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<strong>OnGrade</strong> Operator’s <strong>Manual</strong> Systems and Equipment - 43Downhole Tools• Grade transition sub: is stiffer than standardtransition subs and helps maintain a straightbore path. Reduces the drill head’s tendencyto deviate from a straight line.Backreame14om029t.epsTools• Flail backreamer: provides very thoroughmixing action to create a flowable soil slurryand has support wings to help maintain thevertical position of the reamer in the bore holein softer soils.• Centering tools: are placed in front of thebackreamer on second and third backreamingpasses to help hold the reamer in the center ofthe bore hole. This helps reduce the tendancyof the reamer to lower the bore hole onsubsequent backreaming passes.e14om027t.epse14om028t.epsCMW
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