the principle of the bending process will be explained in detail in connection with fig1 . here , as in the prior art bending processes , a bending mandrel 1 is provided a wire pin 2 of given length is inserted and pressed against the underside of the bending mandrel by a holder ( not shown ). a chain link 3 which has been completely bent during the preceding bending process has here been inserted into a recess in the bending mandrel 1 with the aid of a turning and gripping device of known structure ( which is not shown here in detail ) so that the wire pin 2 to be bent can be pushed through the already completely bent chain link 3 . in this way , a chain is joined together link after link and the links are then individually welded in a known manner in a chain link welding machine . in accordance with the desired chain shape , the bending mandrel 1 is provided at both sides with a semicircular bending profile ( work face ) 4 and the associated center point 5 . a bending tool 6 which is freely rotatably mounted on an actuated member ( such as a pivot lever 11 ) and which is applied with its jaw - like terminus 13 in the end region of wire pin 2 is now guided so that the point 7 where the force is applied moves along a path of movement 8 which corresponds to a circular involute with reference to the curvature of the bending mandrel and its center point 5 . thus , stated differently , as the pin 2 is bent around the mandrel 1 by the tool 6 , the location of engagement between the tool 6 and the pin 2 will not shift relative to the pin 2 , but the tool 6 will be guided in the above - discussed circular involute . this is so because the friction generated by the bending force and the bending resistance of the pin 2 maintains the tool 6 in a fixed contact point relationship with the pin 2 and further , by virtue of the free pivotal motion of the tool 6 relative to the actuated member ( such as the pivot lever 11 ) the tool 6 is capable of maintaining such a fixed contact point as the pin 2 is being wrapped around the mandrel 1 . the illustration of fig1 here shows the various positions of the free end of the wire pin corresponding to the progress of the bending process . the bending force for each individual position is shown with respect to the pin axis as the point of attack of the force . the illustration shows that during the entire bending process the force applied has a direction perpendicular to the pin axis . since for structural reasons each bending tool must be guided at a certain distance from the pin axis , a path of movement 10 results for an assumed point 9 on the bending tool which also constitutes a circular involute but which is shifted in phase with respect to the path of movement of the point of application of force . the illustration here immediately shows that in view of these circumstances the bending tool 6 must perform a relative movement with respect to the guide for generating the path of movement 10 of the bending tool since , in correspondence with the progress of the bending process , the angle enclosed by the effective direction of the bending force continuously changes with respect to the path of movement 10 . in the present case , the relative movement consists of a pivotal movement with respect to the guiding of bending tool 6 . the guiding may here be effected by two carriages which are moved perpendicularly to each other as a function of the law of motion given by the path of movement 10 , one carriage carrying the bending tool 6 . other embodiments will be explained in detail in connection with fig5 and 6 . since the path of movement constitutes a mathematically definable curve , the given sequence of motion can be realized without difficulty with the air of an appropriate control . for the sake of clarity it is pointed out at this time that the described bending process is a symmetrical process . thus , as can be seen in the sketch of , for example , fig4 the two free ends of the inserted wire pin 2 are bent simultaneously and with the same speed so that the machine is likewise stressed symmetrically . fig1 shows a further mode of operation principle in which , instead of the generation of the movement curve by simultaneous movement of the bending tool in the direction of an x coordinate and a y coordinate , the bending process is effected with the aid of an only approximated circular involute . this can be done , for example , by a pivot lever 11 which is stationarily mounted on the machine frame so that the resulting path of movement for point 9 is the dashed curve 10 &# 39 ;. the position of the stationarily arranged fulcrum 12 of pivot lever 11 with respect to the center of curvature 5 of the bending mandrel is here determined by the end position of the bending tool 6 after completion of the bending process so that in the final phase of the bending process the path of movement 10 &# 39 ; which constitutes a circular arc coincides with the path of movement 10 which constitutes a circular involute . the deviations of the actual path of movement 10 &# 39 ; from the exact path of movement 10 occurring in this mode of operation at the beginning of the bending process are without influence in view of the usual dimensional tolerances of the wire pins to be bent and need be considered only in the design of the contact surface of the jaw - shaped terminus 13 of the bending tool 6 . this can be easily seen in the force path diagram of fig7 . the point a identified in the diagram of fig7 corresponds to position a of the free end of the wire pin of fig1 to be bent . up to this position , the bending force to be exerted is only about 1 / 3 of the bending force required to bend the pin into the final position . however , in this position the circular path of movement 10 &# 39 ; coincides , with sufficient accuracy for practical operation , with the exact path of movement 10 which corresponds to a circular involute so that , particularly in the critical region , no adverse influences result from the deviations of the actual path curve from the exact path curve . fig2 shows two courses of movement during the bending of two chain links of the same diameter but of different lengths . the shorter chain link 15 is bent about an appropriately shaped bending mandrel 1 &# 39 ; while the chain link 16 which is shown in dot - dash lines in the area of its curvature is bent about a bending mandrel of correspondingly wider design , the radius of curvature being identical in both cases . if the bending tool 6 &# 39 ; is guided by a simultaneous superposed movement both in the x and y coordinate directions ( corresponding to the drawn coordinate cross ) there again results the solid - line path curve 10 which corresponds to an exact circular involute which has been shifted in phase with respect to the path curve of the point of force application . if the movement is provided by means of a pivot lever 11 , the dashed path curve 10 &# 39 ; results for the point 9 which will be correspondingly shifted . otherwise the sequence of movement of the bending process corresponds to the bending process described in connection with fig1 . if now the longer chain link 16 is to be bent , for which the bending mandrel , the turning device , etc . must be exchanged , the fulcrum 12 of pivot lever 11 must be in the x - direction to position 12 &# 39 ; in order for bending tool 6 to be able to again engage the free end of the wire pin to be bent . the path curve again corresponds to the dashed line 10 &# 39 ; which , in the final phase of the bending process , coincides with the exact circular involute . corresponding to the change in the geometric relationship , when a chain link of the shape of link 16 is to be bent , the distance of point 9 from fulcrum 12 &# 39 ;, i . e . the pivot radius of point 9 , must be increased correspondingly . thus , if pins with greater or smaller diameter than in the illustrated example are to be bent into chain links , fulcrum 12 of pivot lever 11 must be adjusted in the direction of the y axis and / or the x axis to correspond to the changes in geometric relationships . adjustment of the position of fulcrum 12 is effected together with a change of the respective bending mandrel . during the bending process for a given chain link size , however , the fulcrum 12 remains stationary with respect to the bending mandrel . if instead of a pivot lever a carriage guide is employed , the starting position for both guide carriages must be newly positioned to correspond to the change in geometric relationships for bending chain links of different sizes , and the resulting new path of the curve , which in this case each time corresponds to path curve 10 , must be preset in the control device . fig3 shows in a schematic top plan view how an arrangement as that described in connection with fig1 and 2 , respectively , can be structurally designed with the aid of pivot levers . in this illustration the bending mandrel and all other machine parts are not shown , and only the position of wire pin 2 as well as of pivot levers 11 or 11 &# 39 ;, respectively , are shown to which the corresponding bending tools 6 or 6 &# 39 ;, respectively , are fastened . the bending tools 6 or 6 &# 39 ;, respectively , can be articulated to the pivot lever at a distance - which is fixed for each chain link size - from the axis of rotation of the respective pivot lever , or , as indicated by arrows 17 or 17 &# 39 ;, respectively , they can be guided toward the pivot lever as carriages , in which case the control of the pivot movement on the one hand and the radial movement of the bending tool 6 performed with respect to the axis of rotation on the other hand are such that the superposition of both movements corresponds to the respective circular involute . since , however , this path of movement can be precisely defined mathematically , it may be obtained not only by the already mentioned superposition of one movement in each the x and the y direction , but also by a superposition of a circular movement and a movement radial thereto . this can be realized by means of a correspondingly designed control device . while the solutions proposed in fig1 and 3 require a position for fulcrum 12 for the pivot levers which in a chain link bending machine is spatially limited due to the required fastenings for bending mandrel , guide for the turning tongues , etc ., fig4 presents a schematic view of an arrangement in which the required fulcrums for the pivot levers can be arranged outside of this structurally difficult region . this is accomplished in that two parallel pivot levers 18 and 19 are provided which are connected together by means of a coupling rod 20 to form an articulated linkage . one end of the coupling rod is extended beyond the point of articulation 21 at pivot lever 18 . to the end of this extension there is fastened a bending tool 6 so that when pivot lever 18 is pivoted according to arrow 22 , the circular path curve 23 results . the position of fulcrums 24 and 25 , respectively , of pivot levers 18 and 19 , respectively , with respect to the bending mandrel has again been selected so that the path of movement 23 corresponds to a correspondingly associated circular involute in the final phase of the bending process . the bending mandrel 1 as well as the wire pin 2 to be bent , when still in the unbent state and also in the completely bent state , are shown schematically in fig4 . fig4 also shows that - as mentioned earlier - the bending process takes place symmetrically , i . e . both free ends of wire pin 2 are bent around the bending mandrel simultaneously . in the illustrated example the symmetry of movement can be effected , for example , by meshing toothed gears 26 , 26 &# 39 ; which are connected to pivot levers 18 or 18 &# 39 ;, respectively . one of the two toothed gears is connected with a drive . the adjustment of the machine to various pin diameters or lengths in this device too is effected by corresponding displacement of fulcrums 24 , 25 or 24 &# 39 ;, 25 &# 39 ;, respectively , in the direction of the y axis and / or the x axis , as indicated symbolically by the crossed arrows b . with a chain link bending machine of this adjustable design , however , care must be taken that the two pivot levers 18 or 18 &# 39 ;, respectively , are appropriately coupled , so that they can be driven while allowing any desired , but symmetrical shift in the fulcrums 24 or 24 &# 39 ;, respectively , and 25 or 25 &# 39 ;, respectively , in the direction of the x axis and the y axis . also , the articulations between the pivot lever 18 and the coupling rod 20 , between the pivot lever 18 &# 39 ; and the coupling rod 20 &# 39 ; between the pivot lever 19 and the coupling rod 20 , as well as between the pivot lever 19 &# 39 ; and the coupling rod 20 &# 39 ; are adjustable relative to the respective fulcrums 24 , 24 &# 39 ;, 25 and 25 &# 39 ; as indicated symbolically by the double - headed arrows c . in deviation from the above - discussed possibility of producing the path of movement of the bending tool with the aid of two linear , superposed movements in the x and y directions , fig5 shows an arrangement in which two pivot levers 29 , 29 &# 39 ; are fastened on a carriage which can be moved back and forth in the y direction and through which it is possible to impart a movement to the bending tools 6 , 6 &# 39 ; approximately in the x direction . in superposing the two movements , the control of the pivot movement of pivot levers 29 , 29 &# 39 ; must take into consideration that the movement of the pivot levers does not take place exactly in the x direction but constitutes a circular movement . in such an embodiment it is advisable for the pivoting movement of the bending tool 6 or 6 &# 39 ;, respectively , to take place positively as a function of the movement of carriage 28 and bending levers 29 , 29 &# 39 ; so that care is taken that the bending tool is guided accurately . fig5 again shows a wire pin 2 in the unbent state and in the completely bent state , the path curve of fulcrum 30 of the bending tool being indicated by the dashed curve 31 . the end position of the bending tool is also shown . in this figure , the position of the so - called turning tongues 32 is indicated which grip the respective , completely bent chain link , pivot it by 90 ° and insert it into a recess in bending mandrel 1 so that a new wire pin 2 can be pushed through between bending mandrel and chain link . fig6 shows a modified version of the chain link bending machine discussed in connection with fig5 . in this embodiment , each pivot lever 33 , 33 &# 39 ; is fastened to its own carriage 34 , 34 &# 39 ; which is now moved in the x direction . the pivot levers produce the movement in the y direction under consideration of the fact that this is a circular movement . in this embodiment it is also advisable for the bending tools 6 , 6 &# 39 ; to be provided with a drive which effects positive control of the pivoting movement during the bending process . while the chain link bending machine described in connection with fig5 and 6 , in which the movement curve , with the aid of two superposed movements which extend substantially in the x direction and in the y direction , permits guidance of the bending tool on a path which precisely follows the required circular involute , it nevertheless requires considerable technical and structural expenditures . in contradistinction thereto , the structure principle of fig4 requires much less expenditures and one is not limited to the illustrated four - joint linkage . depending on the desired degree of coincidence of the coupling curve performed by the bending tool with the precise circular involute , a plurality of possible coupling drives can be selected from an available collection of coupling curves since each time only part of the coupling curve is required for the bending process .