Health & SafetyMaintenance ofD&T WorkshopEquipmentL254June 2006

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Strictly Confidential

Circulate to members and associates only

As with all CLEAPSS materials, members and associates are free to copy all or part ofthis guide for use in their own establishments.

CLEAPSSBrunel University

UxbridgeUB8 3PH

Tel: 01895 251496Fax: 01895 814372

E-mail: science@cleapss.org.uk© CLEAPSS® 2006 Web site: www.cleapss.org.uk

Contents

1 The scope of this guide 11.1 Introduction 1

1.2 Risk assessments 2

1.3 Maintenance of the learning environment 2

1.4 Maintenance of hand tools and equipment 2

1.5 Maintenance of machines 3

2 General principles of maintenance 32.1 Cleaning 3

2.2 Local exhaust ventilation systems 4

2.3 Electrical and gas installations 4

2.4 Lubrication 53 Detailed maintenance advice on workshop machines 5

3.1 Disc and belt sanding machines 5

3.2 Drilling machine 6

3.3 Bench-mounted jig saw 6

3.4 Band saw 7

3.5 Circular saw 7

3.6 Planing machines for wood 8

3.7 Radial arm saw 8

3.8 Wood-turning lathe 9

3.9 Metal-turning lathe 9

3.10 Milling machine - horizontal/vertical 9

3.11 Power hacksaw 10

3.12 Mortising machine 10

3.13 Double-ended, high-speed grinding machine 11

3.14 Polishing/buffing machine 114 Detailed maintenance advice on metal-heating equipment 11

4.1 Gas safety system 11

4.2 Brazing hearth and/or chip forge 12

4.3 Crucible furnace 125 Guide to cutting speeds 12

5.1 Drilling 13

5.2 Wood-turning lathe 13

5.3 Metal-turning lathe 13

5.4 Milling machine 13Appendix: Equipment register and maintenance log 15

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Guide L254Health & Safety Maintenanceof D&T Workshop Equipment

1 The scope of this guideThese notes have been prepared to give an overview of the way in which maintenanceof equipment will contribute to healthy and safe working conditions in design &technology (D&T), particularly in school workshops. The main focus is on resistantmaterials.

It should be read in conjunction with other CLEAPSS publications, particularly thefollowing.

• Model Risk Assessments for D&T in Secondary Schools and Colleges.

• Guide L225, Local Exhaust Ventilation in D&T.

• Leaflet PS62, LEV in D&T: Suppliers, Testers and Monitoring Equipment.

These, and other CLEAPSS publications relevant to D&T, will be found on theCLEAPSS D&T Publications CD-ROM, which should be in all relevant member schools.Any updates to publications on the CD-ROM, or any new publications, will be foundon the members’ part of the CLEAPSS web site: www.cleapss.org.uk. If you are unsureof your user name and password, please phone the CLEAPSS Helpline 01895 251496 ore-mail: password@cleapss.org.uk, making it clear you want access to the D&T area ofthe members-only web site and giving details of your school’s name and address.

1.1 IntroductionAll equipment used in design & technology will require some sort of maintenanceprogramme. This will range from ensuring that hand tools are maintained with sharpcutting edges to ensuring that machine tools are correctly lubricated and are main-tained in good order. It should be remembered that a blunt cutting tool is more danger-ous than a sharp one, since more force is required to make it cut. This applies to bothhand and machine tools. Cleaning of machines and equipment is an important part of amaintenance programme, since equipment that is clogged with dirt or dust is unlikelyto work in an efficient manner.

A regular maintenance programme should be established which should aim for prev-entative maintenance rather than emergencies. The frequency of maintenance willobviously depend on the amount of use of the equipment and the nature of the hazardsand risks. It is a good idea to have a check sheet for equipment and a plannedprogramme of checks. A sample of a possible check sheet is given in Appendix 1 and itis available on the members’ part of the CLEAPSS web site in an easily-modifiedelectronic file, DL254; see above for access. The checklists in sections 3 and 4 are alsoincluded in this download file. Where technicians are available, they are the obviouspeople to do the maintenance checks but anyone who does such work should betrained to do it properly.

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1.2 Risk assessmentsBefore maintenance of fixed equipment is begun, the hazards of doing it must havebeen identified and the risks assessed and controlled. It is clearly sensible to keep thewritten assessment until it is next needed. Whilst a visual inspection of the condition ofelectrical cables and the supply to fixed equipment such as workshop machines can bedone by anyone, on no account should unqualified people carry out electrical mainten-ance. Maintenance of gas equipment should also be carried out only by a qualifiedperson. If it is necessary to remove covers or guards from machines and other equip-ment, to permit maintenance or repair work, then the equipment should be isolatedfrom the power supply through the use of isolating switches or by unplugging from thesocket outlet. Where possible, isolators should be locked in the ‘OFF’ position. Noticesshould be placed on equipment to state that it is under repair and must not be used.Where possible, cutting tools that have sharp edges should be removed before repairsor maintenance are carried out. Where maintenance is required, but cannot be done atonce, equipment should be taken out of use until such time as the necessary work canbe carried out and a notice fixed to the machine to state that it must not be used.

1.3 Maintenance of the learning environmentThe condition of the learning environment is an important aspect of maintenance.Teaching, preparation and store rooms should be kept in a clean and tidy condition.Where necessary, the daily cleaning schedule should be modified to allow sufficienttime for proper cleaning to take place. Removal of wood dust is best done with a suit-able industrial vacuum cleaner1 rather than by brushing. All waste materials should beremoved at the end of the school day.

Consumable materials, such as timber, should be properly stored in suitable racks andshould not obstruct doorways, fire exits, fire-fighting equipment, emergency-stop butt-ons or machines. The same is true about large items of pupils’ work.

Fire extinguishers should be hung on the correct type of bracket and should not be usedfor propping open doors. They will normally be checked by a competent person on aregular basis and the check should be recorded on the equipment itself. If this is nothappening, the head of department should inform the employer2.

Eye protection should be cleaned regularly. It is best if eye protection is kept in asuitable holder3 located next to the machine with which it is to be used.

1.4 Maintenance of hand tools and equipmentCutting tools with sharp edges should be maintained in good condition.

The frequency of sharpening will depend on the amount of use and the material beingcut. It is obvious that tools need to be sharpened when they are blunt. This means that a

1 A vacuum cleaner designed to collect wood dust must be used. General-purpose vacuum cleaners are unlikely to be

suitable, as they will not trap the fine dust involved. See the CLEAPSS leaflet PS62, LEV in D&T: Suppliers, Testers andMonitoring Equipment for companies that supply suitable models. This leaflet is updated as necessary. Check the latestversion on the members’ part of the CLEAPSS web site.

2 The employer for most maintained schools (strictly, community and voluntary-controlled schools) is the local authority. Forfoundation & voluntary-aided schools, academies, post-16 colleges and most independent schools, it is the governing body.

3 For example, in a self-sealing plastic bag, attached by Velcro to the wall. The bag should be labelled with the eye protectionsymbol. A graphic of such a symbol should be available in the science department, on the CLEAPSS Science PublicationsCD-ROM. We hope to make it available on a future edition of the CLEAPSS D&T Publications CD-ROM.

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planned programme of sharpening them every day, every week or every month maynot be adequate.

Paper for example, blunts scissors and craft knives very easily and it is better to use thetype of craft knife with replaceable blades, rather than attempting to sharpen them.Woodworking with blunt tools causes a particular problem since pupils, who may wellbe inexperienced and physically small, will need to exert excessive effort to cut timber.This then presents an additional hazard because they are unable to control the forceneeded. Chisels and the blades of planes may need sharpening every week, dependingon the amount of use.

Teachers who have a detailed knowledge of woodworking will know that some typesof timber wear down sharp-edged tools very quickly and sharpening may be neededmuch more frequently than once each week. Depending on the amount of use, sawsused to cut timber will typically need sharpening once a year. These days, it is oftencheaper to buy new bench saws than to have the old ones sharpened, especially in partsof the country where it is difficult to find companies with the expertise to carry outsharpening. Proper storage of tools with sharp edges will help to maintain the sharpedge. Planes should be stored so that the blade is not touching a surface; they should belaid on their side on the work bench when not in use. Wood chisels should be stored inproper racks with the cutting edges protected, as should craft knives. Handles of filesneed to be checked for splits, and for tightness of fit onto the tang of the file. Thehammered end of tools such as centre punches and cold chisels will occasionally needgrinding to remove burrs.

1.5 Maintenance of machinesThe amount of machine maintenance will depend on the type of machine and the wayin which it is designed. Many schools still use older machines of heavy cast-ironconstruction. These machines were often designed for industrial use and are normallyvery robust. Whilst sometimes dated in appearance, they will normally last a long timein school use. In contrast, modern machines are frequently constructed from steelpressed into shape and are not nearly as robust as the older models. Some schoolspurchase machines designed for the d-i-y market. These types of machines are designedfor infrequent d-i-y use, rather than the more-frequent use which would be the norm inschools and are unlikely to give long service. Their purchase may prove to be a falseeconomy.

2 General principles of maintenance2.1 CleaningAll machines should be cleaned regularly, although the frequency of cleaning willdepend on the amount of use. This will range from the normal cleaning to removesawdust, chips or swarf after use, to a more-thorough cleaning each week. Woodwork-ing machines such as band saws, circular saws and planing machines should bechecked to see that dust and chips are being removed by the dust-extraction system.Some types of band saw have the collection point for dust located in a poor positionand dust is often not removed effectively from all crevices. In these cases, an industrialvacuum cleaner specifically designed to collect dust should be used to remove it duringgeneral maintenance.

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2.2 Local exhaust ventilation systems4

The filters of dust-extraction systems should be cleaned at frequent intervals, at leastweekly, to remove the dust and the collection bags or trays emptied frequently. Notethat appropriate dust masks should be worn during emptying. (Type FFP2 is suitablefor ordinary saw dust but type FFP3 should be used if there is a lot of fine dust, eg,from MDF.) Wood dust should be disposed of in sealed bags and not tipped looselyinto a dustbin. The ducting of dust-extraction systems needs checking to ensure thatslivers or chips of wood are not obstructing it, especially on bends. This can impede theair flow and reduce the efficiency of the system. Note that the COSHH Regulationsrequire local exhaust systems to be examined at least every 14 months and a recordmaintained of the efficiency of the system. A notice should be fixed to each extractionunit to indicate that it has been checked on a particular date.

2.3 Electrical and gas installationsThe condition of electrical cables, fixed and flexible conduit should be visually checked.The operation of all switches (including isolating, no-volt release and overloadswitches) should be checked. The operation of emergency-stop buttons in workshopsshould be checked once every half term. Flexible conduit in particular needs checkingto make sure that there are sound connections at each end. Isolators need to be checkedby the operation of the lever to ensure that they do in fact cut off the power to themachine and that the lever moves easily. Checking that an isolator breaks all powerconnections to the machine (ie, line and neutral or all three phases and neutral) is bestleft to a person competent to do it. (This is unlikely to be a member of the school staff.)Care should be taken to ensure that access to isolators is not impeded by machines,furniture or materials. The operation of residual-current devices (earth-leakage circuitbreakers) should be checked by the use of the test button on the device.

Portable electrical equipment needs to be checked as required by the Electricity at WorkRegulations. It is for the employer to decide who does the checking. Sometimes, acontractor may go round from school to school. Elsewhere the task may be delegated tothe school which in turn may employ a contractor or use its own, suitably-trained, staff.The time interval for testing is not directly specified but most employers expect mostequipment to be checked annually. However, equipment subject to arduous or heavyuse, such as power tools and extension leads, should be inspected more frequently.Items that are rarely unplugged, eg, refrigerators, may only need checking every 3 or 4years. The operation of electrical interlocks on machine guards should be checked toensure that they function correctly.

Guidance from the HSE5 on the Electricity at Work Regulations suggests that fixed elec-trical installations should be inspected at least every 5 years, although this is normallyarranged by the employer. There is a similar requirement for the inspection of gasinstallations6. However, heads of department should check that this is happening and,

4 For more details, see the CLEAPSS guide L225, Local Exhaust Ventilation in Design and Technology, available on the

CLEAPSS D&T Publications CD-ROM.5 Guidance Note GS23, Electrical safety in schools, HSE, 1990. Although this is now out of print, the HSE has informed

CLEAPSS that it regards most of the advice as still valid.6 IM/25 Guidance Notes on Gas Safety in Educational Establishments, British Gas/DES, 1989, paragraph 2 stated that

checking of the soundness of gas supply pipework should not normally be needed more often than once every five years.However, its replacement IGE/UP/11 Gas installations for educational establishments, IIGEM, 2004, offers morecomplicated advice.

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if not, should take steps to ensure that the employer is informed. The contractor carry-ing out such tests should apply labels to the equipment to indicate when testing hasbeen done. There will also be records made but these may go to the employer or beheld by the bursar.

Hoses on gas equipment should be checked for damage before use and replaced whererequired.

2.4 LubricationMoving parts of machines will require lubrication. Some machine bearings are ‘sealedfor life’ and will not require additional lubrication. For other machines, oil or greasingof bearings will be required. Lathes with geared headstocks, and some drillingmachines that have a gearbox, will have an oil reservoir that will need checking and re-filling as required. The feed drives on planing machines for wood will require checkingand cleaning. Excess dust should be removed and chain drives should be greased.Machines such as metal-turning lathes, milling machines and power hacksaws willneed the slideways lubricated as necessary.

It is good practice to apply a coat of a thin lubrication oil (eg, as used in motor cars) tobright metal parts of tools and machines at the start of holiday periods, especiallywhere there is likely to be excessive moisture in the air.

3 Detailed maintenance advice on workshop machines

3.1 Disc and belt sanding machinesDaily check

• Clean any dust not removed by the extraction system.• Check condition of sanding belt/disc and replace if torn/worn.• Check fit of sanding table to disc/belt (it should be as close as possible, normally

no greater than 2 mm).• Check that quadrant guard is in the correct position.

Weekly check

• Clean filters in dust-extraction system, if fitted.• Empty dust-collection tray/bag if fitted.• Visually check condition of electrical switches, conduit, cable, etc.• Lubricate if necessary.

Termly check

• Check condition of motor, drive system and drive belts, if fitted. Replace if worn.• Lubricate if necessary.• Check operation of dust-extraction system.• Check bearings for wear.

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3.2 Drilling machineDaily check

• Check that the chuck guard is clean, functions correctly and is not cracked/broken.• Make sure that the guard over the driving belt fits correctly and that the inter-

lock or securing device is in place and working correctly.

Weekly check

• Make sure that the chuck key fits correctly and is not worn.• Visually check condition of electrical switches, conduit, cable, etc.• Lubricate if necessary.• Make sure that the drill head clamping bolts are tight and the head locking ring

is in place.• Make sure that the table clamp functions correctly.• Check condition of drill bits. Sharpen as required. Replace twist drills that have

worn shanks.• If wooden blocks are used under the work piece, replace those that are worn.

Termly check

• Check condition of motor, drive system and drive belts. Replace if worn.• Lubricate if necessary. Machines with gears running in an oil bath should have

the oil level checked.• Check bearings for wear.• Check that machine vices and hand vices function correctly and are not worn or

clogged with waste materials.

3.3 Bench-mounted jig saw

Daily check

• Clean any dust not removed by the extraction system.• Check condition of blade and replace if blunt.• Check that blade guard is correctly set.• Where fitted, check that machine ‘foot’ functions correctly.

Weekly check

• Clean filters in dust-extraction system, if fitted.• Empty dust-collection tray/bag, if fitted.• Visually check condition of electrical switches, conduit, cable, etc.• If fitted, check fit of table insert and replace if required.• Lubricate if necessary.

Termly check

• Check condition of motor, drive system and drive belts, if fitted. Replace if worn.• Lubricate if necessary.• Check operation of dust-extraction system.• Check bearings for wear.

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3.4 Band sawDaily check

• Clean any dust not removed by the extraction system.• Check condition of blade; replace if blunt or if welded joint on blade is suspect.• Check that blade guard is correctly set.• Check that machine braking system functions correctly.

Weekly check

• Clean filters in dust-extraction system, if fitted.• Empty dust-collection tray/bag, if fitted.• Visually check condition of electrical switches, conduit, cable, etc.• If fitted, check fit of table insert to blade and replace if required; (the gap

between the insert and the blade should be no greater than 4 mm).• Check blade guides and thrust wheel for wear and adjust/replace as required.• Check tracking setting and condition of rubber tyres on blade wheels, if fitted.

Replace if required.• Lubricate if necessary.

Termly check

• Check condition of motor, drive system and drive belts, if fitted. Replace if worn.• Lubricate if necessary.• Check operation of dust-extraction system.• Check bearings and blade guards for wear and replace if necessary.

3.5 Circular sawDaily check

• Clean any dust not removed by the extraction system.• Check condition of blade and replace if blunt.• Check that top or crown guard is correctly set and connected correctly to the

extraction system, if the latter is fitted.• Check that machine braking system functions correctly.

Weekly check

• Clean filters in dust-extraction system, if fitted.• Empty dust-collection tray/bag, if fitted.• Visually check condition of electrical switches, conduit, cable, etc.• Lubricate if necessary.

Termly check

• Check condition of motor, drive system and drive belts, if fitted. Replace if worn.• Lubricate if necessary.• Check operation of dust-extraction system.• Clean the inside of the machine using an industrial vacuum cleaner.• Check fit of table insert, if fitted, and replace if required.

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• Check bearings and replace if necessary.• Check condition of crown guard and replace if necessary.

3.6 Planing machines for wood:overhand planer, thicknesser, combined planer / thicknesser

Daily check

• Clean any dust/shavings not removed by the extraction system.• Check that all guards are correctly set.• Check that machine braking system functions correctly.

Weekly check

• Clean filters in dust-extraction system, if fitted.• Empty dust-collection tray/bag, if fitted.• Check condition of blades and replace if blunt.• Visually check condition of electrical switches, conduit, cable, etc.• Lubricate if necessary.

Termly check

• Check condition of motor, drive system and drive belts. Replace if worn.• Check condition of feed roller drive, clean, overhaul and lubricate as required.• Lubricate if necessary.• Check operation of dust-extraction system.• Check bearings and blade guards for wear and replace if necessary.

3.7 Radial arm sawDaily check

• Clean any dust not removed by the extraction system.• Check that blade guard and side-protection guards are correctly set and function

as required.• Check that machine braking system functions correctly.

Weekly check

• Clean filters in dust-extraction system, if fitted.• Empty dust-collection tray/bag, if fitted.• Visually check condition of electrical switches, conduit, cable, etc.• Check condition of rear timber support and replace if necessary.• Check condition of blade and replace if blunt.• Lubricate if necessary.

Termly check

• Check condition of motor and drive system.• Lubricate as necessary.• Check bearings and blade guards for wear and replace if necessary.

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3.8 Wood-turning latheDaily check

• Clean any dust not removed by the extraction system, where fitted.• Check functioning of electrical interlock for top guard on headstock, or mechan-

ical fixing as appropriate.• Check that foot switch or other emergency-stopping device functions correctly.• Check that mandrel nose guard for unused spindle nose is in place.

Weekly check

• If fitted, check functioning of dust-extraction system.• Visually check condition of electrical switches, conduit, cable, etc.

Termly check

• Check condition of motor, drive system and drive belts. Replace if worn.• Lubricate as necessary.• Check operation of dust-extraction system.• Check bearings wear and replace if necessary.

3.9 Metal-turning latheDaily check

• Clean chuck guard and any chip screens if fitted.• Check functioning of electrical interlock on chuck guard.• Check that cover plate on outer end of hollow mandrel is in place.• Check functioning of electrical interlock on change wheel guard.

Weekly check

• Visually check condition of electrical switches, conduit, cable, etc.• Lubricate if necessary.

Termly check

• Check condition of motor, drive system and drive belts. Replace if worn.• Lubricate as necessary, including slideways.• On machines with geared headstock, check oil level in gearbox.• Check bearings for wear and replace if necessary.• If fitted, check coolant pump and system; clean if required.

Yearly check

• If a coolant pump is fitted, drain the coolant, flush out the system with cleanwater and replace the coolant every 12 months.

3.10 Milling machine - horizontal/verticalDaily check

• Clean all cutter guards.• Check sharpness of milling cutters; take out of use any that are blunt or damaged.

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Weekly check

• Visually check condition of electrical switches, conduit, cable, etc. This shouldinclude any separate motors used for power feeds.

• Lubricate if necessary.

Termly check

• Check condition of motor, drive system and drive belts. Replace if worn.• Lubricate as necessary, including slideways.• Check bearings for wear and replace if necessary.• If fitted, check coolant pump and system.

Yearly check

• If a coolant pump is fitted, drain the coolant, flush out the system with cleanwater and replace the coolant every 12 months.

3.11 Power hacksawDaily check

• Check condition of blade and replace if blunt, or damaged.• Check that machine functions correctly.

Weekly check

• Clean machine of swarf/metal dust.• Visually check condition of electrical switches, conduit, cable, etc.• Lubricate if necessary.

Termly check

• Check condition of motor, drive system and drive belts, if fitted. Replace if worn.• Lubricate as necessary, especially sliders of saw arm.• Check bearings for wear and replace if necessary.• Check functioning of dash pot and pressure-relief system.• If fitted, check coolant pump and system.

Yearly check

• If a coolant pump is fitted, drain the coolant, flush out the system with cleanwater and replace the coolant every 12 months.

3.12 Mortising machineIn most schools this machine is used infrequently. Therefore, the checks below shouldbe made before use, rather than on a regular basis.

Before use

• Check condition of chisel and auger bit; replace or sharpen if blunt or damaged.• Check that the vice functions correctly.• Check that all guards are in place, including the guard around the auger chuck.• Visually check condition of electrical switches, conduit, cable, etc.• Lubricate if necessary.

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Termly check

• Check condition of motor, drive system and drive belts, if fitted. Replace if worn.• Lubricate as necessary, especially sliders of motor frame.• Check bearings for wear and replace if necessary.

3.13 Double-ended, high-speed grinding machineWeekly check

• Clean eye screens and check that they are in the correct position.• Check position of tool rest and adjust if required; (the tool rest should be as close

as possible to the grinding wheel, normally within 3 mm).• Check condition of grinding wheels.• Visually check condition of electrical switches, conduit, cable, etc.

3.14 Polishing/buffing machineWeekly check

• Check position of spindle guards and adjust if required.• Check condition of polishing mops.• Visually check condition of electrical switches, conduit, cable, etc.

4 Detailed maintenance advice on metal-heating equipment

4.1 Gas safety systemMost school workshops that have several items of heat-treatment equipment will havea gas safety system which will not allow gas to flow through the system if a leak orother fault is detected, and which will stop the flow of gas if the electrical power isstopped, for example, if an emergency-stop button is operated. Where there is only oneitem of equipment, then the safety system is often built into the equipment itself.

The gas installation should be checked by a qualified gas engineer (ie, CORGI-regist-ered) every 5 years. A record of the check should be kept.

The functioning of the gas safety system itself can be checked by normal operation.Normally a warning light will indicate the presence of a fault. Any faults should berectified by a qualified, CORGI-registered gas engineer. The system and equipmentconnected to it should not be used until any faults have been corrected.

A gas shut-off valve should be installed in every room where there is a gas supply. Thisshould be located in an accessible position and should be labelled. It should bestandard practice to turn off the gas supply at the end of the school day, or earlier if theroom is not used in the last period of the day. This leaves the room in a safe conditionand serves as a check that the valve is working.

A shut-off valve should be fitted in the supply pipe to each item of equipment. Thisshould be turned off when the equipment is not in use, and at the end of the school day.

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In order to meet the requirements of the COSHH Regulations, the LEV system for heat-treatment equipment should be checked every 14 months.

4.2 Brazing hearth and/or chip forgeWeekly check

• Check condition of air and gas flexible hoses.• If fitted, check functioning of spark igniter.• Check function of gas shut-off valve.• Visually check extraction system.

4.3 Crucible furnaceNote In most schools this equipment is used infrequently. Therefore the checks belowshould be made before use, rather than on a regular basis.

Before use

• The crucible should be inspected for damage or cracks. Any crucible showingsigns of damage should be immediately discarded.

• Check condition of all personal protective equipment.• Eye protection/face shields should be free of scratches and fit the user

properly.• Gloves should be of an appropriate size, sufficiently flexible to use and free

of holes.• The buckles on aprons should fasten correctly.• Spats should fasten correctly.

• If a tilting type of crucible furnace is used, check that the tilt mechanismfunctions correctly.

• If the crucible is lifted out of the furnace and placed in a pouring ring, check thatthe lifting tongs and pouring ring are a good fit on the crucible.

• If fitted, check functioning of spark igniter.• Check function of gas shut-off valve.• Visually check fume-extraction system.

5 Guide to cutting speedsWhilst this section is not directly about maintenance, using the most appropriate speedwill prolong the life of cutting tools and machines, and will therefore reduce theamount of maintenance and repairs needed. It is possible to do quite complicatedcalculations in order to find the optimum speeds for machines such as drilling mach-ines, milling machines, metal-turning lathes and wood-turning lathes. However, in abusy workshop it may be difficult for a teacher to find time constantly to change thespeed of a machine; often a machine will be set at an ‘average’ speed which will copewith most situations. It is possible to apply some general guidelines for speeds, asdiscussed overleaf.

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As a general rule, the speed should decrease as the size of the cutting tool or workbecomes larger.

Harder materials should be drilled at a slower speed than softer materials. Oneexception is acrylic, for which a slower speed minimises the risk of swarf melting, re-solidifying and jamming the tool.

5.1 DrillingDrill speeds are given in revolutions per minute (rpm). An approximate guide tospeeds that will apply to most materials is given below.

Drill size Speed3 mm 3000 rpm6 mm 1500 rpm8 mm 1000 rpm

12 mm 800 rpm

5.2 Wood-turning latheLarge-diameter pieces of work should be turned at a slower speed than smaller items.The speed can be increased as the workpiece becomes more cylindrical. Often a fairlyheavy cut at a slow speed is more effective at removing materials than a light cut whichwill only remove dust and will blunt the tool more quickly. A fairly average speed forstarting most work is 1000 rpm. When glass papering, the speed can be increased.

5.3 Metal-turning latheThe general rule is that softer materials are turned at faster speeds than hardermaterials but the diameter of the material is important, with larger sizes being turned atslower speeds than smaller sizes. As a guide, 20 mm diameter mild steel should beturned at about 1440 rpm. 20 mm diameter aluminium should be turned at about 12 000rpm. If the tailstock chuck is being used for drilling, then the speeds for drillingmachines should be used as a guide.

5.4 Milling machineAssuming a 12 mm diameter end mill is being used to cut mild steel, the end millshould rotate at about 1450 rpm. On aluminium, the end mill should rotate at about11 000 rpm.

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