JP2001328011A - Throw-away tip and cutting tool for clamping the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent raising of the opposite side of a cutting edge at cutting time in a throw-away tip clamped with a clamping screw by being flatly placed on a seat surface of a tip clamping recessed part. SOLUTION: This throw-away tip 1 is provided with inclined faces 8a and 9a by obtusely crossing a rake surface 2a and a side surface positioned on the side for abutting to peripheral edge wall surfaces 25 and 26 of the seat surface 23 when flatly placed on the seat surface 23 of the recessed part 22. The peripheral edge wall surfaces 25 and 26 of the seat surface 23 are allowed to abut to the inclined faces in the shape of covering to these inclined faces 8a and 9a, and the inclined faces of the tip 1 are pressed down by the wall surfaces 25 and 26. Thus, the raising of an opposite part of the cutting edge can be prevented by sandwiching the clamping screw 10 by main component force at cutting time, and relaxation of the calmping screw 10 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clamp which is placed flat on a bearing surface of a tip clamping recess formed at the tip of a shank among indexable inserts used for turning and boring. The present invention relates to a flat-shaped insert insert to be fixed, and a cutting tool such as a cutting tool or a boring bar obtained by clamping the insert insert.

[0002]

2. Description of the Related Art A throw-away insert having a flat rake face on its main surface side and a clamp hole penetrating in the thickness direction is flat on a seat surface of a tip clamp recess formed at the tip of a shank. It is placed in a state of being placed, and is clamped by screwing a clamping screw (hereinafter also simply referred to as a screw) inserted from a clamping hole into a screw hole provided on a seat surface thereof.

[0003] Such a throw-away tip (hereinafter simply referred to as a tip), for example, has a cutting edge of 8 (corner) on both sides if it is a negative type and 4 if it is a positive type. It usually has a corner cutting edge. On the other hand, the tip clamping recess of the shank that clamps such a throw-away tip has a shape in which the seat surface substantially corresponds to the shape of the main surface of the tip. In the case of a negative type chip clamp, the peripheral wall surface is formed so as to stand at approximately 90 degrees with respect to the seating surface. Is formed so as to rise, for example, to rise at an upward slope of about 80 degrees,
It is formed so as to restrain each chip.

By the way, when turning a workpiece (work material) with a cutting tool which is placed flat on such a shank and clamped with a clamping screw,
The main component of the cutting force acting in the direction from the rake face to the bottom face of the insert causes the screw to be sandwiched and the portion opposite to the cutting edge to be lifted. On the other hand, this effect cannot be countered by the above-described wall surface, but only by tightening (clamping) the tip with a screw. Therefore, during the cutting, a tensile load always acts on the clamping screw.

[0005]

For this reason, in the case of a cutting tool in which a throw-away tip is placed flat and clamped with a clamping screw and the screw is thin, the clamping force becomes insufficient and chatter occurs on the machined surface. Or loosening of the clamping screw. In some cases, the clamping screw cuts during the cutting, causing trouble such as stopping the machine.

In particular, there is provided a protrusion integrally projecting from the clamping portion, and a tip is provided at one end of the projection (or in the vicinity thereof), and the clamping portion is provided with a tip clamp of a shank. In the case of a throw-away tip that is placed flat on the bearing surface of the concave portion and clamped, the cutting edge that receives cutting resistance is at the tip of the protruding portion, and thus tends to be insufficient in rigidity. Therefore, with this, it is easy to cause chatter on the machined surface, and since a large moment acts due to the main component force, of the clamping parts, the part opposite to the cutting edge is easily lifted, and the screw is loosened. High risk.

[0007] It is an object of the present invention to provide a throw-away insert that can solve such problems and a cutting tool that clamps the insert.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the invention according to claim 1 is provided with a rake face on a main surface side of a flat plate and having a clamp hole penetrating in a thickness direction. Then, a throw-away tip that is placed and clamped flat on the bearing surface of the shank tip clamping concave portion, and is placed flat on the bearing surface of the shank tip clamping concave portion when it is placed flat. At least a portion of the side surface located on the side abutting against the wall surface of the peripheral surface of the seating surface near the main surface with the rake surface and an inclined surface formed by intersecting the main surface with the rake surface at an obtuse angle. It is characterized by being.

The throw-away tip is placed flat on the inclined surface of the chip-clamping recess formed so that the wall surface is in contact with the inclined-away tip. The following is a description of the case where the clamping screw inserted from the clamping hole is screwed in and clamped to form a cutting tool, and machining is performed using the cutting tool. In other words, the chip is sandwiched by the main component force of the cutting resistance, and the part opposite to the cutting edge is lifted by sandwiching the screw, but the peripheral wall surface of the seating surface contacts the inclined surface of the chip. Can not be lifted. In other words, the main component of the cutting resistance received by the chip is received not only by the screw for clamping but also by the peripheral wall surface of the seat surface where the inclined surface of the chip comes into contact, so that a stable clamp (fixation) can be obtained. Therefore, it is possible to prevent the clamping screw from loosening and the accident of cutting the screw. In the means, the `` at least a part of the side surface near the main surface with the rake face '' is that the whole of the side surface in the thickness direction and the main surface with the rake face intersect at an obtuse angle, This means that the entire side surface in the thickness direction may be an inclined surface, and that not only the entire surface but also a part of the portion close to the main surface may be an inclined surface.

The chip of the present invention is not limited to a standard shape such as a regular polygon or a diamond. The invention according to claim 2 includes a clamping portion having a flat plate-like shape and having a clamping hole penetrating in the thickness direction, and a projection integrally projecting from the clamping portion. On one side in the vicinity thereof, there is provided a cutting edge having a rake face on the main surface side of the clamping portion, and the clamping portion is placed flat on the seating surface of the concave portion for tip clamping of the shank and clamped. Wherein the clamp portion is located on a side that comes into contact with a peripheral wall surface of the seat surface when the clamp portion is placed flat on the seat surface of the tip clamp concave portion of the shank. And a slope formed by intersecting, at an obtuse angle, at least a portion of the side surface of the use portion near the main surface having the rake surface and the main surface having the rake surface.

According to a third aspect of the present invention, there is provided a throw-away tip having a flat face having a rake face on its main surface side and having a clamp hole penetrating in a thickness direction of the shank. It is placed flat on the seat surface,
In a cutting tool which is clamped by screwing a clamping screw inserted from a clamping hole into a screw hole provided in the seat surface, the throw-away tip is flat on a seat surface of a tip clamping recess of a shank. At least an oblique angle between the main surface with the rake surface and the main surface with the rake surface among the side surfaces located on the side that comes into contact with the wall surface of the peripheral surface of the seat surface when placed in a stationary shape, It has an inclined surface that is crossed, the peripheral wall surface of the seat surface,
It is characterized by being in contact with the inclined surface.

Further, the invention according to claim 4 is provided with a clamping portion having a flat plate-shaped clamping hole penetrating in the thickness direction, and a projection integrally projecting from the clamping portion. At the tip of the part or one side near it,
A throw-away tip having a cutting edge having a rake face on the main surface side of the clamping portion is placed flat on the seating surface of the tip clamping concave portion of the shank, and provided on the seating surface. In the cutting tool, which is clamped by screwing a clamping screw inserted from the clamping hole into the provided screw hole, the throw-away tip has a portion for clamping which is flat on a bearing surface of a tip clamping concave portion of the shank. At least a portion of the side surface of the clamping portion, which is located on a side that comes into contact with a peripheral wall surface of the seating surface when placed on the surface, near the main surface having the rake surface; and a main portion having the rake surface. The seat is provided with an inclined surface that intersects at an obtuse angle, and a peripheral wall surface of the seat surface is in contact with the inclined surface.

[0013]

FIG. 1 shows a first embodiment of the present invention.
This will be described in detail with reference to FIG. FIG. 1 shows a throw-away tip 1 and a shank 2 according to the present invention.
1 is a plan view and an enlarged view of a main part of a cutting tool (bite) 31 clamped at 1; FIG. 2 is a cross-sectional view taken along line AA of FIG. 1; It is sectional drawing.

The chip 1 of this embodiment is made of a cemented carbide or the like, has a substantially square shape in a plan view, has a flat plate shape having a constant thickness, and has a thickness direction substantially at the center of a rake face 2a formed by one main surface 2. Is provided with a clamp hole 4 penetrating through. A counterbore 4a is provided at the opening on the rake face 2a side of the clamp hole 4.
Such a chip 1 is formed so as to be placed flat on the bearing surface 23 of the chip clamping recess 22 of the shank 21 and clamped. However, chip 1
Are inclined surfaces 8a, 9a which form a cross-section linear shape in which two side surfaces 8, 9 sandwiching the corner 7 opposite to the cutting edge corner 6 intersect with the rake surface 2a at an obtuse angle R1 (both are, for example, 95 degrees). The angle R2 between the inclined surfaces 8a, 9a and the bottom surface 3 is 85 degrees. The rake face 2a and the side faces (flank faces) 12 and 13 at the cutting edge corner 6 are cutting edges having a negative angle that intersect at substantially 90 degrees.

On the other hand, the shank 21 has a rod shape with a rectangular cross section, and the seating surface 23 of the tip clamping concave portion 22 provided at the tip thereof has an approximately square shape slightly smaller than the tip 1. A screw hole 24 is provided substantially at the center. The wall surfaces 25 and 26 perpendicular to the periphery of the seating surface 23 in a plan view rise in a straight line in cross section so as to narrow the space on the seating surface 23. The upper edges of the two inclined wall surfaces 25 and 26 are Each inclined surface 8a, 9a of the chip 1
The height and the inclination angle R3 are set (for example, to 83 degrees) so as to come into contact with the upper edge (rake face).
The portions of the wall surfaces 25 and 26 that are orthogonal to each other in a plan view are cut so as to form the escape portions 27 where the corners 7 do not abut.

In this manner, the chip 1 is placed flat so that the chip bottom surface 3 is seated on the seating surface 23 of the chip clamping concave portion 22 of the shank 21, and the clamping holes 4 are provided.
Is clamped by passing the clamping screw 10 through and screwing it into the screw hole 24 to form a cutting tool 31. In this embodiment, when screwing the clamp screw 10, the head (taper) 10 a of the clamp screw 10 is pressed against the corner 7 of the counterbore 4 a of the clamp hole 4, and the inclined surfaces 8 a, 9 a of the tip 1. Are set so as to be pressed against the wall surfaces 25 and 26 of the chip clamp concave portion 22. In this clamped state, the chip 1 has its side inclined surfaces 8a, 9a in contact with the upper edge portions of the wall surfaces 25, 26 of the chip clamping concave portion 22, and the wall surfaces 25, 26 contact the inclined surfaces 8a, 9a. It has a shape to cover.

When turning the work at the cutting edge corner 6 of the insert 1 in the cutting tool 31 of this embodiment, a main component force acts as shown by an arrow P in FIGS. This force P acts on the rake face 2a downward from above, and in the prior art acts to lift the cutting edge corner 6 and the opposite corner 7 so that the clamping screw 10
Is subjected to tensile stress. However, in the present embodiment, the upper edges of the wall surfaces 25 and 26 of the chip clamp concave portion 22 are in contact with the upper edges of the inclined surfaces 8a and 9a, which sandwich the corner 7 on the opposite side. In addition, such lifting is prevented, and a large stress is prevented from acting on the clamping screw 10. As a result, even when the tip 1 is small and the clamping screw 10 is thin, it is possible to prevent the clamping force from becoming insufficient, causing chattering on the machined surface, and causing the clamping screw to be loosened or cut. You.

In the above embodiment, the inclined surfaces 8a, 9a
Is a linear plane in a sectional view, but may be a curved (arc-shaped) curved surface formed in a sectional view, for example, convex. Further, in the above-described embodiment, the entirety of the side surfaces 8 and 9 of the chip 1 in the thickness direction is inclined to form an inclined surface. However, as shown in FIG.
Of the side surfaces 8 located on the side that comes into contact with the peripheral wall surface 25 of the seating surface 23 when the flat surface is placed on the seating surface 23 of the chip clamping concave portion 22 of FIG. For example, about half the thickness of the deviated portion may intersect with the main surface 2 having the rake face 2a at an obtuse angle, and the inclined surface 8a may be formed to be chamfered. In addition, including this embodiment, the angle R1 formed by the inclined surfaces 8a and 9a and the rake face 2a exceeds 90 degrees and is within 100 degrees (preferably 95 degrees ± 3 degrees).
That is, the inclination angle R2 between the bottom surface 3 and the inclined surfaces 8a and 9a is 8
It is preferable that the angle be 0 degrees or more and less than 90 degrees (preferably, 85 degrees ± 3 degrees).

On the other hand, in each of the above-mentioned embodiments, the peripheral wall surface 25 of the seating surface 23 of the tip clamping concave portion 22 of the shank 21,
Although 26 is an inclined wall surface, the wall surfaces 25 and 26 may be any as long as they contact the inclined surfaces 8a and 9a of the chip 1. That is, the wall surfaces 25 and 26 are inclined surfaces 8 of the chip 1.
By abutting on the a and 9a, the abutment is made in a manner that the chip 1 is prevented from being lifted up. Therefore, the wall surface is not limited to such an inclined wall. However, when the wall is inclined, the angle R3 is preferably set to be smaller than the inclination angle R2 of the chip by about 2 degrees.

Next, a second embodiment of the present invention will be described with reference to FIGS. However, in the present embodiment, the tip 41 has a rhombus shape in a plan view, and
This is embodied as a cutting tool 61 clamped to 1 and is essentially a variation of the above-described embodiment, and there is no essential difference. Therefore, only the differences will be described, and the same reference numerals will be used for the same portions. I will stop it.

That is, in the present embodiment, the tip 41 has a substantially rhombic shape in plan view having the cutting edge 6 at one acute angle corner, and the clamping hole 4 is located on the side opposite to the cutting edge 6 from the center of the rake face 2a. Are provided unevenly in the vicinity of the acute angled corner 7. The opposite acute angle corner 7 does not constitute a cutting edge, and sandwiches the acute angle corner 7 which does not constitute a cutting edge.
The two side surfaces 8, 9 sandwiching the acute angle corner 7 are inclined surfaces 8a, 9a so that the two side surfaces 8, 9 and the rake surface 2a intersect at an obtuse angle.

On the other hand, the seating surface 23 of the chip clamping concave portion 22 of the shank 51 has a diamond shape slightly smaller than the bottom surface 3 of the chip 1, and the two wall surfaces 25, 26 rising up with the escape portion 27 interposed therebetween are in the seating surface 23. A wall surface 25 inclined such that a portion closer to the back (escape portion 27) narrows the upper part of the seating surface 23.
a, 26a. In addition, chip 4
When the seat 1 is seated and the clamping screw 10 is passed through the clamping hole 4 and screwed into the screw hole 24 of the seating surface 23, the tip 41 is drawn into the inclined wall surfaces 25a, 26a at the deep portions of the wall surfaces 25, 26. And the tip side 8,
9 inclined surfaces 8a, wall surfaces 25 at which the upper edge portions of 9a are inclined
a, 26a are formed so as to be in contact with the upper edges and clamped.

In this embodiment, when the tip 41 is clamped, the upper edge of the inclined wall surfaces 25a, 26a of the seat surface 23 covers the inclined surfaces 8a, 9a of the tip 41. In contact. Therefore, in this embodiment as well, similar to the above-described embodiment, lifting of the corner 7 opposite to the cutting edge 6 due to the main component force during cutting is prevented, and thus the same effect as in the above-described embodiment is obtained.

As can be understood from this embodiment, in the cutting tool of the present invention, the peripheral wall surface of the seating surface which is in contact with the inclined surface of the insert is not necessarily required to cover the entire periphery of the seating surface. As shown in FIG. Similarly, although not shown, at least the inclined surface formed by intersecting at an obtuse angle a part of the side surface of the chip near the main surface with a rake surface and the main surface with the rake surface is also used for chip clamping of a shank. It is not necessary to provide the entire surface of the side surface located on the side that comes into contact with the peripheral wall surface of the seat surface when the device is placed flat on the seat surface of the concave portion. In other words, of the same side surface of the chip, the part which is likely to be lifted by the main component force, that is, the side opposite to the cutting edge is partially inclined, and the peripheral surface of the seating surface is in contact with the inclined surface. You may. However, as in the above embodiment, an inclined surface is provided in substantially the entire area of the side surface located on the side in contact with the wall surface,
It is preferable from the viewpoint of stability in clamping of the tip that the peripheral wall surface of the seating surface is abutted so as to cover substantially the entire area of the inclined surface.

Next, a third embodiment of the present invention will be described with reference to FIGS. However, this embodiment is essentially the same as the first embodiment except that the chip 71 has a special shape described below. Therefore, only the differences will be described, and the same portions will be described. The same reference numerals are used. FIG. 9 showing a cross section taken along line EE in FIG. 8 is substantially the same as a cross section taken along line AA in FIG. 1 (FIG. 2). FIG. 10 shows FIG.
Is substantially the same as the sectional view taken along the line BB of FIG.

That is, in the present embodiment, the chip 71 has a clamp portion 73 having a square flat plate shape and having the clamp hole 4 penetrating in the thickness direction, and a projecting portion 74 integrally projecting from the clamp portion 73. It has a cutting edge 76 having a rake face 2a on one side of the tip of the projection 74 on the main surface 72 side of the clamping portion 73, and is suitable for small-diameter inner diameter processing.

Such a throw-away tip 71 is
The clamping portion 73 is placed flat on the seating surface 23 of the tip clamping recess 22 of the shank 81 and is placed in the screw hole 24 provided in the seating surface 23 through the clamping hole 4. It is clamped by screwing in the screw 10 to form a cutting tool 91.

The throw-away tip 71 of the present embodiment has a peripheral wall surface 25 of the seating surface 23 when the clamping portion 73 is placed flat on the seating surface 23 of the chip clamping recess 22 of the shank 81. , 26 and the rake face 2
an inclined surface 78 formed by intersecting the main surface 72 having a at an obtuse angle
a, 79a, which are clamped in contact with the inclined surfaces 78a, 79a so that the peripheral wall surfaces 25, 26 of the seating surface 23 cover the inclined surfaces 78a, 79a.

The cutting tool 91 having such a special shape is suitable for the inner diameter machining of the small shaft part W because the cutting edge 76 is located at the tip of the projection 74. The main component force is large because the protruding portion 74 protrudes greatly, so that the moment becomes large.
The inclined surface side opposite to the cutting edge 76 with the screw 10 interposed therebetween tends to lift. However, in this embodiment,
The peripheral wall surfaces 25 and 26 of the seating surface 23 are
3 is in contact with the inclined surfaces 78a, 79a on the side surfaces of the third member 3 so that the third member 3 is prevented from lifting.
Therefore, it is extremely effective in preventing chattering of the machined surface and loosening of the screw 10.

The chip of the present invention is not limited to the shape of each of the above-mentioned forms, but is provided with a rake face on the main surface side of a flat plate and having a clamp hole penetrating in the thickness direction. If it is a throw-away tip that is placed and clamped flat on the bearing surface of the tip clamping concave portion of the shank, it can be embodied as an appropriate shape including its cutting edge shape. In each of the above embodiments, the cutting edge is described as one. However, for example, in the square chip 1 exemplified in the first embodiment, this is a positive type, and the corner 7 opposite to the cutting edge corner 6 is Rake face 2
The main surface on the opposite side (the bottom surface 3 of the chip of the first embodiment) has a cutting edge, and the cutting edge (corner) can be embodied as two.

The shape or structure of the shank may be embodied in accordance with the type of cutting tool, such as a cutting tool or a boring bar, or a tool post on which the cutting tool is to be mounted, or a condition for mounting on a machine.

[0032]

As is clear from the above description, the tip of the present invention is placed flat on the seating surface of the tip clamping recess formed so as to abut the inclined surface so as to cover the wall surface. It is placed in a shape, and a screw for clamping inserted from a hole for clamping is screwed into a screw hole provided on the seat surface to be clamped to form a cutting tool. . That is, the chip
Although the main component of the cutting force sandwiches the screw and lifts the part opposite the cutting edge,
Since the peripheral wall surface of the seating surface abuts on the inclined surface of the chip, lifting is prevented. In other words, the main component of the cutting resistance received by the chip is not only the clamping screw but also the peripheral wall surface of the seat surface where the inclined surface of the chip contacts, so that a stable clamp (fixation) is obtained. It is effective in preventing the loosening of the clamping screw and the cutting accident.

[Brief description of the drawings]

FIG. 1 is a plan view and a main part enlarged view of a first embodiment of a cutting tool which clamps a throw-away tip 1 according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG. 1;

FIG. 3 is a sectional view taken along line BB of FIG. 1;

FIG. 4 is a diagram showing another form of the inclined surface.

FIG. 5 is an enlarged plan view of a main part of a cutting tool according to a second embodiment of the present invention, which is formed by clamping a throw-away tip.

FIG. 6 is a view as seen from the direction of arrow C in FIG. 5;

FIG. 7 is a view as seen from the direction of arrow D in FIG. 5;

FIG. 8 is an enlarged plan view of a main part of a cutting tool according to a third embodiment of the present invention, which is formed by clamping a throw-away tip.

FIG. 9 is a sectional view taken along line EE of FIG. 8;

FIG. 10 is a sectional view taken along line FF of FIG. 8;

[Explanation of symbols]

 1, 11, 41, 71 Throwaway tip 2, 72 Main face of flat throwaway tip 2a Rake face 4 Hole for clamping 6, 76 Cutting edge 8, 9 Tip side face 8a, 9a Tip slope side face 10 Clamp Screw 21, 51, 81 shank 22 tip clamp recess 23 seating surface 24 screw hole 25, 26 wall surface 31, 61, 91 bytes 73 throw-away tip clamping portion 74 projecting portion 78, 79 side surface of clamping portion 78a, 79a Inclined side surface of the clamping part

Claims (4)

[Claims] 1. A flat plate-shaped clamp having a rake face on its main surface side and having a clamp hole penetrating in a thickness direction thereof, the clamp being placed flat on a bearing surface of a tip clamp concave portion of a shank. A throw-away tip, wherein at least the rake of a side face located on a side that comes into contact with a peripheral wall surface of the seat when the flat is placed on the seat of the tip clamping recess of the shank. A throw-away tip, comprising: an inclined surface formed by obliquely intersecting a portion near a main surface having a surface and a main surface having a rake surface at an obtuse angle. 2. A clamp portion having a flat plate-shaped clamp hole penetrating in the thickness direction, and a protrusion integrally projecting from the clamp portion, and a tip of the protrusion or one near the tip thereof. Side having a cutting edge provided with a rake face on the main surface side of the clamping portion, and the clamp portion is placed flat on the bearing surface of the concave portion for tip clamping of the shank and clamped. A tip, a side surface of the clamping portion positioned on a side that comes into contact with a peripheral wall surface of the seating surface when the clamping portion is placed flat on the seating surface of the tip clamping recess of the shank. A throw-away tip, characterized in that it has an inclined surface formed by intersecting at least an obtuse angle of the portion near the main surface with the rake surface and the main surface with the rake surface. 3. A throw-away insert having a flat plate-shaped rake face on its principal surface side and having a clamp hole penetrating in the thickness direction is placed flat on a seat surface of a tip clamp recess of a shank. And, in the screw hole provided in the seat surface,
In a cutting tool, which is clamped by screwing a clamping screw inserted from a clamping hole, the throw-away tip is placed on a seating surface of a tip clamping recess of a shank. At least a part near the main surface with the rake surface of the side surfaces located on the side abutting the wall surface of the peripheral edge of the surface, and an inclined surface formed by intersecting the main surface with the rake surface at an obtuse angle,
A cutting tool, wherein a peripheral wall surface of the seat surface is in contact with the inclined surface. 4. A flat plate-shaped clamping portion having a clamping hole penetrating in a thickness direction, and a projection integrally projecting from the clamping portion, wherein one end near the tip of the projection or one in the vicinity thereof is provided. On the side, a throw-away tip having a cutting edge having a rake face on the main surface side of the clamping portion is placed flat on the seating surface of the tip clamping concave portion of the shank, and In a cutting tool, which is clamped by screwing a clamping screw inserted from a clamping hole into a screw hole provided on a surface, the throw-away tip has a shank whose shank is a seat of a tip clamping recess. A main surface having at least the rake surface among the side surfaces of the clamping portion positioned on a side that comes into contact with a peripheral wall surface of the seat surface when the flat surface is placed on the surface. A cutting tool comprising: an inclined surface formed by intersecting a deviated portion and a main surface having the rake face at an obtuse angle, and a peripheral wall surface of the seat surface is in contact with the inclined surface. .