Brunson 771 - Horizontal Axis Runout

41 Operation and Adjustment Manual

Thisisaquickandeasychecktohelpdetermine
whethertherehasbeenanymajordamagetothehori‐
zontalaxisbearingssuchasballorracedenting.

1.Mountthetransitonastand.Installthemicrome‐
tertoreadhorizontaldeviations(i.e.,positionthemi‐
crometerdrumonthetoporbottomofthetelescope
ratherthanontheside).Holdascalehorizontallyus‐
ingamagnetorotherconvenientmount,about17feet
away,andapproximatelyonalevelsightlinefromthe
telescope.

2.Rotatethetelescopeaboutitshorizontalaxis
roughly5timesinthesamedirection.Thisensures
theindividualballsinthehorizontalaxisbearings 
haveallmadeatleastonecompleterevolution.

3.Makesurethatthehorizontaltangentclampissecured.Using
thehorizontaltangentscrew,achieveaccurateregisterbetweenthe
transit’sverticalreticlewireandsomearbitrarypositiononthe
scale.Notethepositionofthetransit’shorizontalreticlewireso
thatyoucanreturntothesameelevationposition,butkeepthever‐
ticaltangentclamploose.

4.Gentlyrotatethetelescopearounditshorizontalaxisonceinthe
samedirectionthatitwasrotatedinstep2.Re‐pointbacktothe
samescaletarget,puttingthehorizontalwireinapproximatelythe
samepositionasitwasplacedinstep3(ifyouovershootthetarget,
goaroundagain).Measureanyhorizontalerrorwiththemicrome‐
ter.Repeatthisprocess4or5times,notinganyerroreachtime.

Ifanerrorgreaterthan0.001”isobserved,rerunthetesttoensure
thattheobservederrorisactuallybearingrunoutandnotmove‐
mentoftheentireinstrument.Ifitisdeterminedtheerrorisbearing
runout,repairsarerequiredandthetransitshouldbereturnedto
themanufacturerforrepair.

Description:Initialindicationof
whetherthetelescoperotatesaccu‐
ratelyaboutthehorizontalaxis.

Tolerance:±1arcsecond(0.001”in
thistestprocedure.

Affectedparameters:Alladjust‐
ments.

Requiredequipment:Opticalmi‐
crometer,instrumentstand,anda
scaleplaced17feetawayinhorizon‐
talorientation.
HorizontalAxisRunout
NOTE:Itisimportanttosaythatthistestmayindicate
problemswiththehorizontalaxis.Itisatleastagoodinitial
indicatorofproblemslikebearingdenting.However,other
indicatorsofhorizontalbearingproblemsmayshowuplater,
suchasaninabilitytomakeplumblineorcross‐axistelescope
collimationadjustments,evenifthistestdoesnotrevealany
problems.