Cutting by use of rotating axially moving tool – Tool or tool with support – With pitch-stabilizing ridge
Reexamination Certificate
1999-08-04
2001-04-10
Wellington, A. L. (Department: 3722)
Cutting by use of rotating axially moving tool
Tool or tool with support
With pitch-stabilizing ridge
C408S215000, C408S220000, C470S198000
Reexamination Certificate
active
06213693
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a taper tap for pipe threads for cutting female threads, and more specifically, to a high durability taper tap for pipe threads which can cut female threads in a pipe having hardness of approximately more than 50 Rockwell C scales Hardness (HRC).
BACKGROUND OF THE INVENTION
A taper tap for pipe threads (hereinafter referred to as a “pipe taper tap”) is a kind of hand taps and is used for cutting tapered female pipe threads for achieving an air tightness of the threads at the connecting portion of pipes, pipe components or fluid apparatuses. The pipe taper tap is different from a common tapping tool for forming triangle threads, for instance, in some respects. The main differences between these two are as follows. First, the pipe taper tap cuts the pipe threads by the thread portion of the tap tapered in a ratio of 1/16 in order to taper the pipe threads in a ratio of 1/16, while the common tapping tool cuts the threads only by the chamfer. Second, the pipe taper tap cuts the threads not only by the crest but also by the root of the thread in order to improve the air tightness of the pipe thread, while the common tapping tool does not cut the threads by the root of the thread.
As described above, since the cutting area of the pipe taper tap is larger than that of a common tapping tool, the cutting resistance of the pipe taper tap is larger than that of the common tapping tool. Therefore, it is impossible to cut threads in a pipe made of a hard material, such as the one after a heat treatment having hardness of 50 HRC or more, by using a pipe taper tap.
However, sometimes a heat treatment is mistakenly conducted on the material to be tapped before cutting female threads therein. Since such a material becomes hard after the heat treatment, the body of the pipe taper tap is crimped, broken, chipped or abraded in an early stage of use by merely cutting threads in one or two holes by the pipe taper tap. In such an event, the material after the heat treatment has to be abandoned or otherwise conducted an electrical discharge machining process on the material before cutting female threads therein. However, it is difficult to accurately cut threads after the electrical discharge machining. In addition, it takes more than several ten hours to conduct the overall process.
SUMMARY OF THE INVENTION
The present invention was made to solve the above described problems by providing a highly durable pipe taper tap for cutting threads in a pipe made of a hard material which is able to form female threads in a pipe having hardness of approximately 50 HRC or more.
In order to achieve the above object, the first invention of the pipe taper tap for a hard material is to form female threads in a pipe made of hard material, wherein a sum of a width angle of each cutter is set approximately from 110° to 150°, a rake angle of the cutting edge is set approximately from −25° to −10°, a diameter of top end portion at the bottom of the flute is set approximately from 58% to 68% of a diameter of the smaller end of the thread portion, and a taper ratio at the bottom of the flute is set approximately from 1/21 to 1/11.
According to the pipe taper tap of the first invention for cutting threads in a pipe made of a hard material, the sum of the width angle of the cutter is set approximately from 110° to 150°. The larger the sum of the width angle of the cutters, the broader it becomes the width of each of the cutters, and accordingly, the chipping or breaking of the thread portions of the cutter are reduced. On the other hand, if the width of the cutter becomes broader, the contacting area between the tap and the material to be cut becomes larger, causing not only grating sounds when cutting but also a large cutting resistance, which makes the cutting itself difficult. Therefore, in the present invention, taking into consideration of these factors, the sum of the width angle of the cutters is determined to be approximately from 110° to 150°.
The rake angle of the cutting edge is set approximately from −25° to −10°. The smaller the rake angle of the cutting edge (larger in minus values), the larger it becomes the cutter angle defined by the rake face and the peripheral relief, thereby improving the strength and rigidity of the cutting edge, which is able to prevent the breaking or chipping of the cutters. On the other hand, the larger the cutter angle, the larger it becomes the cutting resistance. The taper tap must cut the pipe threads not only at the crest but also at the root of the thread. Therefore, in order to improve the strength of the cutter, the rake angle of the cutting edge is set approximately from −25° to −10° by taking into consideration of these factors.
A diameter of the bottom of flutes at the top end portion is set approximately from 58% to 68% of a diameter of the smaller end potion of the thread portion and is formed larger than that of a common tapping tool. Therefore, the strength of the tap is improved to that extent and the tap is prevented from being broken. If the diameter of the bottom of the flute at the top end portion is formed larger, the sectional area of the flute becomes smaller and consequently chip packing tends to be caused. However, as explained above, since the rake angle of the cutting edge is set approximately from −25° to −10°, the chips are cut in relatively small pieces in a sheared shape. Therefore, even if the sectional area of the flute is small, chip packing can be effectively avoided.
Further, the bottom of the flute is tapered approximately in a ratio from 1/21 to 1/11. Since taper at the thread portion is set in a ratio of 1/16 according to the Japanese Industrial Standard (JIS) specification, the rake angle of the cutting edge from the smaller end to the larger end can be set approximately equally. Since the pipe taper tap of the present invention cuts the pipe threads by using all of the cutters, by setting the rake angle of all of the cutting edges approximately the same, all of the cutters can cut the pipe threads in the same manner.
The pipe taper tap of the second invention for cutting threads in a pipe made of a hard material comprises the taper tap for a hard pipe of the first invention, wherein the number of flutes provided therewith is five or more.
The pipe taper tap of the second invention for cutting threads in a pipe made of a hard material functions in a manner equivalent to the pipe taper tap of the first invention. In addition, the sectional area of the flute for ejecting the chips is set small by forming the diameter of the bottom of the flutes within approximately from 58% to 68% of the diameter of the smaller end of the thread portion. However, since the number of the flutes provided with the taper tap is large, such as five or more, ejection of the chips is smoothly performed, thereby avoiding an increase of the cutting resistance because of jamming of chips. Also, by providing five or more flutes with the taper tap, the cutting amount per cutting edge becomes small, thereby decreasing a cutting load for each cutting edge.
The pipe taper tap of the third invention for cutting threads in a pipe made of a hard material comprises the pipe taper tap of the first or second invention, wherein the rake angle of the cutters is set approximately −20°, the diameter of the bottom of the flute at the top end of the tap is set approximately 60% of the thread portion, the number of the flutes is five and the taper of the bottom of the flutes is made approximately identical to that of the thread portion. By forming the taper at the bottom of the flute approximately equal to that of the thread portion, the rake angle of the cutting edges from the small end to the large end may be set approximately the same. Therefore, it becomes possible for all of the cutting edges to perform the cutting in the same manner.
REFERENCES:
patent: 1881281 (1932-10-01), Lamond
patent: 2145819 (1939-01-01), Swenson
patent: 4708542 (1987-11-01), Emanuelli
patent: 5112168 (199
Carter Monica S.
Muramatsu & Associates
OSG Corporation
Wellington A. L.
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