The present invention relates to an insert holder of the type stated in the claim.

In most prior art insert holders, use is made of mechanical clamping means, such as screws or bodies attachable by screws, which hold the cutting insert m engagement with a seat in the insert holder. For insert holders primarily intended for applications where the available working space is small, e.g. for severing and plunge cutting operations, insert holders have previously been suggested, where the cutting insert is clamped by spring action in a seat facing the workpiece. Such an insert holder is formed with a thicker portion below the seat and a somewhat thinner yieldable portion above the seat. To stabilise the cutting insert in lateral direction, its edges engaging with the sides of the seat are formed with V-shaped grooves matching V-shaped elevations along the sides of the seat.

Since when using prior art insert holders, one must rely on the fact the resilient engaging pressure remains, i.e. that the portion engaging the upper side of the cutting insert is permanently tensioned out of its non-activated position, there is a con¬ siderable risk of fatigue which results in decreasing clamping force and the cutting insert not being uπ- resiliently kept in its seat. Especially when subjected to shock, the cutting insert is liable to be displaced in its seat. Heavy stress can also result in the cutting insert splitting or cracking along its centre plane by cooperation between the V-shaped recess on the lower side of the cutting insert and tne reversed V shape of the edge of the seat.

The object of the invention is to provide an insert holder and a matching cuttinq insert so designed

that the clamping portion of the insert holder is, during operation, substantially unloaded in respect of resilience,, whereby the risk of fatigue is eliminated and the cutting insert is firmly kept in position over a long period, of operation. A further object of the new insert holder is to eliminate the risk of cracking or splitting of the cutting insert when subjected to shock stress.

The characteristic features of the new arrangement are stated in the appended claims.

A preferred embodiment of an insert holder according to the invention and a matching cutting insert will now be described in detail with reference to the accom¬ panying drawing in which: Fig. 1 is a side view of the front portion of an insert holder, and a partly inserted cutting insert,

Fig. 2 shows the same portion of the cutting holder, the cutting insert being in a fully inserted and fixed position, and Fig. 3 is a cross-sectional view taken along line A-A in Fig. 2.

The insert holder which in its entirety is de¬ signated T, comprises a shaft (not shown in detail) which is designed to fit the clamping means. The shaft can, behind the shown front portion, be wider and higher than the front portion adapted to receive the cutting insert. In the front end of the insert holder there is formed a recess 2 adapted to receive the cutting insert which in its entirety is designated 3. The lower side of the recess is defined by a bottom 4 which is sloping downwards-backwards and which, along the major part of its length, is formed of two surfaces 5 arranged in V shape. The inner end of the recess is defined by a rounded edge 6 passing into an upper side 7 which is bent slightly downwards. A nose-shaped projection 8 defining the upper side of the recess 2 extends not quite all the way

to the front end of the insert holder and has a top side 9 facing obliquely upwards and passing over a rounded front end 10 into a substantially planar portion 11 directed obliquely downwards and meeting, while forming a shallow projection, the obliquely downwardly bent upper side 7 of the recess so as to form an abutment edge 12.

The cutting insert 3 of which the cutting edge portion need not be described here, comprises a head 13 and a shank 14. The underside of the cutting insert 3 is formed with a V-shaped longitudinal ridge 15 which is complementary to the bottom 4 of the recess, but the angle of which preferably is slightly more shallow than the angle of the recess. The upper side of the shank 14 is formed, as seen from behind, with an inclined or bevelled surface 16 passing into an abutment and sliding surface 17 which, in the direction of the head of the cutting insert, converges slightly towards a line along the underside 15 of the cutting insert. The deviation is minor and preferably is of the order of 4°. The abutment and sliding surface 17 passes via a rounded surface 18 into an engagement surface 19 extending transversely of the longitudinal direction of the cutting insert. To mount the cutting insert 3 in the insert nolder 1, the V-shaped underside 15 of the cutting insert is positioned m the V-shaped groove 5 at the bottom of the insert holder recess and is pressed inwards. By cooperation between the abutment edge 12 on the lower side of the nose-shaped projection 8 and the bevelled surface 16 of the cutting insert, the nose- shaped portion 8 is bent upwards against its inherent resilience. The outward or upward bending of the portion 8 reaches its maximum at the point 20 in whicn the bevelled surface 16 passes into the abutment and sliding surface 17 and then decreases as tne cutting insert 3 is pushed further into the recess 2. When tne front

end 10 of the nose-shaped portion 8 engages the trans¬ verse engagement surface 19 of the head 13 of the cutting insert, the abutment edge 12 has been moved along the abutment and sliding surface 17 of the cutting insert so far that the outwards resilience of the nose-shaped portion has been reduced to a substantial exten .

It is thus obvious that the mounting of the cutting insert 3 in the recess 2 of the insert holder 1 is, after an initial resistance has been overcome, faci¬ litated by the inherent resilience of the nose-shaped portion 8. Withdrawal of the cutting insert requires, however, a successively increasing force as the nose- shaped portion 8 is forced outwards by the sloping abutment and sliding surface 17.

Since the abutment edge 12 cooperates with the planar surface 17, no defined end or bottom position will arise there, but this position is determined only by the engagement between the end 10 of the nose- shaped portion and the rear surface 19 of the head of the cutting insert. As a result, the requirements for precision when manufacturing cutting inserts can be kept within limits. In other words, certain devia¬ tions from an ideal value, especially with respect to the height of the shank, can be allowed, and yet a fully acceptable clamping is obtained. A negative deviation in vertical direction merely results in a slightly reduced tensional force, whereas a positive deviation results in a slightly increased tensional force.

The design of the guiding portions, i.e. the V-shaped groove 5, in relation to the design of the V-shaped underside of the cutting insert 3 is essential to the function. As is best shown in Fig. 3, the angle between the sides of the V groove deviates from the angle between the surfaces of the cutting insert facing the groove, and more precisely such that engagement

is established only along the edges of the V groove and the cutting insert, respectively, while there is a clearance between the lower edge of the cutting insert and the deeper part of the bottom of the groove. This causes the cutting insert to be firmly located in the groove, and the risk of tilting in lateral direction is eliminated.

The cutting insert engages with the insert holder along three lines, one line along each side of the V-shaped groove 5 and one line oriented transversely of these lines at 12, i.e. the position in which the tip of the projection or the abutment edge 12 engages the planar surface 17. As a result, the desired sta¬ bility is achieved even in cases of cutting insert and insert holder widths of some millimeter.

The angular difference between the surfaces of the V groove and the bottom surfaces of the cutting insert has a further function, i.e. a further possibility of compensating for deviations from tolerances is obtained. Should the cutting insert have an oversize bordering on the permissible, the force of the portion 8, which acts downwards via the abutment edge 12, will be so great that the sides of the V groove can be elastically deformed slightly outwards, while maintaining the engagement with the underside of the cutting insert. The cutting insert 3 thus is firmly supported over its entire length by cooperation between the V-shaped guiding portion on the underside of the cutting insert and the V-shaped groove 5 at the lower edge of the recess 2 of the insert holder, and is kept in firm engagement with this edge by the resilience of the nose-shaped portion 8, which acts along a single transverse line, i.e. along the edge 12 oriented trans¬ versely of the longitudinal direction of the cutting insert. Through the design described above, all tendencies towards tilting of the cutting insert are eliminated, even if it is subjected to heavy shock from the workpiece.

The invention is not limited to that described above and shown in the drawing, but can be modified in various ways within the scope of the appended claims,