US2799028A - Elastic thread-cutting die with automatic adjustment - Google Patents

Description

July 16, 1957 N. PER LAKI 2,799,028

ELASTIC THREAD-CUTTING DIE WITH AUTOMATIC ADJUSTMENT Filed March 12, 1954' 3 Sheets-Sheet l y 1957 N. PERLAKI 2,799,028

ELASTIC THREAD-CUTTING DIE WITH AUTOMATIC ADJUSTMENT Filed March 12, 1954 3 Sheets-Sheet 2 Fig. 6

hp 7 INVENIOR N. PERLAKI July 16, 1957 ELASTIC THREAD-CUTTING DIE WITH AUTOMATIC ADJUSTMENT 3 Sheets-Sheet 3 Filed March 12, 1954 United States Patent ELASTIC THREAD-CUTTING DIE WITH AUTOMATIC ADJUSTMENT Nandor Perlaki, Budapest, Hungary, assignor to Licencia Talalmanyokat Ertekesito Vallalat, Budapest, Hungary, a firm Application March 12, 1954, Serial No. 415,730

Claims priority, application Hungary March 16, 1953 Claims. (Cl. 10111) This invention relates to thread-cutting dies for machining materials and adapted to work with a clearance angle.

Various constructions of thread-cutting dies have hitherto been suggested, their common characteristic feature being stiffness or rigidity during operation in order to ensure the exact size .of the thread to'becut.

The most usual p of Such dies haSQdiSK-HKQShaPB 1 known construction the basic idea is to possibly eliminate with radially arranged edge-supporting members or. cutting lips. Its significance lies in relatively low manufacturing costs and in the possibility of bilateral use. However, in order to permit such bilateral use they have cutting edges when removed from the work-piece. More said drawbacks of the known thread-cutting dies.

over, they are rather sensitive as to the manufacture of the chuck inaccuracies of which entail an uneven load distribution of the cutting lips.

The present invention aims at eliminating the ab loge e invention is based upon the discovery that'in contradist'inction to the hitherto known thread-cutting dies with which rigidity or stiffness in operation was a predominant principle of construction-simple manufacture, good cutting qualities and a long life-time can be obtained if the thread-cutting die as a whole is rendered freely and the drawback that a clearance angle may only be formed with the initial profiles of their cutting edges. The rest of the profiles used for calibrating the threadshaving no clearance angle, the whole of the threaded surface of the cutting lips is exposed, even during removal of the die from the work piece, to the wearing effect of the cut material. A considerable additional turning moment is required thereby resulting in an undesirable friction heat. In consequence hereof the working dimensions of the dies rapidly increase and, at the same time, the Morethread-cutting edges become prematurely dull. over, the lack of clearance angle has the further drawback that' the cutting process is accompanied by a displacement of the material to be machined whereby the wear of the cutting edges is additionally increased and their profiles rendered distorted. Neither the increase of the working diameter nor the distortion of the profiles can be eliminated by re-sharpening' the die as is known to those skilled in the art. Another important drawback of such thread-cutting dies consists in that the cutting edges, because'of the rigid construction of the 'die, are liable to split off when removing the die from the work piece. I

For sake of more favourable cutting conditions it has been suggested to provide even the calibrating cutting edges with a suitable clearance angle either by grinding or by a predetermined permanent deformationof the cutting lips. This is, however, possible only on expenses of the bilateral use whereby the life-time of the dies is considerably decreased. Apart therefrom, the rate of alteration of the working diameter of the die when resharpened as well as its liability as to splitting off of the cutting edges as, to a minor degree, is the case with the previously described dies with no clearance angle, is even increased by the presence of suchan angle. More: over, re-sharpening is relatively more frequently needed since the cutting edges are exposed to an increased wear when removing the die from the work piece.

In order to meet the double requirement as to provid' ing a clearance angle by means of deformation previous to operation of the die and permitting bilateral use thereof it has been proposed to partly give up the principle of rigidity insofar the dies are, by means of radial slots in the cutting lips,- rendered elastically deformable. The needed value of the clearance angle is then obtained by "a suitable predetermined elastic deformation of the cut elastically deformable in operation rather than stiff or rigid. Thus, the new thread-cutting die forms a closed elastic framework selected for elastic deformation under the action of the forces of cutting Whereas with the the deforming effect of the cutting forces on the die proper. The aforesaid free and premeditated deformation of the die is then made use of to constitute the desired clearance angle. Accordingly, the improved thread-cut;- ting die "for machining materials and. adapted to work with a clearance angle, having cutting ,edges and support members for supporting the cutting edgesin the usual manner, comprisesin compliancewith themain feature of the present inventione1astically deformable girder members connecting the support members to one another so as to form a closed elastic system, this system being selected so that the needed value of the clearance angle will, by elastic deformation of the girder members, automatically be obtained upon machining engagement of the cutting edges with a material to be. machined.

' Other features and objects of the present invention will be understood by the following description and. claims reference being taken to the accompanying drawings in which:

Fig. 1 shows, by way of example, the perspective view of an embodiment of the invention.

I Fig. 2 represents the front View of the thread-cutting die according to Fig. 1 in both its inoperative and operative positions. 7

Fig. 3 illustrates, 'likewisely by way of example, the front view of another preferable embodiment of the invention in its inoperative position.

Fig. 4 is a like view showing the thread-cutting die according to Fig. 3 in its operative position.

Figs. 5 to 7 illustrate, on a relativelysmaller scale, a preferable method of manufacturing the bulk of the thread-cutting die according to Figs. 3 and 4 by plastically shaping tubular material. Finally:

Fig. 8 represents the perspective view of theembodiment shown in Figs. 3 and 4 clamped in a chuck in its operative position. Same reference characters throughout the drawings.

Referring to Figs. 1 and 2, the thread-cutting die represented is provided with cutting edges 10 and support members or cutting lips 11 for supponting the cutting edges 10. The support members 11 are-in compliance with themain feature of the inventionconnected to one another by elastically deformable girder members 12 so as to form a closed elastic system. The system is selected so that the needed value of the clearance angle will, by elastic deformation of the girder members 12, automatically be" obtained upon machining engagement of the designate like details cutting edges 10 with a material to be machined as will closure the support members 11 or web portion of the thread-cutting die do not take part individually in the elastic deformation of the circuitous ring shaped body formed by the combination of members 19, 11, 12. Deformation whatever of the cutting edges are obviously to be avoided which means that the support members 11 supporting the cutting edges 16 must not be deformed whenever a deformation of the system as a whole takes place.

With the represented embodiment, the support members 11 and the girder members 12 are symmetrically arranged with respect to an axial centre-line 13 which is also the axis of rotation of a work piece 14 to be machined by the thread-cutting die. The advantage of such an arrangement consists in that the system 1%), 11, 12 is uniformly deformable around the axis 13, that is a certain deformation of one of the girder members 12 entails a like deformation of the rest of such members. Thus, the load of the cutting edges 10 is evenly distributed throughout the thread-cutting die when being in machining engagement with the work piece 14. Furthermore, the uniform deformation of the girder members 12 has, as will be seen, its special significance when adjusting the thread-cutting die within a chuck receiving the same.

Moreover, with the represented embodiment the threadcutting die is built up of three congruent parts each comprising a cutting edge 10, a support member 11 and a girder member 12. Such an arrangement has its significance in that the thread-cutting die is adapted to be centered by supporting at three points. The system 10, 11, 12 proper being elastically deformable, the cutting edges 10 will then in all cases occupy a concentric position with respect to the axis 13 of rotation of the work piece 14 and evenly participate in the load notwithstanding whether the congruancy of the parts of the system 10, 11, 12 is less than perfect or the work piece 14 is not quite rectilinear.

It is noted that the initial pro-files of the cutting edges 10 are shaped so as to form a conical entrance and may have a permanent clearance angle as is well known to those skilled in the art and, therefore, not represented in the drawings.

In Fig. 2, the inoperative position of the die is represented by solid lines whereas the operative position thereof is illustrated by dot-and-dash lines. The free elastic deformation of the die is rendered possible by bracket means 15 engaging the die each between two adjacent girder members 12 and bearing with their front surfaces against the die opposite to the supporting members 11. The dimensions are selected so as to permit rolling of the support members 11 around the axis 16 of the cylindrically shaped bearing surfaces of the bracket means 15.

In operation, when the work piece 14 is rotated in the direction of the arrow 17, the cutting edges 10 get into machining engagement with the material to be machined, i. e. the work piece 14. In consequence hereof, the system 10, 11, 12 becomes elastically deformed as indicated by the dot-and-dash lines so that the radial centre-lines 18 of the support members 11 rotate by an angle on around the axis 16 into a position 18' whereby a clearance angle a appears behind each of the cutting edges 10 the profile of which has to be selected in consideration of this slight rotation as will be obvious to those skilled in the art. The angles a are of the same degree value.

It is clear from the drawing that the cutting edges 10 by rotating around the axis 16 approach the axis 13. Thus, the working radius 19 of the die is less than its radius 20 associated with the inoperative position thereof. Upon removing the die from the work piece 14 the machining engagement between the cutting edges 10 and the work piece 14 is automatically relieved since the die then regains, by means of its elasticity, the inoperative position thereof illustrated by solid lines. Thus, during removal of the die, the cutting edges 10 do not contact with and are not exposed to wear on the threads cut on the work piece 14. Obviously, the possibility of their splitting off is likewisely avoided thereby.

With the embodiment shown in Figs. 3 and 4 the cutting edges 10, the support members 11 and the girder members 12 are formed so as to be symmetrical not only with respect to an axial centre-line, viz. to the axis 13 of rotation of the work piece 14 but also relatively to radial centrelines going through the support members 11, i. e. to the centre-lines 18 of the latter. The main significance of such an arrangement consists in the possibility of using the die bilaterally since, in this case, the system 10, 11, 12 is uniformly deformable in both directions around the axis 13. Moreover, the cutting edges 10 being of circular shape with respect to the axis 13, they require but low costs of manufacture and yet receive a suitable clearance angle in operation. Furthermore, the die retains its working radius 19 as well as the profile of its cutting edges 10 within the limits of the standard tolerances during the whole period of its life-time even if re-shaped as will be clear to those skilled in the art. It is likewisely important that such improved dies are feasible even in case of the smallest standardised working diameters 19.

Otherwise, the represented embodiment differs from the previously described one insofar that the cutting edges 10 are formed by bits 21 fixed by fastening means, e. g. solderings 22, to the support members 11 as is well known to those skilled in the art and, therefore, not described in closer details.

Obviously, the support members 11 might be formed interchangeable, for instance by means of dove-tailed connections between the support members 11 and the girder members 12. However, it is preferable to form the elastically deformable girder members 12 integral with the support members 11 and, mainly in case of small dimensions, with the cutting edges 1% as well. If the system is partly or wholly integral, as described above, the bulk of the thread-cutting die comprising at least the support members 11 and the girder members 12 will preferablybe made of tubular material plastically shaped to the desired profile of the system.

One method of manufacturing the die by the aforesaid plastic shaping consists in drawing a tube of suitable material and dimensions in a number of steps to a predetermined final shape of cross section. The main steps of such a process are shown, by way of example, in Figs. 5 to 7 of the drawings. Fig. 5 illustrates a cross section 23 of the tube selected as the starting material of the process. Fig. 6 illustrates an intermediate cross section 24. The tubular body of this cross section is already suitable for being drawn, by means of plastically shaping the straightlined sections of the profile 24, to the final profile 25 shown in Fig. 7. The microstructure of the bulk of the die examined in a cross section like the profile 25 will obviously show the nature of the manufacturing process by a series of continuous lines following the curves of the support members 11 and the girder members 12.

Another process of plastically shaping tubular materials to the desired profile of the system substantially consists in extruding a tubular body through a die provided with a caliber e. g. of the form shown in Fig. 7 as, otherwise, is well known in the art and, therefore, not discussed here in closer details. Also in this case the nature of the manufacturing process is recognisable by examination of the microstru-cture of the die in-an e. g. axial section since inhomogenities of the material will show a sort of symmetry across the width of the bulk, in contradistinction to cases Where the bulk of the die has, by means of cutting operations, been worked out as a whole from a solid body.

Referring to Fig. 8, the system 10, 11, 12 is surrounded by a chuck means 26 in spaced relationship, the bracket means 15 being attached to the chuck means 26 by means of screws 27 so as to freely support the system 10, 11, 12 by hearing against it at regions opposite to the support members 11. Furthermore, the bracket means 15 are provided, on both their front surfaces,with bracket plates 28 fixed to the former likewisely by means of screws 29.

The bracket plates 28 of which, for sake of clarity, only one is illustrated in Fig. 8 are selected so as to protrude behind the front surfaces of the die thereby preventing it from being pushed from within the chuck means 26 during operation. An adjustable abutment means formed as a screw 31 is arranged on the chuck means 26 in such a manner that its inward end 32 may abut against one of the girder members 12 of the die, the function of the abutment means 31, 32 being to limit the elastic deformation of the system 10, 11, 12 to a predetermined value, i. e. 'to fix the maximum value of the clearance angle a when the work piece 14 is rotated in the direction indicated'by the arrow 30. Such a limiting action may be needed in cases where the material of the work piece 14 is not quite homogeneous and there are regions in it the hardness of which exceeds the preselected value. When going over to cutting such a region the clearance angle at would be altered and the die would cut at a less value of its working radius 19 so that the cutting would result in a work piece 14 of a relatively smaller diameter. In such cases the preselected value of the clearance angle or is maintained by bearing of the abutment means 31, 32 against the outer flank of the girder member associated therewith. The system being uniformly deformable around the axis 13 of rotation, the rest of the members 12 will occupy a like position with the same clearance angle a .without the need of applying further abutment means 31, 32 each associated with one of the girder members 12. If the cutting edges strike upon regions the hardness of which is less than the preselected value, the die is liable to cut threads of an increased diameter. However, the dimensions of the die can obviously be selected so that differences as to the diameter of the thread cut by the die be slight enough to fall within the limits of the standardized tolerances even if free fit of the threads is required. .The chuck means 26 is, by means of two brackets 33, connected to a sleeve 34 adapted to be mounted on the tailstock of a lathe. On the other hand, the work piece 14 is clamped in the headstock spindle of thexsame lathe. Both the tailstock and the headstock spindle of a lathe as well as the manner of mounting a threadcutting die therebetween are well known in the art and, therefore, not represented in the drawing.

In operation, the die is accommodated within the chuck means 26 in the above described mannerandthe screw 31 is adjusted so as to limit the maximum value of the clearance angle a. spindle 35 is caused to rotate and the chuck means 26 is displaced toward the headstock spindle 35'so as to bring the cutting edges 10 and the work piece 14 into machining engagement. As soon as the cutting edges 10 contact with the work piece 14, the system 10, 11, 12 becomes elastically deformed in the above described manner whereby a clearance angle on automatically appears behind the cutting edges 10. If the system 10, 11, 12 tends to become further deformed due to inhomogenities of the material of the work piece 14 one of the girder members 12 strikes against the abutment means 31, 32 associated therewith whereby the system is rendered sulficiently rigid so as to be prevented from any further deformation. As the cutting of threads on the work piece 14 goes on, the chuck means 26 with the die accommodated therein is drawn toward the headstock spindle 35 by means of'the.

the thread-cutting edges 10 and the work piece 14 get disengaged. The disengaged die resumes its inoperative position wherein the thread-cutting edges 10 are distant from the work piece 14 so that neither wearing nor split- Thereafter, the headstock ill ting .off of the former can occur when the die is removed from the material just machined.

' What I claim is: 1. A thread cutting die comprising in combination a plurality of cutting edges lying on the circumference of a circle, a plurality of members for supporting said cutting edges extending radially of the axis and outwardly of the circumference of said circle, and a plurality of elastically deformable arcuate girder members interconnecting adjacent support members at positions on said support members spaced from said cutting edges to form a circuitous body, said cuttingedges when engaging the material to be machined upon 'rotation of the die causing said girder members to deform and the trailing portion of said cutting edges'to be tilted radially away from the material and the forward portion of said cutting edges to be tilted radially inwards of the material so as to produce a proper clearance angle on said cutting edges.

' '2. A thread cutting die comprising in combination a plurality of cutting edges lying on the circumference of a circle, a plurality of members for supporting said cutting edges extending radially of the axis and outwardly of the circumference of said circle, and a plurality of elastically'deformable arcuate girder members interconnecting adjacent support members at positions on supportrnembers spaced outwardly from the circle formed by cutting edges to form a circuitous body, said cutting edges when engaging the material to be machined upon rotation 'of the die causing said girder members to deform and the trailing portion of said cutting edges to be tiltedradially away from the material and the forward portion of said cutting edges to be tilted radially inwards of the material so as to produce a proper clearance angle n'said cutting edges, said girder members being of a predetermined thickness to provide a predetermined deformation when said cutting edges engage the material to produce a predetermined clearance angle.

3. thread cutting die comprising in combination a plurality of cutting edges lying on the circumference of I a circle, three members for supporting said cutting edges and extending radially of the axisand outwardly of the circumference of said circle, and three elastically deform able arcuate girder members each arranged between two of said supporting members, said girder members being connected to adjacent supportmembers at positions on said support members spaced outwardly from the circle formed by said cutting edges to form a closed circuitous ringshaped body, said cutting edges when engaging the material to be machined upon rotation of the die causing said girder members to deform and the trailing portion of said cutting edges to be tilted radially away from the material and the forward portion of said cutting edges to be tilted radially inwards of the material so as to produce a predetermined clearance angle on said cutting edges.

4. A thread cutting die comprising in combination a plurality ofcutting edges lying on the circumference of a circle, a plurality of members for supporting said cutting edges extending radially of the axis and outwardly of the circumference of said circle, anda plurality of elastically deformable arcuate girder members interconnecting adjacent support members at points on said support members spaced outwardly from said cutting edges to form a closed circuitous ring shaped body, said supporting members and said girder members being symmetrically arranged with respect to and around the axis of said circle, said cutting edges when engaging the material to be machined upon rotation of the die causing said girder members to uniformly deform around the axis of said circle and the trailing portion of said cutting edges to be tilted radially away from the material and the forward portion of said cutting edges to be tilted radially inwards of the material so as to produce a predetermined clearance angle on said cutting edges.

5. A thread cutting die comprising in combination a plurality of cutting edgeslying on the circumference of a circle, a plurality of members for supporting said cutting edges extending radially of the axis and outwardly of the circumference of said circle, and a plurality of elastically deformable arcuate girder members interconnecting adjacent support members to form a closed circuitous ring shaped body, said cutting edges, supporting members and girder members being symmetrically arranged with respect to the radial center lines extending from the axis of said circle through each of said support members so as to render said body deformable in both directions around the axis of said circle, said cutting edges when engaging the material at points on said support members spaced outwardly from said cutting edges to be machined upon rotation of the die causing the girder members to deform and the trailing portion of said cutting edges to be tilted radially away from the material and the forward portion of said cutting edges to be tilted radially inwards of the material so as to produce a predetermined clearance angle on said cutting edges.

6. A thread cutting die comprisingin combination a plurality of cutting edges lying on the circumference of a circle, a plurality of members for supporting said cutting edges extending radially of the axis and outwardly of the circumference of said circle, and a plurality of elastically deformable arcuate girder members integrally formed with and interconnecting adjacent support members to form a closed circuitous ring forming the body of the die, said girder members being spaced outwardly from the circle formed by said cutting edges, said cutting edges when engaging the material to be machined upon rotation of the die causing said girder members to deform and the trailing portion of said cutting edges to be tilted radially away from the material and the forward portion of said cutting edges to be tilted radially inwards of the material so as to produce a predetermined clearance angle on said cutting edges, said girder members being of a predetermined thickness to automatically provide said clearance angle upon engagement of said cutting edges with the material.

7. A thread cutting die comprising in combination a plurality of bits forming cutting edges lying on the circumference of a circle, a plurality of members for supporting said bits extending radially of the axis and outwardly of the circumference of said circle, fastening means for securing said bits to said supporting members, and a plurality of elastically deformable arcuate girder members interconnecting adjacent support members at points on said support members spaced outwardly from the circle formed by said cutting edges to form a closed circuitous ring shaped body, said cutting edges when engaging the material to be machined upon rotation of the die causing said girder members to deform and the trailing portion of said cutting edges to be tilted radially away from the material and the forward portion of said cutting edges to be tilted radially inwards of the material so as to produce a predetermined clearance angle on said cutting edges.

8. A thread cutting die mechanism comprising in combination a plurality of cutting edges lying on the circumference of'a circle, a plurality of members for supporting said cutting edges extending radially of the axis and outwardly of the circumference of said circle, a plurality of elastically deformable arcuate girder members interconnecting adjacent support members at points on said support members spaced outwardly from the circle formed by said cutting edges to form a circuitous body,

saidv cutting edges when engaging the material to be ma'- chined upon rotation of the die causing said girder members to deform and the trailing'portion of said cutting edges to be tilted radially away from the material and the forward portion of said cutting edges to be tilted radially inwards of the material so as to produce a predetermined clearance angle on said cutting edges, chuck means surrounding said body in spaced relationship, and bracket means attached to said chuck means and provided to support said body by bearing against it at points opposite said supporting members.

9. A thread cutting die mechanism comprising in combination a plurality of cutting edges lying on the circumference of a circle, a plurality of members for supporting said cutting edges extending radially of the axis and outwardly of the circumference of said circle, a plurality of elastically deformable arcuate girder members interconnecting adjacent support members at points on said support members spaced outwardly from the circle formed by said cutting edges to form a-circuitous body, said cutting edges when engaging the material to be machined upon rotation of the die causing said girder members to deform and the trailing portion of said cutting edges to be tilted radially away from the material and the forward portion of said cutting edges to be tilted radially inwards of the material so as to produce a predetermined clearance angle on said cutting edges, chuck means surrounding said body in spaced relationship, bracket means attached to said chuck means and provided to support Cir said body by hearing against it at points opposite said supporting members and between adjacent girder members.

10. A thread cutting die mechanism comprising in combination a plurality of cutting edges lying on the circumference of a circle, a plurality of members for supporting said cutting edges extending radially of the axis and outwardly of the circumference of said circle, a plurality of elastically deformable arcuate girder members interconnectingadjacent support members at points on said support members spaced outwardly from the circle formed by said cutting edges to form a circuitous body, said cutting edges when engaging the material to be machined upon rotation of the die causing said girder members to deform and the trailing portion of said cutting edges to be tilted radially away from the material and the forward portion of said cutting edges to be tilted radially inwards of the material so as to produce a predetermined clearance angle on said cutting edges, chuck means surrounding said body in spaced relationship, bracket means attached to said chuck means and provided to support said body by bearing against it at points opposite said supporting members, and adjustable abutment means provided on said chuck means and adapted to abut against said girder members to limit elastic deformations of said body to a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 1,220,460 Rioux Mar. 27, 1917 1,564,591 Lansche Dec. 8, 1925 1,796,925 Folman Mar. 17, 1931 1,878,216 Wells Sept. 20, 1932 2,513,864 Haycock July 4, 1950 FOREIGN PATENTS 500,955 Germany Oct. 3', 1930 658,578 Great Britain Oct. 10, 1951

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