Generally 38 ~ 53mm, the drill pipe wall roller reamers drilling thickness is equivalent to 4 to 6 times), has a large gravity and stiffness.
Drill collar during drilling act primarily in the following areas
(1) is applied to the drill bit pressure;
(2) to ensure Hydraulic Drilling jars the necessary strength under conditions of compression;
(3) to reduce the vibration of the drill bit, swing and bounce, so that the drill steady work;
(4) The control deviation.