Portable power tool

A portable power tool for operating a wheel type grinding or cutting working implement comprises a housing (10), a rotating output spindle (11) with a working implement supporting flange (14), a safety guard (16) adjustably supported on a guide flange (15) on the housing (10), and a selectively operable arresting device (18) for positively engaging lock openings (20) on the safety guard (16) for locking the latter in alternative positions relative to the housing (10), wherein the support flange (14) is provided with a number of peripheral indentations (21), and the arresting device (18) comprises a lock bolt (19) which is longitudinally shiftable between a first position in which it engages either one of the lock openings (20) on the safety guard (16), a second position in which it engages either one of the lock openings (20) on the safety guard (16) as well as either one of the support flange (14) indentations (21), and a third position in which it neither engages anyone of the safety guard (16) lock openings (20) nor anyone of the support flange (14) indentations (21). A spring means (28, 29) is provided to bias the lock bolt (19) toward the first position.

This invention pertains to a portable power tool intended for operating a 
wheel type grinding or cutting working implement. 
In particular, the invention concerns a power tool of the above type 
including a housing, a rotation motor, an output spindle drivingly 
connected to the motor, a working implement supporting flange carried on 
the output spindle, a safety guard partially surrounding the working 
implement and movably supported on the housing for movement between 
alternative positions, and a selectively operable arresting device for 
engagement with a lock means on the safety guard in the alternative 
positions of the latter. 
A power grinder of this type is previously described in U.S. Pat. No. 
4,924,635. Each one of the three embodiments or the safety guard arresting 
device shown in this patent comprises a pivotable maneouver lever by which 
latch dogs are disengaged from a safety guard locking means for enabling 
adjustment of the safety guard working position. 
In DE 43 37 023 and DE 43 44 128 there are shown power grinders provided 
with spindle arresting means by which fitting and removal of grinding 
tools on the output spindle is facilitated. 
An object of the invention is to provide a portable power grinder of the 
initially described type in which a safety guard locking means in a 
structively simple way is combined with an output spindle arresting device 
.

The power tool illustrated in the drawing figures comprises a housing 10 in 
which is located a rotation motor (not shown), and an output spindle 11. 
At its outer end, the latter carries a ball type automatic balancing 
device 12 which is formed with a flat radial surface 13 for supporting 
axially a working implement attached to the spindle 11. Accordingly, the 
balancing device 12 forms a support flange 14 for the working implement. 
A balancing device of this type is previously known per se through GB 832 
048 and does not form any part of this invention. 
At the output end of the tool housing 10, there is provided a guide flange 
15 which is located concentrically with the output spindle 11 and on which 
is adjustable mounted a safety guard 16. The latter is rotatably 
adjustable in a well known manner to facilitate operation of the grinder 
in different working positions. 
The housing 10 is provided with a selectively operable safety guard 
arresting device 18 which comprises a bore 17 in the housing 10 extending 
substantially radially in relation to the output spindle 11 and a lock 
bolt 19 which is longitudinally displaceable in the bore 17. The lock bolt 
19 is shiftable between three alternative positions, namely a first 
position in which it locks both the safety guard 16 against movement, a 
second position in which it locks both the safety guard against movement 
and the output spindle against rotation, and a third inactive position in 
which it locks neither the safety guard 16 nor the output spindle 11. 
For obtaining these lock functions, the safety guard 16 is provided with a 
number of through openings 20 arranged in a circumferential row, and the 
balancing device 12 is formed with a number of indentations or dead end 
holes 21 on its periphery. The housing 10 is formed with a heel 22 which 
is located between the safety guard 16 and the balancing device 12 and 
which has a guide bore 23 to form a radial support for the lock bolt 19. 
In its first position, illustrated in FIG. 3a, the lock bolt 19 extends 
through one of the openings 20 in the safety guard 16 and reaches about 
half way into the guide bore 23 in the housing heel 22. In this position, 
the safety guard 16 is locked against rotation. 
This is the neutral position of the lock bolt 19, which the latter normally 
occupies during operation of the tool. 
In its second position, illustrated in FIG. 3b, the lock bolt 19 is 
displaced toward the center of the output spindle 11 and engages by its 
forward end one of the dead end holes 21 of the balancing device 12. In 
this position, the lock bolt 19 prevents positively any rotation of the 
output spindle 11 in order to facilitate mounting or removal of a grinding 
or cutting wheel. 
In its third position, illustrated in FIG. 3c, the lock bolt 19 is 
retracted from the holes 21 of the balancing device 12 as well as from the 
openings 20 of the safety guard 16. The angular position of the safety 
guard 16 may now be altered. 
For manual operation of the lock bolt 19, there is provided a lateral 
handle 24. The latter is secured to the lock bolt 19 by a coaxial pin 25 
and extends to the outside of the housing 10 through a slot 27. 
For centralizing the lock bolt 19 in its first, normal operating position, 
there are provided two springs 28, 29 acting in opposite direction. One of 
the springs 28 acts on the lock bolt 19 in a direction away from the 
spindle locking position, whereas the other spring 29 biasses the lock 
bolt 19 in a direction away from the inactive third position in which the 
safety guard 16 is unlocked. 
The spring 28 encircles the lock bolt 19 and takes support against a 
shoulder 30 in the bore 17, whereas the spring 29 takes support against a 
plug 31 secured in the bore 17. 
At its forward end, the lock bolt 19 is formed with a bevelled end surface 
33 the purpose of which is to prevent the lock bolt 19 from entering the 
holes 21 during rotation of the output spindle 11. The surface 33 faces a 
direction opposite to the direction of rotation of the output spindle 11 
which is illustrated by the arrow in FIGS. 3a-c. An accidental engagement 
between the lock bolt 19 and anyone of the holes 21 on the balancing 
device 12 during rotation of the latter would be hazardous to both the 
tool parts and to the operator. This is prevented by the orientation of 
the surface 33. 
The angle of inclination of the bevelled surface 33 is illustrated by the 
letter .alpha. in FIG. 4. In practice, the inclination angle .alpha. 
should be in the range of 5.degree. to 12.degree. to provide a safe 
operation. An angle of 8.degree. has proven to work well. 
At its rear end, the lock bolt 19 is formed with a tubular socket portion 
34 for guidingly supporting one end of the spring 29. A transverse 
aperture 35 is provided in the lock bolt 19 for receiving the inner end of 
the maneouver handle 24. The coaxial pin 25 is formed with a radial flange 
36 which is engaged by the spring 29 to retain the pin 25 in its handle 
locking position. See FIG. 4. 
By this concept in which a combined safety guard and output spindle 
arresting means is provided, there is obtained a structively simple power 
tool design as well as a simple tool handling. 
It is to be understood that the embodiments of invention are not limited to 
the above described example but could be freely varied within the scope of 
the claims.