Horizontal rotary hook of sewing machine

1. A horizontal rotary hook for a sewing machine, the horizontal rotary hook comprising:

an inner rotary hook including an attracted member comprising a metal in an outer lower surface portion;

a permanent magnet that attracts the inner rotary hook;

a magnet plate accommodating the permanent magnet and provided with a mounting hole at a center of a diameter thereof;

a non-magnetic outer rotary hook accommodating the magnet plate and including a shaft hole at a center of a diameter of an inner bottom portion thereof; and

a hook supporting shaft that is inserted through the mounting hole of the magnet plate and the shaft hole of the outer rotary hook and includes, at an upper end thereof, a flange for rotatably supporting the outer rotary hook and the magnet plate,

wherein an area of a surface of the inner bottom portion, which in a plan view overlaps with the magnet plate, has a coarse surface and one of a surface of the flange of the hook supporting shaft and a surface of the magnet plate that faces the flange is a smooth surface.

2. The horizontal rotary hook for the sewing machine according to claim 1 , wherein a low friction member for reducing a friction coefficient is provided between the flange of the hook supporting shaft and the magnet plate, so that the friction coefficient between a contact surface of the magnet plate that comes into contact with the outer rotary hook and the outer rotary hook is set to be larger than the friction coefficient between the surface of the flange of the hook supporting shaft and the magnet plate.

3. The horizontal rotary hook for the sewing machine according to claim 1 , wherein the flange is subjected to a surface finishing for reducing a friction coefficient between the flange of the hook supporting shaft and the magnet plate, so that a friction coefficient between a contact surface of the magnet plate that comes into contact with the outer rotary hook and the outer rotary hook is set to be larger than a friction coefficient between the surface of the flange of the hook supporting shaft and the magnet plate.

4. The horizontal rotary hook for the sewing machine according to claim 1 , wherein said surface of the magnet plate is subjected to a surface finishing for reducing a friction coefficient between the flange of the hook supporting shaft and the magnet plate, so that a friction coefficient between a contact surface of the magnet plate that comes into contact with the outer rotary hook and the outer rotary hook is set to be larger than the friction coefficient between the flange of the hook supporting shaft and the magnet plate.

5. The horizontal rotary hook for the sewing machine according to claim 1 , wherein the surface of the flange faces the magnet plate.

6. The horizontal rotary hook for the sewing machine according to claim 1 , wherein the surface of the flange of the hook supporting shaft is the smooth surface.

7. The horizontal rotary hook for the sewing machine according to claim 1 , wherein said surface of the magnet plate that faces the flange is the smooth surface.

8. The horizontal rotary hook for the sewing machine according to claim 1 , wherein an uppermost surface of the magnet plate is located below a bottom surface of the permanent magnet.

9. The horizontal rotary hook for the sewing machine according to claim 1 , wherein, with respect to a bottom surface of the magnet plate, a height of an upper surface of the inner bottom portion is less than a height of an upper surface of the magnet plate.

10. The horizontal rotary hook for the sewing machine according to claim 1 , wherein an entirety of the surface of the inner bottom portion includes the coarse surface.

11. The horizontal rotary hook for the sewing machine according to claim 1 , wherein, in the plan view, the magnetic plate extends on the inner bottom portion outside the area of the surface of the inner bottom portion that overlaps with the magnet plate.

12. A horizontal rotary hook for a sewing machine, the horizontal rotary hook comprising:

an inner rotary hook including an attracted member comprising a metal in an outer lower surface portion;

a permanent magnet that attracts the inner rotary hook;

a magnet plate accommodating the permanent magnet and provided with a mounting hole at a center of a diameter thereof;

a non-magnetic outer rotary hook accommodating the magnet plate and including a shaft hole at a center of a diameter of an inner bottom portion thereof; and

a hook supporting shaft that is inserted through the mounting hole of the magnet plate and the shaft hole of the outer rotary hook and includes, at an upper end thereof, a flange for rotatably supporting the outer rotary hook and the magnet plate,

wherein a contact surface of the magnet plate, which comes into contact with the outer rotary hook, is a coarse surface and a surface of the flange of the hook supporting shaft is a smooth surface.

13. A horizontal rotary hook for a sewing machine, the horizontal rotary hook comprising:

an inner rotary hook including an attracted member comprising a metal in an outer lower surface portion;

a permanent magnet that attracts the inner rotary hook;

a magnet plate accommodating the permanent magnet and provided with a mounting hole at a center of a diameter thereof;

a non-magnetic outer rotary hook accommodating the magnet and including a shaft hole at a center of a diameter of an inner bottom portion thereof; and

a hook supporting shaft that is inserted through the mounting hole of the magnet plate and the shaft hole of the outer rotary hook and includes, at an upper end thereof, a flange for rotatably supporting the outer rotary hook and the magnet plate,

wherein a contact surface of the magnet plate, which comes into contact with the outer rotary hook, is a coarse surface and another surface of the magnet plate that faces the flange is a smooth surface.