Abstract:
A cutting insert toolholder for easy indexing in areas of limited access. In an outer end of the toolholder runs a through channel in which a bent bolt is inserted. The channel extends through the toolholder and is open at an outer end of the toolholder.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates to cutting tools with removable inserts, such as indexable inserts, for use in turning and milling operations, and more specifically to cutting tools with insert attachment of a so called screw clamping type. 
     PRIOR ART 
     There is a wide range of various designs present wherein an indexable insert is secured in a toolholder by the use of a screw or a modified bolt. Common to these designs is that the screw, or the modified bolt, is inserted in a thread cutted in a toolholder, directly of via another threaded means. 
     A problem with a design of this type is that the screw or the bolt has to be completely unscrewed in order for the insert to be detached. This means, among others, that there is a risk that some of these articles, which usually are of small size, will be lost. 
     Another problem occurs in situations where accessibility, due to the attachment of the cutting tool in the operating machine, is limited. 
     Securing or detaching of the insert in such situations may necessitate the detachment of the complete cutting tool from the machine, in order to index the insert in a more spacious location. This operation is time consuming. 
     Thereafter, when the cutting tool is returned in place in the machine it has to be carefully calibrated to ensure a proper working position, which results in further losses of time. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to solve the problems above. 
     According to the invention, the insert is secured in the toolholder by the use of a specially designed bolt, said bolt being fitted into an open channel running across an outer end of the toolholder. The bolt is secured in place by a nut due to a tapered portion of said nut that after tightening is in engagement with a corresponding recess in the channel. The tightening also provides a securing force on the insert attached by the bolt. 
     The invention allows the insert as well as the nut to be attached to the bolt during securing or detaching, thereby eliminating the risk of losing separate articles. 
     Further, the assembly formed in this manner may easily be inserted into the channel of the toolholder without any need to detach the toolholder, substantially independent of how the toolholder is mounted in the operating machine. Since there is no need to unfasten the toolholder, and the insert at the same time can be fitted to the proper position with high accuracy, calibration is not necessary after indexing. 
     By the use of a slightly bent bolt the bend can be utilized as counterstay when wrenching the nut, at the same time as a resilient bias is achieved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective top view of a toolholder according to the invention. 
     FIG. 2 is a perspective bottom view of the toolholder of FIG.  1 . 
     FIG. 3 is a cross sectional view taken along the line A—A of FIG.  1 . 
     FIG. 4 is a side elevation view of a bolt, with a nut, according to a first embodiment of the invention. 
     FIG. 5 is a perspective view of a tool holder, according to FIG. 1, including a mounted insert. 
     FIG. 6 is a cross sectional view taken along the line B—B of FIG. 5, including a mounted bolt of a first embodiment. 
     FIG. 7 is a cross sectional view taken along the line B—B of FIG. 5, including a mounted bolt of a second embodiment and an insert for parting. 
     FIGS. 8A and 8B are cross sectional views of two variants of a bolt of the first embodiment of the invention, taken along the line C—C of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     FIG. 1 illustrates an embodiment of a toolholder  1  according to the invention having a recess formed to provide an insert seat  2  adapted for a predetermined insert. A channel  3  that is open toward the outer end  14  of the toolholder runs from the insert seat  2  through the toolholder to the bottom side of said toolholder. 
     FIG. 2 shows the toolholder of FIG. 1 from underneath. It is thereby shown that the channel  3  ends in a substantially tapered recess  4 . 
     The shape of the channel is more clearly illustrated in FIG. 3, said figure showing a cross section along the line A—A of FIG.  1 . According to FIG. 3 a line  16 , parallel to the bottom of the channel, intersects the bottom plane of the insert seat  2  at an angle a &lt;90°. Therefore, the tightening force from a bolt disposed in the channel, as will be disclosed below, will be introduced aslant into the insert, thereby urging said insert downwards against the bottom of the insert seat as well as backwards toward the farther portion of the insert seat. 
     The central axis  15  of the tapered recess  4  is parallel to the line  16 . Further, the minimum diameter  17  of the tapered recess  4  is entirely within the bottom surface plane of the tool holder  1 . This is also substantially valid for that imagined section of the diameter  17  that is located within the channel  3 . In this way a recess is formed that fixates a tightened nut laterally, as will be described in the following. 
     FIG. 4 shows an embodiment of a bolt according to the invention and a corresponding nut  10 . In the present embodiment, the bolt has a length of 12 mm, and a threaded end section  5  of the bolt is provided with a M2.5 thread. 
     The top end of the bolt  19  is provided with a head  8 . The end surface  12  of the head is preferably completely even, while the shell surface  9  is provided with a radius R. The bolt head  8  is joined to a slender portion  7  adapted to ensure clearance with regard to the hole in the insert, since the bolt during tightening will lean somewhat. 
     The bolt  19  has further an intermediate portion  6  so bent that the central axis of the threaded section  5  deviates from the central axis running through the head  8 . In the present embodiment the deviation is 15°. The bent portion  6  contributes to a reliable securing, which is described in the following, but does also provide a counterstay when wrenching the nut  10  since the thereby occurring torsional moment urges the bend of the bolt against one of the sides of the channel. Additionally, at full tightening the bend of the bolt will act as a spring, thereby providing a bias that is advantageous in situations where the working piece vibrates with regard to the insert. 
     The intermediate portion  6  may have a cross section of any applicable shape. Thereby, a circular circumference represents a variant exhibiting favorable manufacturing costs, as illustrated in FIG. 8 a . However, the best mode is assumed to be a modified circular shape with two diametrically opposed substantially plane surfaces, as illustrated in FIG. 8 b . In this best mode the plane surfaces  31  are so oriented that a perpendicular to any of these surfaces is substantially parallel to the imaginary axis around which the portion  6  has been bent. 
     Therefore, in the mode as illustrated in FIG. 8 b , when the bend of the bolt acts as a counterstay during tightening, the point of contact between the bolt and the side of the channel is displaced outwardly from the bottom of the channel, as compared to the case of a bolt with circular cross section. Consequently, the bolt can act more efficiently as a counterstay. At the same time, as the bolt has a reduced diameter when measured across a diameter parallel to the imaginary axis around which the intermediate portion  6  has been bent, the channel may be made more narrow which in turn allows for improved strength of the toolholder. 
     FIG. 6, that shows a cross section of a cutting tool with a secured insert  13 , illustrates that the insert is provided with a through hole  20 , said hole at at least one end being provided with a tapered bevel  18 . 
     During assembly the bolt  19  is inserted though the hole  20  so that the shell surface  9  gets in contact with the tapered bevel  18 . The nut  10 , with its tapered portion  11  pointing towards the bolt head  8 , is wrenched some turns on the thread  5  of the bolt  19 , and the assembly is thereafter fitted into the channel  3  of the toolholder  1  in such a manner that the bend of the bolt is pointing outwardly from the bottom of the channel, the insert  13  is properly positioned in the insert seat  2  and the nut  10  is collinear to the tapered recess  4 . The present embodiment is so shaped that erroneously mounting will be managed only with great difficulty. 
     Next, the nut  10  is tightened while the bent portion  6  of the bolt  19  provides a counterstay. Due to this the central axis through the head  8  will substantially be perpendicularly directed towards the insert and the main plane of the insert seat, resulting in that the insert is urged towards the bottom of the insert seat  2  with a suitable force. 
     However, at the final tightening, since the nut  10  due to the bend of the bolt is inclined with regard to the central axis through the bolt head  8 , the load distribution will be somewhat uneven in the bevel  18 . In a surrounding to point C of FIG. 6 the introduced load will be higher than in an area surrounding point D in said figure. Those load components in the surrounding of C that are directed parallel to the longitudinal direction of the toolholder, the arrow L of FIG. 6, will thereby become larger than the corresponding opposite components in the surrounding D. Consequently, the insert  13  will be urged also towards the inner wall  21  of the insert seat, ensuring that the insert is laterally fixed in place. 
     At tightening, the tapered portion  11  of the nut  10  joins with the tapered recess  4  in the channel  3 , restraining the nut from moving laterally. Thereby is also ensured a secure attachment of the complete assembly. 
     Dismounting of the insert is made inversely. 
     A second embodiment is illustrated in FIG.  7 . This second embodiment differs from the first in that the bent portion  23  of the bolt  22  is integrated with the slender portion  7 , described with the first embodiment. In FIG. 7 is also, by showing an insert for parting, illustrated the possibility to utilize different types of inserts. 
     The second embodiment provides the possibility to manufacture the holder at lower cost, since the precision requirements on the channel  3  are lower. The operation coincides with that of the first embodiment apart from that, in the second embodiment, it is the wall of the hole in the insert that acts as a counterstay when wrenching the nut, while in the first embodiment the wall of the channel through the toolholder provides the counterstay. 
     In addition to the embodiments described above there are many possibilities to make minor deviations to adapt the invention to required machining conditions. For example, measures and shape of the tapered portion of the nut, the recess for this nut, the cross section of the bolt, the bolt head, the hole and bevel of the insert as well as the channel of the toolholder may be changed within the scope of the invention. Further, the design of the insert seat can be adapted to suit each required type of insert and machining. 
     Independent of the embodiment chosen, the present invention allows the toolholder to be so designed that it can be mounted in a cutting tool in a desired manner.