The Back Cut Sub is run at the top of a BHA in assemblies where it is anticipated that squeezing or unstable formations will be drilled through. The design incorporates hardened steel PDC cutter pads held in place by way of the patented wedge lock retention system.
These pads are protected going into the hole by a protective band dressed with hard facing material. These PDC pads are replaceable in the field by following simple instructions.
Such is the placement of the cutters in the body of the Back Cut Sub that the tool will ream from body OD out to the hole diameter.
When tripping out of the hole where tight sections are encountered the top drive should be engaged and the cutters will ream through soft / medium soft formations that may have squeezed or swelled into the bore hole.