an insert 10 according to the invention is shown in the drawing figures . the insert is in the shape of a polygonal body of generally parallepipedic shape . it comprises two mainly plane - parallel side surfaces 11 , 12 , opposed top and bottom surfaces 14 and 13 , respectively , two end surfaces 15 , 16 , and a shoulder 17 . the front portion of the insert is provided with a main cutting edge 18 and a chip forming area 19 . the insert is intended to be secured to a holder body 20 ( fig8 ) provided with an integral clamping arm 21 . the top surface 14 is broken at the vicinity of the shoulder 17 so that an upper surface portion 14 a forms an acute angle with the remainder of the surface 14 . with reference to fig8 the insert 10 is intended to be removably held in a holder , which includes the holder body 20 having an integral clamping arm 21 in a front portion 22 of the holder body 20 and an insert receiving recess 23 in which the insert 10 is to be located . the insert receiving recess 23 communicates at an inner end thereof with an elongated slit 24 which terminates in a circular recess 25 . a clamping screw 26 extends into the holder 20 through the clamping arm 21 and through the slit 24 . when the screw 26 is threaded into the holder , the clamping arm 21 flexes downwardly about the recess 23 and urges the clamping arm 21 into firm clamping abutment with the upper surface 14 of the insert . more specifically , a nose portion of the clamping arm 21 is somewhat inclined downwardly so that the nose matches the inclination of the upper surface portion 14 a of the insert 10 . the bottom surface 13 of the insert is intended to be a first support surface for the insert against the holder body and a portion of the bottom surface 13 is parallel with a neutral plane p ( fig2 ) defined by the axial feed direction of the machine . more specifically , the bottom surface 13 includes two distinct flat surface portions 13 a and 13 d , with two inclined surfaces 13 b and 13 c therebetween . the inclined surfaces 13 b and 13 c are intended to abut with correspondingly inclined surfaces in the insert site of the holder as shown in fig9 . as appears from fig9 the surfaces 13 a and 13 d are not active support surfaces . the top surface 14 constitutes a second support surface for the insert against the holder body 20 . the top surface 14 is oriented parallel with the flat bottom surface portions 13 a and 13 d . the cutting edge 18 is straight and is formed along the intersecting line of a clearance face 16 and a primary land 27 . the clearance face 16 , which is the front end surface of the insert , forms an acute angle α , about 1 °- 15 ° with a normal / n drawn to the primary land 27 ( fig2 ). the primary land 27 coincides with the neutral plane p . the primary land 27 is bordered radially inwardly by an array of spaced recesses or grooves 28 extending on the rake face of the insert starting from the primary land 27 . the width of the primary land 27 varies along the edge 18 such that the width of the primary land 27 is smaller at those portions located next to the front end portions of each recess 28 whereas the width is larger at inclined rake surface portions 29 located therebetween ( fig3 ). the maximum width of each recess 28 is preferably larger than the distance between the depressions . each recess 28 has a depth initially increasing in a direction away from said primary land and thereafter decreasing in that direction . there are a number of the centrally provided oval - shaped recesses 28 having a longitudinal extension , extending perpendicularly from the cutting edge 18 , that is several times larger than the width of the respective recess 28 . additionally there is , on each side of the central group of oval - shaped recesses 28 , a recess 30 having a larger width and shorter length than each of the central recesses 28 . also formed in the top surface 14 of the insert is a recess 31 , which curves inwardly and downwardly from the primary land surface 27 and then curves upwardly to form a rear wall or chip deflector surface 32 . the chip deflector surface 32 terminates in a plateau 33 located approximately at the same level as the neutral plane p . the chipforming area 19 additionally includes a pair of ridges one of which extends from the outer periphery of a respective one of the recesses 30 . more specifically , a front ridge portion 34 a and 34 b are so formed that they converge rearwardly , and they extend rearwardly to the point where they meet with rear ridge portions 35 a and 35 b which are mutually parallel and extend essentially perpendicularly from the cutting edge 18 . furthermore , the front ridge portions 34 a and 34 b are formed with a top surface that is raised rearwardly until the location where the front ridge portion 34 a , 34 b intersects with the rear , straight rear ridge portions 35 a , 35 b at which intersection the top surface of the rear ridge portion has a level that remains constant further rearwardly . the level of the upper surface of the rear ridge portions 35 a , 35 b is located somewhat above , and generally parallel to , the plane p . by arranging the ridges as aforesaid , it is ensured that the chip remains in contact with the forward ridge portions 34 a , 34 b and that the central portion of the chip is urged deeper into the recess 31 . this arrangement further ensures that the total width of the chip is made narrower and becomes more easily manageable so that no harm is made from the chip to the side wails of the groove which is to be formed by the insert during cutting in a metal workpiece . the forward end of the insert 10 additionally is provided with side cutting edges 36 a and 36 b , which merge rearwardly to an intermediate position along the insert , while intersecting with the primary land surface 27 which extends along both the main cutting edge 18 and along the side cutting edges 36 a , 36 b . the clearance faces of the side cutting edges 36 a , 36 b are designated 11 a and 11 b . each clearance face 11 a , 11 b intersects with the land surface 27 at an acute angle β ( fig6 ). by virtue of the particular construction of the chip forming area as aforesaid , it is possible to obtain desirable clock - shaped chips 37 such as shown in fig1 . these chips 37 can be obtained at a feed rate of 0 . 30 mm / revolution . if no proper chip deflection area is provided on the upper rake surface of the insert , chips obtained would otherwise be difficult to manage . also , at moderate feed rates , the chip forming area of this invention effectively contributes to the control and removal of such chips . when large feeds are used , the chip will be pressed against the rear wall 32 of recess 31 which forces the chip to be bent in a favorable manner . the embodiment described above also results in a certain reduction of the cutting forces because the grooves or recesses 28 , 30 reduce the contact area and increase the positive rake angle . due to the fact that a reduced contact area is obtained , a relatively low heat generation is obtained . the principles , preferred embodiments and mode of operation of the present invention have been described . variations and changes may be made and are contemplated within the invention to the extent such variation and changes fail within the scope of the appended claims .