RU2185938C1 - Screw tap - Google Patents

Abstract

FIELD: metal working, mainly thread cutting by means of nut taps. SUBSTANCE: tap includes starting and sizing portions, inverse conicity along thread and teeth with lowered profile angle. In order to enhance accuracy due to elimination or significant reduction of profile angles of threaded openings, halves of profile angles of teeth of starting portion are decreased in comparison with those of teeth on sizing portion by value determined according to given relation. Mean diameter of thread on teeth of starting portion is lowered by value also determined according to given relation. EFFECT: improved accuracy of thread. 3 dwg, 1 tbl

Description

 The invention relates to the field of metalworking, in particular to the manufacture of threads by taps (mainly nuts) by the cutting method, and can be used to increase the accuracy of thread formation, mainly in parts with through holes.

It is known that the combination of reverse taper on the thread of the taps with the teeth of the intake part causes an increase in the angles of the thread profile in the machined holes. This is because the cutting teeth of the intake part, increasing in height in the direction of the calibrating part, are simultaneously reduced in width when there is a reverse taper in the thread. An increase in the angles of the thread profile of the holes causes an increase in their actual average diameter, i.e., a deterioration in the accuracy of thread cutting. This is most pronounced in relation to work with wrench taps, in which the intake part (l _zab ) is elongated, usually equal to at least 12 thread steps. For clarity, the increments ΔD $\genfrac{}{}{0ex}{}{\text{<figure-callout id="2" label="R" filenames="00000012.png,00000013.png" state="{{state}}">R</figure-callout>}}{\text{2}}$ the average diameters of the threads of the holes when they are machined with spanners with a tooth profile hardened to a sharp edge and with a reverse thread taper R = 0.05-0.15 mm per 100 mm of length within the limits specified by the standards, and with a non-hardened tooth profile and reverse taper R up to 0.2 mm per 100 mm length (which occurs in a number of plants) for threads with a pitch of P = 0.75 ... 3 mm are presented in the table.

Comparison ΔD $\genfrac{}{}{0ex}{}{\text{R}}{}$$\genfrac{}{}{0ex}{}{}{\text{2}}$ at R = 0.15 mm for taps with a sharp tooth profile and for R = 0.2 mm for taps with a non-hardened tooth profile with values of the tolerances on the average diameter of the threaded holes that remain on the tearing of the taps, showed that ΔD $\genfrac{}{}{0ex}{}{\text{R}}{}$$\genfrac{}{}{0ex}{}{}{\text{2}}$ with respect to threads with a degree of accuracy of 4H (the most accurate threads machined with nut taps) can be 18-31% and 22-42%, respectively, of these values, depending on the thread pitch. These are already significant quantities, which can become the reasons for the sizes of manufactured threads to exceed the upper permissible limit and, accordingly, the reasons for the decrease in dimensional stability of taps.

 Known designs of taps containing an intake part, a transition section and a gauge part, in which the teeth of the intake part are made with a reduced profile angle and are located on the inverse cone, and the teeth of the transition section, finally forming the thread profile of the holes, are located on the straight cone (see ed. St. USSR 984751 by class B 23 G 5/06 and 1389955 by class and 23 G 5/06). Reducing the profile angles of the teeth on the intake part of these taps can reduce the profile angles of the thread they produce.

 Also known is the design of the tap, containing the intake and gauge parts, the inverse taper of the thread and the teeth with a reduced profile angle along the entire thread length of the tool (see the book "Thread-cutting and thread-rolling tools for metric threads". - Part II. - M., NIITautoprom , 1972. - S. 38-40), selected as a prototype, which forms the angle of the profile of the thread of the holes with teeth with a reduced profile angle. In this case, half of the corners of the tooth profile are connected by a certain dependence with the inverse taper of the thread and the length of the intake part of the tap.

The disadvantage of the prototype is the inability to use it to reduce the above values of the increased angle of the profile of the threaded hollows of the holes and the resulting undesirable value ΔD $\genfrac{}{}{0ex}{}{\text{R}}{}$$\genfrac{}{}{0ex}{}{}{\text{2}}$ .

 The objective of the present invention is to improve the accuracy of threading by taps by eliminating or significantly reducing the increased profile angles of the threaded hollows of the holes.

а средний диаметр резьбы на зубьях заборной части выполнен заниженным на величину
ΔD $\genfrac{}{}{0ex}{}{\text{R}}{\text{2}}$ ≤0,006•k•l_заб, мм,
где R - обратная конусность по резьбе метчика,
φ - угол заборной части метчика,
l_заб - длина заборной части метчика.To solve this problem, the tap containing the intake and calibrating parts, the inverse taper of the thread and the teeth with a reduced profile angle, half the profile angles of the teeth on the intake part are reduced compared to the teeth of the calibrating part by an amount determined by the formula:

and the average diameter of the thread on the teeth of the intake part is made underestimated by
ΔD $\genfrac{}{}{0ex}{}{\text{R}}{}$$\genfrac{}{}{0ex}{}{}{\text{2}}$ ≤0.006 • k • l _zab , mm,
where R is the inverse taper of the thread of the tap,
φ is the angle of the intake part of the tap,
l _zab - the length of the intake part of the tap.

 The reduction of half the profile angles of the teeth and the average diameter of the thread on the intake part of the tap according to the proposed expressions eliminate the deterioration in the accuracy of thread cutting and the associated dimensional stability formed for these reasons.

 Figure 1 shows the design of the intake (cutting) part of the tap; figure 2 is a diagram of the cutting and thread profile of the hole cut by the teeth of a conventional tap; in FIG. 3 is a diagram of the cutting and thread profile of the hole cut by the teeth of the tap of the proposed design.

определяемую из соотношения

а средний диаметр на величину ΔD $\genfrac{}{}{0ex}{}{\text{R}}{\text{2}}$ , определяемую из соотношения:
ΔD $\genfrac{}{}{0ex}{}{\text{R}}{\text{2}}$ ≤0,006•k•l_заб мм,
где R - обратная конусность по резьбе метчика,
φ - угол заборной части метчика,
l_заб - длина заборной части метчика.The tap contains a calibrating part 1 and an intake (cutting) part 2 (l _zab ) with teeth of a reduced profile angle. The calibrating and intake parts are located on the inverse cone. On the calibrating part, the teeth with a reduced profile angle are performed within the limits established by standards or technical requirements. On the intake part, the angle of the tooth profile and the average diameter of the thread are smaller than on the calibrating part. On the intake part, half of the tooth profile angles are reduced by

determined from the relation

and the average diameter by ΔD $\genfrac{}{}{0ex}{}{\text{<figure-callout id="2" label="R" filenames="00000012.png,00000013.png" state="{{state}}">R</figure-callout>}}{\text{2}}$ determined from the relation:
ΔD $\genfrac{}{}{0ex}{}{\text{R}}{}$$\genfrac{}{}{0ex}{}{}{\text{2}}$ ≤0.006 • k • l _zab mm,
where R is the inverse taper of the thread of the tap,
φ is the angle of the intake part of the tap,
l _zab - the length of the intake part of the tap.

на

и средний диаметр резьбы отверстия D₂ по сравнению со средним диаметром d₂ на зубьях метчика на ΔD $\genfrac{}{}{0ex}{}{\text{R}}{\text{2}}$ .
Схема резания метчиком предлагаемой конструкции и образуемый профиль резьбовой впадины отверстия изображены на фиг.3, где 4', 3', 5' - соответственно положения первого и последнего зуба заборной части метчика и первого калибрующего зуба, а 6' и 7' - участки профиля резьбы отверстия, вырезаемые первым и последним зубьями заборной части метчика. При этом величина ΔD $\genfrac{}{}{0ex}{}{\text{R}}{\text{2}}$ у предлагаемого метчика не должна превышать выше указанного ее значения, т.к. в противном случае первый калибрующий зуб метчика будет резать боковыми сторонами на всей их длине, что будет ухудшать условия работы зубом, затруднять стружкообразование и может вызывать ухудшение качества резьбовой поверхности отверстий и уменьшение стойкости инструмента.The combined effect of the inverse taper on the thread of the tap and the teeth of the intake part, worsening the accuracy of thread cutting, is shown schematically in FIG. 2. Figures 4, 3, 5 give the positions of the first and last tooth of the tap sampling part and the first calibrating tooth, respectively; 6 and 7 are the profile sections of the threaded hole of the hole cut by the first and last teeth of the tap sampling part. The specified joint effect increases the angles of the profile of the thread of the hole compared with the profile angles of the teeth of the tap

on the

and the average diameter of the thread of the hole D ₂ compared with the average diameter d ₂ on the teeth of the tap on ΔD $\genfrac{}{}{0ex}{}{\text{R}}{}$$\genfrac{}{}{0ex}{}{}{\text{2}}$ .
The tap cutting scheme of the proposed design and the formed profile of the threaded hole in the hole are shown in Fig. 3, where 4 ', 3', 5 'are the positions of the first and last tooth of the intake part of the tap and the first calibrating tooth, respectively, and 6' and 7 'are sections of the profile hole threads cut by the first and last teeth of the tap intake. Moreover, ΔD $\genfrac{}{}{0ex}{}{\text{<figure-callout id="2" label="R" filenames="00000012.png,00000013.png" state="{{state}}">R</figure-callout>}}{\text{2}}$ the proposed tap should not exceed above its value, because otherwise, the first calibrating tooth of the tap will be cut with its sides along its entire length, which will worsen the working conditions of the tooth, impede chip formation and may cause deterioration in the quality of the threaded surface of the holes and a decrease in tool life.

и ΔD $\genfrac{}{}{0ex}{}{\text{R}}{\text{2}}$ из определяемых по приводимым выражениям полностью устраняют разбивания резьб, вызываемые увеличением углов профиля впадин отверстий и средних диаметров. Одновременно за счет уменьшения вероятности выхода размеров изготовляемых резьб за верхний предел возрастает размерная стойкость инструмента. При других меньших значениях

и ΔD $\genfrac{}{}{0ex}{}{\text{R}}{\text{2}}$ устранение разбиваний резьб по указанным причинам будет неполным.Taps of the proposed design at the highest values

and ΔD $\genfrac{}{}{0ex}{}{\text{R}}{}$$\genfrac{}{}{0ex}{}{}{\text{2}}$ from those determined by the given expressions, the breaking of threads caused by the increase in the profile angles of the hollows of the holes and the average diameters is completely eliminated. At the same time, by reducing the likelihood that the sizes of manufactured threads go beyond the upper limit, the dimensional stability of the tool increases. For other lower values

and ΔD $\genfrac{}{}{0ex}{}{\text{R}}{}$$\genfrac{}{}{0ex}{}{}{\text{2}}$ elimination of thread breaks for the indicated reasons will be incomplete.

и ΔD $\genfrac{}{}{0ex}{}{\text{R}}{\text{2}}$ . На величину

уменьшаются половины углов профиля резьбошлифовального круга. Этим резьбошлифовальным кругом шлифуются зубья заборной части метчика с уменьшением ее среднего диаметра резьбы на величину ΔD $\genfrac{}{}{0ex}{}{\text{R}}{\text{2}}$ .рThe thread of the tap of the proposed design can be made as follows. For the entire threaded length of the tool, teeth are made that do not differ from the teeth on the calibrating part. Values are calculated

and ΔD $\genfrac{}{}{0ex}{}{\text{R}}{}$$\genfrac{}{}{0ex}{}{}{\text{2}}$ . By the amount

half of the corners of the profile of the thread grinding wheel are reduced. This thread grinding wheel polishes the teeth of the tap intake with a decrease in its average thread diameter by ΔD $\genfrac{}{}{0ex}{}{\text{<figure-callout id="2" label="R" filenames="00000012.png,00000013.png" state="{{state}}">R</figure-callout>}}{\text{2}}$ .R

Claims (1)

A tap containing a sampling and calibrating part, a reverse taper on the thread and teeth with a reduced profile angle, characterized in that half the profile angles of the teeth on the sampling part are reduced compared to their values on the calibrating part by an amount determined from the relation:

and the average diameter of the thread on the teeth of the intake part is made underestimated by
ΔD $\genfrac{}{}{0ex}{}{\text{k}}{\text{2}}$ ≤0.006 • k • l _zab , mm,
where k is the inverse taper of the tap thread;
φ is the angle of the intake part of the tap;
l _zab - the length of the intake part of the tap.

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