Prior art In US-A-3,844,008 a tool of the above mentioned type is described. A clamp is activated by a screw for camping the cutting insert in an insert pocket. Often when the screw is tightened the operator over- torques or tightens the screw too much such that the clamp is undergoes a plastic deformation. The plastic deformation of the clamp leads to a less accurate clamping for the next insert to be used since the clamp has been distorted. In SU-A1-1720803 is shown another tool wherein the minimum size of the insert pocket for accuracy reasons is determined by means of a threaded sleeve. The threaded sleeve defines the position of the clamping arm so that the pocket obtains a correct size relative to a self-wedging cutting insert.

Obiects of the invention One object of the present invention is to provide a rigid tool preferably for thin holders and thin cutting inserts.

Another object of the present invention is to provide a tool in which the clamp is not distorted.

Still another object of the present invention is to provide a tool in which the clamping arm is protected from plastic deformation.

These and other objects have been achieved by a tool as defined in the appended claims with reference to the drawings.

Description of the drawings

Fig. 1 shows a tool according to the present invention, in a side view. Fig. 2 shows the tool in a top view. Fig. 3A shows the tool in another side view, partly sectioned in an open position. Fig. 3B shows the tool in a clamped position. Fig. 4 shows a holder in a front view. Fig. 5 shows a cutting insert to be used in the tool in a front view. Fig. 6 shows an alternative embodiment of a tool according to the present invention in a side view.

Detailed description of the invention With reference to Figs. 1-5 is shown a tool 10, including a holder 11 and a cutting insert 12. The holder 11 is of the type where an arm 13, integrated with the holder, constitutes an upper side 15 of the insert pocket 14. The arm is movable about a pivot 27 by means of a screw 17 and a slot 16. The slot 16 terminates in the cutting insert pocket. The stot extends in the longitudinal direction of the cutting insert, an appropriate distance, beyond the screw 17 influencing the arm 13. The screw means 17 as seen in Fig. 3A is provided substantially in the middle of the elongated stot 16. The screw 17 fits into a threaded boring 45 which has a center axis CL. An abutment surface 34 is provided in connection with the lower border line of the slot 16, wherein the surface 34 constitutes a stop for the cutting insert in its longitudinal direction. The upper side 15 has a general convex V-shaped cross-section with flanks converging towards the cutting insert. The flanks form an obtuse, internal angle with each other, which lies in the interval 120° to 160°. A clearance surface is provided between the flanks in order to avoid a central contact with the cutting insert. The arm is intended to clamp the cutting insert against the lower side 19 of the cutting insert pocket. The lower side is formed with a number of from each other separate, identical grooves 26, which in cross section describe a substantially trapezoidal path. The grooves are elongated and extend along the entire lower side 19. The direction F, which is the feed direction when the tool is used as a parting tool and the direction L, which is the feed direction when the tool is used as a tool for longitudinal turning are shown in Fig. 2. The angle a between the directions F and L can be 90° 15°. The groove 26 further has two flanks

which connect to the groove bottom, via a sharp or rounded transition. The flanks form an acute angle with each other.

The cutting insert 12 comprises an upper surface 18, a lower surface 29 as well as side surfaces 20,21,22,23 connecting them, wherein the lines of intersection between the side surfaces 22,23 and the upper surface 18 form cutting edges 24,25. The cutting insert is preferably somewhat wider than the cutting insert pocket, for the sake of clearance. The length of the insert edge 24 is shorter than the height of the cutting insert between upper and lower surfaces 18,29. The upper surface has two flanks which converge towards the lower surface 29 with an external angle substantially corresponding to the above-mentioned internal angle. The lower side is formed by a number of from each other separate, substantially, identical ridges 30. The ridges form a substantially sinusoidal curve, in cross section, which oscillates about a line. The ridges are elongated and extend along the entire lower side 29. The ridge 30 has two flanks which touch and connect to a bottom 31. The flanks form an acute angle with each other.

So far the invention adheres to prior art. The tool according to the present invention however, further comprises an externally threaded sleeve or set screw 40, an annular member or a spacer 41 and a washer 42, all being substantially symmetrically positioned relative to the axis of the screw 17. The axis of the screw 17 is substantially perpendicular to the slot 16. The set screw 40 is of cylindrical shape and has a flange 43 at its free end which is fitted into a complementary, threaded boring 44 in the holder.

The set screw flange 43 and a shoulder of the boring defines the maximum size of the insert pocket. The spacer 41 is preferably a metallic circular ring which is positioned in the slot 16 around the sleeve 40. The spacer 41 is positioned where the clamp means 13 bends as most during clamping of the insert, i e lengthwise in the middle of the slot extension. The width of the slot 16 in mounted position is depicted by E. The thickness of the spacer 41 is depicted by T, which is a distance S thinner than the width E. The distance or gap S allows the arm 13 to deform elastically to a certain extent during tightening of the screw 17, i. e the gap S is provided to be closed during tightening of the screw 17. The provision of the washer 42 allows the shank

of the screw 17 to come into threaded engagement with the boring in the holder, but will stop the head of the screw from reaching the sleeve 40 during tightening. In order to avoid confusion the internal diameter of the spacer 41 is larger than the internal diameter of the washer 42.

Assembly of the tool according to the present invention is done as follows. The spacer 41 is aligned with the center axis CL within the slot 16 on the slot floor 46. The spacer is not supposed to project from the slot outside of the tool and it will not extend to or interfere with the insert pocket.

Then the set screw 40 is screwn into the boring 44 through the spacer and the upper position of the arm 13 is to be determined. When the set screw flange 43 abuts the annular shoulder in the arm 13 the arm will be forced to close the slot somewhat. A reference insert of the type"Go/No go"is inserted in the pocket and the set screw is tightened until only the"Go"part of the insert can be inserted but not the"No go"part. The set screw is preferably provided with a thread lock means to avoid accidental displacement thereof. Then the screw 17 is inserted through the washer 42 and inserted into the boring 45 and tightened somewhat. This is preferably done at the tool manufacturers site. When the screw 17 is untightened and the pocket achieves its maximum size, the cutting insert pocket 14 is widened by releasing induced elastic energy in the arm 13. In doing so, the cutting insert can be aligned with the holder and can be brought into contact such that associated ridges 30 and grooves 26 come into engagement with each other. Subsequently the cutting insert is inserted, which is guided by said engagement, until the insert inner edge surface 23 abuts against the abutment surface 34. Subsequently the screw 17 can be activated such that the flanks of the arm 13 abut against associated flanks on the cutting insert, whereby the ridges are firmly pressed against the grooves. To avoid overclamping of the arm 13 resulting in insert breakage or permanent distortion of the arm the calibrated spacer 41 is used. That is, when the screw 17 is tightened and the insert is firmly clamped, the screw may be further tightened only until the distance S has moved in between the flange 43 and the associated shoulder. In that position the ceiling 47 of the stot abuts the spacer and thus prevents further tightening of the screw. When the

insert is to be replace or indexed, only the screw 17 is untightened such that the gap S will reappear at the position shown in Fig. 3.

In Fig. 6 is shown an alternative embodiment of a tool 10' according to the present invention, wherein the holder 11'is provided with a separate plate 13'intended to be fastened on the holder 11'. In this case the pivot 27'is constituted by two abutment lines or surfaces 48,49. The cutting insert is clamped in the way as described above except that there is no induced elastic energy in the arm. Such energy is then preferably provided by a spring which is applied radially outside and around the spacer.

It should be understood that the sleeve 40 in some cases could be omitted, for example if the arm is very stable. Also if the head of the screw 17 is of larger diameter than shown then the washer 42 can be omitted. Furthermore, the spacer means 41 for restricting overclamping of the clamp means 13 could alternatively be integrated with the clamp means 13 or the tool holder body 11 close to the screw means.

The tool according to the present invention provides the advantages of optimal locking force on insert thereby avoiding breakage or permanent distortion of the clamp, and trouble-free locking mechanism also if the locking screw is over-torqued.