• Portable power tools are commonly used in electrical work. Manufacturers’ instructions must be referred to for step-by-step instructions. Care and maintenance should be observed.

Safety instructions

• Read the manual carefully and learn the applications, operating limitations and potential hazards of the tool before attempting to operate it.
• Pay particular attention to the following important points.
• Keep work area clean. Cluttered areas and benches invite accidents.
• Avoid dangerous environments. Do not expose tools to rain. Do not use power tools in damp or wet locations and keep work area well lit.
• All visitors (and children) should be kept at a safe distance from work areas.
• Store idle tools. When not in use, tools should be stored in dry, high or locked-up places, out of reach of children.
• Do not force a tool or use excessive feed rates. It will do the job better and more safely at the rate for which it was designed.
• Use the right tool. Do not force a small tool or an attachment to do the job of a heavy duty tool.
• Wear the proper apparel. Loose clothing or jewellery will get caught in moving parts.
• Use safety glasses, and also a face or dust mask if the cutting operation is dusty.
• Never carry a tool by the cord or yank it to disconnect it from a receptacle. Protect the cord from heat, oil and sharp edges.
• Secure the work. Use clamps or a vice to hold work. It is safer than using your hand and it frees both hands to operate the tool.
• Do not over-reach: keep proper footing and balance at all times.
• Maintain tools with care. Keep tools sharp and clean at all times for best and safest performance. Follow instructions for lubricating and changing accessories. When servicing, use only identical replacement parts.
• Disconnect tools when not in use, before servicing, or when changing accessories such as blades.
• Remove chuck keys and wrenches. Form the habit of checking to see the keys and adjusting wrenches are removed from the tool before turning it on.
• Avoid accidental starting. Do not carry a plugged-in tool with a finger on the switch. Be sure the switch is off when plugging in.
• Do not operate portable electric tools in gaseous or explosive atmospheres. Motors in these tools normally spark and sparks may ignite flammable gas or vapour.

Extension leads

• When using a tool at a considerable distance from the power source, an extension cord of adequate size must be used for safety and to prevent loss of power and overheating.
• Before using cords, inspect them for loose or exposed wires and damaged insulation. Make any needed repairs or replacement before using your power tool.
• When a tool is used outdoors, use only extension cords suitable for this purpose.
• When extension cords or power tools are being used in open or damp situations, the chance of damage or current leakage to the frame of the tool or the material being machined is very high and could result in severe electric shock. The use of an RCD is mandated in this situation.

Portable electric generators

• Electricity generators are often used in remote locations. The generator is mounted onto a frame and is ideal for lifting into location, see Figure 1.
• The starting operation is similar to a lawn mower in that it has a cord start, petrol mix and a throttle to control speed.
• The speed of the motor is automatically increased as more electrical power is required. This is achieved by means of a ‘governor’.
•  

Figure 1: A portable generator

Electric drills

• Drills most commonly range between 6 and 13 mm sizes for general applications. The size designation of the drill (6, 10 or 13 mm) refers to the maximum diameter drill bit or accessory attachment shank that will be accepted by the chuck of the drill. Generally, as the chuck size increases, so does the power capacity of the drill. The larger drills are geared to deliver slower speeds and more torque, or twisting power.

Figure 2: Example of a portable electric drill

•  

Figure 3: A light-duty portable drill

• A 13 mm drill is the most appropriate for bigger projects and more frequent use in concrete, or with large hole saws. A 13 mm drill is also the best choice for the tradesman or for continuous heavy duty use.

Figure 4: A heavy drill

Cordless drills

• These drills have a rechargeable battery as their power source. They are capable of performing as well as any of the 10 mm drills with the added advantage that they can be used where no electrical power is available.

Electric drills may have additional features, including variable speed, or selectable speed, and hammer action.

• Purpose-built hammer drills are used where masonry drilling is to be carried out. This drill also provides an impact action that helps to break up the masonry at the drill tip.

Figure 5: A hammer drill

Care of electric drills

• Any motor driven device may easily be damaged by stalling. Stalling causes the motor to draw four to six times the normal maximum current, and since the heat produced is proportional to the square of the current, overheating and burnout occurs rapidly.
• Stalling may be minimised by using the correct bit or drill for each job and by keeping it sharp.

Caution When working near live conductors using electric power tools, be careful when using ‘earthed’ appliances as contact with both conductor and appliance case may be fatal! Double insulated types are preferred.

Circular saws

• A wide range of portable circular saws is available today for both home and constructional use. Their cutting power and speed make them useful in many situations. On-the-job portability is another advantage that eliminates the need to manhandle large, heavy or awkward pieces of timber.
• Generally the motors are rated from 1 kW to 2 kW. Where the saw is to be used for heavier work, or consistently for extended periods of time, a heavy duty machine with a larger motor should be used to prevent overheating.

Figure 6: A circular saw

Jig saws

• A jig saw consists of a small blade attached to the tool by means of a mechanical linkage that moves the blade up and down at approximately 2500 strokes per minute. Because the blade is so narrow, it can be used to cut curved lines. The jig saw can also be used for cutting out shapes within a board; in this case a starting hole must first be drilled. Different blades for various materials are available.

Figure 7: A jig saw

Routers

• The router has a cutting tool similar to that of a milling machine, but is generally smaller. The router can be used for cutting grooves, trimming laminates, cutting decorative edgings and a wide variety of joinery work.

Figure 8: A router

Angle grinders

• Angle grinders are used for cutting off metal strips, tubing, angle iron, tiles and masonry. They can also be used for grinding welded joints, or sanding.
• This tool uses two types of cutting disc and various sanding discs, depending on the work material.

Figure 9: An angle grinder

Student exercise 1

1     When using portable power tools you should
(a)   Ensure safety guards are securely in _____________.
(b)   Keep _____________ away from cutting area.
(c)   Keep work area _____________
(d)  Avoid damp or _____________________ environments.
(e)   Discourage children and _____________________.
(f)   When not in use,_____________ tools properly.
(g)   Do not apply excessive _____________.
(h)   Use the _____________ tool for the job.
(i)    Wear _____________ clothing.
(j)    Use _____________ glasses.
(k)   Do not _____________a flexible cord.
(l)    Secure the _____________ piece.
2     How may stalling of a power drill be minimised?


3     The better power drill to use when working near live conductors is

4     What sort of power drill would you find more efficient drilling through masonry?

5     What types of discs can you use on angle grinders?


6     Before using extension cords you should inspect them for


7     What sort of protection device should you use especially when an extension cord or power drill is used in damp situations?


Check your answers with those given at the end of this section.

Grinding

Grinding work may be divided into two principal groups: hand grinding and machine grinding. In this section we will only give a broad outline of the elementary work of hand grinding; further detail and other processes will be dealt within the various areas when required.
Off-hand grinding is grinding work using an abrasive wheel, while the work or portable machine is held by hand.

Portable grinding machines

One type of portable grinding machine is illustrated in Figure 10. This machine is electrically operated and is used for processing surfaces in preference to chipping or finishing after chipping. Portable pneumatic grinders are also available and are very useful for cleaning up rough castings and similar work, and in many cases eliminate the laborious process of hand chipping; they can be moved to any portion of the shop or job so long as electricity or compressed air is available.
Care must be exercised not to start the machine with the wheel in contact with anything. Always lift the machine with the left hand at the spindle casing at A and the right hand on the trigger guard B, and when near position requiring grinding, then and then only press the trigger to operate the wheel.
In the interest of safety it is necessary to have a safety guard on the wheel as shown in Figure 10; this prevents certain potentially dangerous operations from being carried out, as well as minimising danger should the wheel fracture.

Figure 10: A portable grinder

Fixed grinding machines

There are two types of fixed grinder, one having its own pedestal and the other fixed to a bench. Figure 11 illustrates a pedestal type grinder with a wheel at both sides. The wheel guards and rests may be quickly removed. Figure 12 illustrates a bench grinder.
The wheel guards are made with sufficient opening to enable general workshop use. If one of these wheels should break when in operation, serious injury may result to persons even at a distance from the machine unless an adequate guard is provided.

Figure 11: A pedestal grinder

Figure 12: A bench grinder

Grinding wheels

Grinding wheels have been made from natural and artificial material. The term grindstone refers to a wheel cut from natural stone such as sandstone. The natural abrasives are emery and corundum, and for many years grinding wheels were made with these two natural abrasive materials. These abrasives did not produce the uniformity required for the many grinding processes developed in engineering manufacture.
Artificial grinding wheels are usually referred to as grinding or abrasive wheels.  These are composed of:

• abrasive grain or grit, which consists of graded particles of an abrasive such as silicon carbide or aluminium oxide.
• bond, which is a matrix that holds the grains of abrasive, and gives the wheel strength.

Artificial abrasives that meet the modern requirements of industry are aluminium oxide, and silicon carbide, the latter being called carborundum when manufactured by the Carborundum Company. There are numerous trade names given to the finished grinding wheels, details of which will not be given here.
When the wheel is used, the abrasive particles will cut or abrade the metal to be ground, and at the same time, the bond is worn or crumbled away to keep the cutting surface of the wheel sharp and effective as shown in Figure 13.

Figure 13: Enlarged view of a simple grinding wheel
Grinding wheels are referred to by their grit size, consequently, a wheel of No. 30 Grit, means that the abrasive particles before being moulded into a wheel would pass through a 30 mesh screen.
The grade of wheel does not refer to the hardness of the material but to the holding ability of the bond. Thus a Soft Grade refers to a wheel whose grit is easily dislodged. One manufacturer uses the following grades: very soft - soft - medium - hard - very hard.

Abrasive types

Silicon carbide grit breaks away relatively easily so these wheels cut well and do not readily become dull. They are used for soft materials like brass, aluminium, rubber and plastic materials, also for brittle and hard materials such as rough surfaces of castings, stone, porcelain, and marble.
Silicon carbide wheels are also used for sharpening carbide tipped tools for lathes, planers, etc, but it is desirable not to use the wheel for other purposes.
Aluminium oxide is best suited for grinding materials of high tensile strength, but is used for all steels. If a general purpose wheel is required aluminium oxide should be used.
If a very coarse wheel is being used it will leave a relatively rough surface, consequently it is desirable to have a double wheel machine with a fine wheel on one end, and a coarse wheel on the other end.

Student Exercise 2

1     Grinding work may be divided into two groups, they are:

2     What care must be taken with portable grinding machines?


3     What will minimise the danger of a wheel fracture on a portable grinder?

4     Grinding wheels may be divided into two general classes which are:


5     Abrasive wheels consist of:

6     Natural abrasives are:

7     Artificial abrasives are:

8     An artificial grinding wheel that would be used to grind rubber, plastic, rough surfaces of castings and sharpening carbide tipped tools for lathes is:

9     What artificial grinding wheel is most suitable for general purposes?

Check your answers with those given at the end of this section.

Mounting grinding wheels

To obtain best results, it is important that grinding wheels be run at the speed recommended by the manufacturer. It is dangerous to operate wheels at excessive speeds.
Grinding wheels, especially those of thin section, are very fragile, and even the apparently rugged and larger wheels can be damaged when being mounted.
Figure 14 shows the correct method of mounting wheels. The following rules should be carefully studied and followed:
(a)   The wheel should be an easy fit on the spindle but not be slack. A tight fit will cause early fracture, possibly during mounting.
(b)   Check the wheel for cracks by tapping gently with a light metal rod.
(Figure 15)
(c)   The plates must be recessed at least 1 mm deep to the outer face. This ensures even distribution or pressure and reduces the chances of slipping or breaking of the wheel. If the flanges are made flat the tendency is to bear at the inner face and this will cause early fracture of the wheel.
(d)  The flanges should be of equal diameter and at least one- third, but preferably one-half, the wheel diameter, to ensure adequate and equal grip.

Figure 14: Correctly mounted wheel
(e)     The inner flange should be firmly attached to the spindle, preferably keyed, and must be running true before the wheel is mounted. The hole in the outer flange should be an easy sliding fit on the spindle.
(f)      Blotting paper or rubber washers not greater than 0.5 mm thick must be placed between the wheel and each flange. This soft material ensures even bearing all around against the rough material of the wheel, thus providing a positive drive.
(g)     The wheel spindle should be threaded left or right hand so that the wheel tightening nuts will tend to tighten as the spindle revolves.

Figure 15: Testing a large wheel
(h)     Tighten the nut firmly with a hand spanner, but do not over-tighten. Do not hammer the spanner, since, by doing so, the wheel may be fractured; such fractures may only become apparent by the wheel bursting after the machine is started.
(i)      After mounting, revolve the wheel slowly to see if it is running true. Even if it appears to be true, check for out of balance; disconnect belts or drive gear and rotate the wheel several times until it comes to rest.
Mark the lowest position on the wheel each time, and if all marks are together, this indicates the wheel is out of balance. If both the spindle and wheel are the cause of the out of balance, this may sometimes be corrected by slackening off the nut, then giving the wheel a partial turn on the spindle. After tightening up, the assembly should again be tested for balance, and the operation of correction repeated. If several operations do not eliminate the out of balance, then either the wheel or the spindle may be the cause.
(j)      After being proved to run true and in balance, fit the guards and run the wheel gradually up to speed, feeling the stand for any undue vibration. These wheels revolve at high speeds, so that if they burst, the parts, having enormous energy, can do considerable damage or injury. Hence, do not stand in front of any wheel during starting.
(k)     Adjust the tool rest close to the wheel; this space should be adjusted to 2 mm (Figure 16).

Figure 16: Work rests

Truing and dressing

Wheels correctly selected and running at the correct speed wear evenly and are self sharpening. Wheel dressing should only be used to maintain the shape of the wheel. In general workshop practice, however, grinding wheels do not wear evenly. They may develop grooves in the surface due to grinding in the one place, become eccentric, have excessively rounded edges, and/or a sloping face, or, due to being used for all kinds of work, may have become glazed or loaded. For these wheels, the mechanical type of wheel dresser should be used.
For precision grinding, the wheels should be dressed with a sharp diamond. Detail of this type of dresser will be given when precision grinding is required.
Regular dressing of wheels should be done by a qualified person. This work should also be carried out on new wheels before they are used.

Using a grinding machine

Work should not be forced against a cold wheel, but applied gradually, giving the wheel an opportunity to warm up and thereby minimise the chance of breakage. Take care not to overheat the work; do not keep the operation going until a change of colour appears on the surface. Alternate heating and cooling of wheels should be avoided, as this may result in the development of fine cracks not visible to the naked eye.
The front face or edge only of the wheel should be used for general work. Avoid damage to the corners. Grinding on the flat sides of straight wheels is often hazardous and must not be performed when the sides of the wheel will be appreciably worn by such operation or when any considerable or sudden pressure is brought to bear against the side.
Never bounce the work on the wheel, or when using the portable machine, never bounce the wheel on the work. This is one of the surest ways of breaking a wheel. Remember that the pieces of a broken wheel may cause serious or fatal injury. At all times when grinding, vibration of the work must be kept to a minimum, as such vibration is equivalent to hammer blows on the wheel. This causes grit to fly, and the wheel to wear rapidly, with the added tendency to break the wheel.
Always stand squarely on both feet when hand grinding, knees braced and the body well balanced. When grinding at the pedestal or bench machine stand towards the side of the wheel whenever possible.
Special precautions must be observed to ensure that there is no interference with the operator or skylarking in the vicinity of grinding machines.
Sheet metal work is particularly liable to vibrate during grinding, but this may be overcome by:

• grinding along an edge instead of having the work parallel to the wheel axis, or
• if grinding along the edge is not practicable, the work should be held firmly on the rest and tilted upwards at the rest slightly, so that the sheet is just off the rear edge of the work rest.

Thin plate or sheet metal below 0.5 mm thick should not be ground, but cut with shears, snips, etc., then filed if necessary. Thin material, especially short pieces, are easily drawn down between the wheel and rest, and are therefore likely to cause damage and possible injury to the operator.
Small pieces of sheet metal or thin plate of thicker than 0.5 mm should be clamped to a piece of 6 mm plate or bar and then ground in the usual manner. If work is small it should be held in a hand vice.
When grinding small objects hold the work well above the tool rest to ensure it does not become jammed between the work rest and the wheel.
Wheels used in wet grinding should not be allowed to stand partly immersed in the liquid. The liquid-soaked portion may throw the wheel dangerously out of balance.
If there is a large amount of metal to be removed by hand grinding ensure that the work is done reasonably quickly but without overheating. For such an operation a coarse wheel should be used, and the work tilted to present a small surface to the wheel. Do not hold work in contact with the wheel for long as overheating will occur. Changing position of the work to present a small area to the wheel should be repeated until the work is brought near to the finished contour. After this, normal methods should be used and the work ground on a finer wheel to the finished size.

Hand honing

Grinding by abrasive wheels leaves tools with relatively rough edges, and where the tools are required to give a smooth finish to the job, it is necessary to hone the surfaces to give a smooth cutting edge.
Honing improves the cutting efficiency and life of tools; those with rough cutting edges will break down more quickly, and greater heat is generated with rough edged tools than with smooth edges.
To obtain a smooth edge, hone both the surfaces which form that edge with a fine oil stone, using a rotary motion until all traces of the grinder scratches near the edge are removed.
This treatment is beneficial to all cutting tools and is essential for scrapers, form tools, and screwing tools.

Sharpening

Knives

If a knife is dull, the cutting edge may be restored by the use of an oilstone. This may be done by first whetting the oilstone with six drops of light oil. The knife is then held to the stone at an angle of about 30° and rubbed on the stone in a circular motion on each side about 10 times. This is repeated until the desired level of sharpness is achieved.
If the knife edge is blunt, grinding may be necessary. This is done on a fine tool sharpening wheel with the knife held to the wheel by hand so the blade cannot jam between the wheel and the rest. It is essential the knife be cooled regularly to prevent the metal from becoming soft. After the shoulder of the blade has been removed by grinding, the knife may then be sharpened on an oil stone as above.

Wood chisels

Chisels need frequent sharpening to keep their cutting edge. As the chisel cutting edge becomes thicker or gapped, it will need to be ground on a grinding wheel.
Re-grind chisels frequently between sharpening so as to maintain a fine cutting edge. Check the squareness of the blade with a try-square before re-grinding. If not square, grind the chisel back on the wheel until the blade is square and straight.

Cold chisels

Alloy steel chisels must be sharpened with a smooth file only.
Carbon tool steel chisels are sharpened by grinding. Care must be exercised not to overheat the cutting edge or to remove more metal than necessary when grinding.
About 15 mm of the point of a carbon tool steel chisel is hardened. With constant grinding the hardened area is ground away and the point becomes too thick. At this stage chisels need redrawing, hardening and tempering. Similar treatment is required when the cutting edge is badly chipped.

Twist drills

The twist drill is sharpened by holding it against the side of a grinding wheel at an angle of 59°, the point semi-angle will be formed on one side of the drill, so that one lip will be ground. While grinding, the drill is moved clockwise relative to its axis and the tang downwards to the right to form the lip relief (clearance) angle.
The clockwise and downward movement can be produced by either hand control or a special drill-sharpening attachment.
When the drill is secured in the attachment, its movement is mechanically controlled. It is difficult to sharpen the lips to the required dimensions by hand control. However, the action of the attachment can be copied with the use of the grinding machine tool rest as a support for the left hand, and careful control of the movement of the right hand.
It is necessary to check to ensure that the dimensions of each lip are identical. The drill axis must bisect the point angle.
The sharpening of a twist drill requires that the following be considered:

• lip relief (clearance) angle
• point angle
• lips of equal length
• web thinning.

Figure 17: Lip clearance angle of a twist drill

• Lip relief (clearance) angle enables the lips, that is, the cutting edges to penetrate the work. This angle size is dependent upon the material which has to be drilled. Generally angles of 12° to 18° are satisfactory. If there was not a relief angle, the drill would not cut and excessive friction would generate heat with subsequent softening of the drill.

Figure 18: Point angle of a twist drill

• The standard point angle is 118°, which is suitable for general purposes. If repetition drilling in specific materials is to be undertaken, an angle suitable for the material should be used.
• Although an error in the size of the point angle does not appreciably affect the drill efficiency, it is important that the drill axis bisects the point angle.
• Recommended relief angles and point angles for several materials are as follows:
• 12° and 90° for cast iron, hard rubber, aluminium alloys and die castings.
• 12° and 100° for copper and some copper alloys.
• 15° and 118° for brass and soft bronze.
• 17° and 118° for bakelite, plastic and moulded materials.
• 12° and 60° for wood.

Figure 19: Drill faults

• In Figure 19 (a) the semi-angles of the two lips are unequal. Consequently, one lip does most of the cutting and the hole is larger than the drill.
• In Figure 19 (b) the lengths of the two lips are unequal and the point is not in alignment with the drill axis. Consequently, there is machine spindle wobble and the hole is much larger than the drill. The drill may fracture.
• If the drill axis bisects the point angle and the lips, that is, cutting edges are equal in length, then the:
• drill axis will pass through the centre of the chisel edge
• lips will cut equally
• hole will be accurately drilled
• drill will not be subjected to bending forces as the lips cut.

Web thinning

The web thickens towards the shank and after the drill has been re-ground several times the web gradually increases, it is then advisable to re-point the drill a short distance each side to its original thickness using a round faced emery wheel so as to reduce the drilling thrust needed.

Student exercise 3

1     What precautions are taken when fitting a grinding wheel to a grinder?


2     Preferably, the flanges used to mount a grinding wheel should be _________________ the diameter of the grinding wheel.
3     After mounting a grinding wheel it should be checked that it is running and it is not out of _____________ ________________.
4     The space between the grinding wheel and the tool rest should be __________________________.

5     When would you need to dress a grinding wheel?



6     Never ________________ the work when using a portable grinder.
7     When grinding sheet metal on a pedestal grinder it should be tilted _____________ slightly on the near edge of the tool rest.
8     Grinding wheels should not be allowed to stand partly immersed in a liquid because it could make the wheel out of _______________________.
9     After sharpening a tool on a grinder its cutting efficiency can be improved by hand _______________.
10   When sharpening a knife on a pedestal grinding wheel, the knife should be held so that the blade does not _____________ between the wheel and the rest.
11   It is essential that a knife being sharpened on a grinder should be ________________ in a liquid to prevent the temper of the metal from becoming soft.
12   When sharpening a twist drill what parts of the drill are to be considered?
                                                                                                                                                 



Check your answers with those given at the end of this section.

•  
•  

Summary

• Portable power tools are commonly used in electrical work.
• Read the manual carefully and learn the applications, operation limitations and potential hazards of the tool.
• Avoid dangerous environments. Do not expose power tools to rain. Do not use power tools in damp or wet locations. Keep work area well lit.
• Use safety glasses.
• Secure work.
• Disconnect tools when not in use.
• Remove adjusting keys and wrenches.
• Avoid accidental starting.
• Use only extension cords suitable for the environment and load.
• Electric drill features

–   speed variation (mechanical or electronic)
–   different capacity chucks (6 mm to 12 mm)
–   may be of the Hammer type (suitable for drilling masonry)
–   may be used as a powered screwdriver.

• When working near live conductors and using an electrical tool, drill etc, be careful when using ‘earthed’ appliances as contact with both conductor and appliance case may be fatal!
• Drills are most commonly available in 6, 10, and 13 mm sizes.
• Grinding work may be divided into hand and machine grinding. Off-hand grinding applies to work held by hand.
• Care must be exercised not to start the machine with the wheel in contact with anything or with no guards fitted.

• Grinding wheels may be divided into two general classes:

–   wheels cut and shaped from natural stones such as sandstone, and called grindstones.
–   artificial grinding wheels usually referred to as grinding or abrasive wheels.

• The natural abrasives are emery and corundum.
• Artificial abrasives are aluminium oxide and silicon carbide.
• It is dangerous to operate wheels at excessive speeds.
• Silicon Carbide grinding wheels can be used for soft, brittle and hard materials, and for sharpening carbide tipped tools.
• Aluminium Oxide is a general purpose wheel used for all steels.
• Wheels correctly selected and running at the correct speed wear evenly and are self sharpening. Wheel dressing should only be used to maintain the shape of the wheel.
• At all times when grinding, vibration of the work must kept to a minimum.

Check your progress

In questions 1–3 only one of the suggested answers is correct. Place the letter corresponding to your answer in the brackets provided.
1     When using a fixed grinder the distance between the edge of the work rest and the cutting edge of the wheel is:
(a)   0.02 mm.
(b)   0.2 mm.
(c)   2 mm.
(d)  20 mm.                                                                                                                 (   )
2     You need to check before drilling a hole in a wall that:
(a)   you are using the correct size drill.
(b)   place a protective sheet on the floor for debris.
(c)   correctly mark the location of the hole.
(d)  check for electrical wiring behind the wall.                                                         (   )
3     List two causes for a grinding wheel to fracture.


4     How is a groove in the cutting edge of a grinding wheel removed?


5     When drilling near live wires what type of electric drill would you use?

6     When using electric portable equipment in a damp situation, electrical protection must be provided by using ________________________________________.
Answers are at the end of the section.

Answers

Student exercise 1

1    

(a)  place (b)   hands (c)   clean (d)   dangerous (e)   onlookers (f)   store

(g)   force (h)   correct (i)    proper (j)    safety (k)   abuse (l)    work

2     using the correct drill bit and keeping it sharp
3     double insulated (unearthed) or cordless drill
4     impact or hammer drill
5     cutting disc and sanding disc
6     exposed wires, correctly connected conductors and damaged insulation or sheath
7     core balance earth leakage breaker or protection system.

Student exercise 2

1     hand and machine
2     Lift the machine with the left hand at the spindle casing and the right hand on the trigger guard and only press the trigger when near work to be ground.
3     safety guard
4     natural material called grindstones and artificial material called abrasive or grinding wheels
5     abrasive grain or grit, and bond
6     emery and corundum
7     aluminium oxide and silicon carbide or carborundum
8     silicon carbide
9     aluminium oxide

Student exercise 3

1     easy fit on the spindle; wheel tapped gently with a metal rod
2     half
3     true... balance
4     2 mm
5     when the wheel grinding face is out of shape (grooves etc)
6     bounce
7     upwards
8     balance
9     honing
10   jam
11   cooled
12   lip relief (clearance) angle; front point; lips of equal length; web thinning

Check your progress

1     (c)   2 mm
2     (d)   check for electrical wiring behind the wall
3

• cracked wheel
• out of balance
• incorrectly fitted wheel

4     dressing the wheel
5     double insulated or cordless
6     a residual current device (RCD)