bs 907-2008
TRANSCRIPT
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raising standards worldw ide
N O CO PYING W ITHO U T BSI PERM ISSIO N EXCEPT AS PERM ITTED BY CO PYRIG H T LAW
BSI British Standards
Specification for dial gaugesfor linear measurement
BS 907:2008
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BS 907:2008 BRITISH STANDARD
Publishing and copyright information
The BSI copyrig ht no tice displayed in this document indica te s wh en t he
document w as last issued.
BSI 2008
ISBN 978 0 580 62079 9
ICS 17.040.30
The fo llow ing BSI referen ces relate t o t he w ork on this stan da rd:
Com mit t ee ref ere nce TDW/4
Dra ft fo r comm en t 08/30178087 DC
Publication history
First pub lished Novemb er 1965
Second (present) edition, November 2008
Amendments issued since publication
Amd. No. Date Text affected
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BRITISH STANDARD
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Summary of pages
This do cument comprises a fron t co ver, a n inside fron t co ver,
pa ge s i to ii, pag es 1 to 14, a n inside ba ck cover and a ba ck cover.
ContentsForeword i i
1 Scope 1
2 Terms a nd de fi nitions 1
3 General fea tures of design 2
4 Dial 35 Pointer 4
6 Revolution count er 4
7 Plunger 5
8 Conta ct point 5
9 Performance 5
10 Packing 7
11 Marking 7
Annexes
Anne x A (informa tive) Recomm end ed dimen sion s fo r dia l g a ug es 8
Annex B (informa tive) Notes on meth od s of t esting d ial ga uge s 9
Annex C (informa tive) Notes on t he care a nd use of d ial ga uge s 12
Bibliography 14
List of figures
Figure 1 Nomen cla ture o f d ia l ga uge s 2
Figu re 2 0.01 mm, 0.000 1 in or 0.001 in d ial 3
Figu re 3 0.000 5 in d ial 3
Figure 4 Free po sition of point er 4
Figure A.1 Dia l ga ug e d imension s 8
Figure B.1 Calibra tion curve of a dia l g a ug e illustra ting period ic
error 11
List of tables
Ta ble 1 Discrimina tio n ca pa bility 6Ta ble 2 Limits of erro r fo r dia ls w ith sca le divisions o f 0.001 in
a nd 0.000 5 in 6
Ta ble 3 Limits of erro r fo r dia ls w ith sca le divisions o f 0.000 1 in 7
Ta ble 4 Limits of e rror f or d ials w ith scale d ivision s of 0.01 mm 7
Ta ble B.1 Error of rea ding of dia l g a ug e g iven in units
of 0.000 1 in 10
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BRITISH STANDARD
Foreword
Publishing information
This British Sta nd a rd is pub lished b y BSI a nd cam e into eff ect o n
30 Nove mb er 2008. It w a s prepa red by Techn ica l Comm itt ee TDW/4,
Techn ical pro du ct realization. A list o f o rga nizat ions represente d o n
this committee can b e ob ta ined on req uest to its secreta ry.
Supersession
This British Sta nd a rd supersede s BS 907:1965, w hich is w ithd raw n.
Relationship with other documents
BS EN ISO 463 specifi es the mo st impo rta nt d esig n a nd m et rolog ica l
chara cteristics of mechan ica l dial ga uge s.
Information about this document
This new edition ha s been fully revised t o b ring it up to da te.
Presentational conventions
The pro vision s of th is sta nd a rd a re presented in roma n (i.e. upright )
type . Its requiremen ts are expressed in sent ences in w hich th e
principal a uxilia ry verb is shall .
Comment ary, explanatio n and general info rmat ive material is
presented in smaller ital ic type, and does not constit ut e a norm ative
element.
Contractual and legal considerations
This publicat ion d oes no t purport to include a ll the necessa ry provision s
of a contra ct. Users are responsible fo r its correct a pplicat ion.
Compliance with a British Standard cannot confer immunity from
legal obligations.
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1 ScopeThis British Sta nda rd specifi es requirements for d ial ga uge s w ith the
plunger movement pa ral lel to t he plane of the d ial .
The stan da rd is ap plica ble to g a uge s ha ving dial diamet ers from
47.6 mm o r 178in to 63.5 mm or 212in, a s mea sured f rom the out side
of th e scale ma rks, a nd sca le division s of 0.01 mm, 0.001 in (somet imes
sub-divide d int o h a lf division s of 0.000 5 in, in w hich ca se the y a re
commonly design a ted 0.000 5 in g a uge s ) or 0.000 1 in.
NOTE 1 Att ention is draw n to t he fact th at the metr ic dimensions are
no t n ecessarily direct conversions of th e imperial dim ension s.
NOTE 2 Recommend ed dimensions fo r dial gauges are given in Annex A
(Figure A .1) and not es on m eth ods of testin g and on t he care and u se of
dial gauges are given in Annex B and Annex C respectively.
2 Terms and definitionsFor th e purposes of this British Stand a rd th e fo llow ing te rms a nddefi nitions apply.
NOTE The component s of a dial guage are il lustr ated in Figur e 1, w hich
also g ives th e nomenclature.
2.1 minimum scale valuesma llest va lue of t he mea sured qua ntity w hich the sca le is gra dua ted
to indicate
2.2 scale division
pa rt of a sca le delimited by tw o a djacent scale marks
2.3 discriminationsensitiveness of a n instrument , the smallest cha ng e in the q ua ntity
mea sured w hich produces a perceptible movement o f the po inte r
2.4 repeatabilityreproducibility of the read ings of a n instrument w hen a series of tests
is ca rried out in a short interval of t ime under fi xed cond itions of use
2.5 limit of error
positive and /or neg a tive va lue of e rror w hich is not to be exceede dunder te st
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Figu re 1 Nomenclature of dial gauges
1 2
3
6
57
8
9
10
Key
Bezel clam p1
Pointer2
Bezel3
Back lug4
Stem bush5
Tran sparen t d ial cover (or crysta l)6
Plunger7
Removable contact po int8
Stem9
Revolution counte r10
3 General features of designThe mechanism sha ll incorporat e some mea ns to eliminat e b a ckla sh.
The de sign a nd rigidity of the ca se shall be such tha t t he freed om o f
movement of the mechanism is not impaired b y the t ightening o f the
screw s used f or a t ta ching the b ack or by the clamping o f t he stem
of the instrument , provided tha t such cla mping is carried o ut in a n
appropriat e manner.
NOTE 1 See Annex C fo r recommend ation s on t he care and u se of
dial gauges.
The t ran sparen t d ial cover (or crysta l) shall be o f du rab le mat erial
w hich w ill reta in its transparency w ithout un due d iscoloura tion. Both
the t ransparent dial cover and t he case sha ll be d ust proo f.
The g a uge sha ll be provided w ith a sa tisfa ctory means of setting
to zero .
NOTE 2 If th is is achieved by rotat ion of th e bezel then a clampin g screw
may or may not be provided, but care should be taken t o ensure th at t he
sett ing is maint ained on t hose w hich have no m eans of locking.
Back lug fi xing s sha ll be squa re or pa rallel to t he mea suring a xis of
th e instrum ent w ithin 0.150 mm pe r 25 mm o r 0.006 in per inch in thedesign position.
NOTE 3 Back lug fixings may be int egral wit h th e gauge or may be
removable.
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NOTE 4 Gauges sho uld be fitt ed w it h stai nless st eel plu ng ers and
hard ened or stainl ess st eel pin ion s.
NOTE 5 The ranges of m ovement of th e plunger vary w ith th e make
and t ype of g auge, and if th e purchaser has any particular requirement s
in respect of this range of movement, i t should be stated at t he point of
enqu iry and ord er.
4 Dial 4.1 The dia l sha ll be marked with the appropriate minimum scale value,
a s follow s:
metric dials: 0.01 mm;a )
inch dials: 0.000 1 in, 0.000 5 in or 0.001 in.b )
4.2 The scale shall be ma rked w ith clea r lines on a suitab le ba ckgroun d
so a s to b e ea sily rea d. The t hickness of th e sca le ma rks shall be
uniform a nd sha ll be not less tha n 0.152 mm or 0.006 in o r more
th a n 0.254 mm o r 0.010 in.
4.3 Every tent h scale ma rk sha ll be indicated b y a longe r line a nd sha ll be
numbe red. Every fi ft h sca le mark (except on a 0.000 5 in d ial ga uge )
shall be ind ica te d by a line slight ly less in leng th . A 0.000 5 in d ial
ga uge shall ha ve alterna te sca le divisions indica ted by a shorte r line.
NOTE It is recommended that t he lengt h of t he visible port ion of t he
scale mar ks ind icating each scale division should b e appr oxim at ely equal
to the w idth of that division as show n in Figure 2 and Figure 3.
Figu re 2 0.01 mm, 0.000 1 in or 0.001 in dial
1
Key
Lengt h eq uals w idth1
Figu re 3 0.000 5 in dial
1
Key
Lengt h eq uals w idth1
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5 Pointer 5.1 The pointer sha ll mo ve in a clockw ise direction w hen the plunge r is
pressed in.
5.2 The pointer sha ll be at ta ched to its spindle in such a ma nner as to
ensure that there w ill be no relat ive movement bet w een them w hen
the spindle is subjected to rapid a ccelera tion o r decelerat ion, as, for
example, in the event of the p lung er being suddenly released a nd its
motion arrested b y a fi xed stop.
5.3 The leng th of the pointer sha ll be such tha t its tip lies a pproxima tely
over the centre of t he lengt h of t he shortest sca le marks.
5.4 The thickness of tha t portion of the pointer immediat ely over the scale
sha ll not exceed o ne-fi fth o f th e w idt h of o ne sca le division a nd should
preferab ly be of a pproxima tely the sam e t hickness as the scale mark.
5.5 The pointe r tip shall be as close to t he scale a s pra ctica ble in ord er to
minimize pa rallax errors.
5.6 When the plung er is in the position of rest a nd the zero ma rk onthe dial is in the 12 oclock position, t he po inter shall l ie b etw een
th e 9 oclock an d 11 oclock position s (see Figu re 4).
Figu re 4 Free position of pointer
1
3
2
4
Key
9 o clock1
Rang e of the po sit ion of po inter w hen2the plunger is in po sition of rest
11 o clock3
12 o clock4
6 Revolution counter
When a revolution cou nt er is provided , its point er shall correctly ind ica teon its scale the numb er of revolutions mad e by the dial gua ge po inter.
NOTE Preferably the point er on the revolut ion count er wi l l move in a
clockwise direction.
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7 Plunger 7.1 The plung er shall mo ve free ly in th e stem bush, w ith a ny shake,
including rota tiona l sha ke, being insuffi cient t o a ffect the indica tion
of t he instrument by more t ha n the thickness of a scale mark.
7.2 On 0.000 1 in ga uge s w ith a tra vel up to 0.25 in, the w orking fo rce at
a ny position o f t he plunger shall not exceed 170 g.
On 0.000 1 in ga uge s w ith a t ravel grea ter tha n 0.25 in and up t o a nd
including 0.5 in, th e w orking fo rce sha ll no t exceed 227 g .
On 0.000 1 in ga uge s w ith a t ravel great er tha n 0.5 in, the w orking
force shal l be the subject of ag reement betw een ma nufacturer and
purchaser.
NOTE For most pu rpo ses th e force required t o operat e a dial gauge
shou ld b e as light as possible. It shou ld b e measured w ith th e gauge in t he
vert ical posi t ion and w ith t he plunger going in.
The w orkin g f orce on dial gauges, other t han 0.000 1 in gauges, shou ld be
of the order of 57 g at th e beginning of the m ovement and any increasein f orce should no t exceed 14 g f or each successive 0.1 in or 2.54 mm
movement . If l igh ter or h eavier wo rking fo rces are required on 0.01 mm,
0.001 in and 0.000 5 in gauges th ey should be as specified b y th e pu rchaser.
8 Contact pointThe conta ct point shall ha ve as la rge a rad ius a s pra cticable a nd
sha ll be rea dily remo vable from t he plunger fo r the purpose of
replacement o r the substi tut ion o f a conta ct point of di f ferent f orm.
NOTE 1 Dial gauges are normally supp lied wit h a hardened spherically
form ed poin t. If some o ther f orm of point is required, this should be as
specified by t he pu rchaser. (See C.7.)
NOTE 2 It is recommend ed that in all new gauge designs th e dimensions
of the t hreads for the at tachment of the contact point are in accordance
w ith th ose given in Figure A .1.
9 Performance
9.1 General
All mea surement s of th e a ccuracy of perfo rman ce specifi ed in th isClause shall be referred t o t he stand ard reference t emperature o f 20 C.
9.2 Repeatability of reading
The g a uge sha ll repeat its read ings under all ordina ry metho ds of
ope rat ion to w ithin 0.002 mm on m et ric ga ug es, 0.000 2 in on 0.001 in
a nd 0.000 5 in ga ug es an d 0.000 02 in on 0.000 1 in g a ug es. (See C.6.)
9.3 Discrimination
The g a uge sha ll be capa ble of indicat ing small gra dua l cha ng es as
specifi ed in Ta ble 1.
The d eg ree o f d iscrimina tion specifi ed in Ta ble 1 shall be a chieved
w ithout resor t to tapping t he ga uge .
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Ta b le 1 Discrimination capability
Gauge Discrimination Tolerance
Metric 0.25 mm 0.003 mm
0.001 in
0.005 in
0.001 in 0.000 3 in
0.000 1 in 0.002 in 0.000 04 in
9.4 Limits of error
NOTE 1 Errors perm issible in dial gauges diff er accordin g to t he type of
instrum ent and t he magnit ude of the di f ference measured.
Permissable errors for d ifferent t ypes of ga uge s in commo n use sha ll
be a s specifi ed in Ta ble 2, Ta ble 3 a nd Ta ble 4.
NOTE 2 The perf orm ance of t he dial gauge, in terms of limt o f error,meet s specificatio n if th e error of indication is no t g reater t han t he limit s
of error specified in Table 2, Table 3 and Table 4, tak ing int o account th e
un certain t y of m easur emen t accor din g t o BS EN ISO 14253-1.
NOTE 3 Since dial gauges are primari ly int ended f or th e measuring
of small d iff erences in d imensions, th e same o rder o f accuracy of
th e instru ment w hen used fo r th e measuring of small diff erences in
dim ensions w il l not be realized w hen larger d iff erences are concerned.
The error over a n interval of read ing ma y be e ither plus or minus and
the permissible errors sha ll not be exceede d for e ither direction o f
movement of the po inter.
Ca libra tion shall ta ke pla ce from t he fi rst 12 oclock position o f t hepoint er (see Figure 4), unless ot herw ise specifi ed by t he p urchaser.
The perm issible erro rs sta te d in Ta ble 2, Ta ble 3 a nd Ta ble 4 sha ll
a pply to a ny intervals a nd a re not restricted t o tho se comm encing a t
zero; the y sha ll also em bra ce any eccentricity of t he d ia l in relation t o
the a xis of rotat ion o f th e pointer and shal l not be exceeded f or any
position of t he bezel, whe n this is rota ta ble.
Ta b le 2 Limits of error for dials with scale divisions of 0.001 in and 0.000 5 in
Interval of reading Error in reading over
stated interval
in
Any 0.01 in 0.000 25
Any ha lf revo lut io n 0.000 5
Any o ne revo lut io n 0.000 5
Any tw o revo lut io ns 0.000 75
Any la rg er int erva l 0.001
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Ta b le 3 Limits of error for dials with scale divisions of 0.000 1 in
Interval of reading Error in reading over
stated interval
in
Any ha lf revo lut io n 0.000 1Any o ne revo lut io n 0.000 15
Any tw o revo lut io ns 0.000 25
To t a l t ra vel 0.000 7
Ta b le 4 Limits of error for dials with scale divisions of 0.01 mm
Interval of reading Error in reading over
stated interval
mm
Any 0.1 mm 0.005
Any ha lf revo lut io n 0.007 5
Any o ne revo lut io n 0.01
Any tw o revo lut io ns 0.015
Any la rg er interva l 0.020
10 PackingThe g a uge sha ll be pa cked in a suitab le ca rton o r box w hich w ill
protect th e mechanism a ga inst shock due t o possible rough h a ndling
in tra nsport.
11 MarkingEach g aug e shall be legibly and permanently marked w ith t he number
of th is British Sta nd a rd, i.e. BS 907:20081), and w ith t he ma nufacturers
or vendors na me or tra de ma rk.
1) Marking BS 907:2008 on or in relation to a product represents a
man ufacturer s declara tion o f confo rmity, i.e. a claim by or on beha lf
of the ma nufa cturer that t he product meets the requirements of th e
sta nd a rd. The a ccura cy of th e cla im is solely the claima nt s responsibility.
Such a declara tion is not to be confused w ith third-party certifi cation
of conformity.
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Annex A (informative) Recommended dimensions for dial gauges
Figure A.1 Dial gauge dimensions
1
2
3
5
6
4A
0.75 0.01
2
A
0.25-0+0.01
B
All dime nsions in inches unless ot herw ise stat ed .
Key
Lengt h of full thread not less than1 14
Not less tha n2 316and not more than 14
2.5 0.45 mm*3
0.3754
0 0 01 5
0 001
.
.cylindrical to 0.000 2
Side faces of lug to b e fi nished fl at a nd parallel, the fl at surface5to ex tend f rom the cent re o f the hole tow ards the g auge(dimension B) fo r not less tha n 316
Lug t o be o ffset so tha t i f the g aug e is view ed from t he ba ck the6right hand face of the lug coincides w ith the vert ica l centre planeo f t h e ga u ge
* This threa d size is very close to tha t of th e 6 B.A threa d w hich may be used during the t ransition period.
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Annex B (informative) Notes on methods of testing dial gauges
B.1 Repeatability of reading
For limits of e rror see 9.2. The a ccuracy to w hich a dial ga uge w ill
repeat i ts readings can be tested by one o f the f ol low ing met hods.
Having cla mped t he ga uge fi rmly in a suita ble rigid fi xture overa )
a fl a t steel base, roll a t rue cylinder under the conta ct-point a
numb er of times from various directions and no te t he read ing s.
Repeat the test at tw o or three posit ions along t he range o f the
ga uge . Pass the cylinder through a t varying speeds, both slow ly
and rather a bruptly.
Allow the conta ct-point to rest d irectly upon t he fl at ba se belowb)
and to no te the constancy o f the reading obta ined w hen the
plunger is low ered on to the b a se bot h slow ly a nd a bruptly,
and w hen an a t tempt i s made t o ro ta te the p lunger fi rst in one
direction a nd t hen in the ot her.
B.2 Discrimination
It is important tha t a dial gaug e should be free from any trace of
stickiness or b a cklash, particularly w hen it is used for d etecting
sma ll errors in align ment s, or fo r testing t he a ccuracy of t he cente ring
of a w orkpiece mounte d in a ma chine. The most practica l w a y of
test ing a dial gaug e for this type of d efect is to mount it in a r igid
fi xture w ith the end of its plunger in contact w ith the surface of a
slight ly eccentric precision m a nd rel mo unt ed b et w een cent res. The
actual a mount of the eccentricity of the ma ndrel can be d etermined
beforeha nd b y means of a known sensit ive indicator set to rea d o nits surfa ce. For preference t he e ccent ricity should b e o f t he o rder of
on ly 0.025 mm f or 0.01 mm g a ug es, 0.001 in fo r 0.001 in g a ug es an d
0.000 2 in fo r 0.000 1 in g a uge s. When a dial g au ge is tested ag a inst
such a ma ndrel it should indica te t he a mount of eccentricity present
to w ithin the a ccuracy sta ted in 9.3.
B.3 Calibration
The calibra tion o f a dial ga uge is usually ca rried out in a fi xture in
w hich the g a uge is held rigidly oppo site a nd in line with a calibra ted
micrometer head, or abo ve and norma l to a ba se plat e on to w hich
ga uge blocks ca n be w rung. In eithe r ca se a series of read ings ista ken at suita ble intervals througho ut the rang e of the g aug e. If the
ga uge ha s a l imited range of o nly tw o o r three turns of i ts pointer,
the readings can b e ta ken at intervals of a tenth o f a turn throughout
the w hole rang e. Where th is is not pra ctical, i.e. in th e case of g a uge s
w ith longer rang es, a l imited numb er of readings may be ta ken at t he
inte rval of o ne-tent h of a turn during ea ch revolution o f the po inter.
For exa mple, in th e case of a g a ug e ha ving 100 divisions of 0.001 in
a nd a rang e of 0.5 in (fi ve turns of t he pointer), the read ings could
be d istributed in the m a nner show n in Ta ble B.1. Ea ch of t he
read ings show n in Ta ble B.1 represents the mea n error, foun d o n t he
instrument t ested, a t tha t part icular po int of observation, the unit
be ing 0.000 1 in, i.e. one t ent h of a division .NOTE Large errors, as show n in Table B.1, are not t ypical of d ial gauges
but have been chosen f or p urp oses of clear il lustrat ion.
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By sett ing out the read ings in th is ma nner, it is a simple mat ter to
compa re the results w ith th e limits of error given in Ta ble 2 fo r this
part icular type of ga uge. It can be seen that the error over none of
the 0.01 in interva ls tested , i.e. betw een a ny tw o a djacent rea dings,
exceeds the to lera nce of 0.000 25 in specifi ed for t ha t interval. On
the ot her ha nd, o ver intervals of ha lf a turn, i .e. 50 divisions, the
corresponding to leran ce of 0.000 5 in is exceeded over the follow ingtested positions:
Turn I 10 to 60 erro r + 0.000 7 in
Turn III 0 to 50 erro r + 0.000 6 in
Tu rn III 60 to Tu rn IV, 10 e rro r 0. 000 9 in
Turn IV 10 to 60 erro r + 0.000 8 in.
Over one t urn or tw o t urns or a ny long er interval, the errors a re all
w ithin the t olerances allow ed.
This gaug e w ould be rega rded a s unsat isfa ctory on a ccount of thelarge e rrors found over some of the ha lf-turn intervals tested.
It is interesting t o no te t ha t t his pa rticula r ga uge possesses a t ype
of period ic error w hich is not infrequent ly met w ith in this cla ss of
mea suring t oo l. To illustra te t his point , the results of a te st ca rried o ut
on t his ga uge a t every 10 divisions throug hout its ra ng e a re show n
in Figure B.1. It ca n b e seen t ha t t he e rrors in ea ch successive t urn a re
of simila r und ulat ory cha ra cter. This type of error usua lly a rises fro m
centering errors in the tee th o f t he pinion t o w hich the pointer is
at ta ched, or f rom the fa ct that the a xis of rota t ion of the pointer is
not truly central w ith the dial .
The a bb reviat ed t est described a bo ve is suffi cient to det ect this typeof pe riod ic error by rea son o f th e large errors fou nd in some o f t he
read ings of ha lf-turn intervals.
Where the re is any dispute reg a rding a ccuracy, the g a uge block
method should be used, in w hich case the a rithmetical mea n of a
series of a t least fi ve measurements over each of t he points in dispute
should be t aken.
Ta b le B.1 Error of reading of dial gauge given in units of 0.000 1 in
Divisions of dial 0 10 20 30 40 50 60 70 80 90
Turn I 0 1 + 1 + 6 + 4 + 2
Turn II 0 + 2 + 4 + 3 + 2
Turn III 0 + 4 + 6 + 8
Turn IV + 1 1 0 + 7 + 5 + 3
Turn V 0 + 2 + 4 + 5 + 3
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Figu re B.1 Calibration curve of a dial gauge illustrating periodic error
Turn I
0.0010
0.0008
0.0006
0.0004
0
0.0002
0.0002
0.0004
+
-
Turn II Turn III Turn IV Turn V
Y
Key
Y Error in rea ding (inches)
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Annex C (informative) Notes on the care and use of dial gauges
C.1 General care
Althoug h dial ga uges are ma de robust fo r w orkshop use their
mechan ism is simila r to t ha t o f a clock, and a ny fa ll or sharp blow
might da mag e the pivots or upset t he a lignment of t he bea rings. If
it is found a t a ny t ime tha t the mo vement is not smooth, the g aug e
should be checked b y a competen t instrument m a ker or be returned
to the ma kers for ad justment.
C.2 Oiling
It is importan t t ha t t he plunger is not oiled o r grea sed. It is intended
to w ork dry. The plunge r is mad e q uite a close fi t in its bush a nd is
returned t o its zero position b y mea ns of a compa rat ively light spring .
Even a th in oil w ill pick up d irt w hich could ca use the plung er to stick.
C.3 General use
Dial ga uges should preferab ly be used a s compa rato rs and not
a s direct mea suring instrument s. For exam ple, a w orkpiece of
6.35 mm diameter might be t ested w ith a dial gaug e by sett ing t he
ga uge t o zero, raising the spindle to a dmit the w orkpiece and t hen
ta king a read ing. This met hod , how ever, w ould g ive an a ccuracy of
mea surement o nly w ithin the to lera nces a llow ed in the specifi cation
fo r the long er inte rva ls of rea ding.
On the o ther hand , if the ga uge is used a s a comparat or by observing,
fi rst of a ll the read ing w hen set on a 6.35 mm sta nda rd plug or ga uge
block and comparing t his reading w ith t he one ob ta ined on the
w orkpiece, thus det ermining th e size of the la tt er by difference, the
accuracy of mea surement w ill be higher tha n tha t ob ta ined by the
fi rst method.
C.4 Clamping
Dial ga uge s a re usua lly supplied w ith mea ns for a lternat ive metho ds
of fi xing, na mely :
by means of a ba ck lug; ora )
by mea ns of the steel stem.b)
When m etho d a ) is used it is necessa ry for the cla mp t o b e q uite
tig ht , since slip could ot herw ise occur a nd f a lse rea ding s result. When
method b) is adopted it is important tha t care is ta ken not to apply
too great a clamping f orce a s this might cause the plunger to jam in
the stem; it is important tha t t he hole in the fi xture w hich is to ta ke
the stem is smoot hly fi nished a nd t ruly circular a nd a go od fi t o n the
stem. The ste m is purposely ma de cylindrica l to fi ne limits of a ccura cy,
a nd t he hole in the fi xture should be correspond ingly a ccurat e. If the
hole is not true and smoot h, there could be a tendency to nip the
stem across a diame ter, thus disto rting it an d causing the plung er to
bind o r even lock.
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C.5 Stands
It is essential tha t a ny stand in w hich a dial ga uge is used is very rigid
if a ccurate read ings are to b e obt ained.
C.6 Use of plunger lifting lever
Where the plung er is raised b y mean s of a lever to a llow the
w orkpiece to be inserted under the conta ct point i t oug ht no t b e
relea sed so t ha t t he po int hits the w orkpiece w ith force. The use of
a d ial ga uge in this w ay for a ny lengt h of t ime w ill bring a bout a
distort ion of t he teeth o f the ra ck of the plunger at t he point w here
the mechanism is suddenly arrested in its movement. Furthermore,
such use mig ht ca use the po inter to slip on its spindle, w ith
conseq uent ina ccuracy of read ing, particula rly if the g a uge is one o f
high m a g nifi cat ion, i.e. 0.01 mm or 0.000 1 in.
C.7 Contact points
A variety o f cont a ct point t ypes a re supplied b y the ma kers for use
according to the na ture of t he w orkpiece to be t ested. Bal l points are
tho se most commo nly used. Consta nt use of a ba ll point can ca use
w ear, and any result ing fl at on t he ba ll might cause errors of conta ct
resulting in ina ccurat e rea dings.
Particula r ca re should be exercised w hen using fl a t cont a cts of
diamet ers bet w een, sa y, 6 mm or 14in and 13 mm o r 12in. It is essent ial
tha t t he fl at surface of such contacts are truly squa re to t he plunger
and para llel to t he mea suring surface of t he fi xture if a ccurate
readings are to be ob ta ined.
C.8 Choice of an appropriate type of gauge
In choosing a dial ga uge f or a certa in purpose, one should be selected
w ith a ma gn ifi cation w hich is am ple in rela tion to t he accura cy
required on the w orkpiece under te st. For example, if t he t olerance
on t he w orkpiece is 0.001 in th en a 0.001 in g a uge is not the most
suita ble as the movement of t he pointer wo uld be t oo small for
a ccura te rea ding . For such a ca se a 0.000 1 in g a ug e should be selected .
The dial ga uge should be calibra ted a nd t he calibra tion uncertainty
incorporat ed into t he o vera ll mea surement uncertainty. The o verall
measurement uncertainty should be ta ken into account w hen proving
conforma nce o r non-conformance of the w orkpiece under test w iththe specifi ed to lera nce. The w orkpiece under t est meet s specifi cation
if th e mea sured value is w ithin the t olerance ba nd specifi ed,
ta king into account the uncertainty of mea surement according to
BS EN ISO 14253-1.
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Bibliography
Standards publications
For da ted references, only the e dition cited a pplies. For und a ted
references, the la test ed ition o f t he referenced d ocument (including
a ny am endm ents) a pplies.
BS EN ISO 14253-1, Geom et ri cal Product Specificati on s (GPS)
Inspectio n by m easurement of w orkp ieces and measuring
equi pm ent Part 1: Decision rules fo r pro ving conf orm ance or
non -conf orm ance w ith specification s
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