JPH0536582Y2 - - Google Patents

Description

[Detailed explanation of the idea] (Industrial application field) The present invention relates to a tap for cast holes.

(Prior art) Fig. 6 shows a conventional tap for cast holes, in which 101 is the shank part and 102 is the tap screw part.
03 indicates a biting part.

The chamfered portion 103 of the tapped hole tap described above is capable of drilling an advanced hole directly into the tapered tapped hole portion of the workpiece using the blade in the forward direction of the tap without requiring a parallel pilot hole. Perform thread cutting.

(Problem to be solved by the invention) When directly threading a cast hole with such a tap, it is done on the periphery of the cast hole 107 as shown in FIG. There is variation in the accuracy between the axes of the punched holes, and the desired center axis for thread cutting with a tap is slightly offset from the axis of the punched hole 107. For this reason, when thread cutting is performed using a tap, it is necessary to perform thread cutting with the center axis of the tap located at a position slightly offset from the center axis of the cast hole 107. However, with conventional taps, the blade portion at the chamfered portion 103 edge (margin)
The tap is subjected to a larger resistance force than the inner periphery of the cast hole 107a of the workpiece 108, and the tap tends to follow the cast hole, making it difficult to cut the thread at the desired position. When attempting to do so, the amount of scraping on the inner periphery of the cast hole becomes uneven depending on the location, and as a result, the force applied to the tap in the lateral direction becomes uneven, causing bending, which can lead to the tap tipping over or breaking. There was a problem.

Therefore, an object of the present invention is to provide a tap for a cast hole that does not conform to the shape of the cast hole and does not bend, fall down, or break.

(Means and effects for solving the problem) A margin part is formed in the blade part of the tap in the axial direction of the tap or twisted in the rotational direction of the tap and provided in the threaded part of the tap. In the cast hole tap formed with a flank surface, the blade part of the chamfered part of the cast hole tap has a cutout part at the tip in the rotational direction, and the blade part is recessed parallel to the rake surface. None, this blade has a constant width margin smaller than the width of the tap thread margin.

With this configuration, the cutting edge of the tap chamfering portion has a cutting surface that is axially aligned with the tap or twists in the direction of the tap's rotation, and is therefore not subjected to the resistance caused by the spiral point angle, which is twisted in the opposite direction to the direction of rotation and is applied to spiral point taps, etc. Furthermore, since the margin width of the cutting edge is smaller than the margin width of the tap thread portion, the resistance caused by friction with the cutting surface is reduced. Therefore, due to the reduction in cutting resistance, an advance hole can be drilled without following the tapered cast hole whose center is offset, and the cutting performance is improved. At this time, the margin portion ensures the rigidity of the cutting edge, thereby preventing chipping of the cutting edge, and the guiding action of the margin portion against the cutting surface ensures straightness. Furthermore, by making the margin portion of the tap chamfering portion a constant width parallel to the cutting surface, the cutting resistance can be reduced all the way up to the tap thread portion, minimizing deterioration of the sharpness while ensuring the rigidity and straightness of the cutting edge.

(Example) An example of the present invention will be described below based on the accompanying drawings. Note that the same reference numerals in the drawings indicate the same objects.

FIG. 1 is a front view showing a cast hole tap according to a first embodiment of the present invention, and FIG. 2 is a sectional view taken along the line shown in FIG. 1.

In the first embodiment to the second and third embodiments to be described later, the present invention is applied to a straight groove tap, and in the figure, 1 is a shank portion, 2 is a tap screw portion, and 3 is a chamfered portion. The blade part 4 in the biting part 3 has a flank face 4a at the rear thereof in the direction of rotation shown by the arrow A, and a cutout part with a rectangular cross-section over a predetermined depth on the rake face 4b side of the tip part. 5. The cutout portions 5 are arranged in the axial direction with the same width l for the plurality of blade portions 4 in the chamfered portion 3. By providing the cutout portion 5 in the blade portion 4 at the biting portion 3 in this way, the margin 4c of the blade portion 4 is
It is possible to reduce the resistance force received from the inner circumferential end of the cast hole, and prevent lateral forces from acting on the tap.

3 and 4 show a second embodiment of the present invention, with FIG. 3 being a front view and FIG. 4 being a sectional view taken along the line shown in FIG. In this second embodiment as well, the notches 5 have the same width l as in the first embodiment, and are arranged in parallel in the axial direction. The shape is such that the bottom surface is gently curved and coincides with the rake surface 4b to improve the flow of chips and prevent chips from clogging.

FIG. 5 shows a third embodiment of the present invention.
In this embodiment, a notch 5 is provided in a tap having a spiral blade, and similar to the second embodiment, the notches 5 having the same width are arranged side by side. ing. In this case, the notch portion may be rectangular as shown in the first embodiment.

(Effect of the invention) As is clear from the above explanation, according to the invention,
Since a notch is provided at the tip of the blade in the direction of rotation at the biting part of the tap, it is possible to reduce the resistance force that acts in the lateral direction of the tap during thread cutting, which prevents the tap from turning into a cast hole. To provide a tap for a cast hole, which can prevent the tap from bending, suppress the bending of the tap, and effectively prevent the tap from falling down or breaking.

[Brief explanation of the drawing]

Fig. 1 is a front view showing a tap for a cast hole according to the first embodiment of the present invention, Fig. 2 is a sectional view taken along the line of Fig. 1, and Fig. 3 is a cast hole tap according to the second embodiment of the present invention. A front view showing the hole tap, Figure 4 is the same as Figure 3-
A line sectional view, FIG. 5 is a diagram showing a third embodiment of the present invention, and FIG. 6 is a diagram showing a conventional example. In the drawing, 2 is a threaded part, 3 is a chamfered part,
4 is the blade part, 4a is the flank face, 4b is the rake face, 4c
5 is a margin portion, and 5 is a notch portion.

Claims (1)

[Claim for Utility Model Registration] A margin part and a flank are provided on the blade part of the tap in the axial direction of the tap or twisted in the rotational direction of the tap and in the threaded part following this. In the formed cast hole tap, the blade part of the chamfered part of the cast hole tap has a notch at its tip in the direction of rotation and is a blade part that is recessed parallel to the rake surface. A tap for a cast hole, characterized in that the portion has a margin portion having a constant width smaller than the width of the margin of the tap thread portion.