CROSS-REFERENCE TO RELATED APPLICATION:

This Application is a continuation of Indian Patent Application No. 2156/CHE/2011 filed on 22-Jul-2011 now pending. This Application is filed as a Patent of Addition with the said Application as Parent Application.

TECHINCAL FIELD

Embodiments of the present disclosure relate to a drill insert  more particularly embodiments relate to a quadrangular indexable drill insert for a centre pocket of the drill body.

BACKGROUND OF DISCLOSURE

Drilling tools are used to drill cylindrical holes in metallic workpieces. The cutting or boring action of the drill tools may be carried out by an elongated  substantially cylindrical drilling tool  such as a combination of a tool holder and a drill insert  which is selectively attached thereto. Such an arrangement may then be used in an application wherein one end of the tool holder is securely mounted in a driving apparatus  which rotates the holder about its longitudinal axis. At the opposite end of the elongated tool holder  the cutting insert engages the material to be cut. Alternatively  the workpiece may be made to rotate relative to the holder and cutting insert  such as in positioning the holder in the tail stock of a lathe or the like. Further  the tool and workpiece may be made to rotate relative to one another. The use of cutting inserts allows for quick changing of the insert upon wear of the cutting surfaces instead of the entire tool  and allows for one tool to be used for a variety of different boring applications by simply changing the insert and not the entire drill assembly.

The indexable drill inserts play a very important role in drilling because all the sides of insert can be used for cutting one after the other. Further  the use of inserts reduces the manufacturing lead time and assembling time.

The use of quadrangular indexable drill inserts is known in the art. However  the inserts which are in the art comprise four rectangular cutting edges for cutting the workpiece. The use of rectangular cutting edges makes the drill tend to drift away from its centre because the cutting forces act all over the drill body and not exactly at the centre. The drill drift further creates a narrow wall which is not feasible in practical applications. Further  the conventional indexable drill inserts rub the surface of the drilling hole if the diameter of the drill hole is less than the predetermined value.

Further  when the conventional quadrangular indexable drill inserts are mounted such that a portion of the drill insert crosses the centre of the drill body  it forms a reverse cutting operation. During drilling operation  corners of the drill insert would chip out due to such reverse cutting action.

In recent days  many techniques have been introduced by various drill insert manufacturers to balance the cutting forces in the drill body to prevent the drill from drifting from the centre. One such technique is to divide the cutting edge into a plurality of part edges. The part edges are oriented in a predetermined pattern to balance the cutting forces.

Further  the inserts are held in pockets of the drill body to carry out the drilling operation. The provision of a plurality of part edges in each cutting edge of the drill insert will make the pockets in which they are to be secured complex and expensive since the pocket is to be milled to suit each of the part edges in order to hold the drill insert firmly. Conventionally  the pockets are milled using end mills. However  in order to mill a pocket that suits all part edges  manufactures use electric discharge machining  which leads to more expensive manufacturing costs associated with the drill body. In addition  since the contact between pocket and the insert is too small  the insert stability is compromised. Therefore  under extreme conditions of drilling (higher than normal cutting speeds and feed rates)  chances of the insert moving or twisting about its central axis are very much increased.

In light of the foregoing discussion  it is necessary to develop a drill insert having four identical cutting edges with a stable insert seating arrangement to overcome the problems stated above.
SUMMARY OF THE DISCLOSURE

The shortcomings of the prior art are overcome and additional advantages are provided through the provision of a drill insert as claimed in the present disclosure.

Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

The present disclosure provides a quadrangular indexable drill insert comprising: a substantially flat top surface and bottom surface  a side surface adjoining the top and bottom surfaces to form four sides of the drill insert  the bottom surface is smaller than the top surface to provide positive cutting geometry. Four identical cutting edges formed at intersection of the side surface and the top surface  each cutting edge comprising: a concave curved part edge of predetermined radius at corner of the insert; a first part edge oriented towards axis of the drill body and is substantially horizontal  wherein said first part edge is connected to the concave curved part edge through a nose portion of predetermined radius forming a convex curve; a second part edge connected to the first part edge through a transitional edge  said second part edge is tangentially oriented to an imaginary inscribed circle of the insert  wherein said transitional edge makes a concave curve with the first and second part edges; a third part edge connected to the second part edge through a transitional edge  wherein said transitional edge is making a convex curve with said second and third part edges; and a nose portion of predetermined radius adjoining the third part edge with concave curved part edge of succeeding cutting edge. The drill insert also includes a through hole at a center of the drill insert extending between the top surface and the bottom surface of the drill insert for mounting the insert with the drill body; and a chamfer provided at the bottom edge of the drill insert. The concave curved part edge  the nose portion and the first part edge occupy a predetermined thickness out of total thickness of the drill insert.

In one embodiment of the present disclosure  said drill insert is mounted in a centre pocket of the drill body.

In one embodiment of the present disclosure  the radius of the concave curved part edge is in the range of from about 0.4 mm to about 10 mm.

In one embodiment of the present disclosure  the first part edge is linear and is inclined at an angle in the range of from about 0o to about 5o with respect to a horizontal reference axis of the insert.

In one embodiment of the present disclosure  the second and third part edges form a ‘V’ shape and the included angle between the second and third part edges is in the range of from about 1400 to about 1790.

In one embodiment of the present disclosure  the radius of nose portions is in the range of from about 0.1 mm to about 10 mm.

In one embodiment of the present disclosure  the thickness of the concave curved part edge  the nose portion and the first part edge ranges from about 25% to about 40% of total thickness of the drill insert.

In one embodiment of the present disclosure  the radius of the convex shaped transition edge is in the range of from about 0.1 mm to about 5 mm.

In one embodiment of the present disclosure  the radius of the concave shaped transition edge is in the range of from about 0.1 mm to about 100 mm.

In one embodiment of the present disclosure  the through hole comprises a mouth portion and a series of stepped potions for accommodating an insert screw.

In one embodiment of the present disclosure  the angle of the chamfer depends on the thickness of the drill insert. The angle of the chamfer ranges from about and is preferably about 30 degrees with respect to the vertical axis of the drill insert.

In one embodiment of the present disclosure  the top surface is provided with a protruded potion around the mouth portion.

In one embodiment of the present disclosure  corners of the side surface of the insert forms an angle in the range of from about 0 degrees to about 15 degrees with respect to the vertical axis of the drill insert to facilitate clearance between insert and the pocket.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects  embodiments  and features described above  further aspects  embodiments  and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

The novel features and characteristics of the disclosure are set forth in the appended claims. The disclosure itself  however  as well as a preferred mode of use  further objectives and advantages thereof  will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described  by way of example only  with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

FIG. 1 illustrates a top perspective view of a drill insert in accordance with the present disclosure.

FIG. 2 illustrates a bottom perspective of the drill insert of FIG. 1.

FIG. 3 illustrates a top view of the drill insert of FIG. 1.

FIG. 4 illustrates a side view of the drill insert of FIG. 1.

FIG. 5 illustrates a drill body having a drill insert such as shown in FIG. 1 in its centre pocket and a conventional insert in its peripheral pocket.

FIG. 6 illustrates an isometric detail view of the cutting end of the arrangement of FIG. 5.

The figures depict example embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION

The foregoing has broadly outlined features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and example embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure as set forth in the appended claims. The novel features which are believed to be characteristic of the disclosure  both as to its organization and method of operation  together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood  however  that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

To overcome the drawbacks mentioned in the background  a quadra angular indexable drill insert is developed. A drill insert in accordance with the present disclosure consists of four identical cutting edges having a plurality of part edges which direct cutting forces to the centre of the drill body  which helps to prevent drifting of drill body from its centre during drilling operations. Further  a stable insert seating arrangement is made in the drill insert to secure the drill insert in the drill pocket.

FIG. 1 and FIG. 2 are exemplary embodiments illustrating top and bottom perspective views of a drill insert (100). Said drill insert (100) comprises a top surface (101)  a bottom surface (201)  and side surfaces (102) adjoining the top and bottom surfaces (101 and 201). The top surface (101) of the drill insert (100) is bigger than the bottom surface (201) to provide a positive clearance between the drill insert (100) and a pocket (602) [FIG.6] in a drill body (502) [FIG.5]. The four edges of the side surfaces (102) intersect the top surface (101) to form four identical cutting edges (103) [FIG.3]. each cutting edge (103) is divided into a plurality of part edges (104  106  108 and 110) to avoid chipping of the drill insert (100) and to direct the cutting forces toward drilling axis (504) in order to prevent drifting of the drill body (502) from its centre.

A concave curved part edge (104) of radius ranging from 0.4 mm to 100 mm is provided at four corners (102a) of the drill insert (100). Said concave curved part edge (104) prevents the drill insert (100) from chipping off  such as when the drill insert (100) is positioned such that the portion of the drill insert (100) crosses the drill centre (504) [FIG.5] and hence causes a reverse cutting action.

A first part edge (106) is joined to the concave curved part edge (104) through nose portion (105a) which has a radius ranging from 0.1 mm to 10 mm. Said nose portion (105a) forms a convex curve with the first part edge (106) and the concave curved part edge (104). The first part edge (106) is linear and  when drill insert (100) is coupled in drill body (502) such as shown in FIG.5  is oriented towards the drill axis (504) with slope being substantially horizontal (i.e.  substantially perpendicular to drill axis (504)). Further  the first part edge (106) forms an angle ranging from about 00 to about 50  preferably about 00  with respect to horizontal axis (B-B) of the drill insert (100). A second part edge (108) is connected to the first part edge (106) through a transition edge (107) of radius ranging from about 0.1 mm to about 5 mm  which forms a concave curve with the first and second part edges (106 and 108). Referring to FIG.3  the second part edge (108) is tangentially oriented to an imaginary inscribed circle (301) of the drill insert (100). A third part edge (110) is connected to the second part edge (108) through a transitional edge (109) of radius ranging from about 0.1 mm to about 10 mm which forms a convex curve with the second and third part edges (108 and 110). The second and third part edges (108 and 110) form an inverted roof shape or a ‘V’ shape when they are connected by the transitional edge (109). The included angle between the second and third part edges (108 and 110) ranges from about 1400 to about 1790. The cutting edge (103) further comprises a corner nose portion (105b) of radius ranging from about 0.1 mm to about 10 mm which connects the third part edge (110) of the one cutting edge (103) with the concave curved part edge (104) of the subsequent cutting edge (103).

The drill insert (100) further includes a hole (111) extending from top surface (101) to the bottom surface (201) of the drill insert (100) for mounting the insert (100) to the drill body (502). A mouth portion (111a) [FIG.5] is provided around the hole (111) on the top surface (101) and a series of stepped portions (111b) are provided on the circumference of the hole (109) to accommodate an insert screw (601) [FIG.6] for mounting the drill insert (100) in the pocket (602) of the drill body (502). In one embodiment  a protruded portion (112) is provided on the top surface (101) of the drill insert (100). Said protruded portion (112) facilitates cutting of the chip resulting from the drilling operation and directs the chip toward the helical flute portion (503) [FIG.5] of the drill body (502) to facilitate chip evacuation.

Referring to FIG. 6  the side surfaces (102) of the drill insert (100) include portions (102b and 102c) to secure the drill insert (100) inside the pocket (602) of the drill body (502). The portions (102b and 102c) make contact with the walls of the pocket (602) and resist the rotational motion of the drill insert (100) within the pocket (602). Further  corners (102a) of the side surface (102) make an angle of about 11 degrees with respect to vertical axis (A-A) of the drill insert (100) to facilitate clearance between insert (100) and the pocket (602). This clearance is a primary clearance and helps to remove the insert (100) easily from the pocket (602) of the drill body.

FIG. 3 is an exemplary embodiment which illustrates a top view of the drilling insert (100). The division of the cutting edges (103) into a plurality of part edges (104  106 108 and 110) is clearly illustrated in the top view of the drilling insert (100). The concave curved part edge (104) prevents the chipping of the drill insert (100) when part of the drilling insert (100) crosses the drill axis (504). The part edges (106  108 and 110) with transition edges (107 and 109) direct the cutting forces to the centre of the drill body (502) or axis (504) of drilling  which prevents drifting of the drill (500) from its centre. The part edges (104  106  108 and 110) and transition edges (107 and 109) are bound to vary in their sizes or lengths as the inscribed circle diameter (301) increases to accommodate various sizes of inserts  and hence vary proportionately as the size increases. The diameter of the inscribed circle (301) varies with respect to variation in diameter of the drill hole and generally ranges from 5 mm to 20 mm.

FIG. 4 illustrates a front view of the drilling insert (100). The concave curved part edge (104)  the nose portion (105a) and the first part edge (106) of the drill insert (100) will occupy a predetermined thickness (P1) out of the total thickness (P) of the drill insert (100). The thickness (P1) ranges from about 25% to about 40%  preferably about 33% of the total thickness (P) of the drill insert (100). As an example  in the embodiment shown  the thickness (P) is 3 mm and the thickness (P1) is 0.99 mm  which means that thickness (P1) is about 33% total thickness (P). The side face (102) of the drill insert (100) is divided into portions (102b and 102c). The portion (102b) extends all the way below the concave curved part edge (104)  the nose portion (105a) and the first part edge (106) of the drill insert (100)  and it follows the angular orientation as the second cutting edge portion (108). The portion (102c) follows the same angular orientation as the third cutting edge portion (110) to secure the drill insert in the pocket (602) [FIG.6].

Further  a chamfer (113) is provided at bottom edges of the drilling insert (100) towards the bottom portion (201)  as shown in FIG. 4  to facilitate the secondary clearance in the insert (100). The angle of the chamfer (113) ranges from about 0o to about 45o with respect to vertical axis (A-A) of the drill insert (100). In an embodiment of the present disclosure  the angle of the chamfer (113) is 300 with respect to Vertical axis (A-A) of the drill insert (100) and said angle will vary with the variation in the thickness of the drill insert (100). The chamfer (113) prevents digging of the pocket (602) of the drill body (502) which in turn eliminates the wear of the pocket (602) when the drill insert (100) is in operation. The chamfer (113) also eliminates rubbing of the surface of the drilled hole by the drill insert (100).

In one embodiment  the drill insert (100) is used in the peripheral pocket (602) of the drill body (502). The corner portions (108) of the cutting edges (103) enlarge the hole which is produced by the insert in the inner pocket (602) of the drill body (502).

FIG. 5 is an exemplary embodiment which illustrates the drill tool (500) having the drill insert (100) of the present disclosure in its centre pocket (602) and a conventional insert (not numbered) in its peripheral pocket. The drill tool (500) includes a shank (501) of predetermined length and a drill body (502) of cylindrical basic shape. The drill body (502) includes a pair of insert pockets one at its centre and other at its periphery for accommodating the drill insert (100). The drill body (502) also includes helical flute (503) on its circumference for vacating the chips generated during the drilling operation. The chips generated during drilling operation are cut by the protrusion (112) of the drill insert (100) and are guided via the helical flute (503) of the drill body (502) for disposing the same. In one embodiment  an inboard insert (100) and an outboard insert are positioned in the drill body (502) such that the forces generated during drilling operation are directed toward the drill axis (504)  which prevents the drill body (502) from drifting from its centre.

In one embodiment of the present disclosure  during drilling operation  the inboard insert initially applies moderate cutting forces on to the work piece and forms an initial hole in the work piece. Further  a portion of the inboard insert (100) accommodates a corner nose portion of the outboard insert  and hence prevents use of two corners during drilling operation.

FIG. 6 is an exemplary embodiment which illustrates a split view of drill tool (500) having a drill insert (100) of the present disclosure in centre pocket (602) of the drill body (502). The drill insert (100) is positioned in centre pocket (602) of the drill body (502). The shape of the centre pocket (602) matches with the shape of the drill insert (100). Further  the centre pocket (602) includes a threaded hole (not numbered) for fastening the drill insert (100) to the drill body (502) using an insert screw (601). The insert screw (601) includes a series of stepped portions and a threaded portion which passes through the through hole (111) of the drill insert (100) and fastens the same inside the peripheral pocket (602). Further  a conventional drill insert is mounted in the peripheral pocket of the drill body (502).

Further  from FIG.6 it can be inferred that the portion (102b) of the drill insert (100) makes contact with wall portion (602a) of the pocket (602)  and the portion (102c) of the drill insert (100) makes contact with wall portion (602b) of the pocket (602). The wall portion (602a) extends more than 50% of the entire length of cutting edge (103) of the drill insert (100)  in order to achieve more stable seating of the drill insert (100) in the pocket (602).

Advantages

The present disclosure provides a quadrangular indexable drill insert in which all four cutting edges are used for drilling  i.e. when one edge wears out the subsequent edge can be used for cutting.

The present disclosure provides a quadrangular indexable drill insert which has a concave curve at four corners of the drill insert which prevents the chipping of corner portions during drilling operation  if the insert is positioned such that a portion of the insert crosses the drill axis.

The present disclosure provides a quadrangular indexable drill insert which has four identical cutting edges which are divided into a plurality of part edges to direct the forces toward the drill axis  which eliminates drifting of the drill from its centre.

The present disclosure provides a quadrangular indexable drill insert which has a chamfer in its bottom portion which prevents rubbing of the drilled hole by the insert.

The present disclosure provides a quadrangular indexable drill insert which has a protruded portion on its top surface to break the chips generated during the drilling process.

The present disclosure provides a quadrangular indexable drill insert which has a concave curve at four corners of the drill insert which prevents the chipping of the drill insert  when the insert is positioned such that some part of the insert crosses axis of the drill body.

The present disclosure provides a quadrangular indexable drill insert in which the concave curved part edge  the nose portion and the first part edge of each cutting edge occupy a predetermined thickness of the total thickness of the drill insert.

The present disclosure provides a quadrangular indexable drill insert in which a portion of the side wall extends below the concave curved part edge  the nose portion and the first part edge and follows the angular orientation of the second cutting edge portion  and the remaining portion of the side wall has the same angular orientation as the third cutting edge portion in order to secure the drill insert firmly in the pocket.

Equivalents

With respect to the use of substantially any plural and/or singular terms herein  those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that  in general  terms used herein  and especially in the appended claims (e.g.  bodies of the appended claims) are generally intended as “open” terms (e.g.  the term “including” should be interpreted as “including but not limited to ” the term “having” should be interpreted as “having at least ” the term “includes” should be interpreted as “includes but is not limited to ” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended  such an intent will be explicitly recited in the claim  and in the absence of such recitation no such intent is present. For example  as an aid to understanding  the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However  the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation  even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g.  “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition  even if a specific number of an introduced claim recitation is explicitly recited  those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g.  the bare recitation of “two recitations ” without other modifiers  typically means at least two recitations  or two or more recitations). Furthermore  in those instances where a convention analogous to “at least one of A  B  and C  etc.” is used  in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g.  “a system having at least one of A  B  and C” would include but not be limited to systems that have A alone  B alone  C alone  A and B together  A and C together  B and C together  and/or A  B  and C together  etc.). In those instances where a convention analogous to “at least one of A  B  or C  etc.” is used  in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g.  “a system having at least one of A  B  or C” would include but not be limited to systems that have A alone  B alone  C alone  A and B together  A and C together  B and C together  and/or A  B  and C together  etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms  whether in the description  claims  or drawings  should be understood to contemplate the possibilities of including one of the terms  either of the terms  or both terms. For example  the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

While various aspects and embodiments have been disclosed herein  other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting  with the true scope and spirit being indicated by the following claims.

It is to be noted at this point that all of the above described components  whether alone or in any combination  are claimed as being essential to the invention  in particular the details depicted in the drawings and reference numerals in the drawings are as given below.

Referral Numerals:

Referral numeral Description
100 Drill insert
101 Top surface of the insert
102 Side surface of the insert
102a Corners of the side surface
102b and 102c Portions of the side surface
103 Cutting edge
104 Concave curved part edge
105a and 105b Convex nose portions
106 First part edges
107 Concave transition curve
108 Second part edge
109 Convex shaped part edge
110 Third part edge
111 Through hole
111a Mouth portion of the through hole
111b Stepped portions of through hole
112 Protruded portion
113 Chamfer
201 Bottom surface
301 Imaginary inscribed circle
500 Drill tool
501 Shank of the drill tool
502 Drill body
503 Helical flute
504 Drill axis
601 Insert screw
602 Centre pocket
602a and 602b Wall portions of the pocket
A-A Vertical axis of the drill insert
B-B Horizontal axis of the drill insert
P Total thickness of the Drill Insert
P1 Thickness of the concave curved part edge  the nose portion and the first part edge.

We claim:

1. A quadrangular indexable drill insert (100) comprising:
a substantially flat top surface (101) and a bottom surface (201)  a side surface (102) adjoining the top and bottom surfaces (101 and 201) to form four sides of the drill insert (100)  the bottom surface (201) being smaller than the top surface (101) to provide positive cutting geometry;
four identical cutting edges (103) formed at intersections of the side surface (102) and the top surface (101)  each cutting edge (103) comprising:
a concave curved part edge (104) of a predetermined radius at a corner (102a) of the insert;
a substantially flat first part edge (106) connected to the concave curved part edge (104) through a nose portion (105a) of predetermined radius forming a convex curve;
a second part edge (108) connected to the first part edge (106) through a transitional edge (107)  said second part edge (108) being tangentially oriented to an imaginary inscribed circle (301) of the insert (100)  wherein said transitional edge (107) forms a concave curve with the first and second part edges (106 and 108);
a third part edge (110) connected to the second part edge (108) through a transitional edge (109)  wherein said transitional edge (109) forms a convex curve with said second and third part edges (108 and 110); and
a nose portion (105b) of predetermined radius adjoining the third part edge (110) with the concave curved part edge (104) of an adjoining cutting edge (103);
a through hole (111) dispose at a center of the drill insert (100) extending between the top surface and the bottom surface (101 and 201) of the drill insert (100) for mounting the insert with the drill body (502); and
a chamfer (113) provided at a bottom edge (201) of the drill insert (100)
wherein  the concave curved part edge (104)  the nose portion (105a) and the first part edge (106) are of a predetermined thickness (P1) out of total thickness (P) of the drill insert (100).

2. The drill insert as claimed in claim 1  wherein the predetermined radius of the concave curved part edge (104) is in the range of from about 0.4 mm to about 100 mm.

3. The drill insert as claimed in claim 1  wherein the first part edge (106) is linear and is inclined at an angle ranging from about 0o to about 5o with respect to a horizontal reference axis of the insert (100).

4. The drill insert as claimed in claim 1  wherein the second and third part edges (108 and 110) form a ‘V’ shape and the angle between the second and third part edges (108 and 109) is in the range of from about 1400 to about 1790.

5. The drill insert as claimed in claim 1  wherein the radius of the nose portions (105a and 105b) is in the range of from about 0.1 mm to about 10 mm.

6. The drill insert as claimed in claim 1  wherein the concave curve formed by the transitional edge (107) has a predetermined radius in the range of from about 0.1 mm to about 5 mm.

7. The drill insert as claimed in claim 1  wherein the convex shaped transitional edge (109) has a predetermined radius in the range of from about 0.1 mm to about 10 mm.

8. The drill insert as claimed in claim 1  wherein the thickness (P1) is in the range of from about 25% to about 40% of the total thickness (P) of the drill insert (100).

9. The drill insert as claimed in claim 1  wherein the through hole (111) comprises a mouth portion (111a) and a series of stepped potions (111b) for accommodating an insert screw (601).

10. The drill insert as claimed in claim 1  wherein the chamfer (113) is disposed at an angle dependent on the thickness of the drill insert (100).

11. The drill insert as claimed in claim 10  wherein the angle of chamfer (113) ranges from about 0o to about 45o with respect to vertical axis of the drill insert (100).

12. The drill insert as claimed in claim 1  wherein the top surface (101) is provided with a protruded potion (112) around the mouth portion (111a).

13. The drill insert as claimed in claim 1  wherein corners (102a) of side surface (102) of the insert (100) makes an angle ranging from about 0 to about 15 degrees with respect to vertical axis of the drill insert (100) to facilitate clearance between insert (100) and the pocket (602).

14. A drill body comprising a quadrangular indexable drill insert (100) as claimed in claim 1 disposed in a centre pocket (602) and an insert disposed in a peripheral pocket.

15. The drill insert as claimed in claim 14  wherein said drill insert (100) is mounted at centre pocket (602) of the drill body (502).