Brunson 771 - Page 34

Model 771, 75, and 76-RH190 Transits 30
Ifyouwishtomeasurevertically(horizontalwireappearstomove
upanddown)thenmountthetopofthedrumfacingtotherightor
left.
Oncethemicrometerislocatedinthedesiredposition,
tightentheknurledlockingknobtosecureit.Befirm but
don’tuseexcessiveforce.
Next,let’sconsiderhowtomeasuredistancesthatarelar‐
gerthanthemicrometer’sshortrange.Thisisaccom‐
plishedusingopticaltoolingscalesandInvarscaleextension
rods,whicheffectivelyextendtherangeoftheopticalmi‐
crometerbyseveralfeetormetersifnecessary.
Let’slookathowtotakeareadingfromanopticaltooling
scale.Anopticaltoolingscaleislikeaverypreciseruler
whichisoptimizedforviewingthroughatelescope.The
micrometeractsasavernierforthescale,providinganex‐
actmeasurement.
Inthisexample,machinecomponentsareevaluatedforpar‐
allelismtoaknownreferenceline(seeFigure3.14,aview
fromabove).Thetransitisfirstbroughtintoalignment
withthereferenceline(whetherestablishedbytargets,a
mirror,acollimator,etc.)Atthispointitisextremelyimpor‐
tantthatthemicrometer’sgraduateddrumbesettozero.Then,
opticaltoolingscalesareheldhorizontallyagainstmachine
componentswhicharesupposedtobeparallelwiththeref‐
erenceline.
Thescalesmaybeleveledusingscalelevelstoensurethat
theyarehorizontal.Inthisexample,wewilltakeareading
onthefarscale.Let’ssaythatwhenyoufocusonthefar
scale,youseetheimageinFigure3.15.Thereticleoverlays
Figure3.15
Figure3.14