easa mod 7a bk 2 tools

8/21/2019 EASA Mod 7A Bk 2 Tools

1/87

Book 2 Module 7A

CATEGORY B1 B2HAND TOOLS

Licence By Post

For best examinationresults always use latest

issue number.

Licence By PostCopyright B EASA 66 7.3 ISSUE 04 0111


2/87


3/87

Licence By Post

No part of this study book may be re-produced or distributed in any form or by any means, orstored in a data base or retrieval system in whole or in part without prior written permissionfrom Licence By Post.

Books in the LBP series are regularly up-dated/re-written to keep pace with the changingtechnology, changing examination requirements and changing legal requirements.


4/87


5/87

AUTHORITY

It is IMPORTANT to note that the information in this book is for study/trainingpurposes only.

When carrying out a procedure/work on aircraft/aircraft equipment you MUSTalways refer to the relevant aircraft maintenance manual or equipmentmanufacturers handbook.

You should also follow the requirements of your national regulatory authority (theCAA in the UK) and laid down company policy as regards local procedures, recording,report writing, documentation etc.

For health and safety in the workplace you should follow the regulations/guidelinesas specified by the equipment manufacturer, your company, national safety

authorities and national governments.


6/87


7/87

CONTENTS

Page

Machine tools 1Hand tools 5

Hammers 5Punches 6Pliers 7Screwdrivers 8Spanners 9Hacksaws 12Hand files 13

Vices 16Chisels 19

Scrapers 20Drill bits 21

Taps 23Dies 26Reamers 28Rules measuring 30Dividers 30

Trammels 30Scribers 31

The fitters square 31The combination set 32Callipers 33Surface plates 33Marking-off table 33

Vee blocks 34Scribing block 34Key seat rule 35

Marking out 36Precision measuring equipment 38

The micrometer 38The vernier 45The dial test indicator (DTI) 54Bore gauge 55

Feeler gauges 56Radius gauges 56Screw pitch gauges 56

Wire gauge 57Slip gauges 57Sine bars 58Limit gauges 60

The spirit level 61Adjustable level 61Clinometer 62

Powered hand tools 63Torque loading 66

Torque wrenches 69Tensiometers 74The dead weight tester 76


8/87


9/87

HOW TO TACKLE THIS BOOK

This book is reasonably straight forward and with some students will be revision fromtheir days on basic training. However, the contents should be studied and learnt particularly the subject of precision instruments. Ideally check out eachtool/instrument using your own tool kit or tools from the tool store. This isimportant when dealing with precision instruments.

Practice as often as you can on micrometers (English and metric non-digital) andverniers (English and metric 24/25 and 49/50 systems non-digital). Make sure

you can read the various instruments and name the parts. When checking thereadings get some one to verify your readings and if necessary take practice readingson components several times using both micrometers and verniers for the samereading. You can always check your readings using a digital instrument.

There should be no need to commit to memory much detail concerning Machine Toolsbut a good understanding is required for all other tools including Power Tools.

Refer to book 3 in this series on the care, use and calibration of tools and equipment.


10/87


11/87

MACHINE TOOLS

The Lathe

Used for turning, facing, drilling and thread cutting. On modern production lines theyare automatic and controlled by computers.

The part to be worked on is placed in the chuck and when turned is shaped using avariety of lathe cutting tools. Operated by qualified machine tool setters and operatorsthe lathe can be used on a variety of materials including wood, composites andmetals.

Guards should be fitted when in operation.

Fig. 1 THE LATHE

Fig. 2 DRILLING MACHINE OR PILLAR DRILL

- 1 -


12/87

The Pillar Drill

Can be used by less experienced personnel to drill holes in a variety of materials. Mayhave a selection of drilling speeds either by the use of a selector lever or by changingthe belt on the pulley drive system from the electric motor to the drilling pillar. Feedrates usually depend on the operator but may be automatic on some machines.

The part to be drilled should be firmly gripped in a clamp (never held by the fingers),and the guard must be in place.

Milling Machine

Requires a skilled person to operate and may be a horizontal or vertical millingmachine. A horizontal mill is shown and is used for milling down metal to a closetolerance and good surface finish.

The part to be milled in clamped to the moving table which moves back and forthunder the cutting head with a height adjustment after each pass.

Fig. 3 MILLING MACHINE

Grinding Machine (Not shown)

Similar to a milling machine but will grind to closer tolerances and a better finish.

Centre-less grinding produces the most accurate dimensions and is used for theproduction of close tolerance matched cylinders and pistons (injectors).

Grinding Machine Bench Type or Off-Set Grinder

Most workshops and hangars have a grinding machine; the most common type is thedouble-ended bench machine with coarse and fine abrasive wheels or stones.

Tool rests are fitted in front of each wheel to support the item being ground. Guardsare also fitted and the user must wear goggles.

- 2 -


13/87

Tools being sharpened can be ruined if allowed to lose their temper by overheating.The item being sharpened must be dipped in water or oil to keep the tip cool(depending on the type of wheel).

When grinding, move the item being ground from side to side to avoid forming ridgeson the wheel, neveruse the side of the wheel.

From time to time the wheel will have to be dressed. That is, cleaned up and madeflat. This is carried out using a special dressing wheel and must be performed by aqualified person.

Safety Precautions

* ALWAYS wear protective goggles when using a grinding machine.* Make sure the tool rests are as close to the wheel as possible, but not

touching.* Do not grind soft metals or materials such as aluminium, brass,

magnesium etc.* The wheel should be dressed from time to time by a qualified person.

Fig. 4 OFF HAND GRINDING MACHINE

The Guillotine

Used for cutting sheet steel, aluminium, rigid composites, etc. Some machines may besmall enough to be fitted to a bench, others are self standing.

The guard allows only thin gauge metal to be cut and helps to prevent fingers from

being caught by the blade. Some machines have a double safety device fitted in theform of two levers. These are placed so that both hands must be used to operate them

whilst one foot is used to operate the blade. If the levers are not operated the footpedal is locked.

Folding Machine

Folds metals ductile/malleable enough to be bent. Great care is needed to ensure thatthe metal being folded is not cracked in the process. The counterbalance weights onthe machine allow for the considerable weight of the folding blade.

- 3 -


14/87

Fig. 5 GUILLOTINE

Fig. 6 FOLDING MACHINE

Fig. 7 FLY PRESS

- 4 -


15/87

Fly Press

Used to stamp out small sheet metal parts by a downward force of the stamping head.When the handle is pulled round the masses give the system momentum and themale die can be wound down quickly into the female die so pressing out a shape insheet metal.

HAND TOOLS

There is a vast range of hand tools and following is a description of the most of thosein common use.

HAMMERS

Classified by weight and type of head. Conventional hammerheads are forged from

high carbon steels with faces hardened and tempered. Shafts are made from straight-grained ash or plastic.

Some hammerheads are made from copper, plastic, rubber or leather. These headsare designed to allow a part to be hit without causing any damage to the part.

When using a hammer always ensure that the correct hammer is used and that thehead is secure. Hold the handle at the position farthest away from the head.

The main types are:

Ball Pein- The flat surface is used for most general work - the ball pain being used

for peening.

Cross Pein - The pein is at right angles to the shaft. Used for general work, thecross pein being suitable for use where access to the working area is limited(knocking in a small nails held by the fingers, for example).

Straight Pein The pein is inline with shaft and usage similar to the cross pein.

Nylon Faced - Used to deliver blows to the work without damaging thesurface.

Copper or Lead- Similar to the nylon faced hammer in terms of application.

Fig. 8 TYPES OF HAMMERS

- 5 -


16/87

PUNCHES

Centre Punch. Made of high carbon steel hardened and tempered. Used for makingpop marks for indentation to locate the point of a drill at the start of the drilling

operation. A sharp point should be maintained by grinding, the angel should be 90for general work and for light work such as marking out etc should be reduced to 60.

Remember that titanium should not be centre punched as it sets up high internalstresses.

Pin Punches Parallel and Tapered. Are both made of high carbon steel- hardenedand tempered. Punches are used with a hammer to localise hammer blows.

The parallel pin punch is used to drive out rivets, (after head removal), bolts, splitpins, shackle pins etc. Always use the correct size punch and never use a taperedpunch, as this will tend to enlarge the hole.

The tapered punch is used to deliver a blow to a part where access to a hammerheadwould be difficult.

Hollow Punch. Sometimes called a Hole Punch and is used to make small holes in softmaterials such as leather etc. The slot in the side of the punch allows for removal ofthe hole centres.

Rivet Punches. Usually called Set-ups, Snaps etc.

Set-ups, Dollies and Snaps are used in the forming of snap-head rivets. These arecovered in more detail in the books on riveting.

Fig. 9 THE CENTRE PUNCH

Drifts. These are flat ended punches either solid or tubular, which are used forlocalising the effect of hammer blows and preventing damage to finished surfaces.

Also used for dismantling and assembling tight fitting parts. Drifts are made fromcopper, brass, steel or aluminium alloy. Steel drifts only should be used to drive ballor roller bearings as softer drifts may break and fragments from the drift could lodgein the bearing. Ends must be clean and any damage/burrs removed.

- 6 -


17/87

Fig. 10 PUNCHES

PLIERS

There are various types of pliers, each designed for a specific use, eg

Combination. Can be used to hold round or flat material and have cutting edgesfor cutting split pins, locking wire etc.

Flat Nose. Used to hold items where access is limited.

Snip or Round Nose. For twisting locking wire.

Fig. 11 TYPES OF PLIERS

Diagonal or Side Cutting. Used for cutting soft wire and split pins.

Cable Stripping. For removing the insulation from electrical cables.

- 7 -


18/87

Circlip Pliers. Used for removing/refitting circlips, internal and external.

Pliers are classified by type and overall length, usually made of high carbon steel withthe jaws hardened and tempered.

SCREW DRIVERS

Common or flat bladed. Blade made of high carbon or alloy steel the end being groundflat to fit the slot cut in the head of the screw. The handle is made of wood or plastic.Classified by length of blade.

Ratchet. Usually flat bladed. Has a selector to allow for the ratchet to be locked or setfor screw removal or screw fitment.

Watchmakers. Has a long thin blade with a flat plastic handle. Used for smallerscrews such as in electrical work.

Fig. 12 SCREWDRIVERS

Pump Screwdriver. Pump operated on the Archimedes principle. Pushing or pumping

the handle turns the screwdriver via the screw mechanism. May be selected to lock orscrew in or screw out.

Phillips. Blade head has a cruciform shape tapered to the correct angle. The end ismachined with four tapered flutes that provide correct engagement with the slots andfaces of the cruciform recessed head of the screw.

Electric. These are usually battery powered and are re-chargeable. Bits are supplied ofdifferent sizes and shapes that fit into a chuck or adapter. The electric motor can becontrolled in such a way that provides for a varying speed and torque output.

- 8 -


19/87

All screw slots or recess should be cleared of paint or dirt before applying thescrewdriver head and the shaft of the screwdriver should be aligned with the screwduring use. Blade fit in the screw is most important otherwise the screw head will bedamaged making removal or tightening difficult. Use correct size screwdriver andnever grind the flat blade to a chisel head.

Fig. 13 TYPES OF BLADE

SPANNERS

These are supplied in a variety of forms and have the size marking stamped on them.This size relates to the size of nut or bolt to which it fits, eg

BSFBSW

0 BA etc.

or, which is common, the spanner is marked with the across flats size, eg

32mm etc

This size relates to the distance across the flats of the nut or bolt.

Open-Ended Spanners . Made of high carbon steel with a different size at each end.The length of the spanner is indicative of the torque to be applied to the nut/bolt(based on the strength of the average person). The greater the size, the longer thespanner. This rule also applies to ring spanners.

Ring Spanners. These give full enclosure to the bolt head or nut. Each corner fitssnugly with an angle in the aperture of the spanner and is usually bi-hexagonal tofacilitate its use when angular movement is restricted. Supplied in double-ended formto fit nuts of consecutive sizes, the ends are generally off set but straight shank typesare available.

- 9 -


20/87

Fig. 14 OPEN-ENDED SPANNER

Fig. 15 RING SPANNER

Box Spanners. These also fully enclose the nut or bolt head and are particularlyuseful where access to the nut or bolt head is restricted to the centre line of the screwaxis automobile spark plugs for example.

Fig. 16 BOX SPANNER WITH TOMMY BAR

Socket Spanners. These are used with various types of attachments and again thistype of spanner fully encloses the nut or bolt head. The socket aperture is bi-hexagonal at one end and at the other end the aperture is square to take the variousattachments. Attachments can include: extension bar; drive bar; T bar; universal

joint; flexible extension bar and reversible ratchet. Socket spanners are usuallysupplied in sets complete with the requisite attachments.

C Spanners. Used on ring nuts with recesses cut round the circumference toaccommodate the lug on the spanner.

Peg Spanners. Two round pegs protruding from the flat surface engage incorresponding holes in special nut or screw plates.

Splined Spanners. For use on circular splined nuts.

Adjustable Spanners. These are supplied in various forms and should not be used ifthe correct size ordinary spanner is available.

- 10 -


21/87

Fig. 17 SOCKETS & ATTACHMENTS

Fig. 18 C SPANNER

Fig. 19 PEG SPANNER

Fig. 20 SPLINED SPANNER

- 11 -


22/87

Fig. 21 ADJUSTABLE SPANNER

Torque Spanners. These will be dealt with in more detail under the heading TorqueLoading. In most instances a socket is used to fit the square drive of the torquespanner.

HACKSAWS

These are designed to cut most types of metals and other hard materials. They

usually consist of a frame, handle and removable blade.

The frame is made of mild steel and may be of fixed length or adjustable length to suitvarious lengths of blades. The blade is usually located on two pins one at each endof the frame.

There are two main types of blade:

(i) High carbon flexible steel, hardened and tempered.(ii) High Speed Steel, contains 14% tungsten. Remains sharp over a longer

period but is more brittle and expensive.

Blades are classified by their length, material and number of teeth per inch (pitch).The number of teeth per inch varies from 14 (coarse) to 32 (fine). Normal bladelengths are 8 inches (203mm), 10 inches (254mm) and 12 inches (305mm) but otherlengths are available.

Fig. 22 CUTTING THICK & THIN MATERIAL

The choice of blade depends on the type of material to be cut. Soft metals (egbrass, aluminium etc) require coarse pitch blades. Hard metals (eg iron and steel)require fine pitch blades.

The shape and thickness of the material must also be considered. At least threeteeth must be in contact with the material at any time, therefore, fine blades must

always be used for tubing and thin metals.

- 12 -


23/87

QUESTION List the checks and precautions to take when using a hacksaw? (10mins)

ANSWER There are lots of checks and precautions to take. Some are:

(a) Choose the correct type of blade.

(b) Choose the correct length of blade with the correct pitch (teethper inch - tpi).

(c) Fit the blade to the frame with the teeth pointing away from thehandle.

(d) Tension the blade correctly by taking up the slack thenapplying two or three turns of the wing nut.

(e) Make sure that the work is secured in the vice.(f) Use long steady strokes using the whole length of the blade

releasing the pressure on the back stroke.

Other Types of Metal Cutting Saws

Junior Hacksaw. Uses a small flexible blade usually with 32tpi. It is used for generallight work where a standard hacksaw would be too large. The blades have pins ateach end, which fit into slots in the frame. Tension is applied by the elasticity of theframe.

Piercing Saw. Uses a very fine (32 80tpi) blade. The frame is deeper than the JuniorHacksaw and it is used for cutting intricate shapes in sheet metal.

Coping Saw. Uses a coarse (14tpi) blade. The blade fits in a frame similar to theJunior Hacksaw but it can be swivelled to any angle and is used for cutting shapes in

soft materials such as wood.

Tension Files (eg Abrafiles). The blades are made from a specially heat-treated flexiblesteel wire with small burrs cut into them and using links they can be fitted to astandard hacksaw frame. They are useful for cutting intricate shapes as they can cutin any direction and do not clog. Blades are obtainable in three grades:

* Fine* Medium* Coarse

HAND FILES

Used for the removal of metal to an accuracy of plus or minus about 0.001(0.025mm) with skill.

Files are made from High Carbon Steel and consist of the body, which is hardenedand tempered, and a tang which is left relatively soft. A handle is fitted, usually madefrom wood (Beech or Ash) and a ferrule made from steel or brass. The ferrule preventsthe wooden handle from splitting. Some files are supplied already fitted with a plastichandle.

- 13 -


24/87

Fig. 23 A HAND FILE

Classification

Files are classified by length, cut, section and grade.

Length This is the length of the file excluding the tang.

Section This is the cross-section of the file:

(a) Flat Usually a double cut file and is used for general work.Sometimes one edge is left without teeth to permit workingagainst a finished surface.

(b) Half Round This file tapers towards the tip. One surface is flatand the other is curved. It is a general purpose file which can also

be used for filing concave surfaces. It is double cut on both sides.

Fig. 24 FLAT FILE

Fig. 25 HALF ROUND FILE

(c) Triangular or Three Square This file has three sides each at 60

to the others. It tapers towards the tip and is used for filing in

awkward corners and angles less than 90. It is double cut on allsurfaces.

(d) Square Used for slotting, grooving and finishing square edges. Ittapers for part of its length and is double cut on all surfaces.

Fig. 26 THREE SQUARE FILE

- 14 -


25/87

Fig. 27 SQUARE FILE

(e) Round Used for filing out concave surfaces and holes. Usuallydouble cut and tapering towards the end. Small round files aresometimes called rat tails.

Fig. 28 ROUND FILE

Cut

This denotes the type of teeth.

(a) Single Cut Used mainly on hard metals. The teeth are formed by aseries of cuts parallel to each other but at a small angle.

(b) Double Cut Are the most widely used. They have two series of cutswhich cross each other, one series being coarser than the other. Theteeth of these files tend to clog more easily than single cut files.

Fig. 29 CUT OF A FILE

(c) Dreadnought Suitable for heavy cutting of soft metals. They are singlecut files but with teeth curved in an arc.

(d) Rasp These files are used for coarse work on soft materials (eg lead,wood etc). Each tooth is cut separately by a single pointed tool.

Grade

This defines the depth and spacing of the teeth. The grades are (in decreasing order ofcoarseness:

(a) Bastard A coarse grade which removes metal fairly quickly. Intendedfor roughing out, or completion of a job where finish is unimportant.

- 15 -


26/87

(b) Second Cut A finer grade which gives a better finish but is slowercutting. The most common grade.

(c) Smooth The teeth are shallow and closely set enabling a good finish tobe obtained. Cuts comparatively slowly and should be used for finishingwork only.

(d) Dead Smooth The smoothest grade of file. Not often used.

Filing Method

Cross filing (holding the file at both ends and using the file at right angles to the work)is used for general-purpose work and for squaring and roughing down. Draw filing(holding the file in line with the work) is used for finishing and for most filing work.Once the cross filing has been completed, the surfaces can be draw finished until allthe cross filing marks have disappeared.

QUESTION Can you list 4 or 5 precautions to be observed when filing? (10 mins)

ANSWER The precautions include:

1. Never use a file without a handle. Most files are supplied with ahandle attached.

2. Always use the length, type and grade of file appropriate for thejob.

3. Secure the work in the vice (if possible) so that it is rigid andpositioned to enable filing to be done horizontally.

4. Whenever possible use the full length of the file for each stroke.Do no rush, and as the file only cuts on the forward stroke relievethe pressure on the return.

5. Keep the file teeth clean using a scratch card. Where cloggingmaterial cannot be removed by this method, pick it out with asharp point (ice pick). Chalk rubbed on the teeth during the finalfinish helps prevent clogging and produces a finer finish.

6. New files should, if possible, be used first on brass, cast iron orsimilar metals before using on steel. This helps to harden themoff.

7. Files are brittle. To prevent breakage or dulling of teeth, store

them separately after use and do not strike them with, or on, anyother hard material.

VICES

The Bench Vice - provides rigid support for work at the bench. It allows both hands tobe used when sawing, filing, drilling, bending etc.

The body of the vice is normally manufactured from cast iron and has detachablehardened steel jaws. It is made in two parts:

(a) The main body, which contains a fixed nut or half nut and is bolted tothe workbench.

- 16 -


27/87

(b) The sliding part which fits into the main body and is moved backwardsand forwards by means of a screw thread. This screw thread engages

with the nut in the main body. Turning the screw thread, by means of atommy bar, in a clockwise direction closes the jaws and in an anti-clockwise direction opens the jaws.

Some vices have a quick release mechanism, which allows the sliding part to bepositioned quickly. With a quick release mechanism, a half nut is used and operationof a lever disengages the half nut from the screw thread. The screw thread is usually asingle start square or buttress type.

Objects with machined or smooth surfaces can be protected, when held in a vice, byusing clams. These can be made from copper, lead or aluminium. Tubing can beprotected by the use of hardwood V blocks.

Fig. 30 THE BENCH VICE

Precautions and Maintenance

The vice should be mounted such that the top of the vice is level with the workerselbow when he/she is standing (or sitting for some disabled) next to the vice.

Precautions include:

* Ensure the vice securing bolts are tight.* Ensure the vice is clean.* Clean the vice after use.* Keep the screw thread lightly lubricated.* Never use the vice as an anvil for hammering on.

Vices are classified by the width of their jaws, common size being 100mm (4 inches).

- 17 -


28/87

The Machine Vice used on drilling and shaping machines to hold the work piece.

The body of the vice is manufactured from cast iron or steel and the base is slotted sothat it can be bolted down to hold the work steady. For light drilling using a pillardrill, the vice can be held by hand.

The design of machine vices varies, but they all give a parallel grip. As with the BenchVice, one jaw is fixed and the other is sliding. The sliding jaw is moved by a screwthread, which is turned either by a knurled handle, a tommy bar or a cranked handle.No quick release mechanism is fitted to this type of vice.

Take care, when drilling, not to drill into the base of the vice. If possible, position apiece of wood under the work to be drilled.

Fig. 31 THE MACHINE VICE

Toolmakers Clamp - used for holding small pieces of work together for assembling,riveting or screwing.

They are made of case-hardened mild steel. A clip screwed to the top jaw locatesscrew A and thus prevents the jaws falling together when being adjusted. This type ofclamp gives a parallel grip in all positions. The jaws are adjusted to approximately thecorrect position and the final tightening is done by first adjusting screw A and thenscrew B.

The clamp is classified by the length of the jaws (normally 50 to 150mm).

Hand Vice - used for holding work for drilling, riveting etc. The body is made fromsteel and the jaws hardened and tempered. The spring is to keep the jaws apart withthe wing nut providing the clamping action.

- 18 -


29/87

Fig. 32 TOOLMAKERS CLAMP

Fig. 33 HAND VICE

CHISELS

Chisels are made from high carbon steel, hardened and tempered or nickel alloy steelspecially heat-treated to give a lasting cutting edge. The chamfered head is left soft

otherwise it would crack under repeated hammer blows.

Types of Chisels and Their Uses

1. Flat Used for general chipping work such as parting metal sheet orcutting flat surfaces prior to filing.

2. Crosscut Used for cutting grooves in a flat surface.3. Diamond Point Used for cleaning out corners and rectifying incorrect

drill starts.4. Half Round Used for cutting half round bottomed grooves and may

also be used for rectifying incorrect drill starts.

- 19 -


30/87

Selecting the Correct Chisel for the Job

Consideration must be given to both the nature of the work and the material to becut. The nature of the work governs the size and shape of the chisel. The type ofmaterial governs the cutting angle. For example, the cutting angle of aluminium alloy

is 30, mild steel 60and hard steel 70-75.

Care of Chisels

A damaged chisel edge is sharpened on a grindstone and finished on an oilstone.During grinding, the cutting edge must be kept cool by frequent dipping in water. Theend of the chisel struck by the hammer should be kept free from ragged ends and

burrs by grinding.

Fig. 34 CHISELS

SCRAPERS

These are made of high carbon steel hardened or tempered. They are used to producea very accurate finish on the surface that has already been as accurately finished aspossible by filing or machining.

Used mostly on steel. It is essential for scrapers to have a sharp cutting edge and thisis obtained by grinding on a grind stone followed by sharpening on an oil stone. Whennot in use, scrapers should be stored with their cutting edges suitably protected.

The types of scraper in general use are:

1. Flat Used to produce accurate flat surfaces.2. Three Square Useful for working in awkward corners.3. Half Round Used for scraping curved surfaces such as bearings.

To produce a flat surface, it is necessary to use a surface plate and Engineers Blue (ablue marking ink). Make sure that the surface plate and the work are clean.

Smear a thin layer if Engineers Blue on to the surface plate, then place the work onthe surface plate and move it backwards and forwards. Remove the work, and thehigh spots will be coloured blue. Remove the high spots using a scraper and then rubthe work on the surface plate again. Keep repeating the above procedure until the

work is as flat as possible. For some work a dead smooth file can be used in place of ascraper.

- 20 -


31/87

The same procedure can be used with journal bearings by applying engineers blue tothe journal.

Fig. 35 SCRAPERS

DRILL BITS

Used for drilling holes and are available in various forms to meet differentrequirements. Are manufactured from high carbon steel or alloy steel. Alloy steel drillsare sometimes referred to as high-speed drills as they can be used at much highercutting rates than high carbon steel drills. High-speed drills contain 14% tungsten,

which allows them to run hotter without affecting the temper (heat treatment).

The following types of drills are in general use:

Flat Drills Simple to manufacturer but tend to drill inaccurate holes. They are slowcutting, power wasting and do not clear the swarf produced. This leads to clogging

and overheating. The cutting angle varies for 5for hard material, to 20for soft

material such as brass. The point angle is 45.

Bottoming Drills Used to finish the bottom of a blind hole. A standard twist drillcould be modified for the same purpose.

Arboring or Peg Drills Used for counter-boring holes to provide a good seating for aBolt head or nut. It is also used to drill holes to receive a cheese head screw. Theprojecting pin on this type of drill must be the same diameter as the hole to becounter-bored.

Fig. 36 FLAT, BOTTOMING & ARBORING DRILLS

Twist Drills The most common type of drill bit in general use. The shank is the plainportion of the drill that provides the drive. The flutes allow for swarf clearance and

provide a means to allow coolant and lubricant access. The land provides forclearance to reduce friction.

- 21 -


32/87

The web of the drill increases in thickness from the tip to the shank to provide extrastrength. At the tip of the drill, the web forms a chisel edge.

The cutting angel is normally 59, (from the centre line), the cutting edges being of

equal angle and length. The angle between the web and the cutting edge is 130andthe clearance angle is 12. On large drills the web may be thinned by local grinding toreduce the size of this non-cutting edge.

Fig. 37 TWIST DRILL

NOTE. The cutting angel may be altered to suit specific drilling operations, egaluminium 90, brass 118, cast iron 118, copper 90, hard steel 130, mild steel

118, plastics 90.

Fig. 38 DETAILS OF TWIST DRILL ANGLES

Cutting Speeds

This depends on size, type of drill and the material being drilled, eg

twist drill cutting mild steel at 400 rpm twist drill cutting brass at 800 rpm twist drill on a certain metal 800 rpm twist drill on same metal at 200 rpm

- 22 -


33/87

In general, speeds depend on the peripheral speed of the drill so the larger the drillthe slower the rpm and the harder the material the slower the rpm.

Most smaller drill bits are placed in a self centring chuck on the drilling machine andthe grip exerted by the chuck is adequate, but a stronger grip is required with largerdrills so they usually have a Morse Taper terminating in a flat tang. The Morse Taper

(1 in 20) engages directly with the tapered adapter of the drilling machine. A slot isprovided in the adapter to remove the drill by inserting a wedge on top of the drilltang and tapping the wedge with a hammer to free the drill.

Fig. 39 MORSE TAPER DRILL & ADAPTER

QUESTION Do you know of any other standard tapers? (5 mins)

ANSWER Taper pins 1 in 48Taper keys 1 in 100

Lubrication

Prevents excessive heat by reducing friction, and helps preserves the temper of thedrill. It also helps reduce the heat at the cutting edge by transferring it away.

Suitable Lubricants:

Mild Steel Cutting oil or soapy water.High Carbon Steel Turpentine or paraffin.

Aluminium and Aluminium Alloys Paraffin.Brass & Cast Iron No lubricant needed.

TAPS

Taps are used for cutting internal (female) screw threads. They are manufacturedfrom high carbon or alloy steel hardened and tempered. They are fluted to providecutting edges, the shank is tough with the end squared to allow it to be turned with ahand wrench. Taps are supplied in sets of three except for BA sizes where the secondtap is omitted. Markings on the shank include, type of thread, the size and thenumber of tpi.

- 23 -


34/87

Fig. 40 A SECOND TAP

Types of Tap

1. Taper Tap Used for starting the thread and is tapered from the tip tothe sixth thread. The tip diameter is equal to the root diameter of thethreads. It will cut a full thread in a through hole.

2. Second Tap Used to deepen the thread cut by the taper tap in a blindhole or a hole through thick material. It is less tapered than the tapertap.

3. Plug Tap Used to finish the thread cutting at the bottom of a blind holeor a hole through thick material. It is not tapered at all.

QUESTION What is a blind hole? (2 mins)

ANSWER A hole that does not go completely through the metal.

Cutting Internal Threads

(a) The first step in producing a well-cut internal screw thread is to drill a hole ofthe correct size. This should be the core diameter of the thread, but practically,the hole needs to be slightly larger to prevent the tap from binding and possibly

breaking.

- 24 -


35/87

To find the correct drill to use, consult an Engineers Pocket Book, which willgive tapping drill sizes. If the book is not available, the correct drill size may beobtained by:

(i) Measuring the core diameter and taking the nearest size drill which isslightly larger than the core diameter.

(ii) Select a drill which will just pass through a nut of the correct size.(iii) The drill size may be specified on the shank of the tap.

(b) Having drilled a hole to the correct dimensions fit the tap with a hand wrenchand enter the tap into the hole perpendicular to the face. Turn in the cuttingdirection until the tap just starts to cut.

(c) Check the tap is sat in the hole square by using a square.(d) Continue turning in the cutting direction for half a turn, then reverse the

direction for a quarter turn. Continue the process turn forward back -until the tap bottoms in the hole or protrudes from the other side of the hole.

This continuous action will break the cuttings into chips and prevent straining

the tap.(e) Continue cutting the thread as described until either the bottom of a blind holehas been reached or the full cutting length of the tap has been used.

(f) Change to the second or plug tap as required and continue until the thread hasbeen properly cut.

(g) Lubricate the work using the same lubricant as for drilling.

QUESTION Sometimes the tap may break in the hole usually through poorengineering practices. Can you think of any reasons why it might break?(3 or 4 reasons 5 mins)

ANSWER My list is as follows:(a) Using an incorrect tap size.(b) Hole too small.(c) Trying to force a tap too far down a blind hole.(d) Turning tap clockwise all the time.(e) Lack of lubrication.

Removing a Broken Tap

(a) If a sufficient amount of the tap is projecting above the surface it is sometimes

possible to remove the tap with a pair of pliers.(b) Providing the melting point of the work piece is well above the annealingtemperature of the tap, anneal both the work and the tap. The tap can then bedrilled out and the hole re-tapped. (This is a difficult process to do and mayaffect the heat treatment of the work so should only be carried out by qualifiedand experienced engineers).

(c) Large taps may be unscrewed or broken into pieces with a punch or chisel.(d) Broken taps can be removed using an extractor. There are two types:

(i) A screw extractor which has a left-hand thread. It requires the tap to beannealed and drilled.

(ii) For larger taps only, an extractor can be used that has a set of prongs

which fit inside the flutes of the tap. No drilling or annealing is required.

- 25 -


36/87

(e) Using an Ezi-Out. A tapered coarse threaded tap with a left-handed thread,more or less the same thing as an extractor. The broken tap is drilled and theEzi-Out is screwed in anti-clockwise. The Ezi-Out is tapered and as it isscrewed in so it tightens in the hole and will (hopefully) cause the tap to screwout.

Broken taps are notoriously difficult to remove. It is best not to break them in the firstplace.

DIES

These are for cutting male threads. There are two types of die:

Circular This type is generally used for cutting smaller threads. Slight adjustmentcan be effected by the screws in the side of the stock. The die thread is tapered toallow an easier start to be made. When fitting the die to the stock, the tapered side

must always be away from the shoulder of the stock.

Fig. 41 DIE AND STOCK

Rectangular This is a two-piece die which is adjustable and is used for cutting largerdiameter threads. Two or three cuts may be required to cut the full thread, the die

being closed up after each cut. The die has tapered threads to allow easier starting.The engraved numbers on the two halves must be fitted on the same side.

Fig. 42 ADJUSTABLE DIES & STOCK

- 26 -


37/87

Cutting External Threads (Using Circular Die)

(a) Secure the work in the vice.(b) Slightly taper the rod end to assist the start. The round rod must have an

external diameter equal to the major or crest diameter of the thread to be cut.(c) Place the correct die in the stock and slacken the two outer screws. Tighten the

centre screw and re-tighten the outer screws.(d) Place the stock and die squarely on the rod and commence cutting the thread

using the same technique as for taps ( turn forward turn back).(e) With the thread cut, try a new nut on the new thread.(f) If further cutting is required, slightly loosen the centre screw of the stock,

tighten the two outer screws and re-tighten the centre screw.(g) Repeat the process in (d), (e) and (f) until the nut is a good fit on the thread.

Die Nuts

These are similar in shape to a hexagon or square nut and are used to clean orrestore a thread that has become damaged. They are turned using a spanner.

Fig. 43 DIE NUTS

Precautions Result if not observed

1. Use taps in the correct order. Difficulty in starting the thread,possible tap Breakage.

2. Ensure the die is the right way Difficulty in starting the thread.round in the stock.

3. Chamfer the rod before starting Difficulty in starting the thread.the die.

4. Use the correct size tapping drill. Oversize holes result in a partialthread. Undersize holes mayresult in a broken tap.

5. Check for squareness once Broken taps. Badly damagedcutting has started. thread.

6. Ensure blind hole is deep Hole too shallow in depth mayenough to allow for clearance cause a broken tap.of chippings.

- 27 -


38/87

7. Use a cutting solution where Overheating, binding, seizurenecessary. and consequent tap breakage.

Ragged or stripped thread.

8. When tapping a deep blind hole Tap breakage.withdraw the tap occasionally

to clear chippings.

9. Take a roughing cut with an Poorly furnished thread,undersize die first then follow stripped thread.

with a finishing cut.

Note. All thread cutting is done by hand unless you are a Machine Tool Setter andOperator.

QUESTION If you had to cut a male and female mating thread, which one would you

cut first and why? (5 mins)

ANSWER: The female thread should be cut first (taps). When the male thread is cutthe die is set to its largest setting on the first cut and is adjusted onsubsequent cuts so as to obtain a good fit between the male and femalethread, (occasionally trying the male thread in the female).

REAMERS

Reamers are used to finish drilled holes to accurate dimensions and give a smoothinternal finish. They are manufactured from high carbon or alloy steel and the flutes

provide a series of cutting edges. The amount of metal than can be removed by aparallel reamer depends on its size and the type of material being used. As a roughguide, the amount of metal that can be removed from a inch (13mm) diameter hole

by a parallel reamer is about 0.005 inch (0.127mm). With larger holes, acorrespondingly larger amount of metal can be removed.

Type of reamers include:

Parallel These only cut to one size and may have straight or spiral flutes. The size ismarked on the reamer.

Expanding These have separate blades that slide in slots which taper in depth. Theblades are held in position by two nuts. Alteration to the cutting size is made byloosening one nut and tightening the other. They are parallel reamers.

The reamer has 5 blades and therefore cannotbe checked for size by a micrometer orvernier calliper. It has to be checked using a Ring Gauge. (For information onmicrometers, verniers and ring gauges see the section Precision MeasuringInstruments in this book).

Shell These are hollow fixed size reamers used on close fitting mandrels or boringbars, which pass through the hollow centre. Used to ream long or deep holes such asgun barrels.

- 28 -


39/87

Fig. 44 REAMER TYPES

Taper These are used to prepare holes for taper pins. They are supplied in setsnumbered from 0 to 10, the taper being the same as the standard for taper pins (ie 1in 48).

Piloted These ensure that the reamer cuts centrally in the hole and is easier to use.The tapered end makes the reamer cut progressively and also ensures a neater hole atthe entry end.

Machine Reamers Have a tapered drive (Morse Taper) to fit directly into a drillingmachine or lathe.

Precautions During Use

Great care must be taken to ensure that the reamer enters square in the hole.Reamers must be hand turned and onlyin a clockwise direction whilst cutting andremoving. The same lubricants should be used as for drilling.

When drilling a hole that is to be reamed:

* Select a drill 0.005 inch (0.127mm) smaller than the reamer for aparallel reamer or 0.005 inch smaller than the small end of the reamerfor taper reaming.

* Always ream by hand using the correct wrench except for machinereaming and that should be carried out by a qualified person.

* When taper reaming for a taper pin, ream the hole so that the pin is ahand push fit with the small end flush with the bottom of the work. Thetaper pin is then hammered in (gently) so that inch (6.35mm)protrudes from the bottom with inch (3.17mm) showing at the top.

The taper pin is then locked into position by either:

(a) Peening.(b) Bending the legs out (split taper pin).(c) A nut (threaded taper pin).

- 29 -


40/87

RULES - MEASURING

The Steel Rule. Made from high carbon steel hardened and tempered, usuallygraduated in Imperial and metric units. Classified by length. Rules must be kept freefrom rust and must not be subjected to rough usage. After use clean and lightly oil.

Measuring Tapes. Can be obtained in various lengths usually marked off with bothmetric and Imperial scales. Tapes are made of linen, plastic or flexible steel. Whenstoring steel tapes clean and lightly oil. Remember that linen and plastic tapes can bemade to stretch if pulled and this can affect the indicated measurement.

DIVIDERS

Used to set out distances, scribe arcs and circles. The legs are made of high carbonsteel hardened and tempered; the spring of spring steel and the adjusting screw mildsteel. Classified by length of legs. The points should be kept sharp and the legs of

equal length by stoning on the outside. When not in use the points should beprotected by sticking them into a cork.

Fig. 45 DIVIDERS AND RULE

TRAMMELS

These consist of a bar with up to 3 adjustable trammel points attached. Using two ofthe points the trammel can be used to scribe large circles. Using 3 points the trammelcan be used to check bow in a member. The points may be adjusted for both heightandposition on the bar.

- 30 -


41/87

Fig. 46 THREE POINT TRAMMEL

SCRIBERS

Used for marking lines on the surfaces of work. They are made of high carbon steelhardened and tempered. Classified by length, like the points of dividers must be kept

sharp and protected when not in use.

Note. Materials such as aluminium alloy are notch sensitive ie will soon start todevelop

a crack at a notch or scriber mark when under stress. Therefore neverscribe a line onaluminium and its alloys unless it is a cutting line.

THE FITTERS SQUARE

Used for marking off lines at right angles to an edge or surface and checking for

squareness. Squares are made of high carbon steel hardened and tempered. Thesquare should be kept clean, lightly oiled and it its box when not in use.

To check for accuracy, check it against a master square or place on a known trueedge, scribe a line down using the blade as the guide. Reverse the square on theknown true edge and any error will show up as twice the actual error.

Fig. 47 THE FITTERS SQUARE

- 31 -


42/87

THE COMBINATION SET

A combination set is three tools in one, consisting of a blade which is graduated ininch and metric scales and fitted as necessary to one of the heads. There is a centralgroove along its entire length, which accommodates the clamping screw fitted to eachhead. There are three heads made of close grained cast iron:

(a) Square Head This is provided with two working faces one at 90, the other at

45to the blade thus enabling it to be used as a square and as a mitre. Aspirit level is incorporated in the head and a scriber is also fitted.

(b) Centre Head This is used in conjunction with the blade to locate the centre ofround bars, etc.

(c) Protractor Head This is used in conjunction with the blade for checking orsetting any angle up to 180. A spirit level is often incorporated. The accuracy

is 1.

Fig. 48 THE COMBINATION SET

Fig. 49 USE OF HEADS

- 32 -


43/87

CALLIPERS

Inside and outside - are used in conjunction with a rule or other measuringinstrument for measuring distances between or over surfaces or for comparingmeasurements. To set the callipers set them close to size, by hand, then adjust to thecorrect size by tapping one leg (not at the point) against a rigid object. Odd leg

callipers are used for finding the centre of a round bar and for scribing lines parallelto an edge or surface. Sometimes referred to as Jenny Callipers.

Fig. 50 TYPES OF CALLIPERS

SURFACE PLATES

Made of cast iron and accurately machined and hand finished to provide a dead flatsurface. Provided with three feet to prevent rock; the undersides are ribbed to prevent

warping and twisting of the top face. Always keep clean and lightly oiled. When not in

use keep covered with a wooden cover preferably felt lined soaked with oil. Avoiddamaging surface. Do not drop tools or work onto the surface.

Fig. 51 SURFACE PLATE

MARKING-OFF TABLE

Used to support work for marking-out and form a base from which measurements canbe taken. Made of close-grained cast iron and are strongly ribbed on the underside forrigidity. They are free standing usually with 3 legs to prevent wobble.

- 33 -


44/87

The working surface is accurately machined to give a true flat surface and the edgesare square. To preserve the surface no work other than marking out or measurementshould be done on the table. After use the surface should be lightly oiled and thencovered with a wooden cover.

VEE BLOCKS

Used on the marking-off table or a surface plate to support round work, they aremade of cast iron or mild steel case hardened and are supplied in matching pairs,each one of the pair being stamped with the same identification number. All surfacesare accurately machined and the Vee angle is 90. Vee blocks are classified by themaximum diameter of the work which can be held. Can also support square work at

45.

Fig. 52 VEE BLOCK BOLTED TO ANGLE PLATE

SCRIBING BLOCK

Used to mark out lines parallel to a true surface, such as the marking off table orsurface plate. The accurately machined base is made of cast iron or case hardenedmild steel. The scriber is made of high carbon steel hardened and tempered. The pillarangel and scriber height and angle are adjustable. A fine adjustment is provided forthe pillar angle. Dowels in the base can be pushed down to serve as guides againstthe edge of the marking off table so that lines can be scribed parallel to the edge. Are

classified by the height of the pillar.

- 34 -


45/87

Fig. 53 USING VEE BLOCKS SCRIBING BLOCK AND A DTI

Fig. 54 SCRIBING BLOCK BEING USED TO MARK THELARGEST SQUARE ON THE END OF A ROUND BAR

KEY SEAT RULE

Sometimes called a box square and is used for marking off lines parallel to the axis onthe surface of tubes or round bars. Are usually graduated and are classified by theirlength.

- 35 -


46/87

MARKING OUT

To Find Centre of Round Bar

Fit bar in Vee blocks on the surface table; with the scribing block set approximately

one third diameter scribe a line across the end of the bar; rotate bat 90; check withfitters square for verticality; with scriber set at the same height scribe a second line;rotate bar 90; check line is vertical and scribe third line; rotate bar 90; check lineagain with square; scribe fourth line with the square. Join corners diagonally and

where diagonals intersect this is the centre of the bar.

Fig. 55 FINDING THE CENTRE OF A ROUND BAR

To Find The Largest Square on The End of a Round Bar

First find the centre as described above. Scribe a line horizontally across the barthrough the centre. Rotate this line to the vertical and draw another horizontal linethrough the centre. Where these lines touch the outside of the bar draw a horizontalline using the scribing block. Rotate this to the vertical and repeat drawing thehorizontal line. Repeat this process twice more to produce the square.

Marking the Largest Hexagon

Find the centre. Set dividers to a radius slightly smaller than the bar radius andscribe a circle. With the dividers set at this setting, mark off the radius around thecircumference of the circle. Scribe lines from the centre through each of these pointsthen rotate bar till one of these lines is horizontal. Reset scriber, scribe a line acrossthe top of the ends of the two lines. Rotate bar and repeat process till hexagon iscomplete.

- 36 -


47/87

Fig. 56 MARKING THE LARGEST HEXAGON

To Find The Centre of a Tube

There are two methods. One method is to plug the tube with a piece of wood and findthe centre as if it were solid. The other method is described below.

Fig. 57 FINDING THE CENTRE OF A ROUND TUBE

- 37 -


48/87

Set the tube in Vee blocks. Set the scriber by eye to the centre height and make asmall mark at each side. Rotate the tube approximately 180till the mark on the farside comes to the scriber point where the second mark was made, move the scriber tothe other side and make another small mark which will be near but unlikely to be onthe original mark.

Reset scriber towards original mark of the distance between, repeat the markingprocess disregarding the original marks. This time the marks should nearly coincide

with the other mark.

Repeat the operation until the marks agree. The scriber is now set at the centreheight.

PRECISION MEASURING EQUIPMENT

This section deals mainly with micrometers and verniers, the accuracy of whichdepends on:

* The user.* The temperature of the instrument/work place.* The type and quality of the instrument.

The best quality instruments are made from a steel with a low co-efficient of linierexpansion sometimes called INVAR steel, which contains 36% nickel.

Some instruments have a temperature marked on them and this is the temperature at

which they are most accurate. It is usually 68F or 20C.

Modern micrometers and verniers can be electronic. In other words there is anelectronic display on the frame of the micrometer or sliding jaw of the vernier todisplay the reading that the instrument is set to. The value is simply read straightfrom the display. We will concentrate on the non-electronic type sometimes called anon-digital instrument.

In general the accuracy of each instrument is:

English micrometer 0.001in (0.001).English vernier micrometer 0.0001in (0.0001).

Metric micrometer 0.01mmMetric vernier micrometer 0.001mmEnglish vernier calliper 0.001in (0.001).Metric vernier calliper 0.02mm

Vernier Bevel protractor 5min (60 mins in one degree)

THE MICROMETER

The micrometer principle can be applied to:

* Outside micrometers* Inside micrometers* Depth gauges, etc

- 38 -


49/87

The principle of the micrometer is the same in all cases. If we know the numbers ofthreads per inch (tpi) and we know that it is a single start thread, then we know thatthe leadequals thepitch.

QUESTION Some revision on screw threads. What do the following terms mean?

(10 mins)

* Single start thread.* Lead.* Pitch.

ANSWER A single start thread is a thread which only has one helix, ie one singlethread only cut as a helix on the surface of a round bar or on the insideof a hole.

The pitch of a thread is the distance between two adjacent threads.

The lead of a screw thread is the amount of axial movement the nut orbolt makes in one revolution.

So if we know the leadthen we can divide the rotating part into a number of equaldivisions (say N), so each division will represent an Nth of the lead when rotated. Thisis the principle of all micrometers.

The Outside Micrometer (English)

All outside micrometers are similar in construction, it is the thread and type of scaleson them which will dictate whether they are English or metric.

The main components of the instrument are the frame, anvil, barrel, spindle and thesleeve (or thimble).

The frame is suitably machined to receive the anvil, which is usually a press fit. Themating faces of the anvil and the spindle are made of tungsten or tipped with carbideto reduce wear.

The barrel is pressed into the frame to permit rotational adjustment. The barrel is

engraved with a graduated scale equal in length to the range of the instrument,usually 1 inch or 25mm and is bored and internally screwed with an accurate finethread.

An integral sleeve on the spindle surrounds the barrel, this is usually knurled at theouter end to facilitate easy finger action. Incorporated is a ratchet or friction device toeliminate variation of pressure between the contacting faces. The inner end of thesleeve is bevelled to prevent barrel scale shadows and the bevelled portion isgraduated into equal divisions around its periphery.

The micrometer has a range of 1 inch and are supplied as a naught to 1 inchmicrometer, 1 to 2 inch micrometer, 2 to 3 inch micrometer etc. This size is stamped

on the frame.

- 39 -


50/87

Fig. 58 THE EXTERNAL MICROMETER (ENGLISH)

The Principle of the English Micrometer

The spindle has 40tpi. This means that one complete turn of the barrel (and spindle)will move the spindle forward or back by 1/40thof an inch. The thimble is divided into25 equal divisions. This means that one division will have an axial movement of 1/25thof a 1/40th. which equals 1/1000th.

= 1 x 125 40

= 11000

= 0.001in.

Fig. 59 READING THE ENGLISH MICROMETER

- 40 -


51/87

Reading the Micrometer

With anymicrometer the principle is the same note the size of the micrometer (0 to1 inch for example on an English mic) - read all the whole divisions showing on the

barrel (eg all the tenths and the remaining fortieths on an English mic) then notewhich line on the thimble aligns with the datum line on the barrel.

Record each on a piece of paper and add to provide the total this is the micrometerreading. In more detail using figure 59 as an example:

1. First read off the number of inches on the frame (assume a 0 to 1 inch mic).

= 0.000

2. Read the number of complete tenths showing (4).

= 0.400

3. Now the number of complete fortieths showing in this case (3).

= 0.025 x 3 = 0.075

4. Now find the coinciding line on the thimble with the datum line (8).

= 0.008

Adding these figures up we get: 0.0000.4000.075

0.008-------0.483

With no graduation on the thimble coincides with the barrel scale line, the graduationto be read is that nearest to the datum.

THE VERNIER MICROMETER

An additional scale on the barrel based on the vernier principle, gives a greater degree

of accuracy.

The vernier scale on the barrel consists of ten divisions (or 5 where the thimbledivisions are thous and half thous) whose total length is equal to nine divisions on thethimble 9 thous (or 9 half thous). The length of the vernier scale = 0.009 (or 0.0045)and is divided into 10 equal divisions (or 5 equal divisions).

This means that each vernier scale division = 0.0009 in and therefore the differencebetween one vernier scale division (0.0009) and one thimble scale division (0.001) is0.0001.

- 41 -


52/87

Fig. 60 READING THE VERNIER SCALE

The micrometer is read the same as a normal micrometer for the inches, tenths,fortieths and thousandths of an inch. For the ten thousandths of an inch reading thecoinciding line is found on the vernier scale. In figure 60, assuming that the third

vernier division coincides with a sleeve graduation then the reading is:

Barrel Scale = 0.4500Thimble Scale = 0.0195 (Note the thimble scale thous and half thous)Vernier Scale = 0.0003

---------0.4698

THE METRIC MICROMETER

The spindle and barrel threads of the metric micrometer have a pitch of 0.5mm. The

barrel is graduated in millimetres and half millimetres and the thimble is graduatedinto fifty equal division, so that each represents 1/50thof 0.5 = 0.01mm.

The range of the micrometer is 25mm and are supplied as 0 to 25mm, 25 to 50mm,50 to 75mm micrometer etc.

Fig. 61 READING THE METRIC MICROMETER

- 42 -


53/87

Reading the Micrometer

To read the micrometer, the highest figure on the barrel scale is read together withany additional visible half-millimetre division, in the example (figure 61) it is 5mm +0.50 = 5.5mm. To this is added the number of hundredths of a millimetre which areindicated by the co-incident thimble and barrel datum lines, in this case 14, so that

the reading is 5.5 + 0.14 = 5.64mm.

There may also be a vernier scale, the length of the scale is equal to nine thimbledivisions (0.09mm) and is sub-divided into five equal divisions so that each division isequal to 0.018mm. The difference between twothimble divisions (0.02) and one

vernier division (0.018) is 0.02 0.018 = 0.002mm.

Care and Use of the Micrometer

Keep the anvil and spindle end clean. Hold the micrometer truly square with the job.

Turn the thimble by the ratchet stud only this ensures that the same grip is takenat each measurement. Look at the micrometer after it is set, before handing toanother.

(a) Checking Always check for correct zero setting. To do this, screw the spindledown on to the anvil till the ratchet slips (0 to 1in and 0 to 25mm size only).

The reading should be 0.000 in. If incorrect the micrometer must be re-set.

For larger micrometers, test pieces are provided, exactly 1in, 2in, 3in, (or25mm, 50mm, 75mm) etc, which are measured between anvil and spindle.

The micrometer scale should again read zero.

(b) Adjustment The method of adjustment of the zero setting can be by rotatingthe barrel on the frame by using a C spanner, or by adjusting the thimble onthe spindle, or by adjusting the anvil in the frame. Play in the spindle threadsis taken up by adjusting a nut at the thimble end of the barrel; this nut isnormally covered by the thimble.

THE INTERNAL MICROMETER

This is used to measure internal dimensions. It is similar in principle to the externaltype, but usually has in micrometer adjustment only. The micrometer consists of a

micrometer head and different lengths of detachable extension rods, which enable theinstrument to be used for a range of sizes, eg 2in to 8in. (With the 8in set, 6 rods aresupplied, ie 2-3in, 3-4in, 4-5in, 5-6in, 6-7in, and 7-8in. The set comes complete witha collar which allows each rod to measure 2 to 3, 3 to 4 etc. When fitting a rod,the collar must butt against the rod flanges and the micrometer head.

The collar is used to allow an extension to read to its upper limit, eg to measure from7in to 8in the 7in rod is used together with the in collar.

The length marked on the rod includes the 2in length of the micrometer head.

- 43 -


54/87

Fig. 62 INTERNAL MICROMETER

Checking

To check an internal micrometer, set it to read any figure, eg 3 in and measure it withan accurate external micrometer; the readings should coincide.

THE THREE POINT MICROMETER

This type of internal micrometer has three measuring anvils mounted 120to eachother. The inner ends of the anvils are angled and screw cut to suit the conicalmeasuring thread, springs fitted inside the cap ensure contact between them.Generally these instruments have accuracies similar to that of other micrometers but

with the three anvils it is not possible to measure ovality.

MICROMETER DEPTH GAUGE

Used for measuring the depth of holes or recesses and the height of spigots andshoulders from some reference plane on the component.

The instrument reads opposite to the other types of micrometer, ie from right to left.

These instruments are usually supplied with detachable spindles, to increase the

range of measurements.

- 44 -


55/87

Fig. 63 MICROMETER DEPTH GAUGE

OTHER TYPES OF MICROMETER

Other types of micrometers are available including:

* Calliper Micrometer Similar to a vernier calliper but uses a micrometerhead with a range limited to 1in.

* Variable Range Micrometer Has a set of different length detachable

anvils.

* Recess Micrometer Supplied with a long anvil to get into deep recesses.

* Deep Frame Micrometer Has a deep frame for access around sheetmetal plates, etc. May need two people to handle it.

* Tube Micrometer The anvil has a convex face and the micrometer isused for checking the thicknesses of curved surfaces.

* Screw Thread Micrometer The anvil has a Vee slot cut in it and thespindle is ground to a point. It is used for the accurate measurement of

Vee threads.

THE VERNIER

The vernier system consists of a fixed Main Scale and a moving Vernier Scale.Assuming the two scales are of equal length and that the total number of divisions inone scale is greater by one division than the number of divisions in the other scale.

The difference between the length of one division on one of the scales and one divisionon the other scale will give the accuracy of the instrument.

- 45 -


56/87

ENGLISH VERNIER CALLIPER

These have a vernier scale to read to 0.001in. They give inside as well as outsidemeasurements and have a much greater range than a micrometer but are usuallymore difficult to read. They frequently have small target points for setting dividersaccurately. Both English and metric scales may be incorporated in the same

instrument.

The 24/25 System

The main scale is graduated in inches, tenths and fortieths (each fortieth equals0.025). The vernier scale on the sliding jaw is formed by taking a length of twenty-fourmain scale subdivisions (24 x 0.025 = 0.6in) and dividing this into 25 equal parts (0.6

25 = 0.024in). The difference in size between one main scale subdivision (0.025in)and one vernier scale division (0.024in) is 0.001in.

Fig. 64 THE VERNIER CALLIPER

The 49/50 System

The main scale is graduated in inches, tenths and twentieths (one twentieth equals0.050in). 49 main scale divisions are divided into 50 equal divisions to form the

vernier scale. 49 main scale divisions = 49 x 0.050in = 2.450 in (0.050 is the lengthof each main scale division).

One vernier scale division = 2.450 = 0.049in50

But one main scale division = 0.050in

Therefore the difference in size between one main scale division and one vernier scale

division = 0.050 0.049 = 0.001in.

- 46 -


57/87

Fig. 65 THE 49/50 VERNIER SCALE

Note the accuracy of the two systems is the same though some say the49/50 system is easier to read. Im not so sure.

Reading the Vernier

Always read the main scale up to the zero on the vernier. Then read the vernier readingfrom the zero on the vernier scale to the coinciding line.

1. Read the total number of whole inches.2. Then read the remaining number of whole tenths.3. Then read the remaining number of whole twentieths or fortieths.4. Then check the coinciding line on the vernier with any line on the main

scale to give the thousandths reading.

Example 1 English Vernier (24/25)

EXAMPLE 1 24/25 ENGLISH VERNIER

* Reading the inches (1) = 1.000* Reading the tenths (2) = 0.200 (0.100 x 2)* Reading the fortieths (3) = 0.075 (0.025 x 3)* Reading the coinciding line

(9th) on the vernier scale = 0.009TOTAL 1.284in

The reading is 1.284 in.

- 47 -


58/87

Example 2 English Vernier (49/50)

EXAMPLE 2 ENGLISH 49/50 VERNIER

* Reading the inches (5) = 5.000* Reading the tenths (2) = 0.200 (reading up to the zero on

the vernier scale)* Reading the twentieths (1) = 0.050

* Reading the coinciding line(26th) on the vernier scale = 0.026

-------TOTAL 5.276

The reading is 5.276 in.

Note. Try the readings of the verniers shown in figures 64 and 65. The author getsthem to be 1.230in (assuming the 30thvernier division lines up) and 5.148in(assuming the 48thdivision lines up) respectively.

METRIC VERNIER CALLIPER

Again these may be based on the 24/24 or the 49/50 principle.

The 49/50 System

The main scale is graduated in millimetres, each tenth division being numbered 0, 1,2, 3 etc, and centimetres (10 millimetres = 1 centimetre). The vernier scale is formed

by taking 49 main scale divisions (49 x 1 = 49mm) and dividing by fifty (49 50 =

0.98mm). The difference between one main scale division (1.00) and one vernier scaledivision (.98) is 0.02mm. Note. It is not as accurate as the metric micrometer.

The 24/25 System

With this system the main scale is graduated in millimetres and half millimetres andthe vernier scale is formed by taking 24 main scale divisions (0.5mm) and dividing by25 equal divisions which make up the vernier scale. 24 main scale divisions (millimetres) = 12mm. 12mm divided by 25 = 0.48mm. So each main scale division= 0.5mm and each vernier scale division = 0.48mm and the difference between thetwo = 0.02mm.

- 48 -


59/87

Reading the Metric Vernier

1. Read the main scale (total complete divisions) either mm or mmdepending on the system up to the zero on the vernier scale.

2. Read to the coinciding line on the vernier scale to give the reading to anaccuracy of 0.02mm.

Example 1 Metric 49/50 Vernier

EXAMPLE 1 METRIC 49/50 VERNIER

* Read the complete number of millimetresshowing up to the zero of the vernier scale (32) = 32.00mm

* Find the coinciding line on the vernier scale andeither:(a) Count this line (31) and double it (62).

This represents 0.62mm = 0.62mmor

(b) Take the nearest numbered division tothe left of the coinciding line, ie 6 andcall this tenths of a mm = 0.6mmand each division thereafter is equal to0.02mm. In this case = 0.02mm

TOTAL 32.62mm

The reading is 32.62 mm.

Example 2 24/25 Metric Vernier

EXAMPLE 2 24/24 METRIC VERNIER

- 49 -


60/87

* Read the complete number of mm (11). = 11.00mm* Read the complete number of mm (1). = 00.50mm* Read the coinciding line on the vernier

scale (12) and double it. = 00.24mm-------

TOTAL 11.74mm

The reading is 11.74 mm.

Checks Before Use

(a) The zero reading must be checked by cleaning the gauging faces andclosing the jaws using firm finger pressure, securing the frame with thelocking screw. The zero lines of the main scale and vernier scale shouldline up.

(b) Hold the instrument to a good source of light; dirt, wear or strain

causing poor contact will be indicated by light between the faces.(c) Check the vernier scale locating screws for security and check the zeroreading. If the zero marks are not aligned note the error. Adjustmentcan be made by loosening the vernier scale securing screws and re-positioning the vernier scale to read zero, then tightening the securingscrews and re-checking. A magnifying glass will help.

(d) Check a known dimension toward the limit of the instrumentsmeasuring capacity, this checks any distortion or bowing of the beam.

(e) Ideally use the instrument at its calibrated temperature (marked on oneof the jaws). Keep the instrument at this temperature for an hour or soto allow it to acclimatise.

VERNIER HEIGHT GAUGE

This instrument is similar in construction to the vernier calliper except that the fixedjaw is shaped as a base, the lower face of which is accurately ground to form acontact face at right angles to the beam.

The upper face of the moving jaw is the surface from which measurements are taken.This surface is parallel with the under face of the base. The measuring jaw is providedwith a detachable scriber to permit accurate marking out, but can also be used forinternal measurement. The scale of the instrument does not start at zero, the surface

table is in fact the zero.

Precautions

It is essential that the base of the instrument is at all times in contact with thesurface table. It is advisable not to pre-set the instrument, otherwise the scriber mayoverride the work piece. The scriber should be lowered/raised slowly using the fineadjustment until the required feel is obtained.

The instrument is not particularly stable when standing on its base, so when not inuse it is advisable to lay it on its side

- 50 -


61/87

Fig. 66 VERNIER HEIGHT GAUGE

When checking the instrument, since the main scale does not start at zero, it isnecessary to use an accurately ground distance piece, which is usually supplied with

the instrument. Adjustment of the vernier scale is similar to that used for the verniercalliper.

DEPTH GAUGES

The depth gauge is used for measuring the depth of holes and recesses or the heightof spigots and shoulders from some reference plane. In its simplest form the gaugeconsists of a graduated blade or rod, fitted with a moveable head or stock, which can

be locked in any position. Some gauges use a vernier scale or a micrometer head tomeasure with the same accuracies as the ordinary verniers or micrometers. Examplesof the three main types are shown in figure 67.

blank

- 51 -


62/87

Fig. 67 DEPTH GAUGES

THE VERNIER BEVEL PROTRACTOR

The bevel protractor consists of a blade, a graduated protractor head and a stock. Theangles between the stock and the blade are indicated by the position of the zero onthe vernier scale. The main scale is marked off in degrees (0 to 360 or 0 to 90 and 90to 0). The vernier scale/s are formed by taking 23 main scale divisions (23) anddividing by 12.

23 = 1 5512

The accuracy is obtained by comparing onevernier scale division (155) to twomain

scale divisions (2). The difference is 5 (5 mins).

Fig. 68 VERNIER PROTRACTOR

- 52 -


63/87

Reading the Protractor

1. Read from the zero on the main scale to the zero on the vernier scale tofind the degrees.

2. Continue to read in the same directionto find the coinciding line on thevernier scale. This will give the number of minutes.

Example 1 Vernier Bevel Protractor

EXAMPLE 1 VERNIER BEVEL PROTRACTOR

Reading Angle B

* The number of complete degrees to the zero

of the vernier scale. = 63* Continuing to read in the same direction the

coinciding line is found to be 15. = 00 15-------

TOTAL 6315

Reading angle A gives a reading of 11645.

A quick check should show that the sum of the readings should equal 180. If they donot you have mis-read the instrument.

blank

- 53 -


64/87

Example 2 Bevel Protractor

EXAMPLE 2 BEVEL PROTRACTOR

* Reading from the left to the zero on the

vernier scale gives 42 = 42* Continuing in the same direction to find

30 as the coinciding line = 30--------

TOTAL 4230

* Reading from the right to the zero on the venier

gives 137(note that the zero on the vernier hasgone passed the 90mark on the main scale = 137

* Continue reading in the same direction to findthe coinciding line which is 30 = 30

---------TOTAL 13730----------

THE DIAL TEST INDICATOR

This instrument, which is also known as a DTI or Clock Gauge, is used not formeasuring the actual size of a component, but to indicate small differences in size, orfor indicating the amount of eccentricity of revolving parts. It can also be used tomeasure the run out or movement of mechanisms which have a small amount ofmovement. It is graduated in thousandths of an inch every tenth thousandth being

marked and reads up to 0.050in clockwise and 0.050in counter-clockwise. MetricDTIs have a similar range.

In use it is rigidly supported (by being fixed to a scribing block on a marking-off tableor bolted to the component), and is set to the first height (or length) with whichcomparison is desired. This is done by moving the plunger to the first height (orlength). The pointer will settle to any position on and dial. Adjust the zero on the DTI

by turning the bezel until the zero on the dial is under the needle.

If any other height (or length) is measured (by sliding it under the plunger, or bymoving the part to another position) the needle will indicate on the + side it if is larger

and on the side if it is smaller. The difference in size will in each case be read offdirectly on the dial.

- 54 -


65/87

Fig. 69 DIAL TEST INDICTOR

BORE GAUGE

Similar to the DTI but used to measure the ovality of a bore. The contact face of thegauge is operated by a lightly spring loaded plunger fitted to a T shaped head, theplunger movement being transmitted by a small curved rod retained in a slide and along rod housed in the hollow handle. The curved rod limits the plunger movement,so sets of distance pieces and extension rods are supplied to increase the range generally 2in to 6in. The spring-loaded anvil centralises the tool in the bore to ensurethat the spindle and plunger make contact with the wall of the bore across itsdiameter.

Fig. 70 BORE GAUGE

- 55 -


66/87

FEELER GAUGES

Feelers are used to measure small clearances or gaps. The flexible steel blades aregraduated in thickness in most cases from 1 to 15 thousandths of an inch. The

blades are secured in a stock when not in use. Classified by length of blades, Afteruse should be lightly oiled and kept in the stock to prevent distortion. Metric sets are

also available.

Fig. 71 USING FEELER GAUGES

THE RADIUS GAUGE

This is similar to a feeler gauge except that the blades are thicker (and all of the same

thickness) and an internal and external radius is cut on each blade. Each blade isalso marked with the radius size. Metric and English sets are available.

Fig. 72 RADIUS GAUGES

SCREW PITCH GAUGE

Similar to a radius gauge but each blade has teeth cut on its edge and marked withthe number of tpi. The stock into which the blades fit when not in use is marked withthe thread angle.

- 56 -


67/87

Fig. 73 SCREW PITCH GAUGES

WIRE GAUGE

This is used to determine the thickness of wire and sheet metal. It is made of sheetsteel with accurately ground slots round the edges, each slot being numberedaccording to the specification. This could be British Standard Institute (BritishStandard Wire Gauge), or American Wire Gauge for example. To use the gauge try themetal sheet or wire into the slots until the nearest fit is obtained, then read off the

number at the side of that slot.

The gauge may be rectangular or circular in shape.

Fig. 74 WIRE GAUGE

SLIP GAUGES

Slip Gauges or Johannson blocks are mainly used as standards for checking theaccuracy of working gauges. They are simply rectangular blocks of hardened andpolished steel, but they are ground to extremely high standards of accuracy in length,flatness and parallelism. The full set of slips comprises 81 pieces, graduated in size,to enable any length from 0.05in to over 10 inches to be built up in steps of 0.0001in.

The slips are used in conjunction with a set of accessories to produce fixedgauges/angles for a wide variety of purposes. Figure 75 shows three examples ofcheck gauges built-up from slips to give accurate linier measurements and figure 77

shows how they can be used, in conjunction with a Sine Bar, to produce accurateangles.

- 57 -


68/87

Fig. 75 TYPICAL BUILD-UPS OF SLIP GAUGES

As the blocks are manufactured to limits of accuracy of a few millionths of an inch,slips must always be handled with the utmost care; unnecessary wear of the slipsurfaces must be avoided as far as possible. Because of the very high surface finish(smoothness), atmospheric pressure is sufficient to cause the slips to adhere together

with a very tenancies grip, and in this condition they are said to wrung together;when wrung together, a parcel of slips can be handled like a solid block. Wringing isnot possible if the adjacent surfaces of two slips are separated by even the finest filmof dust or oil, or by a layer of air; when building up a gauge length, the slips shouldfirst be wiped with a dry fine chamois leather (not a cloth) and then placed in contact

by sliding one surface onto the other. Conversely, separation of wrung slips shouldalways be done by sliding one slip off the other never try to pull them apart it isnot possible.

Always dismantle slips immediatelyafter use as they will bond together if leftassembled too long. Once bonding has taken place then the slips involved are useless

and they are very expensive. Once wrung apart the separate slips are placed in theirseparate compartments in the boxed set.

SINE BARS

The sine bar is an accurately machined bar which is used on a surface table orsurface plate. It is used in conjunction with slip gauges and rollers to produceaccurate angles (to an accuracy of 1 minute) (60 minutes = 1 degree).

Machined angles can be checked against it as can other instruments such as thevernier bevel protractor, the clinometer etc.

- 58 -


69/87

Fig. 76 THE SINE BAR

To use the sine bar a knowledge of trigonometry is required in particular the SineRatio. (Refer to the books in this series entitled Mathematics).

QUESTION As a quick bit of revision, can you state what the sine of an angle is? (5mins)

ANSWER The sine of an angle (of a right angel triangle) is the ratio of the Oppositeside over the Hypotenuse.

SINE = O (SOH)H

If we know the length of the sides O and H then we can divide O by Hand then find the angle by using Sine tables or a scientific calculator.

For accuracy it is essential that:

(a) The rollers are of the same diameter.(b) The centre distance (L) is absolutely correct.(c) The centre line (XX) of the rollers is absolutely parallel with the edge (YY)

of the bar.

Example

In figure 77, a sine bar (H = 100mm) is set up and the height O of the slip gauges is26.15mm. From the angle theta the opposite side (O) is 26.15mm and H = 100mm.

The angle is:

Sine = O = 26.15 = 0.2615H 100

From the Sine table: = 1510

- 59 -


70/87

Fig. 77 THE SINE BAR IN USE

Another way the sine bar may be used is to calculate the height of the slip gauges toproduce a given angle.

Given an angle of 1811, if a 200mm sine bar is used, the height of the slip gaugeswould be:

O = Sine or O = H x Sine H

O = 200 x Sine 1811

From the tables sine 1811 = 0.3120 so

O = 200 x 0.3120

= 62.40mm

LIMIT GAUGES

Sometimes called GO/NO GO gauges and are used to check that components arewithin wear limits. Used mostly in component bays with the plug gauge used forchecking holes and the gap gauge used for checking shafts.

The ends of the gauges are indicated which is the GO and which is the NOT GO endwith sometimes actual dimensions given as well.

When using a plug gauge the GO end (small end) should go into the hole if it doesnot the hole is too small, and the NOT GO end should not if it does go in it indicatesthe hole is too big (warn beyond limits). The difference between the sizes indicates themaximum permissible wear. The flats on the side of the plugs allow for the checkingof ovality.

For the gap gauge the GO side is the larger (if it doesnt fit, the shaft is too big) andthe smaller end is the NOT GO end indicating the shaft has worn to it's lowest limit.

- 60 -


71/87

Fig. 78 LIMIT GAUGES

THE SPIRIT LEVEL

Consists of a body made of wood or metal which houses a curved glass tube partially

filled with a liquid. The tube is sealed at both ends. Will indicate when a surface ishorizontal by the bubble being central on the zero datum line. Treat the instrumentwith care and check for accuracy before use (reversal on a straight edge held in a vice- the straight edge is protected by a cloth and set level using the spirit level, the levelis turned around on the straight edge and if the bubble still reads zero it is accurate).

Fig. 79 SPIRIT LEVEL

ADJUSTABLE LEVEL

These vary in design but may be used to measure angles up to 10from thehorizontal. The vertical scale reads in degrees and one complete turn of the adjustingmicrometer knob will alter this scale by one degree. The adjusting knob has a scale ofit's own which is divided into 60 equal divisions. Each division represents one sixtiethof a degree which is equal to one minute.

The instrument is placed on the surface to be measured and the knob turned untilthe bubble reads zero - the degrees are read from the vertical scale and the minutesfrom the rotating scale.

To check for accuracy set both scales to zero and then proceed as for the spirit level.

- 61 -


72/87

Fig. 80 ADJUSTABLE LEVEL

CLINOMETER

Used for checking angles from 0 to 90. The mechanical clino shown has amechanism which consists of a worm gear and quadrant. Rotation of the quickrelease knob rotates the worm which moves the quadrant. The spirit level and degreescale are attached to the quadrant. One revolution of the quick release knob movesthe spirit level and degree scale through one degree.

Fig. 81 THE MECHANICAL CLINOMETER

The quick release knob has it's diameter divided into 60 equal divisions so thatmovement of one of these is equal to one minute of ark. The quick release knob may

be moved down against a spring to release the quadrant, thus allowing quickapproximate adjustments of the degree scale. To check the instrument, set bothscales to zero and proceed as for the spirit level.

- 62 -


73/87

Electron

easa mod 7a bk 2 tools

Documents