The biggest hole that can be drilled is normally 13 mm or ½”. These drill bits are held in a chuck. The speed of the machine should be adjusted to suit the drill bit size. Bench Drilling Machine

The work can be held by clamping or bolting to the work table or in a vice which is bolted to the table.

Work must never be held by hand when drilling.

Column Drilling Machines

Like the bench drill with a longer column. The base is secured to the floor to allow larger pieces of work to be drilled.

Holes up to 25 mm or 1” can be drilled as the machine spindle has provision for tapered shank drills to be inserted.

Work can be secured to either the work bench or the machine base.

Pillar Drilling Machine

Radial Arm Drilling Machines

This has a radial arm which swings about a vertical column. The sliding drill head is mounted on the arm.

Radial drilling machine

Drilling operations on several hole locations on the one workpiece can be rapidly carried out since positioning the drill head takes less time than shifting the workpiece for each hole operation.

They are available with radial arms from 600 mm to 3600 mm long and have a wide range of speeds and feeds.

Off-Hand Grinding Machines

There are two types of off-hand grinding machines:

• bench

• pedestal

Bench & pedestal grinders

They use grinding wheels of up to 200 mm in diameter and about 25 mm thick. The floor or pedestal grinder is similar, but larger and heavier. Wheels around 300 mm diameter and 50 mm thick are commonly used in floor models.

The machines are usually double ended to allow the fitting of a roughing wheel at one end and a finishing wheel at the other end. The grit of the roughing wheel is larger than the grit of the finishing wheel, and the grade of the finishing wheel is usually a little softer.

Because the wheel must run at a surface speed of about 1700 m/min there is some danger of the wheel bursting. It is important, therefore, that the wheel be enclosed in a steel guard.

Wheels must not be operated without the guards in place.

At the front of each wheel there is a tool or work rest which steadies the work when grinding. The work rest must be carefully adjusted so that the space between the work and the wheel is very small - between 1 and 1.5 mm.

The machines are also fitted with a toughened glass or plastic eye shield to protect the operator from flying particles.

Bench grinders are used to grind small work and cutting tools.

The work is usually hand held.

Pedestal grinders for larger work.

Portable Power Tools

Portable power tools are powered by electricity, pneumatics or hydraulics. Battery (electrical) powered tools are common.

Drilling Machines

Portable drills vary in drill size capacity and purpose. When drilling larger sized holes a handle is clamped to the machine near the chuck.

Some machines are single speed only, some are two speed and others have variable speeds.

Hammer drills have an internal hammering action that when activated increases the speed of drilling holes in concrete and brick.

Angle head drilling machines allow holes to be drilled in confined spaces.

Grinding Machines

Three types of portable grinders are available:

• angle grinder

• die grinder

• straight grinder.

They are used to grind work where it is easier to take the grinder to the job rather than the job to the grinder. Cut off wheels can be used on angle grinders to cut bar, tube and plate.

Nibblers

Used to cut sheet metal, nibblers have an up and down cutting action which removes a small quarter moon or “c” shaped piece of material with each down stoke. They do not normally distort the material being cut.

Shears

With the same cutting action as a pair of scissors, shears cut neatly and quickly. Shears can distort the material being cut.

Saws

Jig saws and sabre, or all purpose, saws use a reciprocating action to move a blade. The blade must be suitable for the material being cut. If it is not, the blade should be changed.

Woodworking circular saws can also have a metal cutting blade or disc.

Wrenches

Impact wrenches are used to tighten or loosen nuts and bolts quickly. The tightening torque can be adjusted.

Standard drilling machines can also be used to tighten/loosen nuts and bolts but without the advantage of the impact (hammering) action.

Screwdrivers

Specific purpose power screwdrivers or standard drilling machines with screw driving bits are used to tighten and/or loosen all types of screws. Impact screwdrivers are also available.

Chipping Hammers

Chipping hammers and scalers give a straight hammering action without rotary motion. They are used to descale weld slag and clean castings and masonry surfaces.

Work Holding

When the work piece is small and light enough to be moved it also means the cutting action will most likely move the job. This is dangerous. In these cases the job should be either:

• held in a vice

• clamped to a bench

• clamped to a large object

• secured so it can’t move.

In each of the securing situations the operator must make sure the cutting action does not damage anything.

Care Of Portable Power Tools

• always inspect tools for damage before and after use

• tag damaged tools and report or repair them before they are used

• store tools and their leads in a way that prevents damage

• follow manufacturer or workplace procedures for the handling of portable power tools.

Care Of Air Tools

Air has no lubrication properties and so oil can be added to compressed air to reduce wear in tools. This is done using a lubricator.

Air also contain foreign particles and moisture which can damage tools. The amount of these in compressed air can be reduced with filters.

Not all tools in a pneumatic system need to run at maximum system pressure. Pressure to a tool is reduced with a regulator.

When a system has a lubricator, filter and regulator is known as an air service unit.

Some air tools are made with a self lubricating material like Teflon in the bearing surfaces and so don’t need a lubricant in the air supply.

There are also some air tools that have provision for lubrication by an oil can. These also don’t need a lubricant in the air supply.

Air service unit

Safety Reminders:

• Wear safety glasses, safety boots, protection for your hair and avoid loose clothing.

• Horseplay in the workshop is likely to lead to accidents.

• Protect your hearing with ear plugs or muffs over them in a noisy workshop.

• Lift heavy weights in the right way.

Special Rules For Power tools

Portable power tools are dangerous if not used safely.

• Use guards where fitted.

• Ensure the cutting tool is the right one for the job and the power tool.

• Maintain the safe working speed for the cutting tool.

• Hold rotating spindles and wheels well away from your body and clothing.

• Remember the torque of the power tools, which can cause injury if a jam occurs. You could have your wrist twisted or be thrown off balance and fall.

• Your own personnel protective equipment should include:

• protective goggles

• gloves

• ear protection

• helmet (optional)

More Safety Rules For This Section

• Safely manage the power supply leads lines. Check the condition of electrical cables. Don’t use electrical cables while they are rolled up. Don’t leave cables lying on the floor.

• Make sure an earth-leakage protection-device is fitted to the power supply. Electrical tools that are not double-insulated should have their resistance tested regularly and after repairs.

• Disconnect leads before making adjustments to the power tool.

• Switch off power before removing cable.

• Do not use electrical tools in wet conditions.

• Be careful when you are using compressed air.

• Make sure the workpiece is clamped rigidly so it cannot move under the cutting forces.

• Check the condition of all tools and power (electric, pneumatic and hydraulic) leads.

• Do not use any faulty equipment, report it to the appropriate person.

• Wipe/clean up any fluid spills from hydraulic equipment.

Using Fixed Position Grinders

Safety With An Off-Hand Grinder

Use safety glasses/goggles, a face shield and the eye shield fitted to the machine because eyes must be protected from flying particles.

The wheel must be in good condition and not used if there is any reason to believe that it is cracked or has received severe shock. If so, the wheel must be removed and tested by a person competent and authorised to do so.

A badly worn wheel, grooved and uneven on the face and sides must be dressed as it will cause the machine to vibrate or shudder; the work may catch between the work rest and the wheel. The work rest must be correctly adjusted to a clearance of 1 to 1.5 mm.

Effective Grinding

Support the job on the work rest whenever possible.

Use the full face of the wheel by moving the job back and forth across the face. This:

• results in even wear of the wheel rather than creating grooves etc.

• helps keep the job cooler

• grinds quicker.

Re-Sharpening A Twist Drill

Drills are sharpened by holding against the grinding wheel at the point angle on one side of the drill (to grind one lip). As the grinding occurs the drill is twisted clockwise and the tang is moved downwards to the right so forming the lip clearance angle.

The thumb and fore-finger of the left hand are used as pivot and the back of the drill is held with thumb and fore finger and rotated in clockwise direction, advancing it into the wheel.

By setting the hands on the tool rest of the grinding machine and by carefully controlling the movement of the fingers the action of the attachment can be copied.

Whether the drill is sharpened by hand or by attachment it is important to check that the height and length of each lip is the same and particularly when hand grinding, that the axis of the drill bisects the point angle.

The sharpening of a twist drill requires that the following items be considered:

Lip Clearance Angle

Lip clearance angle enables the cutting edges to penetrate the work and cut without rubbing. For average conditions an angle of 12° to 15° is satisfactory.

Point Angle

The standard point angle is 118° general purposes. Where repetition drilling in specific materials is to be carried out an angle suited to the material should be used.

Whilst an error in the size of the point angle would not seriously affect the efficiency of the drill, it is most important that the axis of the drill bisect the point angle.

Faults Due To Incorrect Drill Sharpening

• Lip lengths unequal, lip heights unequal, drill pint on centre.

Result - oversize holes, uneven swarf from each flute, reduced cutting efficiency.

• Unequal angles (chisel edge off centre) lip heights equal.

Result - oversize hole, uneven swarf from each flute.

• Unequal angles, lip heights unequal.

Result - hole oversize, stepped diameters, uneven swarf from the flutes.

• Lip clearance insufficient.

Result - the drill will rub on the heel

• Lip clearance excessive.

Result - this will weaken the cutting edge.

The use of a gauge will ensure uniformity of angles and cutting edges.

This gauge has a small cup which serves to support the end of a straight shank drill and a 60° point which fits into the centre hole of a taper shank drill.

Job PT 1.

Skill Practice Drill Re-Sharpening

Task

To sharpen an 8 mm HSS twist drill to tolerances specified:

• point angle ± 1°

• equal lip length + 0.25 mm

• lip clearance angle + 2°.

Procedure

Drill re-sharpening will be demonstrated by your teacher. Under no circumstances should you attempt this exercise unless you have seen and understood the demonstration.

Sharpening

1 Stand in a comfortable position in front of the machine and slightly to the left of the wheel.

2 Hold the drill between the thumb and index finger of one hand a distance from the point which will allow the drill to pivot correctly on the index finger (see side view).

3 Support the hand on the tool rest with the remaining fingers.

4 Hold the shank of the drill between the thumb and fingers of the other hand.

5 With the drill held level, twist it until one of the cutting edges is horizontal and the centre line of the drill is at approximately 60° to the wheel face.

6 Swing the shank downwards, causing the point to rise, while at the same time rolling the drill clockwise and moving it forward slightly to produce lip clearance.

Note: If considered necessary, these three co-ordinated movements can be practised against a stationary wheel using a correctly sharpened drill.

7 Check the lip angle then repeat the procedure just outlined to grind the other cutting edge.

8 Check periodically to ensure correct point angle and equal lip length using the gauge.

9 Submit the drill to your teacher for checking.

Note: One way of testing the re-sharpening is to drill a hole in a piece of scrap metal.

Two evenly shaped chips

Safety

• Always wear eye protection

• Use only the face of the wheel

• Do not overheat the drill by using excessive pressure

• Do not cool overheated HSS drills in water

Re-Sharpening Chisels

Cold chisels are forged from tool steel. Only the point of the chisel is hardened and tempered, the body is left soft. If the head of the chisel were hard hammer blows would cause it to chip.

The point of the chisel is formed into a cutting edge. This cutting edge is similar in nature to other cutting edges in that it requires the edge to be sharp.

Chisel cutting angles

The size of the cutting angle should be about 70° for soft steel; when chipping harder metals the angle should be a little larger and for softer metals it can be ground smaller.

Grinding the angle off-centre allows the chisel to be held at a convenient angle. if the angle “A” is too large the chisel will dig in; if it is too small the chisel point will rise out of the cut.

Chisel cutting angle off centre

The blows of the hammer will cause the head of the chisel to burr over and form what is called a “mushroomed” head. The burr should be ground off as it appears because of the likelihood of it cutting the hand.

Be careful not to raise the temperatures too much when sharpening the chisel otherwise the hardness of the cutting edge will be spoilt.

Job PT 2

Skill Practice Chisel Re-Sharpening

Task

To re-sharpen a flat chisel.

• cutting angle ± 2°

• equal fact length ± 0.5 mm.

Procedure

Chisel re-sharpening will be demonstrated by your teacher. Under no circumstances should you attempt this exercise unless you have seen and understood the demonstration.

Sharpening

1 Stand in a comfortable position in front of the grinder and slightly to the left of the wheel.

2 Position the chisel against the tool rest so the correct angle will be ground when the facet contacts the wheel. The chisel must be pointing up as shown.

Flat chisel

3 Move the chisel sideways back and forth across the wheel without applying too much pressure. Do not allow the chisel to get too hot, cool it by dipping it in water.

4 Alternate the grinding of each facet to keep the fact lengths about the same.

5 Check the cutting angle then repeat the procedure until the chisel is O.K.

6 Check periodically to ensure correct point angle and equal facet length.

7 Submit the chisel to your teacher for checking.

Re-Sharpening Scribers And Centre Punches

When sharpening a scriber point or centre punch, two things must be considered:

• The grinding of a definite surface at the required angle which must extend back from the point.

• Avoiding damage to the tool by heat.

The ability to grind a definite surface on the tool point is the result of practice. You must learn how to hold the tool in your fingers, which will be supported on the tool rest, and how to press the tool against the wheel in such a way that a clean smooth surface will be ground at the required angle. You must learn how to remove the tool from the wheel, examine it and return it to the wheel to grind a little more off the same face at the same angle as before, or, if necessary, change the angle a little one way or the other.

You must have a clear picture in your mind of the shape you are trying to produce on the tool point.

Tool steels are sensitive to heat, that is they must not be taken above 250°C. A tool can easily be taken above this temperature by a grinding wheel if you are careless. The tool will not be overheated:

• if the grinding wheel is properly dressed,

• if the tool is pressed lightly against the wheel,

• if the tool is frequently dipped into water, and

• if your are attentive to your work.

Job PT 3

Skill Practice Scriber And Centre Punch Re-Sharpening

Suggested Duration

½ hour

Task

To practise the skill of re-sharpening a centre punch and scriber on an off-hand grinder.

Safety

Wear your glasses.

Procedure

1 Tool re-sharpening will be demonstrated by your teacher. Under no circumstances should you attempt this exercise unless you have seen and understood the demonstration.

2 Position the punch against the tool rest so the correct angle will be ground on the point. The punch/scriber must be pointing up as shown.

Centre punch Scriber

3 Rotate the punch moving it sideways across the face of the wheel. Do not allow the punch to get too hot, cool it in water.

4 Check the point angle and repeat the procedure until the punch is sharpened.

5 Repeat the procedure with the scriber taking extra care to avoid overheating of the small diameter point.

Grinding Different Materials

Softer materials such as plastics, aluminium and brass tend to grind away very quickly. Because of its soft nature, the ground material tends to stick into the holes in the grinding wheel clogging it up and making it hard to grind. Whenever these materials are ground the wheel should be dressed (cleaned) by a qualified person before trying to grind other materials.

Steel with a softness/hardness between hardened steel and the softer materials reacts differently again. Cast iron also reacts differently to the others when being ground.

Types of abrasive wheels

Most abrasive wheels are constructed from either aluminium oxide or silicon carbide particles. The silicon carbide are the harder and suitable for grinding stone and ceramic. The particles are bonded together to make the abrasive wheels in three different ways:

Vitrified bond- most common, strong, resistant to water and acids

Silicate bond- has a milder cutting action

Organic bond- the rubber, shellac or resinoid bond makes a tough high speed wheel suitable for portable grinders.

The hardness of the particles and the type of bond is less important than the amount of bond that holds them together. High quantities of bond produce a hard wheel that wears down slowly and low quantities of bond produce a soft wheel that wears down slowly. To abrade a hard material you need the wheel to give up its abrasive particles easily, consequently the general rule is that you:

Use soft bond wheels on hard material and hard bond wheels on soft material.

Letters indicate the type of material or process used for the bond of the wheel:

• V for vitrified

• S for silicate

• B for resinoid

• R for rubber

• E for shellac

There may be a particular variation in the bonding for special applications. This is shown by letters or symbols after the basic bond type.

Example of an abrasive wheel marking

An abrasive wheel suitable for the rough dressing of a steel casting would be marked:

38A. 16. P. 5 VBE.
38 A‑ aluminium oxide abrasive	(abrasive code & type)
16‑ coarse grain size	(grain size)
P‑ medium to hard grade of bond	(bond grade)
5‑ medium to dense structure	(structures 1-12, the higher the more open)
V‑ vitrified bond	(bond type)
BE‑manufacturer's particular bond character	(special code)

Job PT 4

Skill Practice Grinding Other Materials

Suggested Duration

½ hour

Task

To grind a 2 x 45° chamfer on 50 mm pieces of steel and cast iron.

• ± 0.5 mm

• ± 5°

Safety

• Wear your glasses

• Check and if needed adjust the gap between the work rest and wheel.

Procedure

Grinding chamfers on steel and cast iron will be demonstrated by your teacher. Under no circumstances should you attempt this exercise unless you have seen and understood the demonstration.

Grinding

1 Stand in a comfortable position in front of the machine and slightly to the left of the wheel.

2 Rest the 50 mm long piece of steel on the work rest and tilt it to approximately 45°.

3 Move the steel back and forth across the wheel until approximately a 2 mm x 45° chamfer has been ground on the corner. Generally, steel only needs to be cooled in water when it gets too hot to hold.

4 Check the angle, size and uniformity of the chamfer and repeat the procedure until the chamfer is within tolerances.

5 Repeat the procedure with the cast iron.

Using Fixed Position Drilling Machines

Job Planning

An effective job plan:

• ensures the job meets required standards

• lists all operations/steps in a logical sequence

• list equipment and tools needed.

The planning involves:

• gathering all relevant information e.g. drawings and specifications

• determining all the operations to be done

• deciding on the sequence of the operations

• detailing the tools required for each operation.

Sample Plan

Steps	Tooling
1 Check the material for defects, overall dimensions and material	Rule
2 Coat the job with a suitable marking medium	Marking medium

3 Mark the job to the details shown on the drawing	Rule, square, scriber, angle plate, scribing block, clamp, centre punch, hammer, dividers
4 Check marking out conforms to drawing details	Rule, square
5 Grind 45° chamfer all round	Off-hand grinder
6 Clamp the job in a vice. The job should be raised on a piece of timber packing or a pair of parallel strips to prevent damage to the vice	Vice, packing
7 Line up the centre of the drill with the centre of each hole and clamp the vice in place	Clamp/bolts
8 Drill two holes at approximately 450 revs/min using cutting fluid as needed	Bench drill, 10 mm drill bit, cutting fluid
9 Remove all burrs and sharp edges	200 mm flat smooth file, hole deburring tool
10 Check that finished article conforms to drawing details	Rule, square

Using Drills

Before putting a drill in a drilling machine the drill should be checked for the following defects:

• condition of shank

• the size of the drill body

• the condition of the drill point and lands.

Drill Speed

Set the drilling machine to the appropriate speed.

Alignment Of The Drill

To ensure that the drill produces the hole in the correct position it must first be lined up with the centre punch mark, or the existing hole. The drill must be brought into contact with the previously punched/drilled hole while not revolving. Then line up the drill by eye so that the cutting edges touch on both sides. The drill is then turned 90° and checked, as before. The job should then be clamped before drilling.

Drawing Drills Back On Centre

Carefull setting up and use of sharp drills will minimise the tendency for a drill to wander. However, irregularities sometimes cause the hole to start off centre.

If so, the fault can be corrected by chipping a groove with a round nose chisel on the side towards which the drill has to move. The cutting force can now push the drill over into the groove and back onto centre. It may be necessary to repeat this procedure.

This correction procedure should be started when the drill has entered about half way down the point. It must be finished before the body of the drill enters the workpiece, because once the drill is cutting to its full diameter it’s not possible to make any further corrections.

Maintenance

Drilling Machine

• tighten drive belts as required

• remove any table burrs

• clean machine after use.

Vice

• lightly lubricate screw and slides as required

• inspect for, and remove, burrs

• protect vice by using packing under jobs

• clean vice after use

• damaged vices should be reported to the appropriate person

• tag badly damaged vices.

Drill Bits

• sharpen as required

• store to prevent damage to the cutting edges

• destroy drill bits that can’t be repaired.

Safety Reminders

• in the workshop always wear safety glasses, safety boots, hair protection and suitable clothing

• do not use a machine with a danger tag fitted to it

• know where the first aid station is located

• don’t skylark in the workshop.

Job PT5

Drilling Steel

Suggested Duration

½ hour

Task

To mark out and drill 2 x Æ10 mm holes in a piece of steel.

Procedure

Marking out and drilling holes will be demonstrated by your teacher. Under no circumstances should you attempt this exercise unless you have seen and understood the demonstration.

Marking out

1 Coat the material with a suitable marking medium and allow to dry.

2 Clamp the material to angle plate.

3 Use a scribing block and rule to mark the appropriate centre line(s).

4 Rotate the angle plate 90° and mark the remaining centre line(s).

5 Remove the material from the angle plate and lightly punch the centre of the circles.

6 Use dividers to scribe the circle diameters.

7 Lightly punch the four intersections of the circle diameter and the centre lines.

8 Check that your marking out conforms to the drawing.

9 Ask your teacher to check your marking out.

Hole drilling

10 Clean the vice and drill table.

11 Clamp the job, raised on timber packing or parallel strips, in the vice.

12 Put the correct sized drill bit securely into the machine.

13 Align the centre of the drill bit with the centre of one of the marked holes and clamp/bolt the vice in place.

14 Drill the first hole following the procedure shown in the demonstration at approximately 600 revs/min.

15 Repeat steps 13 and 14 for the second hole.

16 Remove the Job from the vice and deburr the holes.

17 Check that the job conforms to the drawing.

18 Clean the machine and vice.

19 Ask your teacher to check your job.

Job PT6

Drilling Cast Iron

Suggested Duration

½ hour

Task

To mark out and drill 2 x Æ10 mm holes in a piece of cast iron.

Procedure

Marking out and drilling holes will be demonstrated by your teacher. Under no circumstances should you attempt this exercise unless you have seen and understood the demonstration.

Marking out

1 Coat the material with a suitable marking medium and allow to dry.

2 Clamp the material to angle plate.

3 Use a scribing block and rule to mark the appropriate centre line(s).

4 Rotate the angle plate 90° and mark the remaining centre line(s).

5 Remove the material from the angle plate and lightly punch the centre of the circles.

6 Use dividers to scribe the circle diameters.

7 Lightly punch the four intersections of the circle diameter and the centre lines.

8 Check that your marking out conforms to the drawing.

9 Ask your teacher to check your marking out.

Hole drilling

10 Clean the vice and drill table.

11 Clamp the job, raised on timber packing or parallel strips, in the vice.

12 Put the drill bit securely into the machine.

13 Align the centre of the drill bit with the centre of one of the marked holes and clamp/bolt the vice in place.

14 Drill the first hole following the procedure shown in the demonstration at approximately 400 revs/min.

15 Repeat steps 13 and 14 for the second hole.

16 Remove the job from the vice and deburr the holes.

17 Check that the job conforms to the drawing.

18 Clean the machine and vice.

19 Ask your teacher to check your job.

Using Portable Power Tools

Portable Power Tool Selection

• Use the right size and type of tool for the job. If a light duty or small tool is used on a large heavy duty job the tool will be damaged.

Safety

• Keep the work area clean and tidy.

• Wear the required clothing and safety equipment.

• Avoid dangerous situations and ensure good ventilation when working in confined places. Do not use compressed air to clean your self, your clothing or any other person.

• Inspect tools, leads and accessories before, during and after use. Make sure the tool is turned off before connecting the power supply. Do not carry the tool by it’s power leads. Ensure cut off material does not fall onto power leads.

• Do not use damaged equipment. It should be reported, repaired immediately by a qualified person or tagged not to be used.

• Use the tool in the correct way. Do not push the machines cutter into the job to stop it after switching it off. Do not put a power tool down until it has stopped completely.

• Secure the work material.

Storing Power Tools

• Store portable power tools so they will not be damaged.

• Power leads should no be bent at sharp angles during storage.

• Cover places where dirt and dust might get in during storage.

Job PT7

Make A Sheet Metal Gasket

Suggested Duration

2 hours

Task

Use portable power tools to make a sheet metal gasket.

Procedure

1 Produce a detailed job plan for making the sheet metal gasket.

2 Submit your job plan to your teacher for approval. DO NOT start the job until your plan has been approved.

3 Using a portable drill, jigsaw, shears and nibbler will be demonstrated by your teacher. Under no circumstances should you attempt to produce the gasket until you have seen and understood the demonstration.

4 Following your job plan mark out and make the sheet metal gasket.

5 Check that your gasket conforms to the drawing and safety requirements.