US2710979A

US2710979A - Die head with self-retiring chasers

Info

Publication number: US2710979A
Application number: US337011A
Authority: US
Inventors: Royce M Strickland
Original assignee: Greenfield Tap & Die Corp
Current assignee: Greenfield Tap & Die Corp; GREENFIELD TAP AND DIE Corp
Priority date: 1953-02-16
Filing date: 1953-02-16
Publication date: 1955-06-21
Anticipated expiration: 1972-06-21

Description

June 21, 1955 R. STRICKLAND DIE HEAD WITH SELF-RETIRING CHASERS 6 Sheets-Sheet l 7 m i I 202 1 Filed Feb. 16, 1953' June 1955 R. M. STRICKLAND 2,710,979 DIE HEAD WITH SELF-RETIRING CHASERS' I e. Sheets-S 2 June 21, 1955 R, M. ASTRICKLAND 2,710,979

DIE HEAD wrm SELF-RETIRING CHASERS v Filed Feb. 16, 1953 6 Sheets-Sheet 3 June 21, 1955 R. M. STRICKLAND 2,710,979

DIE HEAD WITH SELF-RETIRING CHASERS I 6 Sheets-Sheet 4 Filed Feb. 16, 1953 June 21, 1955 R, M. STRICKLAND 2,710,979

DIE HEAD WITH SELF-RETIRING CHASERS Filed Feb. 16, 1953 6 Sheets-Sheet 5 'II/I/Ill, I

R. M. STRICKLAND DIE HEAD WITH SELF-RETIRING CHASERS June 21, 1955 6 Sheets$heet Filed Feb. 16, 1953 A EE 2,710,979 Patented June 21, 1955 2,710,979 I DIE HEAD WITH SELF-RETIRIN G CHASERS Royce M. Strickland, New Haven, Conn., assignor to Greenfield Tap and Die Corporation, Greenfield, Mass., a corporation of Massachusetts Application February 16, 1953, Serial No. 337,011

10 Claims. (Cl. 10-96) This invention relates generally to thread-cutting tools, and more particularly to machine-operated die heads having automatically retiring thread-cutting chasers for quick axial retraction of the die heads from work after the same is externally threaded.

A die head of this type is shown and described in my prior Patent No. 2,557,040, dated June 12, 1951. This prior die head has a carrier in which a plurality of chasers are radially movable by means of cams on an operating ring which is carried by and turnable on the carrier.

The operating ring is normally spring-urged into a retract position in which its cams hold the chasers retracted from the work. On turning the operating ring into a cutting position in which the cams thereon hold the chasers in thread-cutting position, the operating ring becomes locked to a releasable latch to prevent its springreturn into retract position during a thread-cutting operation of the die head. Customarily, a die head of this type performs its designated thread-cutting operation by being advanced axially over the work with its chasers in thread-cutting engagement therewith, while the work is held axially immovable but is turned at a rate appropriate for the formation of the desired thread. At the end of a thread-cutting operation, the latch of my prior die head is released from the operating ring to permit quick spring-return of the latter into its retract position before the die head is axially withdrawn from the threaded work. The carrier of my prior die head also carries an axially slidable trip bar, and the aforementioned latch is a pin on a pivoted lever on a'retainer plate which is mounted on the carrier. The latch lever is normally spring-urged into latching position, and is actuated by the trip bar in either one of two alternate ways to achieve automatic release of the operating ring from the latch pin on conclusion of a thread-cutting operation of the die head. Thus, the trip bar may, toward the end of the axial advance of the die head during a thread-cutting operation on work, move into engagement with a fixed stop and hold the latch lever against further advance movement with the die head, whereupon the operating ring will move out of locking engagement with the latch pin and be spring-returned to its retract position at the end of the thread-cutting operation; As an alternative to using a fixed stop for the tripping of the latch lever, the latter may be linked by the trip bar to a mounting head which is yieldingly connected with the die head and imparts to the same the requisite advance motion for a thread-cutting operation. With this arrangement, the operating ring will move out of locking engagement with the latch pin on stopping the advance motion of the mounting head prior to the conclusion of the thread-cutting operation while the die head is drawn further forward by virtue of the engagement of its chasers with the thread being cut on the turning work.

While it has previously been stated that the operating ring becomes locked to the latch pin on turning the former into its cutting position, the actual lock 15 between the latch pin and an angularly adjustable latch on an auxiliary ring which turns with and is angularly adjustable on the operating ring, permitting thereby radial adjustment of the chasers for cutting thread on work of different diameters on angularly adjusting the "auxiliary ring, and permitting further radial adjustment of the chasers for rough-cutting and fine-cutting, for ininstance, on angularly adjusting the latch on the auxiliary ring. The auxiliary ring and the latch are guided for angular adjustment in an annular recess in the operating ring, and the latch, which is an arcuate member, is retained on the auxiliary ring by having low extension lugs at its ends project beneath releasably mounted gib plates on the auxiliary ring with sufficient lengthwise clearance to permit angular adjustment of the latch on the auxiliary ring. The angular adjustment of the arcuate latch is are complished by manipulating a readily accessible cut-selecting handle which has a circular hub that is fittedly received in a radial groove in the auxiliary ring and provided with an eccentric shank pivotally received in the latch. Normally urging the operating member into its retract position is a compressed helical return spring which extends arcuately in the aforementioned annular recess in the operating ring between the auxiliary ring and the aforementioned retainer plate on the carrier. One end of this return spring bears against one of the aforementioned gibs and the other end thereof bears against a projecting pin on the retainer plate.

It is an important object of the present invention to provide a die head of this type which is of shorter length, has fewer parts, and is quicker and easier assembled and disassembled, than my aforementioned prior die head.

Thus, it is an object of the present invention to provide the auxiliary ring with a peripheral groove with which the arcuate latch is slidably interlocked for its retention on the auxiliary ring, eliminating thereby the aforementioned gibs of my prior die head, and further eliminating the task of mounting these gibs on and removing them from the auxiliary ring, and instead accomplishing the retention of the latch on and its release from the auxiliary ring by mere lateral placement of the latch into interlock with and lateral removal from interlock with the peripheral groove of the auxiliary ring when the latter is removed from the annular recess in the operating ring.

It is another object of the present invention to have the hub of the cut-selecting handle fittedly received in a radial groove in the arcuate latch and pivoted on an eccentric pin projecting from the auxiliary ring into the groove, thereby not only providing for a rotary mount of the handle hub with minimum strain on its pivot, but

also permitting narrower construction of the auxiliary ring and a correspondingly shorter overall length of the present die head as compared to that of my prior die head.

It is a further object of the present invention to provide'the auxiliary ring with a groove in which the return spring for the operating ring extends with part of its diameter, permitting thereby even narrower construction of the auxiliary ring and corresponding further reduction of the overall length of the die head.

It is another object of the present invention to have one end of the return spring for the operating ring bear directly against an end of the arcuate latch, permitting thereby the use of a long spring which not only has I more uniform spring characteristics throughout its aidjustable operating range, but will also tire less over an extended period of use, than the spring in my prior die head which is necessarily shorter because it bears against a gib rather than against the latch directly.

A further object of the present invention is to have provisions for the installation of the aforementioned return spring in and its removal from the present die a head with much less effort and skill than is required for the installation of the return spring in and its re moval from my prior die head.

Another object of the present invention is to have provisions in the present die head to facilitate the task of bringing the cams on the operating ring into cooperative relation with the chasers after installation of the latter in the operating ring.

It is another object of the present invention to have a structurally simple adapter, as a substitute for the structurally more complicated and more costly latching and tripping provisions of the present die head, for the release of the operating ring for spring-return to its retract position when the die head is drawn away from its mounting head by the turning work being threaded after the forward motion of the mounting head has been stopped prior to the conclusion of a thread-cutting operation of the die head.

Further objects and advantages will appear to those skilled in the art from the following, considered in conjunction with the accompanying drawings.

In the accompanying drawings, in which certain modes of carrying out the present invention are shown for illustrative purposes:

Fig. l is a side view of a die head embodying the present invention;

Fig. 2 is a front view of the same die head;

Fig. 3 is a longitudinal section through the die head, taken substantially on the line 3-3 of Fig. 2;

Fig. 4 is a cross section through the die head, taken substantially on the line 4-4 of Fig. 3;

Fig. 5 is a transverse section through the die head, taken substantially on the line 5-5 of Fig. 4;

Fig. 5A is a fragmentary section through a part of the die head;

Fig. 6 is a transverse section through the die head, taken substantially on the line 6-6 of Fig. 4;

Fig. 7 is a fragmentary longitudinal section through the die head, taken substantially on the line 7-7 of Fig. 4;

Fig. 8 is a cross-section through the die head, taken on the line 8 8 of Fig. 1;

Fig. 9 is another cross-section through the die head, taken substantially on the line 9-9 of Fig. 3;

Figs. 10, 11 and 12 are sections similar to Fig. 9 but showing certain operating parts of the die head in different relative positions;

Fig. 13 is a cross-section through the die head, taken substantially on the line 13-13 of Fig. 1;

Fig. 14 is a fragmentary front view of the die head .1

with the thread-cutting chasers removed therefrom;

Fig. 14A is a fragmentary section taken on the line 14A-14A of Fig. 14;

Fig. 15 is a side view of a modified die head embodying the present invention;

Fig. 16 is an end view of a prominent sub-assembly of the modified die head of Fig. 15;

Fig. 17 is a section taken on the line 17-17 of Fig. 16;

Fig. 18 is a part-elevational and part-sectional view of the modified die head;

Fig. 19 is a fragmentary section through the subassembly of Fig. 16, indicating a mode of assembly of certain parts of the sub-assembly;

Fig. 20 is a fragmentary section taken on the line 20-20 of Fig. 18;

Fig. 21 is a section taken on the line 21-21 of Fig. 19; and

Fig. 22 is a perspective view of a certain detail element of the modified die head.

Referring to the drawings, and more particularly to Figs. 1 to 3 thereof, the reference numeral 30 designates a die head having a thread-cutter unit 32 and a mounting head 34 therefor. The thread-cutter unit 32 comprises a chaser carrier 36, an operating member 38, a

retainer member 40, chaser adjustment provisions 42, and automatic chaser retiring provisions 44.

The carrier 36 is cylindrical and provided at its front with an enlarged head 46 which is centrally recessed at 48 and provided with a plurality of equiangularly spaced radial guideways 50 for thread-cutting chasers 52. In the present instance, there are four guideways 50 for four chasers 52. The carrier head 46 is in its rear provided with an annular recess 54 which intersects the guideways St The carrier 36 is at its rear provided with a cylindrical shank 56 for the reception of the retainer member 40.

The operating member 38 is in the form of a ring which is journalled on the carrier 36 (Figs. 3 and 13) and is held with its front face 60 against the adjacent rear face 62 of the carrier head 46 in a manner described hereinafter. Projecting forwardly from the front face 60 of the operating ring 38 and into the annular recess 54 in the carrier head 46 are four identical equiangularly spaced cam lugs 64 (Figs. 2, 3 and 5) which are normally received in transverse grooves 66 in the rear faces 63 of the chasers 52 in the adjacent guideways 50 (Fig. 6). The cam lugs 64 serve to move the chasers 52 in their guideways 59 inwardly into thread-cutting engagement with work and outwardly from cutting engagement with work on turning the operating ring 38 counterclockwise and clockwise, respectively, as viewed in Fig. 2, within a normal operating range to be described.

The carrier 36 is in its periphery provided with a groove 70 (Fig. 13) the angular extent of which defines the aforementioned normal operating range of the ring 38 within which the latter may be turned for moving the chasers 52 into and out of thread-cutting engagement with work. The peripheral groove 70 in the carrier 36 is substantially semi-circular in cross-section (Fig. 3) for the normal fitted reception of substantially onehalf of a steel ball 72 which is also normally received in a cross-sectionally part-circular groove 74 in a plunger 76 in the operating ring 38 to prevent axial movement of the ring 38 on the carrier 36 and permit rotation of the former on the latter within the aforementioned operating range defined by the peripheral extent of the groove '70 in the carrier. The plunger '76 is slidably received in an aperture 78 in the operating ring 38 and is normally urged by a spring 80 into the ball-locking position shown in Fig. 13 in which one end of a peripheral groove 82 in the plunger bears against a stop pin 84 in the operating ring. In order to release the ball 72 from interlock with the groove 70 in the carrier 36, to permit axial removal of the operating ring 33 from the latter or to permit rotation of the operating ring on the carrier outside its normal operating range for purposes hereinafter described, the plunger 76 is deprcssed to bring a groove 86 with a preferably part-spherical bottom 88 in the plunger into registry with the ball 72. The groove 86 in the plunger 76 is sufficiently deep to accommodate the entire ball 72 and thus release the operating ring from the carrier. The opening 89 in the operating ring through which the ball 72 normally projects is of slightly smaller diameter than the ball, so that the latter is retained in the aperture 78 even when the operating ring is removed from the carrier.

The chaser adjustment provisions 42 comprise an auxiliary or adjustment ring 90 and a latch 92 (Figs. 4, 6 and 9), of which the ring 90 serves for the radial adjustment of the chasers 52 for cutting thread on work of different diameters, and the latch 92 serves for radial adjustment of the chasers 52 for selective rough,

" medium and fine cutting performance by the same, all as more fully described hereinafter. The auxiliary ring 90 is turnable in an annular recess 94 in the rear end of the operating ring 38 (Figs. 3 to 7) and rests against the bottom 96 of the recess 94. Projecting from the auxiliary ring 90 into an arcuate groove 98 in the bottom 96 of the annular recess 94 in the operating ring 38 is an adjustment stud 100 (Figs. 3 and 13) which is engaged on opposite sides by adjusting

screws

102 and 104 that are threadedly received in the operating ring 38. The auxiliary ring is thus angularly adjustably coupled to the operating ring 38 by the stud and the

screws

102 and 104, and angular adjustment of the auxiliary ring 90 relative to the operating ring 38 is accomplished by simple adjustment of the

screws

102 and 104 which are readily accessible from the outside of the die head.

The auxiliary ring 90 is provided with a diametrically reduced cylindrical extension 106 which, as shown in Fig. 6, extends to the rear end of the operating ring 38. The ring extension 106, which is interrupted or cut-away at 108 and 110 (Figs. 4, 9 and 10) for purposes which will appear obvious hereinafter, leaves in the annular recess 94 a ring-like space 112 a length of which is occupied by the arcuate latch 92. For its retention on the auxiliary ring 90 and its guidance in an arcuate path into diiferent positions of angular adjustment on the auxiliary ring, the latch 92 is received with a sliding fit between the annular wall 114 of the operating ring 38 and the ring extension 106 and is interlocked over the'greater part of its length with a lateral guide rib formation 1-16on the ring extension 106. The guide rib formation 116 extends from the cut-away 108 in the ring extension 106 approximately to the place indicated at 118 in Fig. 4, and from there extends part-way around the ring extension 106 as a canted lip 120 of the cross-section shown in Fig. 3, for instance. While the rib formation 116 on the ring extension 106 securely retains the latch 92 on the auxiliary ring 90 when the latter is installed in the annular recess 94 in the operating ring 38, the latch 92 may readily be laterally removed from the auxiliary ring when the latter is removed from the annular recess 94 in the operating ring.

The latch 92 is angularly adjustably coupled to the auxiliary ring 90. To this end, the face 122 of the latch next to the auxiliary ring 90 (Fig. 6) is provided with a radial groove 124 (Figs. 5 and 9) for the fitted reception of the circular hub 126 of a cut-selecting handle or lever 128 which for ready manipulation extends through a peripheral slot 130 in the operating ring 38 to the outside of the latter. Projecting from the auxiliary ring 90 into the radial groove 124 in the latch 92 is a pin 132 (Figs. 5 and 9) which serves as an eccentric pivot for the hub 126 of the cut-selecting lever 128. Accordingly, on turning the cut-selecting lever 128 into different angular positions, the latch 92 will be angularly adjusted relative to the auxiliary ring 90. Provisions are also made for yieldingly arresting the cut-selecting lever 128 in a plurality of most frequently used cutselecting positions, in this instance three positions for rough, medium and finish cuts. To this end, the face of the hub 126 of the lever 128 which is adjacent the auxiliary ring 90 is provided with three equiangularly spaced depressions 134 (Fig. 9) any one of which may be engaged by a spring-urged ball-type detent or plunger 136 in the auxiliary ring.

The chasers 52 are normally yieldingly retracted from work by means of an axially compressed helical retract or return spring 140 which extends arcuately in a part of the aforementioned ring-like space 112 and is retained therein by the canted lip 120 on the auxiliary ring 90 (Figs. 3 and 4). The return spring 140 bears with one end against the end 142 of the latch 92, and with its other end against a pin 144 which projects from the previously mentioned retainer member 40 into the ringlike space 112. The retainer member 40 is in the form of a ring which bears against a shoulder 146 on the carrier 36 and is removably mounted thereon by bolts 148 (Fig. 7). The retainer member or ring 40 not only holds the auxiliary ring 90 and latch 92 in the annular recess 94 in the operating ring 38, but also holds the operating ring 38 against axial removal from the carrier 36 even when the hereinbefore described plunger 76 is depressed. When the retainer ring 40 is mounted on the carrier 36 as described, the spring-backing pin 144 thereon will be located in the position shown in Figs. 4 and 11 in which it will hold the return spring 140 axially compressed even when the same is lengthwise expanded to its maximum extent during normal use of the die head, i. e., when the operating ring 38 and the

adjustable parts

90 and 92 thereon are in the retract position shown in Fig. 11 in which the chasers 52 are retired from work. Rotation of the operating ring 38 and parts carried thereby beyond the retract position (Fig. 11) under the urgency of the compressed return spring 140 is prevented by the ball 72 which then bears against the left end of the peripheral groove 70 in the carrier 36 as viewed in Fig. 13.

In order to advance the chasers 52 radially inwardly into thread-cutting engagement with work, the operating ring 38 is, by means of a readily accessible operating or resetting handle 156 thereon, turned against the compression of the return spring 140, clockwise as viewed in Fig. 11, into the cutting position shown in Figs. 4 and 9 in which the latch 92 becomes locked to a yielding latch pin 158 on the retainer ring 40. Clockwise rotation of the operating ring 38 from the retract position in Fig. 11 to the cutting position in Fig. 4 will appear as counterclockwise rotation of the operating ring as viewed in Fig. 2, and it will be readily observed in the latter figure that such counterclockwise rotation of the operating ring will indeed cause the cam lugs 64 thereon to move the chasers 52 inwardly in their guideways 50. Inasmuch as the compression of the return spring 140 is quite considerable when the operating ring 30 is in its cutting position (Fig. 4), the latch 92 is preferably provided with a hardened steel plate 160 which locks with the latch pin 158 and shows little wear even after long,

use. Further, to prevent rapid wear of the mounting bolts 148 of the retainer ring 40 and their subjection to excessive shearing stresses when the latch pin 158 is, through intermediation of thelocked latch 92 (Fig. 4), subjected to the considerable compression of the return spring 140, the retainer ring 40 is coupled to carrier 36 so that the mounting bolts 148 serve merely to hold the retainer ring against the shoulder 146 on the carrier (Fig. 7 The coupling between the retainer ring 40 and the carrier 36 comprises opposite coupling ribs 162 on the retainer ring 40 having opposing machined surfaces 164 which are in coupling engagement with opposite machined surfaces 166 of a central coupling rib 168 on the carrier 36 (Figs. 3, 4 and 9). The end of the coupling rib 168 on the carrier constitutes the shoulder 146 against which the retainer ring 40 is held by the mounting bolts 148 (Figs. 4 and 7).

After a concluded thread-cutting operation of the chasers 52, the operating ring 38 is released for spring return from the cutting position in Fig. 4 into the retract position shown in Fig. 11 on withdrawing the latch pin 158 from locking engagement witth the latch 92. The latch pin 158 is carried by a latch lever 170 which is mounted for pivotal movement on the retainer ring 40 (Fig. 3). The latch pin 158 has a threaded shank 172 which extends through the latch lever 170 and receives a nut 174. Preferably, the nut 174 is sufiiciently tightened against a spring washer 175 to mount the latch pin 158 securely on the latch lever 170, yet permit slight rotation of the latch pin on the latch lever so that the former may be self-positioning for even surface engagement with the latch 92 with a minimum of wear to the latch pin. In order to limit rotatability of the presently square latch pin 158, the same projects into a somewhat wider transverse groove 176 in the latch lever 170 (Figs. 3 and 8). The latch lever 170 itself is removably mounted in a radial groove 178 in the retainer ring 40 (Figs.3 and 8) by means of a spring-urged plunger 180 which is received in aligned notches 182 and 184 in the latch lever 170 and retainer ring 40, respectively, and extends into a recess 186 in the carrier 36. The plunger 180 is at one end provided with a frusto-conical head 188 which is seated in a correspondingly shaped socket-like portion 190 of the notch 182 in the latch lever 170. Surrounding that part of the plunger 180 which extends into the recess 186 in the carrier 36, and interposed between the retainer ring 140 and a head 194 on the other end of the plunger 180, is a compression-type spring 192 which, through intermediation of the plunger 180, draws the latch lever 170 fully into its reception groove 178, i. e., into the position shown in Fig. 3 in which the latch lever and its latch pin 158 are in latching position. Accordingly, the spring-urged plunger 180 not only holds the latch lever 170 yieldingly in its latching position, but acts also as a pivot for the latch lever, as will be readily understood. Moreover, the latch lever 170 is readily assembled with or disassembled from the retainer ring 40 when the latter is dismounted from the carrier 36, by

simply laterally inserting the spring-urged plunger 180 .2

into or laterally removing the same from the aligned notches 182 and 184 in the latch lever 170 and retainer ring 40.

The mounting head 34 comprises, in the present instance, two parts 200 and 202 (Figs. 1 and 3) having

head flanges

204 and 206, respectively, which are secured to each other by means of bolts 208 the heads 210 of which are preferably received in recesses 212 in the flange 204 of the part 200 (Fig. 6). The part 200 is provided with a forwardly extending cylindrical shank 214 on I! which the carrier 36 is mounted for sliding movement. The other part 202 of the mounting head 34 has a rearwardly extending shank 216 which may be mounted in the turret of a screw machine or in any other suitable holder. The flange 204 of the part 200 of the mounting head is also provided with a lug extension 218 which is apertured at 220 for the extension therethrough with clearance of a part of a tripping device 224 to be described.

For a reason which will become evident hereinafter,

the thread cutter unit 32 is operatively connected with the mounting head 34 to permit limited yielding forward movement of the former relative to the mounting head 34. To this end, there are provided two diametrically opposite spring-urged plungers 230 (Fig. 5) each of J which is laterally rcrnovably received in aligned notches 232 and 234 in the retaining ring 40 and extends into a recess 236 in the carrier 36. Each of the plungers 230 extends also beyond the retainer ring 40 and is provided at its outer end with an enlarged head 238 which groove 240 in the head 238 of each plunger 230 for releasably connecting the latter with the mounting head. Surrounding a major length of each plunger 230 and interposed between an end head 248 thereof and a shoulder 250 between the notches 232 and 234 in the retainer member 40 is an axially compressed retraction spring 252. It follows from Fig. 5 that the spring-urged plungers 230, removably mounted as described, will tend to yieldingly retract the thread cutter unit 32 toward the mounting head 34 if the former is moved forwardly in the direction of the arrow 254 (Fig. 5) relative to the mounting head 34.

The thread cutter unit 32 is, despite the tendency of the spring-urged plungers 230 to draw the same into abutting engagement with the mounting head 34, normally held in spaced relation with the latter by means of diametrically opposite spring-urged plungers 260 (Fig. 6) which are slidably received in the retainer ring 40 and have heads 26?. that project into recesses 264 in the carrier 36. Also received in the recesses 264 and interposed between the bottoms of the latter and the plunger heads 262 are compression-type springs 266 which overpower the retraction springs 252 of the plungers 230 (Fig. 5) and normally urge the plunger heads 262 into engagement with the retainer ring 40 so that the plungers 260 will normally yieldingly hold the thread cutter unit 32 spaced from the mounting head 34 to the extent indicated in Figs. 5 and 6.

Inasmuch as the die head is for a conventional threadcutting performance moved axially at a rate required for the formation of a desired thread, but is not rotated, and since the work being threaded is turned for the formationof the thread thereon by the advancing chasers of the die head, provisions are made to hold the thread cutter unit 32 against rotation on the mounting head 34 which is non-rotatably held in the turret of a screw machine or other holder, as previously mentioned. To this end, the retainer ring 40 carries two diametrically opposite coupling pins 270 (Figs. 5A and 8) each of which is slidably received in a bushing 272 in the part 200 of the mounting head 34 and projects into a clearance hole 274 in the other part 202 of the mounting head.

The previously mentioned tripping device 224 (Fig. 3) comprises a tripping bar 276 which is axially slidable in a bracket 278 on the carrier 36 and has its forward end formed as a tripping head 280. The bracket 278 is fittingly received in a recess 277 in the carrier 36 and is removably mounted therein by a screw 279 (Figs. 2 and 3). Threadedly received in the rear end of the tripping bar 276 is a stud 282 having a head 284 which is provided with an elongated slot 286 and a hole 288 that extends transversely of the slot 286. The head 284 on the stud 282 extends with clearance through the aperture 220 in the lug extension 218 on the part 200 of the mounting head 34. A nut 290 serves to lock the stud 282 to the tripping bar 276 in any adjusted position therein. Threadedly received on the stud 282 is a tripping member 292 having a disc portion 294 for engagement with opposite curved projections 296 on the latch lever 170 (Figs. 1 and 3). The tripping member 292 is also provided with a hexagonal head 298 for its ready axial adjustment on the stud 282 by means of a wrench or other convenient tool. Removably received in a hole 300 in the lug extension 218 on the part 200 of the mounting head 34 is a coupling pin 302 which extends through the aperture 220 in the lug extension 218.

The tripping device 224 may be used in either of two alternative ways for the automatic release of the locked operating ring 38 in its cutting position for spring-return to its retract position at the end of a thread-cutting performance of the die head. With the removable coupling pin 302 extending through the elongated slot 286 in the head 284 of the stud 282 of the tripping device as shown in Figs. 1 and 3, the latter is adapted for cooperation with a fixed stop (not shown) to bring about the retraction of the latch pin 158 from locking engagement with the latch 92 at the end of a thread-cutting performance of the die head. Thus, the tripping head 280 of the tripping bar 276 will, during the forward or advance motion of the die head during a thread-cutting operation and just prior to the conclusion of the latter, engage a fixed stop and be held thereby against further advance movement with the die head. Since the disc portion 294 of the tripping member 292 is then in engagement with the curved projections 296 on the latch lever 170 (Fig. 3),

the latter will also be held against further advance movement with the die head, with the result that the latch lever 170 and its pin 158 will soon be rocked out of latching position and release the latch 92 for springreturn of the operating member 38 into its retract position. In order that the latch lever 170 may thus be rocked without interference from the nearby mounting head 34, the head flange 204 of the part 200 thereof is recessed at 306 to provide clearance for the mounting 5 nut 174 of the latch pin 158 (Fig. 3). Of course, threads 9. of variable lengths may be cut by the die head with the arrangement of the tripping device 224 as shown in Fig. 3, by simply adjusting the stud 282 in the tripping bar 276, or the tripping member 292 on the stud 282, or both.

As an alternative to the above-described use of the tripping device with a fixed stop, the tripping device may be linked to the latch lever 170 and to the lug extension 218 on the mounting head 34. To this end, the coupling pin 302 is temporarily removed and the tripping device 224 is turned 90 degrees from the position shown in Fig. 3 to bring the hole 288 in the head 284 on the stud 282 into axial alignment with the hole 300 in the lug extension 218 on the mounting head 34, whereupon the pin 302 is inserted into the aligned

holes

288 and 300 for coupling the tripping device to the mounting head. With this arrangement of the tripping device, the length of the latter which links the latch lever 170 with the mounting head 34 will trip the latch lever and cause it to rock from latching position when the forward motion of the mounting head 34 is stopped while the thread-cutter unit 32 continues its forward motion by virtue of the engagement of the chasers 52 with the work being threaded. As soon as the operating ring 38 is released for spring-return to its retract position, the spring-urged plungers 230 (Fig. 5) will retract the cutter unit 32 into its normal axial disposition on the forward shank 214 of the mounting head 34.

While the operating ring 38 is in its retract position (Fig. 11) the latch pin 158 rests against the adjacent face 312 of the latch 92 (Fig. 4), and the latch pin is ready to snap into locking engagement with the latch 92 on turning the operating ring 38 into its cutting position, as will be readily understood.

Angular adjustment of the auxiliary ring 90 relative to the operating ring 38 by means of the adjusting screws 102 and 104 (Fig. 13) will result in radial adjustment of the chasers 52 for cutting thread on work of different diameters. This Will be more readily understood by assuming that the latch 92 is locked to the latch pin 158 (Fig. 4) when the auxiliary ring 90 is being angularly adjusted. Thus, the operating ring 38 and the

parts

90 and 92 thereon are spring-urged against the latch pin 158, and any angular adjustment of the auxiliary ring 90 relative to the operating ring 38 will inevitably result in relative rotation between the latter and the carrier and, consequently, in like relative rotation between the cam lugs 64 on the operating member and the chasers 52 in the carrier (Fig. 2). Of course, the same radial adjustment of the chasers for cutting thread on work of different diameters is achieved by angularly adjusting the auxiliary ring 90 on the operating member while the latter is in its retract position.

Angular adjustment of the latch 92 on the auxiliary ring 90 by means of the cut-selecting lever 128 will result in further radial adjustment of the chasers 52 in the carrier 36. This will also be more readily understood by assuming that the latch 92 is locked to the latch pin 158 (Fig. 4) when the latch is being angularly adjusted on the auxiliary ring 90. Thus, the operating ring 38 and the auxiliary ring 90 and latch 92 thereon are spring-urged against the latch pin 158, and any angular adjustment of the latch 92 relative to the auxiliary ring will inevitably result in relative rotation between the operating ring 38 and the carrier 36 and, consequently,

in like relative rotation between the cam lugs 64 on the operating member and the chasers 52 in the carrier issu ning that the latch 92 is locked to the latch pin 158, the hub 126 of the cut-selecting lever 128 will, on turning the latter from the position shown in Fig. 9 to that shown in Fig. and by the action of the eccentric pivot 132, turn the auxiliary ring 90 and coupled operating ring 38 slightly clockwise as viewed in Fig. 10, resulting in equal turning movement of the.

- purposes, are eliminated.

cam lugs 64 in counterclockwise direction, however, as viewed in Fig. 2, and hence, in slight radial inward movement of the chasers 52. Accordingly, rotation of the cut-selecting lever 128 from the position in Fig. 9

. to the position in Fig. 10 will result in slight radial inward motion of the chasers 52 for a rough cut by the same. Conversely, rotation of the cut-selecting lever 128 from the position in Fig. 10 to the position in Fig. 9 will result in slight radial outward motion of the chasers 52 for a fine cut by the same. A medium cut by the chasers 52 is achieved by turning the cut-selecting lever 128 into a position intermediate those shown in Figs. 9 and 10.

If desired, a thread may first be formed on work with a rough cut by turning the cut-selecting lever 128 into the rough-cut position shown in Fig. 10. After the thread is roughed in the work, the thread may be finishcut by turning the cut-selecting lever 128 into the fine-cut position in Fig. 9. At the end of the fine-cut performance of the chasers 52 on the work, the operating ring 38 will be spring-returned to its retract position and the inertia then imparted to the cut-selecting lever 128 will jar the same from its fine-cut position (Fig. 9) and throw it into its rough-cut position (Fig. 10), ready for the initial rough cut on the next work to be threaded.

The instant die head is, in comparison to my aforementioned prior die head, simpler in construction, of shorter overall length, and easier to assemble or disassemble. Thus, by slidably interlocking the latch 92 directly with the ring extension 106 on the auxiliary ring 90, as described, the gibs used heretofore for the retention of the latch on the auxiliary ring and the task of mounting these gibs on and dismounting them from the auxiliary ring for latch assembly and disassembly In slidably interlocking the latch 92 with the auxiliary ring 90, as described, the return spring 140 for the operating ring 38 may be made longer than heretofore, securing thereby the advantage that the spring will have more uniform spring characteristics throughout its adjustable operating range and will tire less over an extended period of use. The overall length of the present die head is reduced from that of my aforementioned prior die head by providing the radial groove 124 for the reception of the hub of the cut-selecting lever 128 in the latch 92, rather than in the auxiliary ring as heretofore. The overall length of the present die head is further reduced by a further reduction of the width of the auxiliary ring and latch assembly which is accomplished by providing the auxiliary ring 38 with an arcuate groove 320 in which 'the return spring 140 extends with part of its diameter (Figs. 3 to 6). Further, the mounting of the hub of the cut-selecting lever 128 on the eccentric pin 132, which is, in turn, mounted in the auxiliary ring 90, saves the eccentric pin from undue strain and wear from the hub 'of the cut-selecting lever.

ring-like space 112 defined by the auxiliary ring 90 in the annular recess 94 in the operating ring 38 (Fig. 4), and underneath the canted lip on the ring extension 106 without interference from the spring-backing pin 144 on the retainer ring 40. However, the then non-compressed return spring thus placed in the die head will, even when bearing against the end 142 of the latch 92 (Fig. 4), be in the way, and prevent the entry into the ring-like space 112, of the spring-backing pin 144 when the retainer ring 40 is re-mounted on the carrier 36. Ac-

cordingly, the non-compressed return spring 140 will have to be moved out of the way of the spring-backing pin 144 on the retainer ring in order to permit the reas= sembly of the latter with the rest of the thread-cutter unit' 32. To this end, the spring-urged plunger 76 is depressed to release the operating ring 38 for rotation on the carrier 36 outside of its normal operating range, whereupon the operating ring 38 and the

parts

90 and 92 carried thereby are turned counterclockwise from the position in Fig. 4 into a position like or similar to that shown in Fig. 12. In the course of such out-of-normal-range rotation of the operating ring 38 and the

parts

90 and 92 thereon into the position shown in Fig. 12, the auxiliary spring retainer pin 322 will engage the adjacent end of the return spring 140 and move the same out of the region in the ring-like space 112 into which the spring bac'king pin 144 on the retainer ring 40 will normally project when the latter is re-mounted on the carrier 36 (Fig. 12). After remounting the retainer ring 40 on the carrier 36, the operating ring 38 and the

parts

90 and 92 thereon are returned to their normal operating range on the carrier by clockwise rotation of the operating ring as viewed in Fig. 12 into its normal retract position (Fig. 11) in which the ball 72 is again interlocked with the left end of the peripheral groove 70 in the carrier (Fig. 13). During this return rotation of the operating ring 38 from the position shown in Fig. 12 into the normal retract position shown in Fig. 11, the return spring 140 will follow the auxiliary spring-retainer pin 322 until the latter passes the spring-backing pin 144, whereupon the return spring will bear against the latter and become axially compressed thereby, during the remainder of this return rotation of the operating ring, to the extent required for normally urging the latter into its retract position.

For initial assembly of the chasers 52, or their reassembly after sharpening, with the carrier 36, or for replacement of a chaser 0r chasers, the spring-urged plunger 76 is depressed to release the operating ring 38 for rotation on the carrier 36 outside its normal operating range into a position like or similar to that shown in Fig. 14 in which the cam lugs 64 on the operating ring are fully retracted from the guideways in the carrier 36. The chasers 52 may thereupon be radially inserted in the guideways 50. In order to facilitate the entry of the cam lugs 64 into the tranverse grooves 66 in the rear of the inserted chasers 52 on returning the operating ring 38 to its normal operating range on the carrier 36, there are provided in the front face of the operating ring 38 four pairs of spring-urged detents 330, one pair for each chaser, which are exposed to the guideways 50 when the operating ring is turned to the out-of-normal-range posi* tion shown in Fig. 14. Each of these detents 330 is in this instance a steel ball (Fig. 14A) retained in a cage 332 in the carrier and normally urged by a compressiontype spring 334 to project slightly forward of the front face 60 of the carrier. The spring-urged balls or detents 330 of each pair are spaced radially from each other to such an extent that they will yieldingly engage the opposite side walls of the transverse groove 66 in the adjacent inserted chaser 52 and thus yieldingly hold the latter with its transverse groove 66 in alignment with the adjacent cam lug 64 which will move into registry with the groove 66 on returning the operating ring from the chaser-inserting position shown in Fig. 14 into its normal operating range on the carrier 36.

The operating ring 38 is also provided with a stop pin 336 (Figs. 7 and 12) which projects through a periphcral notch 333 in the auxiliary ring 90 into the ring-like space 112 and engages the spring-backing pin 144 on the retainer ring 40 when the operating ring 38 is turned into the chaser-inserting position shown in Fig. 14 in which the pairs of spring-urged detents 330 are fully exposed in the guideways 50 in the carrier 36. To accomplish engagement of the stop pin 336 with the spring-backing pin 144 for full exposure of the spring-urged detents 330 in the guideways 50, it may be necessary to change the angular adjustment of the auxiliary ring on the op erating ring 38.

Reference is now had to Figs. 15 and 18 which show a modified die head 30. More particularly, the modified die head 30' is in all respects like the hereinbefore described die head 30, except that the retainer ring 40, the latch lever 170, the tripping device 224 and the mounting head 34 of this previously described die head 30 have been replaced by a structurally much simpler and less costly adapter 340. The adapter 340 comprises two main parts 342 and 344 (Figs. 16 and 17) of which the part 342 takes the place of the previously described retainer ring 40,. and is received on the rearwardly extending shank 56 on the carrier 36 (Fig. 18) and mounted on the latter by the same bolts 148. Like the previously described retainer ring 40, the part 342 has in its front face 346

opposite coupling ribs

348 and 350 which in the mounted condition of the part 342 are in coupling engagement with the central coupling rib 168 at the rear end of the carrier 36 (Fig. 4). The part 344 of the adapter 340 takes the place of the previously described mounting head 34 and is provided with a head flange 352 and a rearwardly extending shank 354 which is mounted in the turret of a screw machine or any other holder. The part 344 is normally yieldingly drawn with its flange 352 into an annular recess 356 in the rear of the head flange 358 of the part 342 by means of two diametrically opposite spring-urged plungers 360 which are laterally removably received in notches 362 in the flange 358 of the part 342.

One end of each plunger 360 carries a head 364 which is provided with a V-shaped peripheral groove 366 and is slidably received in an aperture 368 in the flange 352 of the part 344 (Fig. 17). Each plunger 360 is releasably connected with the part 344 of the adapter by a set screw 370 the conical tip 372 of which is received in the V- shaped peripheral groove 366 in the head 364 of the plunger. Surrounding the plungers 360 and interposed between heads 374 thereon and the flange 358 of the part 342 are compression-type springs 376 which, through intermediation of the plungers 360, yieldingly draw the flange 352 of the part 344 of the adapter into the annular recess 356 in the flange 358 of the part 342. in the mounted condition of the adapter 340, the plungers 368 project into the recesses 236 in the carrier 36 (Fig. 5). The plungers 360 carry transverse pins 377 which on engagement with the part 342 limit further yielding separation of the

parts

342 and 344. When the adapter 340 is rnounted, a pin 144' (Fig. 16) on the retainer part 342 projects into the ring-like space 112 in lieu of the previously described spring-backing pin 144 (Fig. 4) and holds the return spring 144 in axially compressed condition.

The part 342 of the adapter 340, which is directly mounted on the carrier 36 of the thread-cutter unit 32',

is further coupledto the part 344 of the adapter by coupling studs 380 (Fig. 16) which are slidably received in bushed apertures (not shown) in the flange 352 of the part 344 of the adapter.

Mounted in aligned

apertures

380 and 382 in the

flanges

358 and 352 of the

parts

342 and 344 of the adapter 340 is a bushing 384 (Figs. l8 and 19) for sliding reception of a latch pin 158', having a shank 386 extending into a peripheral notch 388 in the flange 352 of the part 344. Surrounding the shank 386 of the latch pin 158' and interposed in the bushing 384 between the bottom 392 thereof and the latch pin 158 is a compression-type spring 394 which normally urges the latch pin into the latching position shown in Fig. 18 in which a releasahly interlocked key 396 on the shank 386 of the latch pinbears against the bottom 398 of the peripheral notch 388 in the flange 352 of the part 344.

in operation of the modified die head 30', the same is advanced over the turning work being threaded the same as the previously described die head 30. Toward the end of a thread'cutting performance of the modified die head, the mounting part 344 of the adapter 340 is stopped while the thread-cutter unit 32' and the retainer part 342 of the adapter 340 continue to move forwardly by engagement of the chasers with the work being threaded, with the result that the key 396 holds the latch pin 158' against further forward movement with the threadcutter unit 32' and the latch 92 of the latter will soon be released from locking engagement with the latch pin 153' and permit spring-return of the operating ring 38 into its retract position. As soon as the chasers are retracted from the work, the spring-urged plungers 360 will retract the yieldingly advanced thread-cutter unit 32 with the retainer part 342 of the adapter 340 into engagement with the mounting part 344 of the adapter, as will be readily understood.

Since the mounting screws 148 for the retainer part 342 of the adapter 340 are not accessible without first removing the mounting part 344 of the adapter, and since the key 396 prevents removal of the mounting part 344 of the adapter from its retainer part 342 even after releasing the set screws 370 from the heads 364 of the spring-urged plungers 360 (Fig. 17), it is, for the removal of the thread-cutter unit 32' from the adapter 348, necessary to first release the key 396 from interlock with the shank 386 of the latch pin 158. This is accomplished with the aid of a split ring 400 which is locked in a peripheral groove in the shank 386 of the latch pin 158' directly beneath the key 396 which is normally inter-' locked with the shank 386 by having a straight portion 4% of a slot interlocked with intermediate opposite fiats 464 on the shank 386 (Figs. 18 and 20). For the removal of the key 396 from interlock with the shank 386 of the latch pin 158', the shank 386 together with the key 396 thereon are lifted in any convenient manner against the compression of the spring 394 into a position like or similar to that shown in Fig. 19 in which the tip 406 of a screw driver, for instance, may be applied to the ring 409 to hold the shank 386 with the key 396 thereon outside the confines of the peripheral notch 388 in the flange 352 of the adapter part 344 to permit lateral outward motion of the key out of interlock with the flats 49-4 on the shank and into the position shown in Fig. 21 in which a circular portion 408 of the slot in the key surrounds the shank 386 and permits removal of the key from the shank axially thereof. In mounting the threadcutter unit 32' on the adapter 340, the part 342 of the latter is first assembled with the thread-cutter unit, whereupon the part 342 of the adapter is assembled with the mounted part 344 thereof by locking the heads 364 of the spring-urged plungers 360 to the set screws 370 and interlocking the key 396 with the shank 386 of the latch pin 158 in a manner which is obvious from the foregoing description of the release of the key from the shank of the latch pin.

Since the modified die head of Figs. 15 and 18 dispenses with the previously described tripping device 224, including the bracket 278 thereof, the recess 277 in the carrier.

36 (Figs. 2 and 3) is closed by a filler piece 410 (Figs. 15 and 22) which is retained in the recess 277 by the same screw 279.

The invention may be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention, and the present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

What is claimed is:

1. In a die head having a carrier with substantially eral groove for circular guidance of said latch in said.

recess and its retention on said auxiliary member; an angularly adjustable coupling between said latch and auxiliary member; a projection on said carrier extending into said recess; and a compressed helical spring extending circularly in said recess and being interposed between said projection and one end of said latch, said spring normally urging said operating member into a retract position in which said chasers are disengaged from work, the other end of said latch becoming locked to said latch pin on turning said operating member into an operative position in which said chasers are in thread-cutting engagement with work.

2. The combination in a die head as set forth in claim 1, in which said arcuate latch has in one face thereof a radial groove, and said coupling comprises an operating lever projecting to the outside of said operating member and having a circular hub fittedly received in said groove in the latch, and a pin projecting from said auxiliary member and serving as an eccentric pivot for said hub.

3. In a die head having a carrier with substantially radial guideways for thread-cutting chasers, the combination of an operating member turnable on said carrier and having an annular recess in one end, a shoulder and angularly spaced first and second projections extending within the confines of said recess toward said one end of the member, and cams for moving said guided chasers on turning said members; a retainer element removably mounted on said carrier adjacent said one end of the operating member and having a projection extending into said recess in the latter; cooperating means on said carrier and operating member normally limiting rotation of the latter on the former to a certain operating range of a partial revolution, and operable to release said operating member for rotation outside said operating range, said second projection on said operating member being arranged to pass said projection on said retainer element on rotation of said operating member on said carrier outside said operating range; a releasable latch on said retainer element; and a compressed helical spring extending circularly in said recess and held therein by said retainer element, said spring normally bearing with one end against said first projection on said operating member and with its other end against the projection on said retainer element so as normally to urge said operating member within said operating range into an end position in which said chasers are disengaged from work, said shoulder on said operating member becoming locked to said latch on turning said operating member within said operating range into an operative position in which said chasers are in thread-cutting engagement with work, and said second projection on said operating member engaging said other end of said spring and holding the latter out of that region in said recess in the operating member into which said projection on said retainer element will extend on mounting the latter on said carrier while said carrier and operating member assume an angular relative position outside said operating range.

4. In a die head having a carrier with substantially radial guideways for thread-cutting chasers, an operating member turnable on said carrier and having an annular recess in one end and cams for moving said guided chasers on turning said member, a retainer element removably mounted on said carrier adjacent said one end of the operating member and having a projection extending into said recess, cooperating means on said carrier and operating member normally limiting rotation of the latter on the former to a certain operating range of a partial revolution, and operable to release said operating member for rotation outside said operating range, and a releasable latch pin on said retainer element, the com bination of an auxiliary member turnable in said recess in the operating member and angularly adjustably coupled to the latter for rotation therewith, said auxiliary member having a shoulder and angularly spaced first and second lateral projections extending within the confines of said recess toward said one end of the operating member, said second projection being arranged to pass the projection on said retainer element on rotation of said operating member on said carrier outside said operating range; and a compressed helical spring extend ing circularly in said recess and held therein by said retainer element, said spring normally bearing with one end against said first projection on said auxiliary member and with its other end against the projection on said retainer element so as normally to urge said operating member within said operating range into an end position in which said chasers are disengaged from work, said shoulder on said auxiliary member becoming locked to said latch pin on turning said operating member within said operating range into an operative position in which said chasers are in thread-cutting engagement with work, and said second projection on said auxiliary member engaging said other end of said spring and holding the latter out of that region of said recess in the operating member into which said projection on said retainer element will extend on mounting the latter on said carrier while said carrier and operating member assume an angular relative position outside said operating range.

5. The combination in a die head as set forth in claim 4, further comprising a latch angularly adjustably coupled to said auxiliary member for rotation therewith, one end of said latch constituting said first projection and the other end of said latch constituting said shoulder.

6. In a die head having a carrier with an enlarged front head provided with an annular recess in its rear end and substantially radial guide slots for the reception and guidance of thread-cutting chasers having in the rear transverse grooves within the confines of said annular recess in the carrier head, the combination of an operating member turnable on said carrier and having an end face extending to the rear end of said carrier head and forming with said radial slots guideways in which said chasers are fittedly received, said end face being provided with cam projections extending into said annular recess in the carrier head and being received in the grooves in said chasers, respectively, for moving the latter into and from threadcutting engagement with work on turning said member in opposite directions within a certain operating range; and yielding detent means on said end face of said member located between successive cam projections, respectively, and registering with said guideways only when said cam projections are retracted from the latter on turning said member into a certain position outside said operating range, said detent means being arranged yieldingly to engage the opposite side walls of the transverse grooves of said chasers, respectively, to hold said chaser grooves in alignment with the adjacent cam projections for assured entry of the latter into the former on turning said member from said certain position back into said operating range.

7. The combination in a die head as set forth in claim 6, in which said detent means between each pair of successive cam projections are two spring-urged balls retained in said member and slightly projecting beyond said end face thereof, said balls being spaced radially of said carrier head so that they yieldingly engage the opposite side walls, respectively, of the transverse groove in the adjacent chaser in a radial position of the latter in its guideway in which said transverse chaser groove is in alignment with the adjacent retracted cam projection on said operating member.

8. In a die head having a carrier with substantially radial guideways for thread-cutting chasers, and an operating member turnable on said carrier and having cams for moving said guided chasers on turning said member, and an annular recess in one end and spaced shoulders within the confines of said recess, the combination of a retainer member having front and rear faces and being releasably mounted with its front face on said carrier adjacent said one end of said operating member, said retainer member having at its front face a projection extending into said recess and being provided in its rear face with an annular recess; a helical return spring extending circularly in said recess in the operating member and being held therein by said retainer member, said spring being axially compressed and bearing with its ends against said projection on said retainer member and one of said shoulders on said operating member, respectively, and normally urging the latter into a retract position in which said chasers are retracted from work; a mounting member having a flange received in said recess in the retainer member, said mounting member being coupled to said retainer member and normally yieldingly retained with its flange in said recess in the retainer member, and said retainer member and flange of said mounting member being provided with aligned apertures having a stop shoulder and said flange being provided adjacent said stop shoulder with a peripheral notch into which said aligned apertures lead and which is exposed at the rear face of said flange; a latch pin received with a sliding fit in said aligned apertures and having a cylindrical shank normally extending into said peripheral notch and being within the confines of the latter provided intermediate its length with opposite flats; a key substantially fittedly received in said peripheral notch and having a slot of which a first portion is circular and the remaining portion is straight and interlocked with said flats on the latch pin shank when said key is fittedly received in said peripheral notch; and a compression type spring in said aligned recesses and interposed between said stop shoulder therein and said latch pin to urge the latter into latching position in which to lock with the other of said shoulders on said operating member on turning the latter against the compression of said return spring into an operative position in-which said chasers are in thread-cutting engagement with work, said latch pin being retracted from its latching position to release said other shoulder on said operating member for spring-return of the latter into said retract position on yielding separating movement of said retainer and mounting members, and said key being removable from interlock with the shank of said latch pin on depressing the latter in said aligned apertures to project said key outside the confines of said peripheral notch and registering said circular slot portion in said key with said latch pin shank for axial removal of said key therefrom.

9. The combination in a die head as set forth in claim 8, in which said latch pin shank is between said latch pin and said flats and immediately adjacent the latter periphorally grooved for the reception of a split ring with which to hold said shank with its fiats outside the confines of said peripheral groove for interlock of said key with said shank when said retainer and mounting members are assembled with each other and with said carrier.

10. The combination in a die head as set forth in claim 8, in which said peripheral notch has straight opposite side walls so that the fittedly received key therein will prevent rotation of said latch pin.

References Cited in the file of this patent UNITED STATES PATENTS 2,557,040 Strickland June 12, 1951