

always tie it at the back and never in front of you

Personal Grooming (Preparations)

3. Never wear gloves when operating a machine.

4. Wear safety shoes5. Long hair must be protected 6. Remove wrist watches and

rings

Housekeeping

The following points should beobserved.• Always stop the machine

before you attempt to clean it. • Always keep the machine and

hand tools clean and tidy.• Always use a brush, not a piece

of cloth to remove any metal chips.

Housekeeping

• Oily surfaces can be dangerous. • Never place tools or materials on the

floor close to a machine. • Sweep up the metal chips on the floor

frequently.

• Do not place tools and materials on the machine table; use a bench near the machine

Housekeeping

• Never use compressed air to remove chips from a machine. Not only it is a dangerous practice because of flying metal chips, but small chips and dirt can become wedged between machine parts and cause undue wear.

• Return bar stock to the storage rack after cutting off the required length.

Safe Work Practices

• Do not operate any machine before understanding its mechanism and knowing how to stop it quickly.

• Before operating any machine, be sure that the safety devices are in place and in working order.

Safe Work Practices

• Always disconnect the power when making repairs to any machine.

• Always be sure that the cutting tool and the workpiece are properly mounted before starting the machine

• 5. Never use a rag near the moving parts of a machine.

Safe Work Practices

• Keep hands away from moving parts.

• Never measure, clean, or make any adjustment unless the machine is stopped.

• Never have more than one person operate a machine at the same time.

Safe Work Practices

• Never start a machine until you are sure that the cutting tool and machine parts will clear the workpiece.

• Before you handle any workpiece, remove all burrs and sharp edges with a file.

• Do not attempt to lift heavy or odd-shaped objects that are difficult to handle on your own.

Safe Work Practices

• For heavy objects, follow safe lifting practices:– Assume a position in which you keep

your knees bent and back straight. – Grasp the object firmly.– Lift the object by straightening your

legs and keeping your back straight.

• Be sure the work is clamped securely in the vise or to a machine table.

Safe Work Practices

• Get first aid immediately for any injury, no matter how small. Report to your instructor.

• Use the proper wrench for the job, and replace nuts with worn corners.

• It is safer to pull on a wrench than to push.

Fire Prevention

• Always dispose oily rags in proper metal containers.

• Know the location and the operation of every fire extinguisher in the shop

• Know the location of the nearest fire exit.

• Know the location of the nearest fire-alarm box and its operating procedure.

Electric hazards

Stick to the rules and proceduresregarding the electric hazards andsafety provided through out theelectrical course.

Worksheet

Solve the worksheet in class.

SAFETY CONTRACT•I RECOGNIZE THAT:

• Safety is my responsibility when using a tool.• Safety regulations have been provided to me.• The possibility of accident and injury increases if I do not follow all the safety

guidelines.• I must act responsibly to ensure my own safety AND the safety of others in the work

area. •I AGREE TO:

• Never work in the shop without my teacher supervision.• Read and practice all the safety regulations that have been handed over to me in this

course or have been posted in the work areas.• Act in a responsible manner at all times in the workshop.• Follow all instructions given by the teacher.• Immediately report any unsafe condition or activity to my teacher.• Wear eye protection at all times when working with tools or working anywhere near

someone who is using tools. • Cut or Tie back long hair, remove jewelry, secure loosed clothing, and wear safety

shoes in the Workshop. • Clean all work areas and put equipment away before leaving the workshop. 

Student signature _____________________ Section__________I, ________________________________________, have read and agree with all the safety

instructions .Date____________________________ Student ID_______

References

• Technology of Machine Tools. Seventh Edition, McGraw-Hill Companies,

• Machine tool and Manufacturing technology, Steve F. Krar, Mario Rapisarda, Albert F. Check., Delmar Publishers.

• championmedicalservices.wordpress.com.