JPH0417302Y2 - - Google Patents

Description

[Detailed description of the invention] A. Field of industrial application The present invention relates to an improvement of a spiral point tap for thread cutting.

B. Prior Art In order to improve the sharpness of the tap and increase its durability, it is known to provide a relief in the threaded portion and to provide a back taper. Further, a spiral point tap is already known as a tap that discharges chips in the advancing direction (forward) of the tap to prevent chip clogging.

Among conventional spiral point taps, Fig. 1 shows a spiral point tap in which a margin 1 is left on the cutting edge side and a relief 2 is provided only on the back blade side, and Fig. 2 shows a spiral point tap in which a relief 2 is provided from the cutting edge. be.

The spiral point tap shown in Fig. 1, which leaves a margin on the cutting edge side, has poor sharpness and also has poor durability due to frictional heat at the margin.

In the case of a spiral point tap with a relief 2 from the cutting edge without leaving a margin on the cutting edge side as shown in Figure 2, the cutting edge 4 of the spiral point tap groove is larger as it goes toward the tip in the circumferential direction than the cutting edge 3 of the parallel groove. It's retreating.

As shown in Fig. 3A, the thread of the tap has a back taper for clearance in the feed direction, but by providing the clearance from the cutting edge in the threaded portion described above, the cutting edge 4 of the spiral point groove can be tapered. The amount of reverse taper (1/Tc) of the diameter of the threaded portion is the back taper (1/Tc) provided on the thread of the tap.
If it is smaller than Tb), the back taper of the cutting edge of the spiral point groove is a positive value and there is no problem, but as shown in Figure 3A, if it is larger, it becomes a negative back taper and the tap escapes in the feed direction. This will result in a loss of sharpness and durability.

If the amount of reverse taper of the cutting edge of the spiral point groove caused by providing relief from the cutting edge in the threaded portion is 1/Tc, then 1/Tc=2tan・tanβ.

Here α: spiral point angle β: Thread relief angle.

When the back taper provided on the thread of the tap is 1/Tb, a spiral point tap with 1/Tb<1/Tc=2tan・tanβ has a negative back taper of the thread in the spiral point groove, and its sharpness is significantly impaired.

These specifications of a standard spiral point tap are shown below.

Spiral point angle: 20 degrees Thread clearance angle: 10 to 40 minutes Back taper: 2/10000 to 3/1000 As shown in Figure 4, within the specification range of general standard taps, most spiral point grooves have threads at the cutting edge. The back taper of the mountain is negative. One way to prevent this negative back taper is to make the back taper of the thread in the parallel groove larger than the amount of reverse taper described above, but in order to make the spiral point groove have a normal back taper, it is necessary to A large back taper is required, which does not serve as a guide for the threads in the parallel groove, and causes enlargement of the internal thread, which is inappropriate.

In short, in conventional spiral point taps, where the cutting edge side of the land of the chamfered part of the straight groove tap is shaved diagonally so that chips can be easily sent out in the direction of tap movement, this part has a negative back taper and the total It was not possible to make the back taper at the cutting edge position of all threads a uniform positive value, and the sharpness and durability were impaired.

C. Purpose of the invention In order to provide a high-performance spiral point tap that is much sharper and more durable than conventional spiral point taps, the present invention forms a particularly large back taper to reduce the negative back taper described above. The purpose is to make the back taper at the entire cutting edge position a substantially uniform positive value without preventing the above.

D. Structure of the device The device of the present invention obliquely shaves off the cutting edge side of the land of the chamfered portion of a straight groove tap so that chips can be easily sent out in the direction of travel of the tap, and all threaded portions of the tap are In a spiral point tap with relief from the cutting edge, the back taper of all threads is set to an almost uniform positive value 1/Tb at the cutting edge position over the chamfered part and the complete thread part, and the axis-parallel position in the land is set to 1/Tb. In this case, the parallel groove part has a substantially uniform positive value 1/Tb, and the diagonally cut spiral point groove part has a correction value of 1/Tb and 1/Tc=2.
The value is the sum of tanα and tanβ, where α:
Spiral point angle, β: Characterized by the thread clearance angle.

1/Tc=2・tanα・tanβ will be explained in more detail.

In the well-known spiral point tap, as shown in Fig. 9, the thread part has a relief parallel to A to C in Fig. 8, and the back taper has a diameter that gradually becomes smaller on the C side than on the A side. Processed. Therefore, the radius on the cutting edge side becomes A to C in FIG. 10, and the change in radius on the back edge side becomes D to E.

In FIG. 8, the cutting edge when a spiral point groove is provided is A'BC, and the radius at that time is A'BC in FIG.

At this time, on the tip side, due to the thread clearance angle β and the spiral point angle α, the radius on the cutting edge side becomes smaller at A' than at A by the amount δ shown in FIG.

At this time, δ is as follows from Figure 9: Since β is an infinitesimal angle in triangle AA′A″, δ≒tanβ・′ In practice, δ can be set as tanβ・′.

Also, according to Figure 8, in triangle ABA' ′=L・tanα.

∴δ=tanβ・L・tanα.

In Figure 11, Since tanγ=δ/L If the amount of change in radius between A and B is tanγ, tanγ=δ/L=tanβ・L・tanα/L It is indicated by.

Since the taper, which is the diameter, is 2 x slope (radius), the taper at this time is 2 x tanγ, and therefore,
If the taper is 1/Tc, then 1/Tc=2・tanβ・tanα.

Therefore, by adding this to the back taper at the axis parallel position of the spiral point groove and correcting it, the radius at the cutting edge position can be adjusted as shown in Fig. 11.
It can be pulled up from A'-B to A-B, that is, on the extension line of C-B.

E. Function and effect of the invention The 1/2 ratio caused by the presence of the spiral point angle α and the relief angle β of the screw thread in the back taper at the axis parallel position of the spiral point groove.
By correcting by adding the opposite taper amount of Tc=2tanα・tanβ, it is possible to make the back taper at the cutting edge position a substantially uniform positive value over the spiral point portion and the complete thread portion.

The tap of this invention was devised in response to the difficulty of cutting materials for space, nuclear power, and aircraft, which has recently become a particular problem, and is particularly effective in cutting performance for such difficult-to-cut materials. . These materials have extremely low coefficients of thermal diffusion, are easily work hardened, cause the female thread to become smaller, tighten the tap, cause welding, and breakage, resulting in an extremely short service life. An example of the performance of the tap of the present invention on titanium alloy, one of the typical materials, is shown in the following document 1.

Material 1 Cutting performance of this invented tap 1 Type of tap used: Spiral point tap Nominal size: M6 (shown in Figure 7) Number of grooves: 3 grooves Spiral point angle: 20 degrees Spiral point groove length: 6 Length of chamfered part: 4 Relief angle of chamfered part: 5 degrees 32 minutes Material: Powder HSS-T15 2 Working conditions Work material: Titanium alloy 6Al4V HRC 39~40 Solution treatment/precipitation hardening heat treatment Prepared hole: φ5.0×10mm Tapping length: 10mm Machine: Tabletop tapping board Rotation speed: 430r・p・m (8.1m) /min) Cutting oil: Water-insoluble cutting oil 3 Results of use Figure 7 shows a comparison of cutting resistance from tap breakage to the end of its service life.

The tap of the present invention has a positive back taper at the cutting edge of the spiral point groove, and the female thread accuracy fully satisfies JIS grade 2, providing better sharpness and 5 to 6 times more durability than conventional taps.

This will greatly contribute to the improvement of tapping technology for difficult-to-cut materials related to space development, which is said to be entering a new era.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of a conventional spiral point tap that leaves a margin on the cutting edge side and has a relief only on the back blade side. Figure 2 is an explanatory diagram of a conventional spiral point tap that has a relief from the cutting edge. Figure 3 is an explanatory diagram of the taper of the cutting edge of the spiral point tap shown in Figure 1, and Figure 4 shows the clearance angle of the thread in the conventional tap shown in Figure 2, the back taper of the thread in the parallel groove section, and the cutting edge of the spiral point groove. An explanatory diagram showing the relationship with the back taper of the thread, Fig. 5 is an explanatory diagram of the tap of the present invention, and Fig. 6 shows the effective diameter reduction amount of the thread portion at the cutting edge position from the tip of the tap toward the shank side. Fig. 7 shows the performance test results of the conventional type and the inventive type, Fig. 8 is a view of the land portion of the spiral point tap viewed from the thread surface, and Fig. 9 shows the performance test results of the conventional type and the inventive type. Figure 10 is a view of the land viewed from the end face on the chamfering side, and Figure 11 is a diagram in which the radii at points A to C on the cutting edge side are continuously plotted when there is no spiral point tap groove.
The figure is a diagram in which the radius of the cutting edge side A'BC is continuously plotted when a spiral point tap groove A'B is provided. 1... Margin, 2... Relief part, 3... Cutting edge of parallel groove part, 4... Cutting edge of spiral point groove part.

Claims (1)

[Scope of utility model registration request] The cutting edge side of the land of the chamfered part of the straight groove tap is shaved off diagonally so that chips can be easily sent out in the direction of travel of the tap, and all threaded parts are provided with relief from the cutting edge. , the back taper of all threads has an almost uniform positive value 1/ at the cutting edge position over the chamfered part and the complete thread part.
In the axis-parallel position in the land, the parallel groove part has an almost uniform positive value 1/Tb, and the diagonally cut spiral point groove part has the correction value 1/Tc=2・tanα・tanβ added to 1/Tb. The value was taken as
However, here, α: spiral point angle, β:
A spiral point tap characterized by a thread clearance angle.