Patent
1981-07-22
1983-10-18
Combs, Ervin M.
B23G 702
Patent
active
044096984
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to the art of manufacturing products having elements of helical shape by plastic deformation of the metal of a work piece and may be utilized for pressing internal threads of an elastic profile in through and preferably blind holes.
BACKGROUND ART
Known in the art are taps for pressing elastic thread profiles capable of tapping through holes only.
After the thread has been cut the tapped part is screwed off the tap and released over the shank of the tap.
Such a tap for pressing elastic thread profiles comprises a groove forming portion and a thread forming portion arranged on the tap axis in series and having points and threads of equal pitch. These portions are interconnected by a neck portion having a length which is less than that of the thread to be tapped. Also, the crests of the thread forming portion are axially displaced from those of the groove forming portion.
The amount of displacement is that of half the pitch of the thread to be tapped.
Motion of the groove forming portion through the hole of a part produces a helical groove either by cutting or pressing. At the moment the thread forming portion comes into operation the groove forming portion acts as a threading block providing a lead to the thread crests of the thread forming portion between the valleys of the helical groove that has been formed.
The thread forming portion impresses a thread by reshaping the helical groove into a confined space, which is arranged in the core of the thread profile that has been formed. The space reduces the sectional area of the thread profile formed, which makes it possible to increase elastic deformation of the profile along the axis of the thread.
This ensures a more favorable load distribution between threads of a threaded connection and improves its strength (SU, Inventor's Certificate No. 625,824 published Apr. 19, 1977, Int. Cl. B 21 H 3/08, of Dniepropetrovsky ordena Trudovogo Krasnogo Znameni gorny institut im. Artema).
This tap is unsuitable for pressing elastic thread profiles in blind holes because the groove forming portion, as the tap is being backed out of the hole, will distort the thread that has been formed by reason of the axial displacement of its crests from those of the thread portion.
DISCLOSURE OF THE INVENTON
The invention has for its object to provide a tap for pressing elastic thread profiles in blind holes, wherein the groove forming portion and the thread forming portion are so connected that in backing the tap out of the threaded hole the crests of the thread of the groove forming portion are disposed in the roots of the thread profile formed and do not distort the thread.
The object set forth is attained by the provision of a tap for pressing elastic thread profiles, comprising on the shank of a groove forming portion a thread forming portion such that the thread pitch thereof is equal to that of the groove forming portion, the crests of the thread forming portion being axially displaced from those of the groove forming portion, wherein according to the invention the thread forming portion is positioned behind the groove forming portion for axial movement on the shank, the movement thereof being limited by a stop arranged on the shank.
According to a preferred embodiment of the invention the groove forming portion has flutes such that the cutting edges thereof are adjacent the heels of the sides of the flutes on the back of the groove forming portion.
The tap of the invention provides for pressing elastic thread profiles in blind holes due to the fact that as the tap is backed out of the threaded hole the groove forming portion does not distort the thread.
Because the groove forming portion moves on the internal thread of the thread forming portion in a similar way as along a threading block, as the tap is backed out the result is, that the crests of the thread of the groove forming portion are disposed in the roots of the thread formed, which makes it possible to simultaneously screw out the two portions.
By cutting away the remaining
REFERENCES:
patent: 188405 (1877-03-01), Peterson et al.
patent: 279360 (1883-06-01), Douglas
patent: 1041675 (1912-10-01), Robinson
patent: 2204866 (1940-06-01), Parish
patent: 2301679 (1942-11-01), Bouget
patent: 2369273 (1945-02-01), Bakewell
Badyaev Valery G.
Shamenko Stepan P.
Toropov Gennady A.
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