US2026471A

US2026471A - Die head

Info

Publication number: US2026471A
Application number: US1771A
Authority: US
Inventors: Hoelzel Otto
Original assignee: EASTERN MACHINE SCREW CORP
Current assignee: EASTERN MACHINE SCREW Corp
Priority date: 1935-01-14
Filing date: 1935-01-14
Publication date: 1935-12-31
Anticipated expiration: 1952-12-31

Description

Dec. 31, 1935. I Q. HQELZEL 2,026,471

DIE HEAD Filed Jan. 14, 1935 4 Sheets-Sheet l man p Dec. 31, 1935.

- o. HOELZEL DIE HEAD Filed Jan. 14, 1935 Dec. 31, 1935. o. HOELZEL 2,026,471

DIE HEAD Filed Jan. 14, 19.35 Sheets-Sheet 3 FIG. 5

, FIG. 6

0. HOELZEL Dec. 31, 1935.

DIE HEAD Filed Jan. 14, 1935 4 Sheets-Sheet "4 Patented Dec. 31, 1935 UNITED STATES PATENT OFFICE DIE HEAD Otto Hoelzel, New Haven, Com, assignor to The Eastern Machine Screw Corporation,

New

Haven, Conn., a corporation of Connecticut 'Application January 14, 1935, Serial No. 1,771

Claims. (01. Ill-420.5)

My invention relates to die heads and while, more particularly, it relates to die heads for cutting taper threads, many of its features are applicable to die heads for cutting straight threads.

Under present commercial practice, it is customary to employ chasers having taper cutting edges to cuttaper threads and the taper of the chaser controls and determines the taper of the threads. The cutting of taper threads in this manner is objectionable because, instead of only the forward or leading teeth of the chasers doing the cutting, as is usual in cutting straight threads, substantially all of the teeth (the num-' ber depending upon the number of threads being cut) of each. chaser join in the cutting operation. This not only throwsa great strain on the teeth behind the forward or leading teeth, but, due to the fact that the chasers make a broad out, each of them, where it stops cutting, leaves a shallow shoulder extending transversely of the threads. Moreover, by having the chasers make a broad cut, there is a tendency to break teeth out of the chasers and the power required to make such a cut is considerably greater than required when the cutting is confined to the leading teeth.-.

Another and important objection to cutting taper threads in this manner is that the taper depends entirely upon the accuracy of the taper originally given to the chasers.

The principal object of the present invention is to provide a die head with simple and improved means for cutting taper threads by gradually moving the chasers, whereby the same free cutting action is obtained as when cutting straight threads.

Another object of the invention is to provide improved means for automatically causing the chasers to move into inoperative positions, after the desired number of threads have been cut.

A further object of the invention is to provide a die head with improved means for chamfering the end of the work being threaded.

A primary feature of the invention consists in providing a die head with rectilinearly movable means cooperable with the chasers for moving them with respect to the body member on which they are mounted for cutting taper threads and v in combining therewith relatively rotatable means for controlling the movement of the rectilinearly movable means.

Another feature of the invention consists in providing the die head with axially movable means adapted to be operated by the work being cut for actuating mechanism controlling the movement of the chasers.

Another and more specific feature oftheinvention consists in providing a die head having a body member and a shank extending rearwardly therefrom with means movable longitudinally of the shank for actuating the chasers which are movably mounted on the body member and with means encircling the shank and rotatable relatively thereto for controlling movel0 ment of the movable means.

A further feature of the invention consists in providing a die head with movable means engageable by the work being threaded for operating the mechanism controlling movement of the .15

chasers, the movable means being provided with spring pressedmeans for chamfering the end of the work being threaded.

Other and more specific features of the invention, residing in advantageous forms, combinations and relations of parts, will hereinafter appear and be pointed out in the claims.

In the drawings, illustrating a preferred eme bodiment of the invention,

Figure 1 is a side elevational view of the di head, with parts thereof broken away, showing the head in closed oroperative position.

Figure 2 is a view similar to Figure 1, additional parts of the head being broken away, showing the head in open or inoperative position.

Figure 3 is a longitudinal sectional view .of the die head.

Figure 4 is an. end view of the die head.

Figures 5 and 6 are sectional views taken on lines 5--5 and 66, respectively, of Figure 3. Figure 7 is a side elevational view of the operating plunger.

Figure 8 is a side elevational view of the opera-ting plunger taken at right angles to the view ure 6.

Figure 14 is a sectional view of the collar and cam ring.

Figure 15 is a sidev elevational view of .the cam ring.

Figure 16 is a side elevational view of the sleeve to which the .cam ring is secured.

Figure 17 'is a front end view of the sleeve shown in Figure 16.

Figure 18 is an elevational view of the ring disposed within the chaser actuating collar.

Figure 19 is a fragmentary end view of the collar.

Figure 20 is a side elevation of one of the'carriers andits associated chaser.

Figure 21 is a fragmentary sectional view taken on a line corresponding to line 68 of Figure 3 of a modified form of the invention.

Referring more particularly to the drawings, 1

designates the body member of the die head which is provided with a rearwardly extending tubular shank 2 for connecting the head to any suitable machine.

for receiving carriers 4 for the chasers 5. The grooves 3 intersect the axial work or stock receiving opening i of the head and they are preferably disposed radially with'respect to the opening. The chasers 5 are preferably of the type disclosed and claimed in the Warren Patent No. 1,937,418 dated November 28, 1933, each being immovably secured to its carrier by a locking screw 1.

The front or leading side of each carrier is provided with an inclined recess 8 for receiving means to be hereinafter described adapted .to move the carrier toward and away from the work receiving opening. 1

The carriers are retained in the grooves 3 by segmental plates-9 secured to the front face of the body member I and they are respectively provided with portions adapted to extend into grooves or recesses l formed in the front or leading side of the carriers.

Encircling the shank 2 and movable longitudinally thereof is a collar. ll having forwardly projecting pins or studs 12 which are adapted to extend into openings in the body member I communicating with the carrier receiving grooves 3. The forward end of each of the pins l3 has a laterally projecting inclined lug I 3 for cooperat- 4 ing with the inclined recess 8 in the adjacent carrier. As the recesses 8 of the carriers are inclined with respect to the axis of the head, it will be appreciated that, when the collar H is moved axially thereof, the carriers and consequently the chasers will be moved either toward or away from the axis, depending upon the direction of movement of the collar with respect to the body member.

Operatively interposed between the collar and head are a plurality of springs ll normally tendmg to move the collar rearwardly with respect to the head. The springs are preferably disposed within oppositely arranged recesses in the head' and collar and, to prevent them from collapsing laterally, centering pins l which extend rearwardly from the head into the springs may be conveniently employed.

Encircling the shank 2 and extending between the latter and the collarll is a sleeve l5 which,

is relatively rotatable with respect to both the shank and collar. Adjacent its inner end, the sleeve is provided with diametrically opposed forwardly extending lugs l1, each of which is pro% vided on one side with a Step portion. to provide a shoulder IS. The lugs I! are preferably formed integrally with a. circumferentially adjust-able The front face of the body member is formed with a plurality of grooves 3 ring l9 which is secured to the sleeve It at the inner end thereof. To prevent relative circumferential movement between the sleeve l6 and ring l9, after these parts have been adjusted in the desired position the inner end of the'ring 5 is serrated, as indicated at 2|, for cooperating with serrated portions provided on the front face of an outwardly projecting annular flange 22 which may be advantageously formed integral with the inner end of the sleeve. Relative axial movement of the ring and sleeve may be conveniently prevented by two screws 23, the inner ends of which are adapted to extend within a circumferential groove 24 formed in the exterior surface of the sleeve closely adjacent the

annulair flange

22, 7

While the sleeve l6 and the ring I9 are relatively rotatable with respect to the shank 2, means is provided for locking these parts against relative axial or longitudinal movement. This means comprises a split nut 25 which is preferably made in two semi-circular sections, the inner surfaces of which are threaded to cooperate with-screw threads 26 formed on the exterior of the shank. Each section of the split nut-has a 25 forwardly extending annular portion 21, the inner surface of which is formed with a groove for receiving a rib or fin 28 projecting outwardly from the annular flange 22 of the sleeve It. The split nut is maintained in assembled position by 30 two screws 29, which may be tightened sufficiently to rigidly clamp the nut to the shank. When in clamping engagement with the shank, the nut prevents relative longitudinal movement between the shank and sleeve, but suflicient clearance is provided between the cooperating portions of the nut'and sleeve to enable the latter to rotate relatively to the nut and consequently also the shank. The forward ends of the lugs H on the ring I! are inclined, as shown at 30, with respect to the 40 longitudinal axis of the head and they are adapted to cooperate with the collar H for restraining the latter from moving rearwardly under the influence of springs I4. Instead of having the lugs I'l engage the collar itself, it is preferred to have them engage a circumferentially adjustable ring 3! which is disposed within an annular re- I cess formed in the rear face of the collar. This ring, which is shown in detail inFigure 18, is retained in assembled relation with the collar bylugs 32 which project inwardly into the recess formed in the rear face of the collar and overlap portions of the outer face of the ring. To enable the ring to be readily assembled with and disassembled from the collar, it is provided on its outer side with recesses or notches 33 of sufficient length to receive the lugs 32. In assembling the ring with the collar, the ring is positioned so that the notches 33 are opposite the lugs 32, at which time the ring may be moved into the recess of .the collar and then subsequently rotated, so that the lugs will overlap portions of the ring on opposite sides of the notches. Theinner surface of the ring 3| is also provided with notches or recesses 34, which,. in addition to affording shoulders 35 with which the inclined ends 30 of the lugs I! are adapted to engage, provide spaces into which the lugs l7 mayproject after the latter have been moved from engagement with the shoulders 35. The inner end 'of the recess of the collar in which the ring 3| is'disposed is preferably additionally ated by the work as threads are being cut thereon is preferably employed for rotating the cam ring Hi. The plunger comprises a hollow cylindrical body portion 3'! having a removable extension 38, the forward end 39 of which is of reduced cross sectional area and has a front face 40 affording an abutment adapted to be engaged by the work during the thread cutting operation. Portion 39 of the extension is preferably of substantially cruciform shape in cross section to provide spaces into which the chasers may, if necessary, extend.

The extension 38 extends rearwardly into the body portion 31 of the plunger, being locked against relative rotation thereto by a key 39a, and it terminates in a threaded stud 4| for receiving a nut 42 for rigidly connecting the extension to the body. -The plunger is provided with oppositely projecting removable shoes or'the like 43 having reduced inner end portions 44 extending within openings in the body portion 31 and enlarged flattened portions 45 projecting into longitudinally extending slots 46 in the shank 2. The

outer ends of each of the shoes is formed with an inclined head or lug 41 which extends into a steep- 1y inclined spiral groove 48 in the inner surface of sleeve I6. The plunger is normally urged forwardly within the spindle by a helical spring 49, one end of which bears against a shoulder within the plunger and the other end of which bears against an annular shoulder 50 projecting into the bore of the spindle. i

The outerend of extension 38 is provided with a transverse groove 5| for receiving a chamfering 'tool.52. This tool is formed with inwardly converging cutting edges 53 adapted to cooperatewith the exterior of the work being threaded for chamfering the outer side of the adjacent end thereof and it is alsoprovided with a nub or the like 54 extending, forwardly between the cutting' edges 53 and having cutting edges 55 for chamfering or reaming theinner side of the work being threaded.

The chamferingtool is loosely connected to the operating plunger so that it may move lonigtudinally with respect thereto and also transversely thereof, the latter movement enabling the tool to adjust itselfto the work and thereby cut evenly.

This loose connection. between the chamfering .tool and the plunger may be advantageously accomplished by providing the tool with an elongated slot 56 for receiving a screw or the like 51 which extends transversely of the groove 5|, the diameter of the screw being somewhat less than the width of the slot.

The screw 51 and slot 56 are so related that, when the chamfering tool is moved forwardly with respect, to the operating plunger, the inner end of the slot engages the screw, but, when the tool is moved rearwardly with respect to the plunger, its inner end engages the bo'ttombr end 58 of the groove 5| in which the tool is disposed.

. The inner end of the chamfering tool is normally maintained in spaced relation to the bottom 58 of groove 5| by a spring pressed'pin 59 which tool and thereby normally maintaining the latter in spaced relation to the bottom of the groove 5|. The chamfering tool is normally disposed in such a position that it will not operatively cooper- ,work before the abutment, the work may engage the abutment without the chamfering tool neces- 10 sarily performing any of its cutting function, because the tool may recede or move inwardly relatively to the plunger by compressing the spring 6|. However, the spring 6| and the pin 60 maintain the chamfering tool in engagement with the 15 work and the tool will continue to gradually out until .its relative forward movement is. arrested by the inner end of the slot 56 engaging the screw 51. Under ordinary conditions, however, the chamfering tool will have completed its cutting 20 operation by the time the work engages the abutment of the plunger. By loosely connecting the chamfering tool with the operating plunger, it will be perceived that not only will the tool readily adjust itself to the pipe or the like being 25 threaded, but, should a split develop in'the pipe, as sometimes occurs, the tool will not be damaged as it may move inwardly into the plunger. More-- over, as the work being threaded cooperates directly with the plunger itself and not with the 30 chamfering tool for causing the plunger to move or three threads will be out before engagement of the chamfering tool and work and, after one or two more threads are cut, the'work engages the outer end of the operating plunger. As stated 45 before,- the chamfering may occur before the work and plunger engage or it may continue after this time. As the thread cutting Operation continues, the plunger in contact with the end of the work is moved inwardly relatively to the so head, thus causing rotation of the sleeve|6 by means of the shoes 43 riding in the spiral grooves 48 on the inner surface of the sleeve. The cam ring l9 being rigidly secured to the sleeve rotates therewith relatively to the collar and its 5 5 associated ring 3 During rotation of the sleeve, the cam or incline surfaces of the lugs I! move along the cooperating shoulders 35 of ring 3|,- thus enabling the collar I I under the influence of springs l4 to move rearwardly slowly with re- 60 spect to the body ,As this occurs, the chasers are gradually retracted by the lugs l3 on the studs l2 carried by the collar working in the inclined recesses 8 in the sides of the chaser carriers. Gradual retraotion'of thechasers will, of course, produce the desired taper threads and, since the rate at which the chasers are retracted determines the amount of taper, any desired taper may be formed by varying the inclination of the forward ends of-lugs I1. I Although it is preferred to employ chasers having a taper corresponding to the taper of the threads to be cut, such chasers are merely used so that the rear teeth can control the longitudinal moverhent of the die head or work in accordance with the pitch of the thread.

As the relative rotation between the cam ring l9 and the collar continues, the inclined forward endsv of the lugs I! pass from engagement with the shoulders 35, at which time the thread of the desired length has been cut and the collar is projected rapidly rearwardly by the springs It, thus causing the chasers to move into inoperative position out of engagement with the work. The

, rapid rearward movement of the collar is arrested by the ring 3| engaging the shoulder l8 on the cam ring and, when the parts are in this position, the lugs H are disposed within the notches or recesses 34 of ring 3|. If desired, shoulder 8 may be formed with a forwardly projecting rib 63 which is adapted to extend within a groove 64 in ring 3| to arrest relative rotation between sleeve i6 and collar As the length of the thread being cut is determined by the amount ,of initial overlap between the cam lugs l1 and the shoulders 35, the length of the thread may be adjusted by varying the amount of this overlap. Two separate means are provided for this purpose, one for obtaining fine adjustment and the other for obtaining a comparatively coarse adjustment. The fine adjustment .is obtained by rotating the ring 3| relatively to the collar and the coarse adjustment is obtained by shifting the ring i9 circumferentially of the sleeve l6.

While any suitable means may be provided for rotatably adjusting the ring 3|, it is preferred to employ a worm 65 which is rotatably mounted in the collar Hand is adapted to cooperate with a gear sector 66 formed on the outer surface of the ring 3| within one of the recesses 33 thereof. The worm 65 may be. conveniently formed on a rod, one end of which has an enlarged cylindrical head 81 journaled within an opening 68 of the collar and the other end 63 of which is of reduced diameter and is screw threaded to receive a nut I0, the nut being journaled in an opening 'll formed in the collar in alignment with opening 68. The inner end of nut'lll is adapted to bear against a shoulder 12 in the collar, so that the worm may be firmly locked against rotation. When it is desired to actuate the worm for rotating ring 3| into a new position of adjustment, it is only necessary to back off nut 10, then rotate the worm, after which the nut may again be tightened to secure the 'ring in its new position of adjustment. It will thus be observed that ring collar II and, at their inner ends, they cooperate with a ing 15 which projects radially from the ring- 3| and is preferably formed integrally therewith. Except for the lug 15, ring 3| corresponds in substantially all details with ring 3|. It will be perceived that ring 3| may be readily 'and quickly rotated into a new position of adjustment by simply backing off one screw 13 and tightening the other one. i k

To obtain a coarse adjustment for the length of thread, it is mere y necessary to loosen binding screws 23 and, with the die head closed as much as possible (that is, with the collar moved forwardly withrespect to the body member I out,

of engagement with the lugs disengage the notched or serrated portions of ring" and sleeve l6 by moving the ring forward slightly, rotate the ring relatively to the sleeve the desired amount, then'move it rearwardly to cause the serrated portions to again cooperate, after which the binding screws may be tightened and the ring thus secured in a new position of adjustment.

The die head may be adjusted to cooperate with work or stock of different diameters by shifting the sleeve l6 and consequently the ring I9 longitudinally of the shank 2. This may be easily accomplished by slightly loosening the screws 23 which clamp the split nut 25 to the shank to enable the split nut to be rotated relatively to 'the shank. Rotation of the split nut in one direction will cause the sleeve l8 and cam ring I! and consequently collar to move forwardly relatively to the body member and thus move the chasers inwardly for cooperating with-work of relatively small diameter, while rotation of the split nut in the opposite direction will cause movement of the sleeve and cam ring and consequently the collar away from the body member and thus 26 position the chasers to cooperate with work of larger diameter. After the split nut has been properly adjusted, the screws are then tightened to clamp it rigidly to the shank and thus prevent longitudinal shifting of the sleeve I6 and cam ring l9 relatively to the shank.

From the foregoing, it will be perceived that eificient and comparatiyely simple means have been devised for gradually moving the chasers to cut taper threads and that the mechanism for 36 actuating the chasers includes means for effectively chamfering the end of the work being threaded.

What I claim is:

1. In a die head, the combination with a body 40 -member having a work receiving opening, of

chasers movably mounted on said body member, and mechanism for gradually moving said chasers transversely of the axis of said opening for cutting taper threads, said mechanism including means movable axially of said opening for actuating the chasers, spring means normally tending to move said movable means, means relatively rotatable with respect to said movable-means for permitting gradual movement of the latter by said spring means during'the cutting of a plurality of threads whereby said chasers are actu-' ated to out taper threads, and means for effecting gradual rotation of said rotatable means during the cutting operation. 56 2. In a die head, the combination with a body member, of chasers movably mounted on said body member, mechanism for gradually moving said chasers with respect to said body member to cut taper threads, said mechanism involving 60 rectilinearly movable means cooperable with the chasers for moving the latter, spring means normally tending to move said movable means, means cooperable with said movable means and relatively rotatable with respect thereto for permitting gradual movement of said movable means by said spring means during the-cutting of a. plurality of threads, and means operated by the work being out for gradually actuating said rotatable means timing the thread cutting open.- tion.

member, having a work receiving'opening and provided with=a rearwardly extending shank, of

thread cutting chasers movably mounted on said (I s. In a die head, the combination with a body means to gradually mo e the chasers, and spring means disposed within said shank and cooperable with the slidable means for returning said rotatable means to normal position.

' 4. In a die head,gthe combination with a body member having a work receiving opening, of chasers movably mounted on said body member, mechanism for gradually-moving said chasers transversely of the axis of said opening for cutting taper threads, said mechanism including means movable axially of said. opening for actuating the chasers, spring means normally tending to move said movable means, means relatively rotatable with respect to said movable means for permitting gradual movement of the latter by said spring means during the cutting of a pluralityo'f threads, and means movable within the opening and actuated bythe work being threaded for causing said rotatable means to gradually rotate during the cutting-of said plurality of threads. 1

5. In a die head, the combination with a body member having a work receiving opening, of a plurality of chasers movably mounted on said body member, means movable. axially of said opening for moving the chasers transversely of the axis of said opening, spring means for actuating said movable means, means relatively rotatable with respect to said movable means normally restraining movement thereof by said spring means, said rotatable means and said movable means respectively having engaging portions one of which is inclined to the axis of said opening whereby upon relative rotation of said means said movable means is permitted to move axially of the opening to cause gradual movement of said chasers for cutting taper threads, and means actuated by the work being threaded for gradually rotating said rotatable means during the threading operation.

6. Ina die head, the combination with a body member, having a rearwardly extending shank, of chasers movably mounted on said body member,.means movable longitudinally of the shank cooperable with said chasers for actuating the latter, means rotatable relatively ,to said movable means encircling said shank, said rotatable means having a cam surface cooperable with said. movable means for permitting the latter to move during the cutting of a plurality of. threads so as to cause gradual movementof the chasers for the cutting of taper threads, and means engageable by the workfor gradually rotating said rotatable means during the cutting of said plurality of threads.

7. In a die head, the combination with a body member having a rearwardly extending shank, of chasers movably mounted on said body member, means movable longitudinally of the shank for moving the chasers relatively to the body mem ber, a sleeve rotatable relatively to said means encircling the shank, and a ring secured to said sleeve and having a cam surface cooperable with said means for controlling movement of the latter to cause gradual movement of the chasers for cutting taper threads, said ring being rotatably chasers movably mounted on said body member,

adjustable on said sleeve to regulate the length of thread to be cut.

- 8. In a die head, the combination with a body member having a rearwardly extending shank, of chasers movably mounted on said body mem- 5 her, mechanism for moving said chasers relatively to the body member, said mechanism including a collar movable longitudinally of the shank, a

. sleeve encircling the shank between the latter and the collar and being rotatable relatively to 10 the collar, a ring circumferentially adjustable on the sleeve having a portion engageable with the collar for controlling movement of the latter, andgmeans movable within said shank for rotating the sleeve. l5 9. In a die head, the combination with a body member having a rearwardly extending shank, of chasers movably mounted on the body member,

- means for moving said chasers involving arotatable sleeve encircling said shank and having a 20 cam groove on its inner face, an axially movable collar encircling said sleeve and having portions cooperable with the chasers, a ring circumferentially adjustable on the sleeve having portions engageable with the collar, and a plunger mov- 5 able within said shank having a. portion disposed within said ca'm groove for rotating the sleeve and ring for controlling movement of said collar.

10. In a die head, the combination with a body member having a rearwardly extending shank? of 30 chasers movably mounted on the body member, means movable longitudinally of the shank for moving the chasers relatively to the body member for cutting taper threads, means rotatably mounted on the shank for controlling movement of said movable means, said rotatable means being movable longitudinally of the shank to assume different positions of adjustment, and means adapted to overlappingly engage opposite sides of a portion of said rotatable means for securing the latter in a desired position of adjust-, me'nt against movement longitudinally of the shank. I

11. In a die head, the combination with a body member having a rearwardly extending shank, of chasers movably mounted on said body member, a collar member movable longitudinally of the shank for gradually moving the chasers relatively to the body member for cutting taper threads, said collar member having a rotatably adjustable ring and being provided with portions overlappingly engaging opposite sides of the ring preventing the ring from moving axially relatively to the collar, and means encircling the shank rotatable relatively to said collar and having a portion engageable with said ring for controlling movement of said collar.

12. In a die head, the combination with a body member having a rearwardly extending shank, of chasers movably mounted on the said body member, a collar member movable longitudinally of the shank and having means cooperable with s) said chasers. for'moving the latter. relatively to the body member, said collar having a ring rotatably adjustable with respect thereto, means 65 carried by the collar for rotating said ring, and means encircling the shank relatively rotatable with respect to the ring, said encircling means having a member I circumferentially adjustable thereon adapted to engage the ring for controlling 7 movement of said collar member. v

13. In a die head, the combination with a body member having a work receiving opening, of

mechanism for moving said chasers relative to the body member, means for actuating said mechanism, said means including an abutment en gageable by the work being threaded, and a chamiering tool normally disposed in advance of said abutment, said tool being movable with respect to said means to enable the work to engage said abutment.

14. In a die head, the combination with a body member having a work receiving opening, 01' chasers movably mounted on said body member, mechanism for moving said chasers relative to the body member, means operable by the work being threaded for actuating said mechanism,

recede with respect to said means during the threading operation and for yieldably maintaining the tool in engagement with the work.

15.. In a die head, the combination with a body member having a work receiving opening, of chasers movably mounted on the body member, mechanism for moving the chasers relative to the body member, movable means extending within the opening and operable by the work being. threaded for actuating said mechanism, said 10 means including an abutment engageable by the work, spring means opposing movement of said movable means, a chamtering tool movably mounted on said movable means, and yieldable means normally maintaining said tool in advance 15 oi said abutment.

O'I'I'O HOELZELJ