Hand gripping machine with a suction device

A hand-held grinding machine with a device for the suction of grinding dust comprises a motor with a motor shaft, an eccentric drive for driving a support of a grinding sheet. The machine further includes a fan wheel which carries an element for compensating for imbalance mass of the eccentric drive.

BACKGROUND OF THE INVENTION 
The present invention relates to a hand-held grinding machine. 
Hand grinding machines of the type under discussion include a suction 
device for sucking dust produced during the grinding process, an eccentric 
drive for driving a grinding sheet support and a fan wheel. 
One of conventional grinding machines of the foregoing type has been 
disclosed in European patent application No. 0,138,278. The disadvantage 
of this known grinding machine is that a great number of structural 
components arranged one after another are required in order to transmit 
the drive movement of the motor shaft to the support of the grinding sheet 
and also to provide a suction air flow. This requires a relatively large 
structure height. 
Furthermore, the mass compensation due to the provision of the fan wheel is 
not ideal in the known grinding machine because the balancing mass act far 
from the imbalance mass. Therefore a tilting torgue is produced from the 
action of the imbalance mass and the compensating mass, which unfavorably 
affects the grinding process. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved hand-held 
grinding machine. 
It is another object of the invention to provide a grinding machine which 
is simple and compact. 
These and other objects of the invention are attained by a hand-held 
grinding machine, which comprises a motor having a motor shaft; a grinding 
sheet support; an eccentric drive for said support, connected to said 
motor shaft; and a fan wheel which has an imbalance mass compensated by a 
mass of said eccentric drive. Said wheel has a bore concentrical with the 
motor shaft and receiving an end of the motor shaft, and a recess 
eccentrical to said bore. A pin is received in said recess via at least 
one bearing, said pin holding said grinding sheet support. 
Said fan wheel has vanes and an air guiding ring which forms a portion of 
an end face of the grinding sheet support and has a varying thickness for 
compensating for imbalance mass. 
The fan wheel may have vanes of various thickness for compensating for mass 
imbalance. 
At least one vane may be omitted to compensate for mass imbalance. 
The motor shaft may be supported in a machine housing via the fan wheel. 
One ball bearing or two bearings, of which one is a ball bearing and 
another one is a needle bearing, may be positioned in the fan wheel to 
support said pin therein. 
The fan wheel may be formed of good heat-conductive material. 
Two rows of air-guiding vanes may be provided in the fan wheel, of which 
one row serves for dust suction and cooling the bearings and another row 
serves for cooling the motor. 
Air-admitting openings may be provided in the fan wheel and the housing. 
Due to the provision of the small fan wheel with the compensating mass for 
the drive of the grinding sheet support, the imbalance masses and 
mass-compensating masses can be interchanged. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings in detail, and firstly to FIG. 1 thereof 
which shows the first embodiment of the invention, it will be seen that 
the grinding machine has a housing 1 having a hand grip 2 and an 
additional handrip 3. A drive motor 4 with a fan wheel 5 which serves to 
cool the motor, a further fan wheel 6 and an eccentric drive 7 are 
accommodated in the housing 1. 
A switch 8 with an actuation knob 9 is mounted in the handgrip 2. Motor 4 
is screwed by bolts 10 in the motor housing. The rotor 11 of motor 4 is 
supported on a motor shaft 12 which in turn is supported in ball bearings 
13 and 14. Carbon brushes 15 correspond to a collector 16 of the rotor 11. 
The fan wheel 5 is rotation-fixedly supported on the motor shaft 12 by 
means of a key 17. A collar 18 of the motor shaft 12 and a safety washer 
19 inserted in a recess of the motor shaft 12 secure the fan wheel 5 
against the axial displacement. The same safety washer 19 also serves as a 
stop for a hub 20 of the fan wheel 6. Hub 20 is secured at the end of the 
motor shaft 12 by means of a threaded pin 21. The extension of the hub 20 
receives the ball bearing 14 which forms the second bearing for the motor 
shaft. Accordingly this ball bearing 14 is held on the other side in the 
housing 1. 
The hub 20 carries fan vanes 22,and a ring 23 which can be of various 
thickness. Hub 20 also includes a stepped sylindrical recess 24, the 
central axis of which is parallel to the central axis 26 of the motor 
shaft 12. Recess 24 is positioned eccentrically in respect to the motor 
shaft 12. This recess receives, via two bearings 27 and 28, a pin 29, to 
which a grinding sheet support 30 is connected. A hexagonal portion 31 of 
the pin 29 acts as a rotation transmitter. Hexagonal portion 31 is fit in 
a respective recess of the grinding paper support 30 whereas a bolt 32 
screwed into the threaded bore, provided in the pin 29, holds the grinding 
sheet support 30 on the pin 29 by a washer 33. 
The grinding sheet support 30 includes a soft pad 34 to which a suitable 
grinding sheet 35 is glued or otherwise secured, for example by Velcro 
means. 
A circle 36 indicated by dash-dotted line shows schematically an air outlet 
connection in housing 1, though which connection an exhaust air can flow 
outside. 
Housing 1 is formed of two cover-shaped halves which are held together by 
means of screw connections 37. Bolts 10 also serve to connect these two 
housing halves to each other. An assymetrical material concentration or 
thickening 38 of the ring 23 serves here as a compensating or balancing 
mass for the eccentrically positioned pin 29 with the grinding sheet 
support 30 carried thereby. The compensating mass can be additionally 
obtained such that in the region of the thickening 38 of the ring 23 at 
least one of the vanes 22 would be thicker than others, and at least one 
vane diametrically opposing the thicker vane would be omitted. A 
compensation for a dynamic imbalance can be further obtained by that the 
portion of the ring 23, which is diametrically opposed to the thickening 
38, would be axially offset relative to the thickening 38. Openings 39 
which extend through the grinding sheet 35, pad 34 and grinding sheet 
support 30 form a part of trajectory or path of the suction, which is 
indicated by arrow 40. 
As clear from FIG. 1, imbalance producing masses and imbalance-compensating 
masses can be reversed. It is also clear that fan wheel 6 which has three 
functions has also a space-saving effect. 
In the embodiment shown in FIG. 2, housing 41 is provided with a main 
handgrip 42 and an additional handgrip 43 with a motor 44. A motor shaft 
46 of this motor which carries a rotor 45 is supported in housing 41 by 
means of a ball bearing 47. The end of the motor shaft 46 provided with a 
threaded pin 48 is screwed in a hub 49 of a fan wheel 50. A ball bearing 
52 is inserted in an eccentrical recess 51 of the hub 49. The ball bearing 
52 receives a pin 53 which is secured against an axial displacement, by 
means of a safety washer 54. Bolt 55 can be screwed in the pin 53. Bolt 55 
in turn rigidly connects a grinding sheet support 56 with the pin 53. Hub 
49 forms a disk-shaped rib or web 57 which is concentrical to the motor 
shaft 46. This rib 57 separates two rows of vanes 58 and 59 from each 
other. Both rows of vanes 58, 59 are supported by the hub 49. An annular 
rib 60 formed on the inner wall of the housing 41 engages in a similar 
manner in a respective recess 61 provided between vanes 58 and 59. An 
exhaust air connection indicated by circle 62 overlaps both rows of vanes 
58 and 59. 
A cover 63 which is screwed to the end face of the hub 49 rigidly holds the 
ball bearing 52 in the recess 51. 
Similarly to the embodiment of FIG. 1, the grinding sheet support 56 has a 
soft pad 64 with a grinding sheet 65 connected thereto. Openings 66 are 
provided to guide therethrough the exhaust air. A central opening 67 
formed in the end wall of the housing 41, which faces the grinding sheet 
support 56, defines a further path of exhaust air, which is indicated by 
arrow 68. 
A housing wall 69 has openings 70 through which a cooling air flowing 
through the motor 44 towards the fan wheel 50 can pass to the row of vanes 
58. This embodiment shows that by means of the single fan wheel 50 a 
suction air flow through the row of vanes 59 and a cooling air flow for 
the motor 44 through the row of vanes 58 can be generated. Both air flows 
pass towards the air exhaust connection encircled by reference s 2. 
Therefore, the embodiment of FIG. 2 is even more compact than that of FIG. 
1 and presents a further improvement of the invention. The 
imbalance-compensating mass can be carried out in the device of FIG. 2 in 
the same manner by various thicknesses of the vanes or by the enlargement 
of the mass of the hub. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
hand-held grinding machines differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
hand-helf grinding machine, it is not intended to be limited to the 
details shown, since various modifications and structural changes may be 
made without departing in any way from the spirit of the present 
invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention. 
What is claimed as new and desired to be protected by Letters Patent is set 
forth in the appended claims.