US20120167420A1

US20120167420A1 - Polygon-shaped carbide tool pick

Info

Publication number: US20120167420A1
Application number: US13/340,783
Authority: US
Inventors: Joseph Fader; Kenneth Monyak
Original assignee: Sandvik Intellectual Property AB
Current assignee: Sandvik Intellectual Property AB
Priority date: 2011-01-03
Filing date: 2011-12-30
Publication date: 2012-07-05
Also published as: DE102011056363A1; PL397702A1; CN102535561A; CA2757795A1; AU2011253551A1

Abstract

A polygonal tool pick formed entirely of a single hard material, including a head, a shoulder extending rearwardly from the head and having an outer dimension at least as large as a largest outer dimension of the head, a shank extending rearwardly from the shoulder and having an outer dimension smaller than the outside dimension of the shoulder, and a tail extending rearwardly from the shank and having an outer dimension larger than the outer dimension of the shank, wherein the head, the shoulder, the shank, and the tail each have a plurality of faces with at least one pair of opposed faces being parallel to each other.

Description

RELATED APPLICATION DATA

This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/429,298, filed Jan. 3, 2011, entitled “Polygon-Shaped Carbide Tool Pick”, the entire contents of which are incorporated herein by reference.

FIELD

The present disclosure relates to a tool pick having an overall polygonal shaped that is formed entirely from a hard material such as cemented carbide (“carbide”), and in particular to a carbide tool pick having a polygonal shape along its entire length that can be mounted in a wheel used for microtrenching.

BACKGROUND

In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Tool picks known in the art typically employ a cemented carbide tip that is brazed to a steel shank having an enlarged tail at an end of the shank opposite the tip. In part, this construction is used because it would be excessively expensive to produce and entire tool pick out of cemented carbide, without commensurate benefits in performance. The pick is commonly retained in a cylindrical bore of a holder using a cylindrical spring retainer positioned around the shank. When installed in the bore, the spring retainer presses against the inner wall of the bore, creating a frictional force that resists movement of the retainer with respect to the bore. The shank has an outer diameter slightly smaller than the inner diameter of the spring retainer so that the pick can rotate freely within the retainer, while spring retainer has an inside diameter smaller than that of the tail to prevent axial movement of the pick out of the bore. Therefore, the enlarged tail is essential to maintaining the pick within the holder, such that if the tail is worn away, the pick may be lost.
Microtrenching is a low-impact method of burying conduit by digging a narrow slot-cut trench in the ground typically between about 19 mm and about 25 mm wide and less than about one foot deep, laying the conduit in the trench, and backfilling the trench. Microtrenching machines commonly employ a vertical rotating wheel on which are mounted a plurality of tool picks. As the wheel rotates, a tip of each pick cuts into the ground. Commonly, diamond-tipped saw blades are used for microtrenching.
Because of the narrow trench width and relatively shallow depth in microtrenching applications, tool picks for mounting on a microtrenching wheel require a short shank length, as well a small shank diameter of typically less than about 10 mm. When mounted with lean and skew angles required for microtrenching, the tail of the pick shank is exposed at the opposite end of the holder from the pick cutting tip, causing the tail to be worn away significantly by microtrenching debris. The wear on the tail causes the tail to become sufficiently small that it no longer is larger than the retainer. As a result, the retainer is no longer confined such that the pick may fall out of the holder.
The cost to manufacture a small carbide tip and narrow steel shank for microtrenching is actually higher than that to produce similar larger picks due to difficulties with the small scale. Additionally, because of the small size of the carbide tip and the small diameter of the steel shank, brazing the carbide tips to the steel shanks is difficult, in part because the slimness of the steel shank makes it especially susceptible to overheating during brazing.

SUMMARY

An exemplary embodiment of a polygonal tool pick is formed entirely of a single hard material. The tool pick includes a head, a shoulder extending rearwardly from the head and having an outer dimension at least as large as a largest outer dimension of the head, a shank extending rearwardly from the shoulder and having an outer dimension smaller than the outside dimension of the shoulder, and a tail extending rearwardly from the shank and having an outer dimension larger than the outer dimension of the shank. The head, the shoulder, the shank, and the tail each have a plurality of faces with at least one pair of opposed faces being parallel to each other. In one embodiment, the head includes a pyramidal cutting tip terminating in a frontward tip end and a truncated pyramidal base supporting the cutting tip and disposed rearwardly with respect to the cutting tip, the pyramidal cutting tip having a steeper slope than the truncated pyramidal base with respect to an axis of the tool pick.
Another exemplary embodiment of a polygonal tool pick is formed entirely of cemented carbide. The tool pick includes a pyramidal cutting tip terminating in a frontward tip end, the cutting tip having an even number of equally sized faces, and a truncated pyramidal base supporting the cutting tip and disposed rearwardly with respect to the cutting tip, the truncated pyramidal base having a shallower slope than the pyramidal cutting tip with respect to an axis of the tool pick, the base having an even number of equally sized faces aligned with the faces of the cutting tip. A shoulder extends rearwardly from the head and has an outer dimension at least as large as a largest outer dimension of the base, the shoulder having an even number of equally sized faces aligned with the faces of the base. A shank extends rearwardly from the shoulder and has an outer dimension smaller than the outside dimension of the shoulder, the shank having an even number of equally sized faces aligned with the faces of the shoulder. A tapered frontward seat is located between the shoulder and the shank, the seat being tapered from a smaller outer dimension at a junction with the shank to a larger outer dimension at a junction with the shoulder, the frontward seat having an even number of equally sized faces aligned with the faces of the shank. A tail extends rearwardly from the shank and has an outer dimension larger than the outer dimension of the shank, the tail having an even number of equally sized faces aligned with the faces of the shank. A tapered rearward seat is located between the tail and the shank, the seat being tapered from a smaller outer dimension at a junction with the shank to a larger outer dimension at a junction with the tail, the rearward seat having an even number of equally sized faces aligned with the faces of the shank.
An exemplary embodiment of a pick assembly includes a holder having a cylindrical bore, a polygonal tool pick, and a compressible cylindrical retainer for holding the tool pick within the cylindrical bore of the holder. The polygonal tool pick is formed entirely of cemented carbide. The tool pick includes a pyramidal cutting tip terminating in a frontward tip end, a truncated pyramidal base supporting the cutting tip and disposed rearwardly with respect to the cutting tip, the truncated pyramidal base having a shallower slope than the pyramidal cutting tip with respect to an axis of the tool pick, a shoulder extending rearwardly from the base and having an outer dimension at least as large as a largest outer dimension of the base, a shank extending rearwardly from the shoulder and having an outer dimension smaller than the outer dimension of the shoulder, and a tail extending rearwardly from the shank and having an outer dimension larger than the outer dimension of the shank. The cutting tip, the base, the shoulder, the shank, and the tail each have an even number of faces with at least one pair of opposed faces parallel to each other, the faces of each of the cutting tip, the base, the shoulder, the shank, and the tail being aligned. When the retainer is compressed, the retainer is located between the shank and the cylindrical bore, and the inner diameter of the compressed retainer is less than the outer dimension of the tail and the outer dimension of the shoulder.
An exemplary embodiment of a microtrenching wheel has a disk and a plurality of pick assemblies mounted around the circumference of the disk. Each pick assembly includes a holder having a cylindrical bore, a polygonal tool pick, and a compressible cylindrical retainer for holding the tool pick within the cylindrical bore of the holder. The polygonal tool pick is formed entirely of cemented carbide. The tool pick includes a pyramidal cutting tip terminating in a frontward tip end, a truncated pyramidal base supporting the cutting tip and disposed rearwardly with respect to the cutting tip, the truncated pyramidal base having a shallower slope than the pyramidal cutting tip with respect to an axis of the tool pick, a shoulder extending rearwardly from the base and having an outer dimension at least as large as a largest outer dimension of the base, a shank extending rearwardly from the shoulder and having an outer dimension smaller than the outer dimension of the shoulder, and a tail extending rearwardly from the shank and having an outer dimension larger than the outer dimension of the shank. The cutting tip, the base, the shoulder, the shank, and the tail each have an even number of faces with at least one pair of opposed faces being parallel to each other, the faces of each of the cutting tip, the base, the shoulder, the shank, and the tail being aligned. When the retainer is compressed, the retainer is located between the shank and the cylindrical bore, and the inner diameter of the compressed retainer is less than the outer dimension of the tail and the outer dimension of the shoulder.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWING

The following detailed description can be read in connection with the accompanying drawings in which like numerals designate like elements and in which:

FIG. 1 is a side perspective view of an exemplary polygon-shaped carbide tool pick.

FIG. 2 is a side view of the tool pick of FIG. 1 showing a parting line from pressing.

FIG. 3 is a top end view of the tool pick of FIG. 1.

FIG. 4 is a bottom end view of the tool pick of FIG. 1 inserted in a holder having a cylindrical bore.

FIG. 5 is a side view of a microtrenching wheel supporting a plurality of tool picks as in FIG. 1.

DETAILED DESCRIPTION

FIGS. 1-4 illustrate an embodiment of a polygonal tool pick 10. The pick 10 has a front end 16 and a rear end 18. Through its entire length, the pick 10 has a polygonal shape. Because the entire cross-section of the pick is polygonal shaped with alternating faces and edges, the cross-sectional size of the pick at various points is described here with reference to an “outer dimension” rather than a “diameter.” When comparing the relative sizes of various portions of the pick 10, the outer dimension may be obtained by measuring the width of the pick between opposed edges on opposite sides of the pick (i.e., a maximum outer dimension), or alternatively by measuring the width of the pick between opposed faces on opposite sides of the pick.
The pick 10 includes a head 12 having a base 30 supporting a cutting tip 20 that projects frontwardly from the base 30. The base 30 and the cutting tip 20 are joined at a junction 26. A shoulder 40 is disposed rearwardly adjacent to the head 12 and joins with the head 12 at a junction 36. A shank 60 projects rearwardly with respect to the shoulder 40. As depicted, a tapered frontward seat 50 provides a transition from the shoulder 40 to the shank 60. The seat 50 is joined to the shoulder 40 at a junction 46 and to the shank 60 at a junction 56. Extending rearwardly from the shank 60 is an enlarged tail 80. As depicted, a tapered rearward seat 70 provides a transition from the shank 60 to the tail 80. The seat 70 is joined to the shank 60 at a junction 66 and to the tail 80 at a junction 76.
The cutting tip 20, as the frontwardmost portion of the tool pick 10, provides a primary cutting surface during use of the pick 10. The cutting tip 20 has a plurality of faces 22, with each pair of adjacent faces 22 being joined at an edge 24. The cutting tip 20 has a pyramidal shape, tapering frontwardly from a largest outer dimension at the junction 26 to a smallest outer dimension at a tip end 14. The taper of the cutting tip 20 is relatively sharp, and is preferably angled at about 20° to about 60° with respect to an axis of the pick 10. More preferably, the pyramidal faces 22 and the edges 24 of the cutting tip 20 are angled at about 30° to about 50° with respect to the axis of the pick 10, and most preferably at about 35° with respect to the axis of the pick 10. The tip end 14 may be pointed, blunt, or rounded, depending on the desired application. In the depicted embodiment, the tip end 14 of the cutting tip 20 is blunted.
The base 30 of the head portion 12 has a truncated pyramidal shape that supports the cutting tip 20. The base 30 has a plurality of faces 32, with each pair of adjacent faces 32 being joined at an edge 34. The faces 32 and the edges 34 of the base 30 are aligned with the faces 22 and the edges 24, respectively, of the cutting tip 20. The base 30 tapers frontwardly from a largest outer dimension at the junction 36 to a smallest outer dimension, matching the largest outer dimension of the cutting tip 20, at the junction 26. The taper of the base 30 is shallower than that of the cutting tip 20, and is preferably angled at about 5° to about 30° with respect to the axis of the pick 10. More preferably, the pyramidal faces 32 and the edges 34 of the base 30 are angled at between about 10° to about 20° with respect to the axis of the pick 10, and most preferably at about 15° with respect to the axis of the pick 10.
The shoulder 40 has a polygonal disk shape defined by a plurality of faces 42, with each pair of adjacent faces 42 being joined at an edge 44. The faces 42 and the edges 44 are aligned with the faces 22, 32 and the edges 24, 34, respectively, of the cutting tip 20 and the base 30. The shoulder 40 has an outer dimension at least as large as the largest outer dimension of the base 30. In the depicted embodiment, the outer dimension of the shoulder 40 is larger than the largest outer dimension of the base 30 such that a radially outer portion of a forward face 38 of the shoulder 40 is exposed adjacent to the junction 36.
The shank 60 has an elongated polygonal shape defined by a plurality of faces 62, with each pair of adjacent faces 62 being joined at an edge 64. The faces 62 and the edges 64 are aligned with the faces 22, 32, 42 and the edges 24, 34, 42 respectively, of the cutting tip 20, the base 30, and the shoulder 40. The shank 60 is sized to be received into a sleeve retainer within a cylindrical bore 102 of a holder 100 when the pick 10 is in use. The shank 60 has an outer dimension smaller than the outer dimension of the shoulder 40, such that when the pick 10 is installed in the bore 102 of a holder 100, the shoulder 40 is adjacent to a front face of the holder 100 but does not fit within the bore 102.
The frontward seat 50 provides a transition between the larger outer dimension of the shoulder 40 and the smaller outer dimension of the shank 60, eliminating a stress concentration that might otherwise exist should the shoulder 40 and the shank 60 be joined at a perpendicular junction. The seat 50 has a truncated pyramidal shape and has a plurality of faces 52, with each pair of adjacent faces 52 being joined at an edge 54. The faces 52 and the edges 54 of the seat 50 are aligned with the faces 22, 32, 42, 62 and the edges 24, 34, 44, 64, respectively, of the cutting tip 20, the base 30, the shoulder 40, and the shank 60. The seat 50 tapers rearwardly from a largest outer dimension at the junction 46 to a smallest outer dimension, matching the outer dimension of the shank 60, at the junction 56. In the depicted embodiment, the outer dimension of the shoulder 40 is larger than the outer dimension of the seat 50 such that a radially outer portion of a rearward face 48 of the shoulder 40 is exposed adjacent to the junction 46. The taper of the seat 50 is preferably angled at about 30° to about 60° with respect to the axis of the pick 10. More preferably, the pyramidal faces 52 and the edges 54 of the seat 50 are angled at about 40° to about 50° with respect to the axis of the pick 10, and most preferably at about 45° with respect to the axis of the pick 10.
The tail 80 has a polygonal disk shape defined by a plurality of faces 82, with each pair of adjacent faces 82 being joined at an edge 84. The faces 82 and the edges 84 are aligned with the faces 22, 32, 42, 52, 62 and the edges 24, 34, 44, 54, 64 respectively, of the cutting tip 20, the base 30, the shoulder 40, the seat 50, and the shank 60. The tail 80 has an outer dimension greater than largest outer dimension of the shank 60, but equal to or slightly smaller than the inner diameter of the bore 102 so that the edges 84 are circumscribed by the bore 102 when the pick 10 is installed in the holder 100.
The rearward seat 70 provides a transition between the larger outer dimension of the tail 80 and the smaller outer dimension of the shank 60, eliminating a stress concentration that might otherwise exist should the tail 80 and the shank 60 be joined at a perpendicular junction. The seat 70 has a truncated pyramidal shape and has a plurality of faces 72, with each pair of adjacent faces 72 being joined at an edge 74. The faces 72 and the edges 74 of the rearward seat 70 are aligned with the faces 22, 32, 42, 52, 62, 82 and the edges 24, 34, 44, 52, 64, 82, respectively, of the cutting tip 20, the base 30, the shoulder 40, the frontward face 50, the shank 60, and the tail 80. The seat 70 tapers frontwardly from a largest outer dimension at the junction 76 to a smallest outer dimension, matching the outer dimension of the shank 60, at the junction 66. In the depicted embodiment, the outer dimension of the tail 80 is larger than the outer dimension of the shank 60 such that a radially outer portion of a forward face 78 of the tail 80 is exposed adjacent to the junction 76. The taper of the seat 70 is preferably angled at about 30° to about 60° with respect to the axis of the pick 10. More preferably, the pyramidal faces 72 and the edges 74 of the seat 70 are angled at about 40° to about 50° with respect to the axis of the pick 10, and most preferably at about 45° with respect to the axis of the pick 10.
The pick 10 can be of any polygonal shape having at least one pair of opposite sides that are parallel to each other, to enable the pick 10 to be pressed into shape. In particular, the tool pick 10 is preferably formed from cemented carbide or other hard material, and more preferably from cemented tungsten carbide. The hardness of the tool pick material is preferably at least about 1200 as measured on the Vickers scale. The tool pick 10 is preferably formed by pressing, which is facilitated by having a parallel portion or flat on both sides of the pick 10 where the top and bottom pressing dies meet. FIG. 2 shows a side view of the tool pick 10 having a parting line on the parallel portion wherein the top and bottom dies met during pressing.
Typically, but not necessarily, a polygon having at least one pair of opposite sides that are parallel will have an even number of sides. In the depicted embodiment of FIGS. 1-4, the pick 10 has a regular octagonal shape, i.e., it has eight approximately equal sides. Alternatively, the pick 10 can have any even number of sides greater than or equal to four. For example, the pick 10 can have a number of sides including, but not limited to, four, six, ten, or twelve. It is also understood that the sides need not necessarily be equal. For example, an embodiment of a tool pick may have eight sides that are alternately longer and shorter. It is also understood that should the number of sides become large, the pick will have an approximately circular cross section.
Manufacturing the entire pick 10 from a hard material such as cemented carbide provides a tail 80 that is more resistant to wear, which prolongs the operating life of the tool by keeping the retainer groove intact. In addition, a pick 10 made entirely from carbide also does not suffer from steel wash on the head 12 of the pick 10, and thus avoids the lost productivity and cost of wash-out. In contrast, in conventional picks having a steel shank with a carbide tip, the steel shank is prone to wear more rapidly than the carbide tip due to abrasion from cutting debris, and often enough steel is eroded that the steel shank can no longer support the carbide tip, causing the tip to fall off the steel shank prematurely. Further, in conventional picks, the steel shank typically includes a relatively deep socket or receptacle for holding the carbide tip, so that only a small portion of the cutting tip is available for cutting. Therefore, when the socket wears away prematurely, a large portion of the cutting tip remains unused when the carbide tip “washes out” or becomes detached from the steel shank. A washed-out tool results in lost productivity, due to the less effective cutting capability of a tool after the cutting tip has become detached, as well as the downtime required to replace the washed-out tool. But these problems do not occur with a tool pick 10 as disclosed herein, in which the entire pick 10 is made from carbide or other hard material.
As disclosed herein, the tool pick 10 preferably has a weight in the range of about 10 grams to about 60 grams, depending on the overall size of the pick 10 and the grade of carbide used. Tool picks 10 larger than 60 grams can readily be made as well; however, based on current material and manufacturing costs, a tool pick 10 weighing equal to or less than about 60 grams is economically competitive with a conventional tool pick of similar size having a steel shank and a carbide tip. It is believed that a tool pick weight less than about 10 grams would probably have insufficient mass to be effective at cutting and would be relatively more prone to fracture on impact. In one embodiment, the tool pick 10 weighs about 40 to about 42 grams.
As shown in FIG. 5, a microtrenching machine includes a mounting wheel 110 with a disk 112 having a plurality of holders 100, each holder 100 holding a rotatable tool pick 10 that rotates about its own axis during operation. Each holder 100 can be oriented so that its respectively tool pick 10 extends radially outward from the disk 112 or is canted at an angle to one side or the other. As the cutting tip 20 of the pick 10 contacts the surface of the ground that is to be cut, the frictional forces of cutting can cause wear of the cutting tip 20 and the base 30. To maximize the working life of the cutting tip 20, and thus of the pick 10, continuous rotational movement of the pick 10 is essential. Rotation enables the cutting tip 20 to be exposed to the ground from all angles and thus to wear substantially uniformly around its outer surfaces.
The polygonal faces 22 of the cutting tip 20, along with the polygonal faces 32 of the base 30, enhance rotation of the pick 10. During operation, debris, such as fines, dust, grit, pebbles, dirt, and the like, is produced and pushes against the faces 22, 32, causing the pick 10 to constantly be caused to rotate about its axis on one direction or another.
The polygonal shape of the shank 60 and the tail 80 also provides advantages that cannot be obtained with a pick having a cylindrical shank. When mounted, the polygonal shank 60 is circumscribed within the cylindrical retainer (not shown) and the tail 80 is circumscribed within the cylindrical bore 102 of a holder 100, such that the distance between opposite edges 64 of the shank 60 is at least slightly less than the internal diameter of the retainer and the distance between opposite edges 84 of the tail is at least slightly less than the internal diameter of the bore 102. Due to the polygonal shape of the shank 60 and the tail 80, a clearance gap exists between the faces 62 of the shank 60 and the retainer and between the faces 82 of the tail and the bore 102, which enables fines to move freely through the bore 102 without binding rotation of the tool pick 10.
Although described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without department from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A polygonal tool pick formed entirely of a single hard material, the tool pick comprising:

a head;

a shoulder extending rearwardly from the head and having an outer dimension at least as large as a largest outer dimension of the head;

a shank extending rearwardly from the shoulder and having an outer dimension smaller than the outside dimension of the shoulder; and

a tail extending rearwardly from the shank and having an outer dimension larger than the outer dimension of the shank;

wherein the head, the shoulder, the shank, and the tail each have a plurality of faces with at least one pair of opposed faces being parallel to each other.

2. The polygonal tool pick of claim 1, wherein the number of faces is an even number.

3. The polygonal tool pick of claim 1, wherein all of the faces are of equal size.

4. The polygonal tool pick of claim 2, wherein the number of faces is at least four.

5. The polygonal tool pick of claim 4, wherein the number of faces is eight.

6. The polygonal tool pick of claim 1, wherein the single hard material is cemented carbide.

7. The polygonal tool pick of claim 1, the head comprising:

a pyramidal cutting tip terminating in a frontward tip end; and

a truncated pyramidal base supporting the cutting tip and disposed rearwardly with respect to the cutting tip, the pyramidal cutting tip having a steeper slope than the truncated pyramidal base with respect to an axis of the tool pick.

8. The polygonal tool pick of claim 7, wherein the pyramidal cutting tip has a slope of about 30° to about 60° and the truncated pyramidal base has a slope of about 5° to about 30°.

9. The polygonal tool pick of claim 1, further comprising a tapered frontward seat located between the shoulder and the shank, the seat being tapered from a smaller outer dimension at a junction with the shank to a larger outer dimension at a junction with the shoulder.

10. The polygonal tool pick of claim 1, further comprising a tapered rearward seat located between the tail and the shank, the seat being tapered from a smaller outer dimension at a junction with the shank to a larger outer dimension at a junction with the tail.

11. A polygonal tool pick formed entirely of cemented carbide, the tool pick comprising:

a pyramidal cutting tip terminating in a frontward tip end, the cutting tip having an even number of equally sized faces;

a truncated pyramidal base supporting the cutting tip and disposed rearwardly with respect to the cutting tip, the truncated pyramidal base having a shallower slope than the pyramidal cutting tip with respect to an axis of the tool pick, the base having an even number of equally sized faces aligned with the faces of the cutting tip;

a shoulder extending rearwardly from the head and having an outer dimension at least as large as a largest outer dimension of the base, the shoulder having an even number of equally sized faces aligned with the faces of the base;

a shank extending rearwardly from the shoulder and having an outer dimension smaller than the outside dimension of the shoulder, the shank having an even number of equally sized faces aligned with the faces of the shoulder;

a tapered frontward seat located between the shoulder and the shank, the seat being tapered from a smaller outer dimension at a junction with the shank to a larger outer dimension at a junction with the shoulder, the frontward seat having an even number of equally sized faces aligned with the faces of the shank;

a tail extending rearwardly from the shank and having an outer dimension larger than the outer dimension of the shank, the tail having an even number of equally sized faces aligned with the faces of the shank; and

a tapered rearward seat located between the tail and the shank, the seat being tapered from a smaller outer dimension at a junction with the shank to a larger outer dimension at a junction with the tail, the rearward seat having an even number of equally sized faces aligned with the faces of the shank.

12. The polygonal tool pick of claim 11, wherein the number of faces of each of the cutting tip, the base, the shoulder, the shank, the frontward seat, the rearward seat, and the tail is eight.

13. A pick assembly comprising:

a holder having a cylindrical bore;

a polygonal tool pick formed entirely of cemented carbide, the tool pick comprising:

a pyramidal cutting tip terminating in a frontward tip end;

a truncated pyramidal base supporting the cutting tip and disposed rearwardly with respect to the cutting tip, the truncated pyramidal base having a shallower slope than the pyramidal cutting tip with respect to an axis of the tool pick;

a shoulder extending rearwardly from the base and having an outer dimension at least as large as a largest outer dimension of the base;

a shank extending rearwardly from the shoulder and having an outer dimension smaller than the outer dimension of the shoulder; and

wherein the cutting tip, the base, the shoulder, the shank, and the tail each have an even number of faces with at least one pair of opposed faces being parallel to each other, the faces of each of the cutting tip, the base, the shoulder, the shank, and the tail being aligned; and

a compressible cylindrical retainer for holding the tool pick within the cylindrical bore of the holder, such that when the retainer is compressed, the retainer is located between the shank and the cylindrical bore, and the inner diameter of the compressed retainer is less than the outer dimension of the tail and the outer dimension of the shoulder.

14. A microtrenching wheel having a disk and a plurality of pick assemblies mounted around the circumference of the disk, each pick assembly comprising:

a holder having a cylindrical bore;

a pyramidal cutting tip terminating in a frontward tip end;