US1521322A - Method of making thread-rolling dies - Google Patents

Description

E.H.REED

METHOD OF MAKING THREAD ROLLING DIES Dec. 1924- 1,521,322

Filed Aug. 22, 1923 P W "WW" W Patented Dec. 30, 73 24.

UNITED STATES.

EDGAR H OWARD REED, OF WORCESTER, MASSACHUSE'JPIES.

METHOD OF MAKING THREAD- ROLLING DIES.

Application filed August 22, 1923. Serial 1T0. 658,707.

To all whom 2' t may concern:

Be it known that I, EDGAR HOWARD REED, a citizen of the United States, residing at \Vorcester, in the county of Worcester and State of Massachusetts, have invented certain new and useful Improvements in Methods of Making Thread-Rolling Dies, of which the following is a specification.

The present invention relates to the making of dies adapted for forming screw threads by the rolling method.

Up to the time of the present invention, it was generally considered by those skilled in this art, that the rolling method of forming screw threads is adapted only to the production of commercial threads where a wide tolerance of irregularities in their production is allowable, for example, such as the threads oniwood screws, machine screws, bolts, and. similar articles.

Several factors have been recognized as interfering with the production of fine and accurate screw threads by means of rolling dies. One factor is theimpossibility of pre venting the bulging and warping of thread rolling dies during thehardening operation to which they must be subjected after they have been cut to the desired form; This warping and bulging of the dies has resulted in the distortion of their working surfaces,

and consequent irregularities in the'threads which are cut by them; Up to the time ofthe present invention, no methods have been" known for entlrel preventing or correctingl such distortion 0 the working surfaces of thread rolling dies.

Another factor which has interfered-with the production of fine and accurate threads by the rolling method, has been the pitting and roughening of the working surfaces of! the dies during the hardening operation, due principally to oxidation during the heating and cooling treatments. Attempts have been made to prevent or cure this roughening of the die surfaces, but without complete success, and the making of finethreads with thread rolling dies has been considered impractical largely for this reason.

Still another factor which has prevented the production of fine and accurate threads by the rolling method has been inaccuracies in the cutters by which the grooves in the dies have been cut. Even if such cutters are made with extreme care, the warping which takes place when they are hardened and tempered often introduces irregularities made in" afccordan v in their cutting surfaces which are repeated 1 in the dies cut by them. One of the most serious of such irregularities, whenthe aim is to produce fine and accurate threads, is the difference between the lead of adjacent grooves in the dies. Such irregularities, if left in the completed dies, of course are repeated in the screw threads produced by them.

The general object of the present invention is to provide a method of making thread rolling dies which are substantially free of the objectionable characteristics above mentioned. More specifically stated, the object of the invention is to provide a method for producing thread rolling dies in which the pitch plane of the thread cuttin grooves is substantially a plane surface, an in which the working surfaces of the dies are smooth and free from pitting by oxidation, and in which the lead between adjacent threads of the dies is substantially uniform. The acthe production of thread. rolling dies which are so nearly periectfthatwith them screw threads mayi be' roljl'ed fcommercially which are actually "superiorito similar threads producedscomnie ciall b cutting operations, Fo exa pl ti i poss lebyz-means of dies p "with the method hereinafter described, t term 'satisiactorythreads upon the sflindleslof micrometers and simiiiie'n'tsin which threads osefaocuracy are required) The method-which earths subject of "rthef present inventionjis}.characterized by the fact that after the-thread rolling dies havev been cut to; the desired shape and have been hardened'and tempered, ithey are ground by reciprocating them with their grooved surfaces in engagementwith acorrespondingly grooved lap the surface of which is charged with abrasive material. This grinding treatment serves to eradicate inequalities in the die surfaces due to any bulging and warping which occurred during the hardening and tempering operation, and smooths the faces of the grooves in the die which may have become roughened or pitted. By reciprocating the dies in engagement with different portipns of the grooved lap, the grinding operation also serves to equalize the lead between adjacent grooves in the dies.

-of a form adapted for the rolling The invention will be understood from the following description in connection with the accompanying drawing in which Figure 1 is a plan view of a thread rolling die of the kind which my method is adapted to make; Figure 2 is an end elevation, on a somewhat larger scale, of the die shown in Figure 1; Figure 3 is a plan of a fiat lap showing a die thereon in position to be ground; and Figure 4 is an end elevation, on a somewhat larger scale, of the lap and die shown in F i re 3.

' n carrying out my improved method, a piece of tool steel is formed to the desired shape, preferably by planing or milling, in the usual manner. Figures 1 and 2 show a die 4 having a grooved working surfaee 3 0 threads on a suitable spindle, it belng understood that two dies of this kind are employed in the usual way. After the die has been cut to the desired shape, it is hardened andtempered in any preferred manner, with the usual recautions to reduce to a minimum the ulging, warping and roughening of the working surface which usually occurs. All portions of the working surface of the die are then ground by reciprocating the die in engagement with a correspondingly grooved lap the surface of which is charged with abrasive material such as oil and fine emery. "In Figures 3 and 4, there .is shown a lap 7, of cast iron or other suit- As shown in the drawing, a die 4 is laidwith its working face downward in engagement with the correspondingly" grooved top of the lap, after the lap has been charged with the abrasive material. The die is then reciprocated longitudinally of the lap, either by hand or-by some suitable mechanism, and the grinding of'all portions of the working surface of the die begins. Cast iron, by reason of its nature, tends to hold the particles of abrasive material, and such particles present their angles and edges .to the die as it is reciprocated over the lap. As

the grinding proceeds, the high spots or areas in the working surface of the die produced by the hardening operation are ground down, thereby making the pitch plane of the grooves or threads of the die more nearly a true plane surface. This operation does not materially change the form of the die threads, as the cutting off of the peaks of portions of the die threads and the deepening of portions of the grooves between the die threads is accompanied by corresponding cutting of the side slopes of the threads. From time to time, as the grinding operation proceeds, the die is lifted and moved transversely of the lap so that the die will cooperate with different portions of the lap. By so changing the co-operative relation of the die and lap, slight differences in the lead between adjacent threads of the die are substantially equalized by grinding action, therebyv producing a die having a substantially constant lead between threads. The grinding operation also smooths the working surfaces of the die which may have become pitted during the hardening and tempering operation.

Although Figures 3 and 4 show the die resting wlth its working surface downward in engagement with the upturned face of the lap during the grinding operation, it is to be understood that this relative arrangement of the lap and die is neither necessary nor desirable under all conditions. The drift of the abrasive loosened during the lapping or grinding operation being downward, there is a tendency for the grinding operation to take a little more off the tops or peaks of the threads of the die than off the bottoms of the grooves between the die threads, when the-die is ground with its working surface downward. Under some circumstances, it may be desirable to counteract this tendency or produce the opposite effect by reciprocating the lap and die with reference to one another, with the working surface of the die facing upwardly and theworking surface of the lap facing downwardly. It may even be that other relative positions of the lap and die may be found desirable under some conditions, bearing in mind the objects of the grinding operation, as herein described.

The grinding operation above described is continued until the working surfaces of the die have been given the advantageous characteristics hereinbefore mentioned, whereupon the die is ready to be used in cooperation with a similarly made die for the production of screw threads which will accurately conform to the desired shape.

While the method of making thread-rolling dies which forms the subject of the present invention, has been described in connection with the making of the flat type of thread-rolling dies, it will be understood that it is equally applicable to the making of the cylindrical or rotary type of threadrolling dies. After the working surfaces of such rotary thread-rolling dies have been formed to the desired shape and hardened in the usual manner, they can be finished in the manner herein described and claimed, it

being of course understood that the laps used for finishing them have grooved cylindrical surfaces, the pitch radii of which correspond to the pitch radii of the cylindrical surfaces of the respective dies, such laps being fiat in this sense.

What I claim is:

'1. The method of making rolling dies which consists in forming the working surface of the die to the desired shape, hardening and tempering it, and then reciprocating it with its working surface in engagement with a correspondingly formedflatia'p the surface of which is charged with abrasive material.

2. The method of making thread rolling dies which consists in forming the working .surface of the die to the desired grooved shape hardening and tempering it, and then reciprocating it with its grooved working surface in engagement with a correspondingly grooved flat lap the surface of which is charged with abrasive material.

3. The method of making thread'rolling dies which consists in forming the working surface of the die to the desired grooved shape, hardening and tempering it, and then reciprocating it with its grooved surface in engagement with different portions of a correspondingly grooved lap the surface of which is charged with abrasive material.

4. The method of making thread rolling dies which consists in cutting the working surface of the die to the desired grooved shape,hardening and tempering it, and then reciprocating it with its grooved surface in engagement with a correspondingly grooved flat lap the surface of which is charged with abrasive material.

5. The method of making thread rolling dies which consists in cutting the working surface of the die to the desired grooved shape, hardening and tempering it-,- and then reciprocating it with its grooved surface in engagement with different portions of a correspondingly grooved lap the surfacle of which is charged with abrasive-materia 6. The method of finishing the grooved working surface of a thread rolling die which consists in reciprocating the die with its working surface in engagement with the surface of a correspondingly grooved flat lap which is charged with .abrasive material.

'Z. The method of finishing the grooved working surface of a thread rolling die which consists in reciprocating the die with its working surface in engagement with different portions of a correspondingly grooved lap which is charged with abrasive material.

8.. The method of finishing the grooved working surface of'a thread rolling die which consists in placing the die with its working surface in engagement with the surface'of a correspondingly grooved lap which is charged with abrasive material, and'then reciprocating the die and lap with reference to one another, part of the time with the working surface of the lap downward and the remainder of the time with its working surface upward.

9. The method of finishing the grooved working surface of a thread rolling die which consists in placing the die with its working surface in engagement with different portions of the surface of a correspondingly grooved lap which is charged with abrasive material, and then reciprocating the die and lap with reference to one another, part of the time with the working surface of the lap downward and the remainder of the time with its working surface upward.

Signed at Worcester, Mass, this 20th day of August, 1923.

EDGAR HOWARD REED.

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