chapter4 Tools and the work processes used in the MES sector OVERVIEW

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OVERVIEW

The Mechanical Engineering Services industry is an amalgamation of engineering, plumbing, refrigeration science, electrical and general building construction. The engineers in the course of their daily routine utilise these skills and knowledge to prepare components for use and afterwards correctly install them into systems. This chapter concentrates on the tools and skills for those materials that MES engineers must be able to handle, primarily metals (copper, aluminium and steel sheet materials, tube and pipe) and plastic sheet and pipe. We will look at them under the following headings:

• jointing processes and techniques • fixing devices

• drilling

• bending and folding • materials cutting.

The safe methods of working and safe use of tools is interwoven throughout the chapter and located next to the work process being covered.

Tools and the work

processes used in the

MES sector

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80 Role of engineers

Qualified MES (mechanical engineering services) engineers may install domestic or industrial heating systems, work on building services plant as service engineers or be refrigeration engineers installing and servicing the array of cooling equipment available across domestic, commercial or industrial systems. Through experience and training they will develop a wide range of technical skills and knowledge. For example:

•

AC (air conditioning) engineers installing an air conditioning system may be required to install cabling and piping throughout a building, so knowledge of fixing options and how to use them would be essential.

•

Refrigeration engineers installing and servicing commercial refrigeration systems, such as those found in supermarkets, would need not only knowledge of piping and fixing but about how these can affect the environment.

•

Heating fitters installing pipe work for a heating system would need to know about the various methods of joining pipes together and select the correct one to avoid leakage in service.

•

Service engineers need to know about nuts, bolts and other fastenings to dismantle and reassemble components, for tasks like replacing a circulating pump in a swimming pool plant room.

Jointing processes and techniques

At the end of this section you should be able to:

•

identify the principal methods of jointing materials in the MES industry

•

describe in simple terms the techniques of each jointing method listed in Table 4.01 (less self-tapping screws which are covered under ‘Fixings devices’ later in the chapter).

Mechanical Heat Adhesives

bolting seaming riveting

self-tapping screws threaded pipe joints compression pipe joints crimp joints

soft soldering brazing and silver soldering

fusion welding electrofusion

solvent anaerobic

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81

open-ended ring combination socket wrench adjustable torque wrench

Figure 4.03 Types of spanner

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HED Mechanical Eng BW PDF AW_003_J6990 AW by HL Studios open-ended ring combination socket wrench adjustable torque wrench

Mechanical methods of jointing

Bolting

Mechanical fastenings in the form of nuts, bolts and studs are extensively used to join parts together. Examples of this can be found in everyday objects and specific MES plant like pumps and compressors.

A joint is established by first making a hole through the components and inserting a bolt through the hole. The parts are then forced together by tightening a nut on to the bolt. Holes need to be big enough to let the bolt pass through and access to both sides of the joint is required for spanners. A disadvantage is the increase in weight, especially if several fastenings are applied this way. On the plus side, the joint can be broken and remade if required, thus very suitable for pipe work flange joints or brackets and supports.

Thread forms can be imperial (Whitworth, UNC etc.) or metric, with metric becoming the norm. Preferred sizes of ISO metric coarse threads are: M6, M8, M10, M12, M16, M20.

A range of different spanners is available to tighten nuts and bolts, depending on the location. Adjustable spanners fit a range of nut sizes. Torque wrenches are designed so they can be set to slip when the nut has been tightened the correct amount.

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Figure 4.01 Types of screwed

joint

Did you

know?

Did you know that the M denotes metric thread?

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Figure 4.02 Flange joint

Definition

Torque is the turning force applied to something, measured as the force times distance from the axis around which it causes rotation

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82

When bolted parts are subject to vibration, for example in fan assemblies, there is a tendency for the nut to work loose, which could result in damage or an accident. This can be prevented by using a locking device to secure the nut in place, of which there are several options:

•

Locknut. A second nut positioned above the main nut, after it has been tightened. Friction between the nuts prevents movement.

•

Simmonds locknut. This has a nylon insert into which the end of the bolt bites as the nut is tightened. It can only be used once.

•

Spring washer. As the nut is tightened the spring washer compresses, causing sharp chisel ends on the washer to dig into the nut and the surface of the material through which the bolt protrudes. Washers can have a single or double coil.

•

Serrated washer. This works in a similar way to the spring washer but has several sharp teeth to bite into the nut and the surface of the material. Because the teeth are flattened during compression, these washers should only be used once.

•

Tab washer. This has two tabs protruding from the washer edge. It can only be used where the bolt is close to the edge of the material being bolted; but, when correctly positioned, provides a very strong lock. After the nut is tightened, one tab is bent over the edge of the material, the other over the opposite nut face.

•

Split pin. This can be used with any nut, and additional to other locking devices, provided the bolt can protrude two to three threads through the nut. After tightening, a hole is drilled through the bolt just above the nut and a split pin inserted. One end is bent up to prevent it coming out. Though the nut will not come undone, locking tightness depends on how close the hole is drilled to the nut surface. Split pins should not be used more than once.

•

Castle nut. This is a special sort of nut designed to take split pins. It has grooves in an extension on the top. After tightening, a hole is drilled through the nut in line with one of the grooves and the split pin inserted through both grooves and hole. It is less dependent on accurate drilling of the hole through the bolt as the split pin in the grooves prevents the nut from rotating.

Use the correct spanner for the size of nut or bolt. An over size spanner could slip and cause injury or damage the head of the bolt.

Do not use stretched or worn out spanners. These could slip or break in service and cause injury.

Do not over tighten fastenings. This would put too much tension on the bolt and may strip the thread, causing failure of the fastening.

SAFETY TIP

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83 Riveted joints and techniques

Riveting provides a permanent way to join components together and

requires the same conditions as bolting; that is, the correct sized hole in each component to allow the rivet to pass through and access to both sides of the joint for tools to fix them in place. A range of rivets are commercially available, designed to cope with different materials, thicknesses and load.

Cold riveting (Figure 4.05) depends on mechanical force to hold the materials together while the rivet is fixed in place. The rivet is solid and the end is spread out using a tool called a snap and set. This prevents it coming back through the hole. It is used to join thin sheet materials together.

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HED Mechanical Eng BW PDF AW_005_J6990 AW by HL Studios Drawing-up tool Support dolly Support dolly 2 Swell shank 1 Draw up 3 Rough form head 4 Finish head

Figure 4.05 Closing a cold rivet

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HED Mechanical Eng BW PDF AW_006_J6990 AW by HL Studios a Insert rivet b Mandrel is withdrawn forming head c Mandrel breaks off at neck d Finished joint

Figure 4.06 Pop riveting

If access is limited to one side of the joint, then a blind or pop rivet can be used.

With blind or pop rivets, the rivet has a mandrel built into it and is set by a tool designed for the purpose. The rivet is pushed through and the mandrel withdrawn, forming a head on the blind side of the material. The mandrel then breaks off, as shown in Figure 4.06.

This technique is especially useful for joining lightweight duct work and sheet metal components like boiler casings.

Seaming

If you look closely at the edges of manufactured ductwork you will see that the sheet material has been folded in a special way, which locks the edges together. This process is normally performed at the factory on ready made duct work. It gives a good strong joint with little air leakage. An adaptation of this is where ‘S’ and ‘D’ cleats are used to secure ends of duct work together. The cleats do not completely close the gap and therefore are normally sealed with duct tape.

Definition

A mandrel is a cylindrical rod around which metal or other materials can be shaped

‘S’ cleat

‘D’ cleat Lock formed

joint

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84 Threaded pipe joints

To provide a leak free joint in steel pipe work the most common method uses a tapered male thread on the end of the pipe and a female thread on the inside of a fitting. The pipe is inserted into the fitting, with some form of jointing material around the male thread to fill up any gaps between the two threads. As either the fitting or pipe is rotated the threads engage and the joint becomes tighter and leak proof. Surplus jointing material should be cleaned off at the conclusion of the operation.

Types of joint material for threaded joints include traditional hemp and paste jointing, thread tape or numerous potable water pastes and specialist materials for oil, gas, and other chemicals.

The thread form for pipe used in this country is the British Standard Pipe, taper, (BSPt), or British Standard Pipe, parallel (BSPp). Internal, or female, threads and external, or male, threads can be cut to produce a tapered or parallel thread. Therefore, it is possible to form a joint using taper-to-taper or taper-to-parallel connections. Parallel-to-parallel threaded pipe joints should never used

The BSPT thread form is shown in Figure 4.10. To obtain reasonable accuracies during assembly, and a leak free joint, the correct thread must be formed on the end of the pipe; and the pipe installer must match the male pipe thread to that of the female thread fitting.

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Screwed and socketed taper/paralled joint on Medium or Heavy tube

Screwed and socketed taper/taper joint

on Medium or Heavy tube

Figure 4.08 Taper-to-taper taper-to-parallel pipe joints

Tools for turning pipework need teeth to grip the round surface. Two examples are the Stillson and chain pipe wrench.

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Hacksaw

Chain wrenches can be used in many situations where the Stillson type would be unsuitable

Figure 4.09 Stillson and chain pipe wrenches

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Chain wrenches can be used in many situations where the Stillson type would be unsuitable

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Chapter 4 Tools and the work processes used in the MES sector

In Figure 4.10 the gauge length of the thread denotes the limit that can be engaged using the hand and is calculated to be three to five turns (dependent upon the pipe size) from the open end of the pipe. This is then followed by two to three turns allowance for tightening further with a wrench. Finally, it is good practice to leave two to three threads exposed outside the fitting. This exposed thread is the incomplete thread formed by the cutting tool and, if lost into the fitting, will result in a loose joint. Following this format will ensure that installing accuracy will be maintained and the chance of leaks minimised. Table 4.02 gives standard lengths of thread that can be used as a reference.

Pipe size Thread inside fitting Thread outside fitting Total thread length

15nb 13 mm 4 mm 17 mm 20nb 15 mm 4 mm 19 mm 25nb 17 mm 6 mm 23 mm 32nb 19 mm 6 mm 25 mm 40nb 19 mm 6 mm 25 mm 50nb 24 mm 6 mm 30 mm

Table 4.02 Pipe thread engagement

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Swiss or needle files Three-square file

Half-rounded file

Total thread

Useful thread (not less than gauge length plus fitting allowance)

Complete thread Incompletethread Washoutthread

End of longest permitted internal thread at hand tight engagement Gouge plan

Wrenching allowance Gauge length

Fitting allowance

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86

The name of the tool for cutting an external thread is a die. Pipe threading dies consist of four chaser dies held in a stock. The stock is rotated by a handle or an electric motor whilst the pipe is held securely in a pipe vice.

Compression pipe joints

The non-manipulative compression fitting has been developed for joints on copper pipe, steel tube and plastic waste fittings, to avoid the use of pipe threading equipment and also to join thin wall pipe. The fitting slips over the end of the pipe, which is cut and trimmed square. The action of tightening the nut of the fitting squeezes a soft ring on to the outside of the pipe, making a leak free joint (this type of joint is not preferred in the refrigeration industry).

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Set of chaser dies

Figure 4.11 Stocks and dies

When I try to hold a piece of pipe it keeps

slipping out of the vice. What can I do to work

more safely?

We use a pipe vice to hold round objects and an engineering vice for flat, square or hexagonal objects. This helps to hold the items securely when working on them.

When low carbon steel pipe work has to be joined,

what accuracy can be achieved?

With careful cutting and threading, accuracies of plus or minus 2 mm can be consistently maintained.

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Nuts on manipulative fittings are soft brass and easily marked, so for good practice we would use an adjustable wrench for tightening.

Another type, termed a manipulative compression fitting, requires the end of the pipe to be swaged. When the nut is tightened the end of the pipe is trapped between the body and nut, thus producing a seal. This is used primarily on copper pipe and is excellent for smaller bore copper pipe carrying oil or gases, where approved. Heinemann NVQ2 Plumbing 9pt Zurich BT fig0067 19/04/05 James Petrie

Backnut Compression ring Fitting body Tube

Figure 4.12 Non-manipulative pipe fitting

Heinemann NVQ2 Plumbing 9pt Zurich BT fig0065 19/04/05 James Petrie

Tube Swaged end

of tube Adaptor Fitting body Tube

Figure 4.13 Manipulative compression fitting

Offset

Hex Wrench WrenchSpud

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Figure 4.14 Adjustable

spanners for pipes

Definition

Swaging means to distort the end of the pipe so that it forms a bell shape that locates onto the opposite part of the fitting which is shaped with a cone (chamfer) and produces the surfaces for the seal to take place

Crimp joints

A newer development for producing a sound pipe joint is the crimp joint. This technique uses a slip on fitting, which contains a rubber ‘o’ ring on the inside. The pipe end is cleaned of any surface rust or contaminant, cut square and free from any burr, and then inserted into the fitting.

Definition

A ‘burr’ is the sharp edge left on the cut edge after a cutting operation

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88 Good tool care practice

•

Check that pipe wrenches are in good condition, rejecting any that are over strained, have cracked or broken teeth. Defective pipe tools can cause minor injuries.

•

Specialist tools used in the RAC industry, such as rachet spanners, vacuum pumps, manifold gauge sets, refrigerant recovery machines, torr gauges etc, will require particular care and good practice when being used.

•

Do not use hammers that have a loose head or are chipped or cracked. The head may fly off and injure someone.

•

Make sure that hammer shafts are not split or cracked. These are signs that the tool is unsafe.

•

Check that punches are not distorted or heavily mushroomed over.

Reject them if they are, as pieces could fly off and injure eyes.

•

Keep blind rivet pliers in good condition, with all parts intact and lubricated to enable them to work correctly.

•

Crimping tools require regular inspection and lubricating in order to keep them working as they should.

SAFETY TIP

A crimping tool is used to squeeze the fitting on to the pipe. The final result is a secure joint with the ‘o’ ring preventing any leakage. An advantage of this type of joint is the range of different materials that may be joined to each other. The technique does not use heat, therefore is safe to use in heat sensitive areas, like timber roof spaces.

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Figure 4.15 Crimp joint

Joining by heat

Soft soldering

Solder is a low heat method of joining two components together. The joint must be designed to have overlapping surfaces and the material to be joined must be compatible with the jointing material. Soldering is mainly used to join non-ferrous electrical components, sheet materials and pipe work. The jointing material can be lead based, or lead free using tin as the main ingredient.

Did you

know?

Ferrous means iron, so ferrous material is something that contains iron, including steel; non-ferrous material thus contains no iron

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The completion of a solder joint entails mechanically cleaning each mating surface of the joint, then applying a chemical cleaner called a flux. Soft solder fluxes consist of cleaning agents mixed in a resin base. After cleaning and assembly the joint is heated until the internal solder ring melts or solder is run into the joint from the outside; this forms the joint. Because a low heat is applied there is little deformation of the components to be joined.

Some modern fluxes are self-cleaning, so do away with the need to use wire wool for the initial cleaning. However due to their design after heat is applied residual flux must be wiped away using a damp cloth.

Heinemann NVQ2 Plumbing 9pt Zurich BT 19/04/05 James Petrie Solder-ring fitting End-feed fitting stop solder already in fitting

solder fed in by operator Figure 4.16 Soldering pipe joints

Remember

Lead based solders are not to be used to make joints on potable water systems

Brazing and silver soldering

Brazing and silver soldering, as a method of joining, are very similar to soft soldering but use higher temperatures and a copper alloy jointing material. Temperatures used are below the melting point of the parent material. The jointing materials are either copper/silver alloys (silver soldering) or copper/tin/ zinc/phosphorus alloys (brazing alloys). The range of alloys to choose from is wide and a filler alloy would be matched to the service requirements of the components involved. For instance, the process of silver soldering a copper fuel oil supply line would use a 3 per cent silver, 97 per cent copper solder as a filler material.

Brazing is a typical technique employed for joining refrigerant pipe work together. The inside of a refrigeration system is required to be free from all contamination, such as water, grease, oil or scale. Hence we keep the pipe ends covered at all times, replace the air on the inside of the pipe with nitrogen (called a purge) and when making joints, we use a copper/phosphorus filler material, which does not require a resin based flux.

Before any brazing or soldering takes place, the refrigerant must be removed from the pipework or system being worked on, using the correct methods for refrigerant handling. All health and safety requirements such as Hot Work Permits, suitable Fire Extinguisher and notices must be observed. After a joint is completed upon a refrigerant system the required suitable pressure and strength tests should be completed before recharging the refrigerant into the system. Joint configuration for brazing is similar to that used with soft soldering techniques. Propane/air gas burners are normally used to achieve the extra heat required.

Definition

An alloy is a metal made from two or more metallic elements. The elements combine when molten and on cooling produce a new metal. Many alloys are produced, each with its own characteristics, such as improved strength or resistance to corrosion

Definition

A purge is used to cleanse something and keep it free of contamination

Definition

Potable water means water supplied for drinking

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90 Fusion welding

Low heat soldering and brazing use a different joint filler material from the parent materials that are being joined. In fusion welding the final joint is formed from the same parent and filler materials. You may have seen electric arc welding. Here the parent materials are heated above their melting point and allowed to flow together to form a joint. Joints made by fusion welding are very strong. Common MES materials that are fusion welded include steels or polymer plastics. Because of the high heat input to the joint the process has limitations but is readily employed on large steel pipe work fabrications, the jointing of plastic sheeting for non-corrosive duct work and the jointing of corrosion resistant piping systems.

The principal disadvantages are the high level of safety precautions required when using welding equipment, especially on site, and the high level of distortion of the parts to be joined by applying enough heat to melt them.

Electrofusion jointing

Electrofusion jointing is employed in the joining of larger bore gas and water pipe work. The technique uses a fitting that has a heating element embedded in each end. When the element is energised, the inside of the fitting and the outside of the pipe heat to melting point and join together, forming a fusion joint. A similar technique uses a heated tool to melt the surface of the pipe and fitting before they are firmly pushed together.

Hot work permits

The activities of welding, soldering or brazing on site are defined as ‘hot work’. When undertaking any hot work it is normal practice to control these activities by issuing a ‘Hot work permit’. This will be issued by the person designated as the Safety Advisor for the site and will stipulate safety requirements to be observed.

Take extra care when using propane heating equipment in any low, confined space. Propane is heavier than air and, if there is a leak from the equipment, the gas can collect in depressions in the ground or basements of buildings, providing the right conditions for an explosion. Therefore:

•

ensure adequate ventilation at all times and make doubly sure that the equipment is turned off when not being used

•

get a competent person to inspect the equipment regularly

•

do not use the equipment if you suspect it is faulty.

SAFETY TIP

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Adhesive jointing

There are many adhesive jointing materials now available to support modern manufacturing processes. We will look at just two types often used in the MES industry.

Solvent weld adhesives

As the name implies, these adhesives melt the mating surfaces of the joint, allowing them to flow together, just like in fusion welding but without the need for heat. The limitation is the range of materials that will react this way, primarily polymer plastics like ABS and unplasticised PVC (uPVC).

An example of this method of jointing would be the joints made between pipes and fittings in waste systems. To ensure a successful joint:

•

cut the pipe clean and square

•

remove burrs and chamfer the end at approximately 45° on the outside

•

lightly abrade the pipe approximately the depth of the socket on the fitting, and the inside of the socket, using clean, medium glass cloth or emery paper

•

thoroughly clean both surfaces using a cleaner recommended for the adhesive being used

Follow all of the requirements for the site. The instructions are there to reduce fire hazards.

Also:

•

Make sure all heating/welding equipment is checked over by a qualified person at regular intervals, so that the chance of something failing when being used is reduced.

•

Beware of the harmful effects of welding, brazing and soldering fumes. Use in well ventilated areas only.

•

Beware of heat damage to the surrounding environment. You could start a major fire, so protect with heat proof mats if required.

•

Always replace lids on containers and store all unused consumables in a dry safe place to reduce fire hazards (and also not to waste materials).

•

Have a suitable fire extinguisher close by in case of an emergency when using heating equipment.

•

Any electrical power tools that are to be used should have been subject to a current Portable Appliance Test (PAT) by an approved person.

•

Check that all power tools have a current electrical PAT certificate, safe power leads and plugs. This will help prevent electrical hazards.

SAFETY TIP

Definition

A chamfer is created by cutting back the edge of something at an angle, often to make it easier to engage the ends of the pipe into the fitting

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92

When using adhesives:

•

Read and follow manufacturers’ product data sheets, which will specify the requirements for safe use.

•

Only use adhesives in well ventilated areas, as the fumes given off can be toxic.

•

They are also highly flammable, so do not smoke while using

adhesives and ensure that there is no source of ignition in the working area likely to start a fire.

•

Clean away any surplus adhesive from the finished joint (which also makes the joint look neater).

•

Keep lids on containers when not in use to avoid fumes. This will also prevent waste by evaporation.

SAFETY TIP

On the Job: Repairing a component

Mike, an RAC engineer, has found that the thread inside a component has been damaged. Before replacing the component back into the system, what should Mike do with the part?

Fixing devices

Installers and service engineers spend a fair amount of time fixing items to various structural surfaces, such as walls and ceilings; therefore knowledge of the range of fixing devices available is recommended. A fixing device should ensure a good hold without causing damage to either the surface or the component. The correct fixing will depend upon the structure to be fixed to, and the load to be supported.

•

longitudinally apply two coats of the adhesive to both surfaces, avoiding excess on the inside of smaller fittings

•

immediately push the pipe fully home into the fitting without twisting and allow to dry.

Anaerobic adhesives

The name ‘anaerobic’ means that these adhesives set or cure in the absence of air. In a joint configuration, where the two mating surfaces can be brought very tightly together, air is naturally excluded, which make the conditions perfect for this type of adhesive. It is commonly used as a thread jointing material on screwed pipe work.

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Most fixings that MES engineers use are secured with screws of some sort. Fixing holes should be made with a drill, and the fixing, screw and drill should all be of the correct size with respect to each other. A twist drill is used for timber and metal, while a tungsten carbide tipped drill is used for masonry. Slow speed drilling with a hammer or percussion facility is best for masonry. At the end of this section you should be able to:

•

state the various types of fixing device

•

determine the correct fixing for the load and structure

•

identify the techniques for drilling into masonry and for drilling metals.

Light fixing devices

As their name implies, these are used for relatively light loads, for example pipe work brackets, panel radiators or air conditioning units. The main ones are as follows:

•

Plastic plugs. These have effectively replaced older fibre plugs, being sold in strips of different sizes to match screws. They are not suitable where the fixing can get hot, as the plastic could melt.

•

Gravity toggles. These are designed for fixing to vertical hollow partition walls, such as plasterboard, at least 10 mm thick. Once through the wall, the toggle drops down to a vertical position and locks the fixing in place.

•

Spring toggles. These are similar but have wings that

are spring activated once the fixing is through the surface, so can also be used on horizontal surfaces like ceilings.

•

Expansion toggles also operate in a similar way, but are designed to give permanent fixing to thin sheet

materials.

Commonly used colour coding for plastic plugs is shown in Table 4.03.

Colour Screw sizes

White 4 – 6

Yellow 6 – 8

Red 8 – 10

Brown 10 – 12

Blue 12 – 14

Table 4.03 Colour coding for plastic plugs

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94 Heavy fixing devices

Heavier loads, such as boilers, storage tanks or heaters can only be fixed to surfaces able to support them. There are several ways for doing this but the two most widely used are the ragbolt and various types of expansion anchors. Ragbolts are inserted into an over large hole and then concreted in. They have fluted ends, which key into the concrete to prevent them pulling out.

Expansion anchors are popular and come in many different designs with the ‘non-drill anchor’ being the most widely used. This comprises a steel shell, one end of which is slotted to provide expansion and the other end internally threaded to receive a suitable fastener (bolt, stud etc.). A suitable sized hole is drilled into the structure to a depth slightly deeper than the length of the anchor. The anchor is inserted with the slotted end first, and the internal expander plug is driven fully home to expand the slots, thus permanently fixing a threaded socket into the concrete to which a component can be secured.

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1

Drill hole Insert anchor2 Expander plug Setting tool 3 Drive plug in with hammer and setting tool

Figure 4.18 Setting a non-drill anchor

On site you will normally be told what to use by the design engineer but, as you gain experience, you will be able to match fixings yourself with the load to be supported.

Screw fixings

Screws are an effective way of joining and fixing a wide range of materials, which may need to be removed. They come in many shapes and sizes and it is important to use the correct screw for the task and also the correct screwdriver blade for the screw head.

Remember

If you damage the screw head by using the wrong screwdriver, someone else in the future may not be able to remove it

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Self-tapping screws are an alternative to bolting or riveting sheet materials together, and fixing items to surfaces made from sheet metal. A pilot hole smaller than the screw is drilled through the two surfaces to be joined and the screw inserted and turned until the joint is drawn tight. Access is required only from one side and the joint can be undone if required; therefore it is very useful for temporary repairs. There are several designs available to match requirements.

Wood screws are primarily used when fixing to timber. They are also commonly employed in conjunction with plastic wall plugs when fixing to masonry. countersunk head round head raised head pin head mushroom head

Figure 4.19 Self-tapping screws

Heinemann NVQ2 Plumbing 9pt Zurich BT fig0078 22/04/05 James Petrie

The wall is drilled with the correct size masonry drill

The correct size plug is inserted into the hole

The right size screw is driven into the plug

Figure 4.20 Fixing operation using plug and screw

When ordering screws for a particular job it is necessary to quote the correct description of the screw.

The four factors required are:

•

Size of screw. This is the diameter under the head and is sized by a number, for example 6, 8, 10 or 12, or by metric measurement, for example 5.5 mm.

•

Length of the screw in millimetres. This is the length overall for flat headed screws, or from under the head to the tip for a round head.

•

Type of head. See Figure 4.21 for a selection. Cross head screws are

increasingly replacing slotted head screws, designed to give a more secure location of the screwdriver in the head, especially when using power tools.

•

Type of metal the screw is made from, for example steel or brass.

Figure 4.21 Screw head types

Did you

know?

Steel is an alloy of iron and carbon; brass an alloy of copper and zinc

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96 Drilling

Drilling is the act of creating a hole through any material by means of a rotating bit.

The stock-in-trade drill for the MES engineer is the twist drill, which is made up of a spiral part, a tip and a shank. The tip of the drill is where the work of cutting occurs.

The standard jobber’s twist drill is sharpened to a point angle of 118° and with a lip clearance angle of 5°. The leading edge cuts away the material in the form of swarf, which is cleared away by the spiral flutes. When drilling metals the drill should be lubricated to keep the tip cool and help to clear the swarf. The masonry drill is made from especially hardened steel with a tungsten carbide insert in the cutting tip, which is capable of cutting into masonry. It also has flutes to clear away the debris. It does not require lubrication. It should be used with a percussion drilling machine, which vibrates the tip to give a ‘hammer’ effect as it cuts. Most drilling machines have a dual purpose facility to enable the selection of either rotary only or percussion with rotary action.

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HED Mechanical Eng BW PDF AW_013_J6990 AW by HL Studios Helix angle (rake) Clearance angle Cutting edges Point angle

Figure 4.22 Twist drill

cutting angles

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Hammer drill bits

A taper K taper H type and SDS+ Figure 4.23 Types of drill shank

On the Job: Fixings

Raki, an apprentice service engineer, has been sent to a school to replace a heater that has ‘fallen’ off the wall. The heater weighs about 10 kg and the wall is constructed from good, strong bricks that have been plastered over.

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The opposite end of the drill to the tip is called the shank. This is the part that is gripped in the drilling machine chuck, and the shape dictates what chuck is required. A standard three jaw chuck takes a parallel sided shank. Other drill shanks, especially for masonry drills, include taper, H type or SDS type, each requiring their own matching chuck.

Larger holes can be drilled out by using a core drill. These drills consist of a hardened steel tube with cutting teeth around the rim. These can be similar to saw teeth for soft materials, including wood, but industrial

diamonds or tungsten carbide tips are inserted into the leading edge for

use on masonry. The action of the drill through the material creates an annular hole leaving the centre core free. Sizes of holes can vary from 40 mm to more than 100 mm.

Bending and folding of sheet materials

Plate and sheet is made by rolling red hot ingots of metal in a steel mill until the required thickness is obtained. During this process the grains of the metal become squeezed in one direction causing the material to be weaker across the direction of rolling.

The MES engineer becomes familiar with forming sheet materials into

various shapes through preparing components for installation. It is normal to purchase parts made out of sheet materials from a specialist manufacturer. However, during installation these often need to be trimmed and shaped to fit the job. Therefore, the engineer must be able to manufacture or modify items on site. Generally speaking, forming parts into desired shapes, as opposed to cutting and joining, can save on materials, fittings and fastenings, thus saving time and money.

Sheet metal components are most likely to be made by cold working the material. Cold working includes hand operated methods for folding and bending thin sheet.

•

describe the methods of bending and folding sheet material

•

identify the correct tool for a given material

•

describe common faults that occur when folding and bending.

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Figure 4.24 Core drill

Definition

In a foundry, metal is normally cast into long lengths, called ingots, before being worked

Definition

Forming covers any action designed permanently to change the shape of material

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98 Bend or fold?

Before deciding to form a component out of sheet it should be remembered that folding creates a sharp deflection in the material and a small radius of curvature, which can be prone to fracture along the line of the fold. Bending with a larger curvature reduces this tendency but can result in inaccuracies in the finished article.

J6990

HED Mechanical Eng BW PDF AW_019_J6990 AW by HL Studios Large bend Bending Metal stretched Sharp fold Folding Small radius

Figure 4.25 Bending and folding

J6990

HED Mechanical Eng BW PDF AW_019_J6990 AW by HL Studios Large bend Bending Metal stretched Sharp fold Folding Small radius

The outside of any turn is stretched, and therefore under tension, while the inside is squeezed, or under compression. Both tension and compression increase with the thickness of the material. Somewhere in the middle lies an area that is neither under compression nor tension, called the neutral line or neutral axis.

Folding may enable a more exact fit than bending but, as the turn radius becomes smaller, the tension and compression increase, resulting in the possibility of material failure. Hence, folding is more suitable for thinner sheet materials, especially cold working on site.

Material can be wasted very easily by not using correct methods. It is

important to remember that materials have thickness and this must be taken into account when undertaking the process of bending or folding. Quantities of material can be calculated and cut to length before being shaped.

Example 1 (Figure 4.26). A simple section

formed by bending where the dimensions required are internal. The cutting size will be:

30 mm + 30 mm = 60 mm.

J6990

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30 mm 30 mm

Figure 4.26 Cutting size to match

internal dimensions

Example 2 (Figure 4.27). A similar section, but

the dimensions required are now external. The cutting size is now:

(30 − 3) mm + (30 − 3) mm = 54 mm.

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30 mm 30 mm

Figure 4.27 Cutting size to match

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99 Spring back

Metals have an in-built resistance to being formed and will attempt to return to their original shape after working. Therefore, if folding or bending operations are carried out, as soon as the tension is relaxed the material will ‘spring back’ a small amount, which is known as elastic deformation. Allowance should be made for this. For example, if the fold or bend is required to be 90° the forming process should over bend the item, allowing for a few degrees of spring back. The amount of spring back is dependent upon several factors, including the type and condition of the material, its thickness and the amount of bend. The allowance to be made is determined by experience.

J6990

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Original shape before application of bending force

Elastic deformation No stress

Shape under bending force

Shape while under more bending force

Angle of springback

Shape while under more bending force

Figure 4.28 Spring back

Folding and bending methods

and equipment

A ‘folding bar’ can make small one-off items in sheet material. The material is placed in between the bar, with the fold line along the edge of the bar, and is clamped up. The sheet is dressed over the bar using a soft mallet until the required angle is obtained.

Definition

Elastic deformation refers to the deformation that occurs when a force is applied to a material; this deformation disappears when the force is removed allowing it to return to its original shape

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100 Heating and Ventilation, Air Conditioning and Refrigeration

For larger items a ‘beam’ or ‘clamp folder’ is used. This machine consists of a beam or clamp with a blade attached, around which the metal is folded. The clamping action applies pressure to hold the work on to the bed or base of the machine. The actual bend is formed by lifting up the folding handle, which swings the folding beam around the top blade, making the fold.

Figure 4.30 Beam folder

A ‘roll bender’ can be used to manufacture circular items in sheet material, or bars with round, square or other cross-sections. It consists of three parallel rolls, two that pinch the material to provide grip and a third roller that is used to set the metal to the desired radius. By turning the handle the material is drawn through the rollers and is bent into a circular shape until both edges meet.

J6990

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rolls

Thickness (upper roll) adjustment

Pressure rolls

Adjustable bending roll (back roll)

Back roll adjustment End frame Operating handle Pedestal

Figure 4.31 Roll bender

J6990

HED Mechanical Eng BW PDF AW_024_J6990 AW by HL Studios Bed Folding blade End frame Pedestal Folding beam Radius adjusting screw Beam operating lever

Beam operating cam

Clamping cam

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When using bending equipment:

•

Take great care to keep fingers away from moving parts, as they may become trapped, causing injury.

•

Adjust to allow for thickness of the material, reducing the strain on the equipment in use.

•

Keep moving parts lubricated for ease of use.

•

Do not use folders for thin strip material. This tends to break the edge of the blade.

•

De-burr the edges of sheet parts after cutting and before folding to reduce the chance of cutting yourself.

Hot bending of steel bar and rod

In most cases, pipe clips and supports will be bought in, but occasionally the MES engineer will need to form steel strip and rod into brackets and supports. Using a bench and a vice the metal is cut to length, marked off, then ‘hot worked’ to form it into the item. This requires a heating medium, like the oxyacetylene blowtorch, to heat the metal to red hot, when it becomes soft enough to form into the required shape. An example of this would be a U-bolt for securing pipe work to steelwork.

Safety when hot bending:

•

Be aware of objects around the work area that may become hot to touch.

•

Wear gloves to protect hands from minor burns.

•

Use clear safety glasses to prevent hot scale from getting into the eye.

•

Use heating equipment only when you have been trained in its use. Improper use can cause serious injury.

•

Shut down equipment when not in use to prevent fire and explosions.

•

Have a suitable fire extinguisher available.

•

Have heating equipment checked over by a qualified person at regular intervals to enable defective equipment to be identified and replaced.

•

Store all hot articles safely away from where others could inadvertently touch them.

•

Remember tools such as lifting tongs will get hot; therefore cool them at regular intervals so that you and others will not get burnt.

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102 Hot and cold bending of tube and pipe

Bending pipe, rather than using fittings, has the following advantages:

•

It produces a longer radius bend than an elbow fitting. The latter forces the fluid flowing in the pipe to turn a sharp angle, creating a frictional resistance to the flow.

•

Bends cost less than fittings.

•

Fabricating longer lengths of pipe can save time.

•

It reduces the number of joints that could leak.

Pipe and tube resist being bent and, if not carefully handled, they will go out of shape. The common defects that occur are:

•

flattening on the outside of the bend

•

rippling on the inside of the bend

•

distortion of the bore of the tube or pipe taking on an oval shape

•

thinning of the wall of the pipe

HED Mechanical Eng BW PDF AW_026 _J6990

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Ovality

After bending

Thinning

Before bending After bending Outside of bend

Buckling Flattening

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103 Hand bending of copper tube

Small-bore copper tube can be readily bent. However, it has a thin wall, which requires supporting by either an internal bending spring or an external bending spring to prevent the wall collapsing.

When using an internal or external spring there are a few things to remember:

•

Do not try to bend a piece of pipe that is too short. It would require a good deal of physical effort, which could lead to injury.

•

Do not make the radius of the bend too tight or it will be found that the spring cannot be removed.

•

The spring has a hook at one end. This is to enable the spring to be removed at the finish of a bending operation.

•

If it is still difficult to remove, over pull the bend and then go back a little. This helps to release the spring.

Figure 4.33 Internal and external bending springs

Overpull for a 90º bend

Spring

Bar used to tighten spring to make removal easier

A

C B

Gain in length is due to the measured length A–B–C being longer than the actual length A–C

Figure 4.34 Copper tube bending with an internal spring

Heinemann NVQ2 Plumbing 9pt Zurich BT fig0049/50 11/04/05 James Petrie Overpull for a 90º bend Spring

Bar used to tighten spring to make removal easier

A

C B

Gain in length is due to the measured length A–B–C being longer than the actual length A–C

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104

Copper tube can be made easier to bend by hand by annealing the copper tube first. This is achieved by heating the tube to cherry red and cooling in water or allowing it to cool in the air. The tube will then be softer and easier to bend.

To lay out a hand bend in copper tube, the radius of bend is required. This is calculated as four times the diameter of the pipe. For example, for a 15 mm pipe the radius would be 15 mm × 4 = 60 mm. The amount of pipe taken up by a 90° bend (bend length) is then 1.5 × the radius, in this case 1.5 × 60 mm = 90 mm.

Other angles of turn would be a proportion of that calculated for a 90° bend. For instance, for a 45° bend divide the bend length by 2, i.e. 45 mm; for a 30° bend divide by 3, i.e. 30 mm and so on.

Bending copper tube by machine

This is the most common method for bending copper tube. Bending machines can be either hand held or free standing and they use leverage to make the work easier. The smaller hand held benders will bend pipe sizes from 6 mm to 22 mm and are very useful for working in restricted spaces. The free standing bender has a range from 15 mm to 42 mm. Copper pipe work above this size would be installed using fittings.

Definition

Annealing is heat treating a metal to bring it to a state soft enough to work easily

Figure 4.35 Hand bender Figure 4.36 Stand bender

A variant called a ‘minibore bender’ is used in the RAC industry for bending refrigeration tube.

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Cold bending of steel pipe

Compared with copper, steel tubing is strongly resistant to bending. Thus, hydraulic press bending machines are required. In these, a hydraulic ram pushes a former of the correct size for the pipe against two stops. The pipe bends around the former, which supports the pipe against deformation.

Such machines can handle any size of pipe, but pipes over 50 mm are normally installed using fittings.

Safety when using bending machines:

•

Be careful to keep fingers away from moving parts.

•

Keep bender parts clean and lubricated; they are less likely to cause injury and also work a lot better.

•

Inspect for damage before use. Reject any worn or damaged parts that may cause injury.

•

When using a bender in occupied premises be mindful of others or objects in the area. Long lengths of pipe in a hand bender may damage the customer’s property.

SAFETY TIP

Remember

Store all bender parts together; it saves time in searching for bits

Definition

A former is something made to a particular shape from strong material, against which other material can be forced so that it adopts the same shape

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106 Hot bending of steel pipe

Hot bending of steel pipe is more of a ‘get-out-of-a-problem’ skill than a production option but, nevertheless, it is useful for the MES engineer to know about. Traditionally the pipe would be filled with dry sand to prevent the wall of the pipe from collapsing. Modern heavy grade pipe, however, is made from better quality material. Therefore it can be heated and bent unfilled without deforming, as long as the pipe is marked out for a radius of turn no less than four times the bore size of the pipe.

Lengths of bends are calculated in the same way as for hand bending of copper pipe. That is, the radius of turn equals 4 × pipe diameter and bend length equals 1.5 × radius of turn.

Heating is normally done using oxypropane or oxyacetylene equipment. Practice in applying the correct heat and pressure is essential for success.

Safety when using a hydraulic press bender:

•

Ensure that the former is correct for the size of pipe.

•

Ensure that the pins are in the correct holes for the relative size of pipe and are properly located.

•

Keep the hydraulic reservoir topped up with the correct oil.

•

Do not use a hammer to remove the former after finishing the bend.

SAFETY TIP

•

Do not use heating equipment until trained in its use. Improper use can lead to fire or injury.

•

To protect other workers, ensure that there is a clear space to work in.

•

To reduce the risk of fire, clear the work area of combustible materials.

•

Wear eye protection when heating pipes, as sometimes hot scale is emitted from the hot pipe.

•

Have a suitable fire extinguisher available.

•

Place all hot objects out of reach of others and mark them ‘hot’ with chalk. This will reduce the risk of minor burns.

•

Turn off equipment when not in use and stow it away safely. This will reduce the chance of fire or explosion.

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Cutting of materials

Principal cutting activities undertaken by MES engineers are:

•

filing

•

sawing sheet and tube materials

•

shearing sheet materials

•

chiselling

•

tube cutting

•

carborundum disc cutting.

Marking out and cutting materials to shape differs if the task is undertaken in a workshop or on site. The focus here is for site-based cutting activities relating to both sheet materials and pipes.

•

list the main cutting methods used in the MES sector

•

state what factors must be considered when cutting out in various materials

•

list the techniques and methods used for various cutting out operations

•

describe the tools and equipment required for cutting out materials

•

describe the care and maintenance of cutting equipment

•

identify the most suitable cutting technique for a particular operation

•

recognise unsafe conditions during cutting activities and take necessary precautions.

Files

A file is a tool that can be used to remove material by the action of rubbing the file over the surface. It cuts into the material in the same way as other cutting tools, as it comprises lots of small cutting teeth. The primary MES use is for ‘cleaning up’ cut items.

All cutting tools will produce a sharp ‘burr’ on the cut edge. This is

unsatisfactory in that the burr could cause an injury to those handling the materials and, in the case of an internal burr in pipe work, if left in place it would restrict the flow of products through the pipe. The burr can be removed with a file or, in the case of tube or pipe, a spiral pipe reamer.

Files are made from very hard steel and come in various lengths and ‘cut’. Cut is the size of the teeth that do the work. The grade of cut ranges from fine, medium to rough. Very rough files with individually formed teeth are generally referred to as rasps, mainly used on wood and other soft materials.

Definition

A reamer is a tool used to widen a hole in material

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108

The sectional shape of the file is important for the job to be done. Main shapes are:

•

Standard hand file. Parallel in width and tapering slightly in thickness towards the tip; diagonally cut in both directions on the main faces to form the teeth; flat edges, one of which has teeth formed by single cuts, and the other none (the safe side).

•

Flat file. For general use; double cut on both sides and single cut on both edges.

•

Half-round file. For filing concave surfaces and internal corners; double cut on the flat face and single cut on the curved side.

•

Square file. For rectangular holes, slots and keyways; double cut on all sides.

•

Round file. For concave surfaces and circular holes; double cut all round.

•

Triangular, or three-square, file. For sharp internal angles; double cut on all sides.

•

Knife file. For filing inside sharp angles; double cut on both sides and a single cut edge.

•

Warding file. For narrow slots; double cut on both sides and single cut on both edges.

•

Needle files (Swiss pattern or jeweller’s files). For precision work, usually sold in sets with different shapes, lengths and cuts.

There are some general safety precautions that should be observed when using cutting tools:

•

Do not use powered disc cutters unless trained and qualified to do so.

•

Use the correct tool for the material and situation.

•

Use eye protection if there is any chance of particles flying off during the cutting process.

•

Protect others and property.

•

Assemble cutting tools correctly.

•

Be aware of the area under and behind the cutting area.

•

Do not use tools with defective or worn teeth or blades.

•

Clean tools regularly.

•

Lubricate working parts regularly.

•

Carry out pre-checks on power tools each time they are used (including PAT certificate, leads and plugs).

•

Prevent cut parts from falling on to people or damaging the area around.

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J6990

HED Mechanical Eng BW PDF AW_032_J6990 AW by HL Studios Flat file Square file Round file Knife file Warding file

Swiss or needle files Three-square file

Half-rounded file

The first seven types of files below taper slightly towards the tip, but not the needle file

Figure 4.38 Types of file

Sawing sheet and tube materials

The usual tool for cutting metals, except for sheet material, is the hacksaw. It consists of a frame with a handle and a replaceable blade. Typically, blade sizes are 150 mm long for a ‘junior’ hacksaw and 300 mm for a standard hacksaw. The blade has teeth, which do the cutting, and they are rated by the number of teeth per inch (tpi). A careful look at the blade will reveal that the teeth point in one direction only. They are also ‘set’ to allow the blade to move easily through

Definition

The set of a saw blade describes the way the teeth are alternately bent out to right and left, so that the cut is wider than the blade, otherwise it could bind in the material

Definition

A tang is the extension to the blade of a tool, usually pointed and tapered, designed to fit tightly into a handle

It is important to keep the teeth clean of cut material. All files, except very small ones, must be used with a handle to prevent injury from the tang. The handle should be undamaged and offer a firm, comfortable grip.

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110

When sawing:

•

make sure that you have a comfortable stance with feet apart

•

have a relaxed grip on the saw

•

keep fingers outside of the frame

•

use slow, steady rhythmical strokes

•

keep an eye on the direction of the cut.

The hacksaw is limited in use when cutting a large flat sheet of material as the frame gets in the way. It is normal now to use a powered jig saw. This is a tool normally used for cutting flat sheets of timber, but fitted with an appropriate sawing blade it will perform well on metal and other materials.

Hacksaw Thick sections less teeth Set of teeth Thin sections more teeth

Figure 4.39 The hacksaw

Points to remember:

•

When loading a blade into the frame the teeth must point away from the handle.

•

No less than three teeth must in contact with the material to be cut at one time. Therefore, for thin sections like copper pipe use a 32 tpi blade, and 24 tpi blades for steel pipe and thicker sections.

•

Use a lower tpi blade for soft materials as they tend to clog the blade.

Remember

Three main blades used by MES engineers are 18, 24, 32 tpi

Remember

Use the correct blade for the thickness and type of material

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111

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Figure 4.41 Reciprocating saw

An improvement on the jig-saw for MES applications is the hand held

reciprocating saw. It differs in the way that the blade protrudes from the front of the machine. It will also take larger blades, enabling thicker sections to be cut.

Shearing sheet materials

The best tool for sheet steel is the powered nibbler or shear, which is an adaptation of the sheet metal hand shear called a Gilbow shear. Hand shears are used, and are very handy when electrical power is not available or for work of a short duration. The tool operates like a pair of household scissors, which use the cutting action of two blades crossing over each other to shear the material.

Figure 4.42 Hand shears Figure 4.40 Powered jig saw

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112 Pipe and tube cutting

Pipe and tube can be cut using a hacksaw quite successfully. The operator must control the saw so that the cut is square across the pipe and remains square as the cut is made down through the pipe. Some people find this difficult, so the pipe cutter has been developed to enable a repeated number of cuts to be made with less difficulty, and produce a pipe end that is square in both directions.

The pipe cutter has a hardened steel cutter wheel, two rollers held in a moving carriage, and a handle. The handle moves the carriage up and down, closing or opening the gap between the cutter and the rollers.

With the pipe marked out for length, the cutter is aligned so that the cutter wheel is on the mark. When the handle is tightened, the rollers meet the pipe and cause the cutter to bite into it. By rotating the whole cutter around the pipe and, at the same time, tightening the handle, the cutter slowly severs the pipe. The offcut of pipe should be supported so that it does not nip the blade, as this could cause it to break.

There are variations to this design, and roller cutters can be purchased to suit a range of pipe sizes and material. Some are specifically designed to enable pipe work to be cut when in position. A three wheel cutter is useful for awkward

Use eye protection when chiselling, especially metal or masonry, and be aware of others nearby, as the action will cause pieces to fly off, which can cause injury.

Keep the cutting edge of chisels sharp.

Ensure that the end being struck by the hammer has not ‘mushroomed’, as bits of metal can also fly off the chisel.

Do not use a chisel that has been ground down too short to handle with safety.

SAFETY TIP

Chiselling

Chisels come in a wide variety of shapes and sizes for different materials. They can require considerable skill to use properly, especially when working with wood or stone. MES

engineers are most likely to use just ‘cold chisels’ on metal or brickwork to remove material; for example, removing rusted or damaged nuts and bolts or cutting off rivet heads. The tip of the chisel, correctly positioned against a solid surface, will produce a shear effect when hit with a hammer.

Figure 4.43 Cold chisels

Remember

It is good practice to always remove the cutting debris from the pipe ends before it is jointed.

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113

Figure 4.44 Pipe cutters

Chop saw

The chop saw, or carborundum disc cutter, is gaining in popularity with MES engineers.

The tool uses a thin carborundum disc (similar to a grinding disc) mounted on an arm and driven by

a motor. The object that is to be cut is clamped tightly under the tool and the spinning disc

is brought into contact with it. The disc removes metal by grinding its way through

the object until it is severed. The machine will successfully cut pipe, sections, rod

and bar.

These tools are dangerous if used in the wrong way. Waste material is ejected as hot sparks, and the discs are thin and brittle and

sometimes break, which can cause pieces to fly off.

Figure 4.45

Chop saw

Remember

Do not use powered disc cutters unless trained and qualified to do so

locations. This has both rollers replaced by cutters, so now the cutter requires only the space for just over a third of a turn, instead of a full 360° rotation; very useful for work in a confined space, such as against a wall or in a corner.

Pipe cutters need to be well maintained, if they are to work efficiently. Ensure that you:

•

keep the tool well oiled

•

check pins for wear at regular intervals

•

check for broken or chipped wheels before use

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114

1. Describe the technique of soldering a copper fitting to a copper pipe.

2. List the tools required for cutting a small bore carbon steel pipe and the personal protective equipment that should be used when cutting pipework.

3. List two screwed pipe jointing materials. 4. Explain what a roll bender is.

5. List three safety practices associated with using a hydraulic press pipe bender.

6. Explain how a bolted joint is made.

7. List three types of spanners that may be included in an engineer’s tool kit. 8. List the four factors required when ordering fixing screws.

9. Explain how a bolted joint could be protected from shaking loose.

Knowledge check

Use the chop saw only where other people will not be affected. Use away from combustible and inflammable materials. Use a full-face visor.

Wear gloves to reduce the effect of vibration. Wear ear defenders.

Make sure that the material to be cut is clamped securely. Make sure all machine guards are in place.

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OVERVIEW

At first the novice engineer working on a site may be surprised at the amount of verbal instructions given and the freedom of the experienced MES engineer to adapt and improvise during the

working day. However, a closer look will reveal that these discussions are based upon plans and specifications for the

particular contract.

This chapter looks at the role of a MES engineer in:

• reading and interpreting plans and drawings • determining areas, volumes and quantities • understanding potential sources of error in

marking out, and how to reduce them

• marking out and setting out centre lines, angles,

parallel lines, squares and rectangles

• marking out pipe and tube for fabrication

Calculate and quantify

from drawings and

mark and set out

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116 The role of the engineer

Chapter 3 looked at engineering drawings and specifications. The skilled engineer is able to read a drawing of a component, noting size, shape, dimensions and relationships to other parts. He then will be able to transfer the information and mark out the details on the materials ready for cutting and shaping or set out locations for the installation of components. For example:

•

A service engineer needs to manufacture a replacement part that has a series of holes in it. They will determine the position of the holes from the drawing and mark out the centres and centre punch them before commencing drilling.

•

The installer consults the drawings and specifications to ascertain the positions of components. They then set out the positions by marking out the building structure for the bracket fixing positions.

•

The site foreman estimates the quantity of fittings required for the day ahead. They use their knowledge of drawing scales, graphic symbols and the contract specification to make up an order list.

Reading and interpreting plans and

drawings

Chapter 3 looked at the information that is to be found on engineering drawings, and other information that the MES engineer can expect to work with. A key element on any drawing is the title block, which shows the project that the document refers to and the version number.

Having confirmed that the document is the correct one for the task, the MES engineer must now be able to extract accurate information from it.

Remember

Always ensure that you are using the latest version of any document A 1050 1150 550 B C 400 450 500 D E 400 200 100

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If the drawing is produced with all dimensions marked, as in Figure 5.01, then we can work out quantities directly from this. For example, we could work out the total pipe requirements by adding up the lengths as marked and then estimate the fixings for each pipe length.

However, it is impractical to enter all the dimensions on a complex plan. It is better if the drawing is to scale and we can then measure all the dimensions from it. In general terms, MES drawing scales will be 1:100, 1: 50, 1: 20 and 1: 5. The scale is noted on the drawing in the title block.

The scales mean that if, for example, a line between two points on a drawing is measured with a rule and is 50 mm:

•

On a 1: 100 scale the true length would be 50  100, which is 5000 mm or 5 m.

•

On a 1: 50 scale the true length would be 50  50, which is 2500 mm or 2.5 m.

•

On a 1: 20 scale the true length would be 50  20, which is 1000 mm or 1 m.

•

On a 1: 5 scale the true length would be 50  5, which is 250 mm or 0.25 m. Direct reading from a drawing is made simpler by using a scale rule, which is marked out with the most commonly used scales.

Figure 5.02 Using a scale rule

Calculating areas, volumes and

quantities