Grinding Machine

1. Field of the Invention

This invention relates to a grinding machine of the type designed to be held by hand for operation.

2. Prior Art

There are known various compact grinding machines which can be held by hand and operated for finishing a welded portion and for removing flashes from a molding. One such conventional grinding machine 10 shown in FIG. 1 is a pot-type one. The grinding machine 10 comprises a cylindrical housing 12 having one end opened, and a high-frequency induction motor 14. The motor 14 includes a cylindrical casing 14a having one end opened and supported within the housing 12, a lid 14b attached to the open end of the casing 14a for closing it, a rotatable shaft 14c extending through the lid 14b and an end wall 14d of the casing 14a and rotatably borne by a pair of bearing members 16 and 18 secured respectively to the end wall 14d and the lid 14b, a rotor 14e fixedly mounted on the shaft 14c for rotation therewith, and a stator 14f mounted within the casing 14a in surrounding relation to the rotor 14e. The shaft 14c extends outwardly of the housing 12, and a flange member 20 of a disc-shape is fixedly mounted on the outer end portion of the shaft 14c. A grinding wheel 22 is mated with the outer face of the flange member 20 in coaxial relation thereto. A retaining member 24 is snugly fitted in central apertures of the grinding wheel 22 and flange member 20, and a bolt 25 is passed through the grinding wheel 22 and the flange member 20 and is threaded into the outer end of the shaft 14c, so that the grinding wheel 22 is clamped between a flange 24a of the retaining member 24 and the flange member 20 and is retained in place. Thus, the flange member 20 serves as a grinding wheel-mounting member. A propeller-type fan 26 for cooling the motor 14 is fixedly mounted on the inner end of the shaft 14c for rotation therewith. An annular passageway 28 is defined by the inner peripheral surface of the housing 12 and the outer peripheral surface of the casing 14a. A plurality of intake apertures 12a are formed through an end wall 12b of the cylindrical housing 12. With this construction, upon rotation of the motor 14, the fan 26 is rotated to feed the air through the intake apertures 12a and the annular passageway 28 and is discharged from an open end 28a of the passageway 28 as indicated by arrows in FIG. 1, so that the lid 14b and the peripheral wall of the casing 14a are cooled by the air so introduced into the housing 12 to thereby prevent an undue heating of the motor 14.

It is desirable that the grinding machine of this type can be as compact and lightweight as possible since it is held by hand and operated to carry out the grinding. The conventional grinding machine 10 has been found not entirely satisfactory, however, in these respects because of the fact that the fan 26 and the flange member 20 for supporting the grinding wheel 22 are mounted separately on the shaft 14c and is spaced along an axis thereof.

It this therefore an object of this invention to provide a grinding machine of the type which is more compact and lightweight and can be manufactured at lower costs.

According to the present invention, there is provided a grinding machine which comprises a casing having intake port means for introducing the air and discharge port means for discharging the air; a motor mounted within said casing and having a rotatable shaft; a fan member fixedly mounted on said shaft for rotation therewith and having a mounting portion and a plurality of blades provided on said mounting portion for flowing the air through said casing from said intake port means to said discharge port means for cooling said motor; and a grinding wheel secured to said mounting portion.

FIG. 1 is cross-sectional view of a grinding machine provided in accordance with the prior art; and

FIG. 2 is a cross-sectional view of a grinding machine provided in accordance with the present invention.

A grinding machine 30 shown in FIG. 2 comprises a casing or housing 31 composed of a cylindrical body 32 having one end 32e opened and a lid 34 of a generally disc-shape attached to the open end 32e by screws 35. The cylindrical casing body 32 is defined by a peripheral wall 32a and an end wall 32b formed at one end of the peripheral wall 32a remote from the open end 32e. The end wall 32b has a central tubular portion 32c formed at its inner face. A plurality of intake apertures or ports 32d are formed through that portion of the end wall 32b lying between the peripheral wall 32a and the tubular portion 32c. The lid 34 has a central hollow hub 34a having an aperture 34b formed therethrough. A plurality of discharge apertures or ports 34c are formed through a radial outer portion 34d of the lid. A motor 14 comprises a rotatable shaft 14c rotatably borne by a pair of bearing members 36 and 38 received respectively in the hub 34a of the lid 34 and the tubular portion 32c of the end wall 32b, the shaft 14c extending through the aperture 34b of the lid 34. The motor 14 also includes a rotor 14e fixedly mounted on the shaft 14c for rotation therewith, and a stator 14f mounted within the casing body 32 in surrounding relation to the rotor 14e.

A fan member 40 of a one-piece molded construction is fixedly mounted on the outer end of the shaft 14c for rotation therewith. The fan member 40 includes a tubular hub portion 40a snugly fitted on the shaft 14c, a mounting portion 40b of a generally disc-shape formed around the hub portion 40a at its outer end and disposed generally perpendicular to the shaft 14c, and a plurality of blades 40c formed on the inner face of the mounting portion 40b facing the lid 34 and extending radially of the hub portion 40a. The outer face of the mounting portion 40b is depressed at its inner radial portion to provide a circular recess 40d.

A grinding wheel 22 is offset at its central portion to provide a circular projection 22a which is generally complementary in shape to the recess 40d, and a central aperture 22b is formed through the central portion of the grinding wheel 22. The grinding wheel 22 is mated with the outer face of the mounting portion 40b of the fan member 40 with the projection 22a fitted in the recess 40d of the mounting portion 22. A retaining member 24 is fitted in the central aperture 22b and the hub portion 40a, and a bolt 25 is threaded through the retaining member 24 into the outer end of the shaft 14c, so that the grinding wheel 22 is firmly clamped between a flange 24a of the retaining member 24 and the mounting portion 40b to hold the grinding wheel 22 against movement.

A handgrip 44 is fixedly secured at one end to the peripheral wall 32a of the casing body 32, and a switch 46 for operating the motor 14 is mounted on the handgrip 44 handgrip 44.

In operation, the switch 46 is operated to drive the motor 14 to rotate the shaft 14c together with the fan member 40 and the grinding wheel 22, so that the air is drawn by the blades 40c of the fan member 40 through the intake apertures 32d into the casing body 32, and is passed through the motor component parts in the casing body 32 and is discharged from the discharge apertures 34c, as indicated by arrows in FIG. 2. Thus, during the passing of the air through the casing body 32, the motor 14 is suitably cooled.

The fan member 40 serves as both a cooling fan for cooling the motor 14 and a grinding wheel-mounting member. More specifically, the provision of the mounting portion 40b of the fan member 40 obviates the need for a separate grinding wheel-mounting member. Therefore, the shaft 14c can be reduced in length, so that the overall size of the grinding machine 30 can also be reduced. In addition, in this embodiment, there is not required a housing for accommodating the casing body 32 as is the case with the prior art grinding machine shown in FIG. 1. This also contributes to the reduction of the size and weight of the grinding machine. Further, since the air is passed through the casing body 32, the motor 14 can be cooled efficiently. Further, the fan member 40 is disposed outwardly of the casing body 32, the diameter of the fan member 40 can be suitably increased to provide an increased cooling capacity. Thus, the motor 14 is cooled so efficiently that the core of the motor can be reduced in thickness since a great radiation is not required for the core. As described above, the number of component parts of the grinding machine 30 can be reduced so that it can be manufactured at lower costs.

In comparison with the conventional grinding machine 10 shown in FIG. 1, the grinding machine 30 according to the present invention is about 30% less in weight and is about 25% less in length along the axis of the shaft 14c.

While the grinding machine according to the present invention has been specifically shown and described herein, the invention itself is not to be restricted to the exact showing of the drawings or the description thereof. For example, although the fan member 40 is made of a one-piece molded construction, the blades 40c may be fixedly secured to the mounting portion 40b by an adhesive, screws or welding to form a unitary construction.