Claims
- 1. A rolling cutter drill bit for drilling through underground formations, said bit comprising:
- a main body having an upper end adapted for interconnection in a drilling string;
- a plurality of legs extending downwardly from said body, each having an inwardly projecting bearing journal formed thereon;
- a generally frustoconical cutter rotatably mounted on each said bearing journal, having a rotational axis generally coinciding with the central axis of said journal, and having a plurality of hard metal cutting elements inserted therein and protruding from the surface thereof;
- bearing means between each said cutter and bearing journal;
- said drill bit having a cutting diameter defined by the radially outermost located of said cutting elements on each said cutter and having a bit rotational axis passing longitudinally therethrough; and,
- the central axes of said journals being offset from said bit axis by an amount ranging from about one-sixteenth inch per inch to about one-eighth inch per inch of bit cutting diameter.
- 2. The rolling cutter drill bit of claim 1 wherein said legs and cutters each number three and said cutting elements protrude at least one-half of the insert diameter from the cutter surface; said inserts being formed of a tungsten carbide-cobalt material wherein the cobalt content by weight ranges from about five percent to about twenty percent and the hardness of said insert is from about 85 Rockwell A to about 90 Rockwell A.
- 3. A tri-cone rolling cutter drill bit comprising:
- a bit body having an upper threaded pin end for engaging a section of drill string, and further having an axis of rotation;
- three downwardly extending, generally equispaced legs on said bit body, each having a cylindrical bearing journal extending radially inward and downwardly from the lower end thereof;
- a generally frustoconical cutter rotatably mounted on each said bearing journal, and having a rotational axis generally coinciding with the central longitudinal axis of said journal;
- bearing means between each said cutter and bearing journal;
- a plurality of hard metal cutting elements inserted in each said cutter and protruding outwardly therefrom; and,
- wherein said cutter rotational axes are offset from said bit rotational axis by a distance of from about one-sixteenth inch per inch to about one-eighth inch per inch of the diameter of said bit.
- 4. The tri-cone drilling bit of claim 3 in which said cutting elements comprise tungsten carbide grains in a cobalt matrix and the shape of the cutting elements protruding outwardly beyond the cutter surface is substantially conical with a rounded top.
- 5. The tri-cone drill bit of claim 4 wherein the portion of each cutting element protruding beyond the cutter surface is of generally conical shape and has a rounded tip.
- 6. The tri-cone drill bit of claim 3 wherein at least one of said cutting elements comprises a tungsten carbide-cobalt insert having a chisel-shaped protruding portion.
Parent Case Info
This is a continuation of application Ser. No. 132,951, filed Mar. 24, 1980, now abandoned.
US Referenced Citations (7)
Non-Patent Literature Citations (2)
Entry |
"A Study to Determine the Optimum Bit Offset at Various Drilling Depths", by Terra Tek, Inc.--Oct., 1978-DOE. |
"Rotary Drill Bit/Rock Model with Cutter Offset", by E. I. Umez-Eronini. |
Continuations (1)
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Number |
Date |
Country |
Parent |
132951 |
Mar 1980 |
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