Cutting by use of rotating axially moving tool – Tool or tool with support – With pitch-stabilizing ridge
Patent
1995-08-10
1998-03-10
Howell, Daniel W.
Cutting by use of rotating axially moving tool
Tool or tool with support
With pitch-stabilizing ridge
408222, 470198, B23G 506
Patent
active
057253366
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thread tapping cutting tool which, due to increased room for accommodating chips and a reduced load on the cutting wings, is especially suitable for thread tapping (preferably with increased speed) in a range of increased sizes, preferably from M 12 to M 58 or from C1/4" to C3 ".
2. Description of Relevant Materials
It is well known that taps are multiple-edge cutting tools for cutting threads in bores. The thread tapping tool (tap-drill) can be considered a screw in which flutes are machined in order to form cutting edges. The tap drill as known has a working part, provided with a chamfer portion and a control portion, arranged at one end of a generally cylindrical shank. The remaining end of the shank is preferably of rectangular section for fitting purposes. The working part has at least two cutting wings separated by flutes formed therein. The flutes store the chips already separated and introduce cooling and/or lubricating media if necessary.
During thread tapping, the two basic requirements are accuracy and productivity. As is well known, accuracy in tapping is assured by the accuracy of the tool itself and by means of proper guiding of the tool. At the same time, productivity is obtained by increasing the cutting speed, limited by production of heat and chips that must be removed from the bore at the rate of production. Two contradictory requirements must be balanced: the working surface of the tapdrill in contact with the part to be machined shall be as large as possible in order to achieve analcurate guiding, but at the same time, the reduction of friction and heat generation requires that the active cutting surface be minimized. (Dr. Bakondi --Dr. Kardos: Manufacturing Technology, Vol. 1 , p. 226 , Educational Publisher, 1963 .)
The status of technology is well reflected in section 6.3 ("Tap drills") in the book: Mrs. L. Arateo --M. Vagi: Screw Threads, (Tancsics Publisher, 1968 ) which presents a detailed description of the tap-drills known and used at present, together with their design, geometry and dimensions. According to this reference, the recommended value for the width of the cutting wings (land width) is 0.35 D in the case of three-flute tap-drills and 0.28 D in the case of four-flute tap-drills (where D represents the tap-drill outer diameter). According to the literature, the flute depth is defined by the core diameter d.sub.t which is equal to 0.4 to 0.5 D. The core diameter d .sub.t is selected as a result of a tradeoff so as to obtain a chip-room as large as possible while maintaining the proper strength. Otherwise, experience shows that chips clogging the flutes due to improper flute section results in tap breakage more frequently than insufficient strength of the tap-drills.
It is also well known that a tap-drill has a working part provided with a chamfer portion and a control portion arranged at one end of the shank. Within the working part, the proper selection of the lengths of the chamfer and control portions is essential. The chamfer length is always determined by taking the cutting conditions into consideration. For example, the chamfer length is different in the case of hand or machine tapping (drill-set), or screw tapping in soft or hard materials etc. Generally, tap-drills with short chamfer lengths are used in the practice, and the length of the control portion exceeds - often by several times - the chamfer length. Based on the related literature, the land relief in the chamfer portion of the tap-drill is absolutely necessary. However, land relief is unnecessary (even disadvantageous) in the control portion, except in the cases of machined or milled nut-taps where the tap-drill is not reversed. When machining threads in nuts (in fact, for nut-taps) the chips accumulated in the flutes cannot be crowded between the land and the machine surface. The value of the relief angle in the chamfer portion is conventionally 10 to 12 degrees in the case of machine-taps and nut-taps, and 6 to 8
REFERENCES:
patent: 1210508 (1917-01-01), Marye
patent: 1478414 (1923-12-01), Wells
patent: 1508594 (1924-09-01), Brubaker, Jr.
patent: 1693768 (1928-12-01), Steinruck
patent: 3945069 (1976-03-01), Cecil
patent: 4181457 (1980-01-01), Holmes
Dr. Bakondi-Dr. Kardos: Manufacturing Technology, vol. I, p. 226, Educational Publisher, 1963.
Section 6.3 "Tap Drills" in the book Mrs. L. Arato-M. Vagi: Screw Threads, Tancsics Publisher, 1968, pp. 238-245.
Simon Janos
Vilmanyi Gabor
Vilmanyi Laszlo
Vilmanyi Laszlone
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