Scrape-type cutter for drill bits

Abstract

A drill bit for drilling large diameter holes in the earth has drag or scraper-type cutters substituted for some or all of the usual roller-type cutters. The drag-type cutter may be adapted for limited rotational movement about its axis so that the drag cutter assumes a first cutting position when the bit is rotated in one direction, and automatically assumes a second cutting position when the bit is rotated in an opposite direction.

Description

SUMMARY

The present invention relates to earth boring bits and to cutters mounted thereon of the type particularly useful in the drilling of tunnels or the like.

It is an object of this invention to provide new and improved replaceable drag-type cutter assemblies which are adapted to fit into roller cutter supports of the type usually employed with such drill bits.

Another object is to provide drill bit cutter assemblies which are suitable for large hole earth drilling bits, which can readily be replaced without replacement of the entire drill bit, and which assemblies can be disposed between cutter support legs of existing mounting saddles on cutter heads for tunneling machines or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bottom plan view of the drill bit of the invention.

FIG. 2 is a view, partly in section, taken along line 2--2 in FIG. 1, showing cutter traces, and with some of the cutters being rotated into the plane of the paper.

FIG. 3 is an enlarged, side elevational view of a drag-type cutter assembly.

FIG. 4 is a view taken along line 4--4 in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A cutter assembly 10 is shown mounted on a steel cutter support or saddle 11. The saddle 11 has a base 12 which may be welded as at 13 to a drill bit head 14. The bit head 14 here includes steel plates 15 and 16 which are joined together by welding circular members 17 and 18 therebetween. The plate 16 is adapted to be operably connected to a drilling machine (not shown).

Some of the cutter saddles 11 may have removably mounted therein roller cutters 20. An example of this type of cutter mounting is shown in U.S. Pat. No. 3,747,999 to Dan B. Justman, patented July 24, 1973.

Some of the cutters 20 may be dispensed with and, in lieu thereof, the drag or scraper-type cutter assembly 10 may be employed. If the formations being encountered are relatively easy to drill, all of the cutter saddles 11 may be supplied with drag-type cutter assemblies 10.

Referring to FIGS. 3 and 4, the drag-type cutter assembly 10 includes a frusto-conical steel body 21 mounted for limited rotational movement on a steel shaft 22 which extends between the legs 23 and 24 of the saddle 11. The ends of the shaft 22 may be rectangular in shape to fit into complementary openings in the legs 23 and 24. The shaft 22 is secured to the saddle legs by bolt means 25.

The cutter assembly 10 may have steel ribs 26 welded to the conical body 21. The ribs 26 have slots 27 into which are disposed cutting teeth 28 which may be secured to the ribs 26 by screw means 29, or in any other suitable manner.

The body 21 has welded thereon steel stop arms 30 and 31 which serve to limit the rotational movement of the cutter assembly 10 about its axis. Thus when the drill bit is rotated in the direction of the arrow 32, the cutting teeth 28 are positioned as shown and the stop arm 30 engages the base 12 of the saddle 11.

When the drill bit is rotated oppositely, as shown at 33, the stop arm 31 engages the base 12, as shown in dotted lines in FIG. 4. When this occurs, the cutting teeth 34 (which are similar to cutting teeth 28 but face in the opposite direction) are positioned in a similar but opposite position to that shown for the cutting teeth 28 in FIG. 4.

In drilling tunnels, for example, the drilling machine rotates the bit head 14 and drives it forwardly into the formation. As drilling progresses, the drilling machine tends to twist about the axis of bit rotation because of the torque required to drive the bit head. Thus the drilling machine may tend to deviate from its desired level and plumb position.

To compensate for this condition, the drilling machine may be rotated in the opposite direction, which requires that the scraper-type cutter 10 be repositioned in order to achieve an optimum cutting position for the cutter teeth 28 or 34. In my invention, this is automatically accomplished since the frictional engagement of the cutter assembly 10 with the formation being encountered rotates the cutter assembly 10 about its axis until such rotational movement is stopped by stop arms 30 or 31 depending upon the direction of rotation of the bit head 14.

The useful life of the cutter assemblies is thus extended since two sets of cutting teeth are employed on each cutter assembly.

The cutting teeth 28 and 34 may comprise various shapes, sizes and materials. For example, the cutting teeth may be inserts pressed into the ribs 26. They may be made of tool steel or tungsten carbide. The cutting teeth may employ wear-resistant pads or be dressed with hard surfacing materials, it being understood that the cutting teeth shown are examples of those that can be used.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the shape, size, locations and materials, as well as in the details of the illustrated construction may be made within the scope of the appended claims without departing from the spirit of the invention.

Claims

What is claimed is:

1. A drill bit head including a plate member having a plurality of support saddles mounted thereon in spaced relation to one another, said saddles having spaced apart legs,

rolling cutters and at least one drag type cutter disposed in said support saddles with said drag type cutter being interchangeable with a rolling cutter, said drag type cutter including a body mounted for rotational movement on a shaft disposed between the legs of a saddle,

means on said body engagable with said saddle to limit the rotational movement thereof,

said body having cutting members mounted thereon and adapted to assume a first cutting position when the drill bit head is rotated in one direction, and

adapted to assume automatically a second cutting position when the drill bit head is rotated in an opposite direction.

2. A drill bit head as set forth in claim 1 wherein said body is of frusto-conical shape and is provided with slotted ribs for holding a plurality of cutting teeth.

3. A drill bit head as set forth in claim 1 wherein said means includes diametrically disposed arms secured to said body.

4. A drill bit head as set forth in claim 1 wherein said cutting members may be formed of tungsten carbide.

5. A drill bit head as set forth in claim 1 wherein said cutting members may include tool steel.