Morisette expansion reamer

Morisette expansion reamer

[′mär·ə‚set ik′span·chən ‚rē·mər]
(mining engineering)
A reaming device with three tapered lugs or cutters designed so that drilling pressure necessary to penetrate rock with a noncoring pilot bit forces the diamond-faced cutters of the reamer to expand outward, thereby enlarging the pilot hole sufficiently to allow the casing to follow the reamer as drilling progresses.