Thread forming tap and threading method

Details Thread forming tap and threading method Thread forming tap and threading method

2001-03-09

2002-05-14

Eley, Timothy V. (Department: 3723)

Abrading

Abrading process

Drill, thread, thread cutter, reamer, or rotary cutter abrading

C408S219000, C408S222000, C451S057000, C470S198000

Reexamination Certificate

active

06386954

ABSTRACT:

The entire disclosure of Japanese Patent Application No. 2000-064427 filed on Mar. 9, 2000 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thread forming tap and a threading method.
2. Description of the Related Art
As shown in
FIG. 6
, a conventional thread forming tap has a threaded portion
100
comprising a chamfer
101
which is tapered to form a complete mountain-like (angle) shape (see inclination angle in FIG.
6
), and a parallel thread
102
which is formed continuously with the chamfer
101
. The thread forming tap also comprises a plurality of oil grooves disposed in a circumferential direction of the thread forming tap.
When the thread forming tap is ground, as shown in
FIG. 7
, an end of the thread forming tap (raw material) W on the side of the threaded portion
100
and an end of the thread forming tap on the side of a shank
103
are supported by center portions
104
a
and
104
b
of a thread grinder, the thread forming tap W is rotated and in this state, the thread forming tap W is constantly fed to a rotating grinding stone
105
to carry out a traverse grinding.
In the conventional thread forming tap, since the chamfer
101
is tapered to form the complete mountain-like shape, the grinding stone
105
goes in and out from the chamfer
101
deeply (as compared with the parallel thread
102
) correspondingly at the time of grinding.
Therefore, if the thread forming tap has a small diameter (like a miniature thread such as a hard disk), there is a problem that a tip end of the grinding stone
105
abuts against the threaded portion-side center portion
104
a
to damage the latter, and the chamfer
101
can not be formed.
Further, according to the conventional grinding method, since the thread forming tap is fed constantly, in the chamfer
101
immediately before it is fed to the parallel thread
102
, a pitch of any of a crest and a root of the thread is formed differently.
Thus, at the time of tapping, in the chamfer
101
immediately before it is fed to the parallel thread
102
, an excessive force is applied to a front or rear flank of the thread, there is a problem that an amount of heat is increased, and this shortens the life of the tap.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the above circumstances, and it is an object of the invention to provide a thread forming tap to which a chamfer can easily be mounted, and a general threading method.
To achieve the above object, according to the present invention, there is provided a thread forming tap having a threaded portion comprising a tapered chamfer and a parallel threaded portion which is formed continuously with the chamfer, wherein a depth of root of the chamfer is set equal to that of a root of the parallel threaded portion constantly.
The invention also provides a threading method for a thread forming tap having a threaded portion comprising a tapered chamfer and a parallel threaded portion which is formed continuously with the chamfer, wherein after a parallel portion from the chamfer to the parallel threaded portion is continuously ground, a front flank to a rear flank of the chamfer are ground while alternately and gradually changing a feeding ratio between a tip end and a rear end of the chamfer and then, an outer diameter portion of the chamfer is ground.
The invention also provides a threading method wherein a front flank and a rear flank of a thread are formed while alternately and gradually changing a feeding ratio between a tip end and a rear end of threaded portion and then, a parallel threaded portion is formed and thereafter, an outer diameter portion of the thread is ground.


REFERENCES:
patent: 1542893 (1925-06-01), Kreutzberger
patent: 3775792 (1973-12-01), Leonard
patent: 5797710 (1998-08-01), Sawabe et al.
patent: 5928084 (1999-07-01), Green
patent: 396 577 (1933-05-01), None
patent: 601 122 (1926-01-01), None

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