43 Operation and Adjustment Manual
Horizontalcenteringisalsocalled“side‐to‐side”cen‐
tering.Forthistest,placeamirroronastablevertical
surfacesuchasawall,column,ormachine.Our
magneticmirrorsareveryusefulforthistypeofap‐
plication.Next,mountascalehorizontallyunderthe
mirror(Figure4.3).Themirrorwillprovideaninfin‐
itytarget,andthescalewillprovidea“near”target.
Youcanalsouseamirrorwhichhasatargetim‐
printedontheface,suchasourmodel6250,rather
thanthemirror‐and‐scalecombinationdescribed
here.
Thetransitmustbeequippedwith
alightedeyepiece
andalightsourceforthistest.Followthesesteps:
1.Situatethetransitapproximatelyfivefeetfromthe
mirror,andmakesurethemirrorisnominallyona
levelsightlinefromthetelescope.
2.Installthemicrometersothatthedrumisfacingupor
down,
andsetthemicrometertozero.
3.Autocollimatethemaintelescope’svertical
reticlewirepreciselyonthereflectedimagein
themirror(describedinChapter3ofthis
manual).Thehorizontalwireshouldbeclose
tocenterbutisnotrequiredtobeprecisely
set.Thisrepresentsaninfinitytargetforour
test.
4.Nowtiltthetelescopeslightlyandfocuson
thescale.Thetransitwillbepointingatsome
randompointonthescale.Notethisreading
usingthemicrometer.
5.Releasethehorizontaltangentclampand
rotatethetransit180°aboutitsverticalaxis.
Releasethevertical
tangentclampandplunge
thetelescope180°.Autocollimateonceagain
onthemirrorandmakecertainthattheverti‐
calreticlewireispreciselyinregisterwithits
reflection.Besurethehorizontaltangent
clampissecuredwhendoingthis.
6.Tiltonceagaintothescale,andtakea
reading.
Determinethedifferencebetween
thisreadingandthereadingtakeinstep4.If
thedifferenceis0.002”(0.05mm)orless,the
horizontalcenteringiswithintolerance.The
actualerrorishalfoftheobservederror.If
thehorizontalcenteringisoutoftolerance,
theinstrumentshouldbeadjustedinacali‐
brationlaboratory.
Description:Determineifthelineof
sightintersectstheverticalaxis(or
whetheritpassestotherightorleft
oftheverticalaxis).
Tolerance:±0.001inch.
Affectedparameters:None.
Requiredequipment:Instrument
standwithprecisionliftandlateral
slide,lightedeyepieceadapterand
lightsource,opticalmicrometer,
mirrorandscale.
HorizontalCentering
Figure4.3
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