US2256269A - Thread rolling die - Google Patents

Description

Set, le?,V 1941. A STOLL 2,256,269

.THREAD ROLLING DIE Original Filed Dec. 4, 1936 2 Sheets-Sheet 2 ALBERT STOLL Patented Sept. 16, 1941 THREAD ROLLING DIE Albert Stoll, Detroit, Mich., assigner to Clare L. Brackett, Detroit, Mich.

Original applications Dece 114,259, and January 27,

Divided and this app Serial No. 157,195

4 Claims.

This invention relates to die apparatus for making' self-locking screw-threaded elements. Thel present application constitutes a division of my prior copending applications, Serial No. 114,259, filed December 4, 1936, and Serial No. 122,629, filed January 27, 1937.

Self-locking screw-threaded elements, for example, valve tappet adjusting screws, are sometimes formed by providing two spaced threaded portions connected by a resilient portion whereof the threads of each are relatively oiTset in an axial direction. By this construction, insertion of the element in the threaded bore of a receiving member, such as a valve tappet bore or other device, places the resilient connecting portion under tension and locks the element in place against accidental displacement. The formation of screw-threaded elements of this character presents a difficult problem, particularly in the formation of the threads to produce the desired axial oiiset necessary to secure self-locking.

An object of the present invention is to provide a novel die apparatus for rolling offset screw threads on spaced threaded portions of screwthreaded elements,

Other objects and advantages will be apparent from the description.

While the present disclosure constitutes an exposition of embodiments by which the invention may be-reduced to practice, it is to be understood that the same may be varied as desired Within limits not inconsistent with the scope of the invention as claimed.

In the accompanying drawings which form a part of thisspecification and wherein like characters of reference denote like parts throughout the several viewsz- Figure 1 is substantially an end elevation of a pair of dies in thread forming engagement with a screw blank, the upper die being shown in section.

Figure 2 is an end elevation of one of the dies as provided with spacer means for producing a desired thread offset, a portion being shown in section.

Figure 3 is a face plan view of a finished die as ready for use.

Figure 4 is an end elevation oi an alternative embodiment of a pair of thread rolling dies for simultaneously rolling opposed pairs of blanks, as operatively engaged with such blanks.

Figure 5 is a fragmentary end elevation of one of the dies of Figure 4, illustrating by dotted line prolongation the offset of the adjacent thread forming portions.

mber 4, 1936 Serial No. 1937, Serial N0. 122,629;

lication August 3, 1937,

tik,

Figure 6 is a face plan View of one of the dies of Figure 4. l

Figure 7 is an end elevation of a further alteri-n a longitudinalv groove 22aI in the meeting surface of die part 2) to maintain the die parts in parallel relation to each other. rThe faces of the two parts are provided with Vinclined serrations 23 which produce the screw thread in a rolling operation.

As shown in Figure 1, the dies are employed in pairs to roll threads 24 and 25 on a blank II,

headed as at I2, the threaded portions 24 and 25 being spaced axially of the blank lby a circumferentially undercut unthreaded portion having slots I4 by which resiliency is imparted thereto,

the threads 24 and 25 being staggered relative to each other by virtue of an axial offsetting.

In order to produce the desired axial offset in the screw thread Whenrolled on the blank the serrations 23 of the. die part I9 areA offset or staggered relative to the serrations 23 of the die part 20, as seen in Figure 3, so that when a blank is placed between a pair of such dies the threads 24 on the screw are formed by the serrations of the die parts I9 while'the threads25 on the leading end of the screw are formed bythe serrations of the die parts 2i).

The serrations 23, on the die parts` I9 and 2U are of the same depth and pitch so that the threads 24 and 25 on the finished screw will have the same depth and pitch and will mesh with the threads of the element with which they engage in service, such as a tappet or socket having uniform and continuous threads. When the axially offset threads 24 and 25 engage such uniform and continuous threads the slotted resilient portion is distorted and consequently forces the threads 24 and 25 into frictional locking engagement with the threads of the tappet or socket.

As shown in Figure 2, the die parts I9 and 2D are assembled with spacers or shims 26 placed therebetween before the serrations 23 are cut into the die faces, the thickness of such spacing means determining the amount of axial stagger or offset in the serrations of the two die parts. The

serrations are then cut in the die faces in a single operation, as by a hob or the like, the method of cutting being disclosed in my copending application entitledv Method of forming thread rolling dies, filed concurrently herewith.

After the serrations 23 are formed the spacers 26 are removed and the die partsI heat treated for hardening.- They are then assembled as shoWn'in Figures .1 and 3, without the spacers, which results in the serrations of die part I9 being staggered or oiset with respect to the serrations of die part 2U, as seen in Figure 3.

vIn the embodiment illustrated. in Figures 4; 5

and 6 each die is of integral construction, having a plurality of thread forming-face portionsZ'l,

V8 and 29 comprising zones-or Vbands disposed longitudinally o-f the die in parallel relation and spaced apart transversely of the die by defined areas 30, each of which is incapable of formative engagement with a blank being rolled. These areasSll are devoid of thread forming serrations and they may be provided in various ways as by gaps or plane surfaces. In the illustrated -embodiment they constitute gaps, preferably formed byflongitudinally groovingthe die'. faces to an appropriate depth. The gaps are so located that when blanks 3l are engaged between a pair of the dies,l as in lFigure 4, they register with the undercut portions 32 ofthe blanks.

VThe thread forming serrations 27,- 28 and 29 on the respective die face portions are each` oiset with respect to those of the adjacent .thread forming portion on the same die, so that on comformed with 4threads of `the same pitch diameter and pitch but the threads on one portion will be Y set with respect to the thread forming .serrationsA pletion of a thread rolling operation each blank f 'will have its threaded shank portions 33 and 34r offset axially of the blank relative to the threads y 0n the other portion.

It should here be stated that dus to the onset' relationship of the threaded portions 33 and 34 an axial stress will be set up inthe body of the screw kas it is threaded home in a female member, whereby thev reduced spacing portionV 32 will berplacedunder tension, thus providing a highly effective self-locking means. The degree of tension varies with the amount of thread offset, s0

` thatY any desired tension may be obtained.

The method of forming the serrations in the , portions 2l, 28 and 29, andof oisetting them, is

disclosed in my aforesaid concurrently led copending application entitled Method of forming thread rolling dies. l Also embodied in said application is a disclosure of ,the method` employedvi'n securing the desired thread forming offset in the alternative embodi` ments of dies shown in Figures 7 'and 8.

In the form illustrated'in Figure 7 the die 35 is formed-with a pair of overlapping closely adthe die faces. The slot 36 opens to the working face of the die and extends nearly to its opposite Y face while the slot 31 opens to the die face opposite its Working face and Vextends toward the Working face. The slots are of equal length and extend longitudinally of the die for its 4full length, opening to its ends. In lthis embodiment'the slots provide the gaps separating the thread forming face portions 38 and 39 on which the thread forming serrations are mutually oiset.

The die 40 shownin Figure 8 is similar to the die of vFigure '7, being likewise provided with slots 4l and 42 similar to the slots 36 and 31 except that they are of greater width dueto the eX- panding action of. .spacer members 43. engaged in the slots to cause a transverse expansion of the die body which resul-ts in offsetting the thread serrations on the die face portions 44 and 45.

Having thus described the invention, what is claimed is:

1. A thread rolling die for yproducing axially offset threads on spaced portions of a blank, co'mprising a onefpiece die member having a plurelation, each saidvface portion having thread forming serrationsiof equal pitch and form offof thenext adjacent face portion.

2. A threadrolling dierfor producing axially oifset threads on spaced portions of a blank, comprisingfa one-piece die member having a longitudinal groove deining spaced parallel thread forming face portions, each said face portion having thread forming serrations of equal pitch and form oiset kwith respect to the thread forming serrations of the Vnext adjacent face portion.

`3. A thread rolling die for producing'axially offset threads on spaced portions of a blank, comprising a one-piece die member having a plurailty of thread forming face portions in spaced relation, Veach said face portion having thread forming serrations ofequalrpitch and form offset with'respect'to the thread forming serrations A of' the next adjacent face portion, and means for adjusting the spacing of said faceY portions to vary the oifset of the thread forming serrations.

4. A thread rolling die for producing a selflocking screw with axially offset threads, comprising a one-piece body having `a working face j provided with thread forming Yserrations of equal pitch and form arranged as a plurality of spaced parallel zones, the body being cut away ,between said zones to provide the spacing therefor, and

Vthe serrations of each zone `being oiset relative to theserrations of the adjacent/zones. l

ALBERT STOLL,

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