Electrical hand tool with reciprocating drive

The invention relates to an electric hand tool comprising a housing, a reciprocating carrier for an operating member drivable by means of an electric motor placed in the housing, wherein the carrier is guided by at least two guide members fixed in the housing, wherein the guide members each comprise two guides placed on either side of the carrier, wherein one of the guides is fixedly attached and the other guide is provided with means for urging the guide against the carrier. The occurrence of play, wear, noise nuisance and vibrations is thus avoided. According to a preferred embodiment, both guides forming part of a guide member are formed by guide rollers received in a frame and the frame is fixedly mounted by means of a shaft extending through one of the guide wheels and a spring is placed between the housing and the frame such that the spring urges the other guide wheel into contact with the carrier.

The invention relates to an electric hand tool comprising a housing, a 
reciprocating carrier for an operating member drivable by means of an 
electric motor placed in the housing, wherein the carrier is guided by at 
least two guide members fixed in the housing. 
Such devices are generally known, for instance in the form of electric saws 
or files. 
The operating member, that is, the saw blade or the file, is attached to a 
carrier, which carrier forms part of the electric hand tool. The carrier 
is guided by at least two guide members and driven by means of a 
crankshaft mechanism. 
As a result of the varying loads during use of the electric hand tool, 
great changes occur in the loads of the guide members. As a consequence, 
when the latter are embodied rigidly, as known in the prior art, play will 
occur after a period of use, which stimulates further wear, produces noise 
nuisance and causes vibrations which are perceived as unpleasant by the 
user. 
The object of the present invention is to provide such an electric hand 
tool wherein the above stated problems are avoided. 
This object is achieved in that the guide members each comprise two guides 
placed on either side of the carrier, wherein one of the guides is fixedly 
attached and the other guide is provided with means for urging the guide 
against the carrier. 
According to a preferred embodiment both guides forming part of a guide 
member are formed by guide rollers received in a frame and the frame is 
fixedly mounted by means of a shaft extending through one of the guide 
wheels and a spring is placed between the housing and the frame such that 
the spring urges the other guide wheel into contact with the carrier.

Shown in the FIGURE is an electric saw 1 formed by a housing 2 in which an 
electric motor is placed whereof the anchor 3 is shown. The motor shaft 4 
which is mounted in the housing 2 by means of a bearing 5 is provided with 
a toothing 6 which is in engagement with a gear wheel 7. The latter is 
formed by two halves so that it is possible to manufacture each of the 
gear wheel halves by means of stamping, which considerably limits the 
production costs. 
The gear wheel 7 is mounted about a shaft 8 which is fixed in a disc 9 
enclosed in the housing 2. Fixed eccentrically to the gear wheel 7 is a 
shaft 10 on which a crankshaft 11 is rotatably mounted. The crankshaft 11 
is likewise rotatably connected to a carrier 12. The latter is received 
for movement between two guide members 13 and 14 respectively which will 
be elucidated hereinafter. Further, a pin 15 is arranged diametrically 
opposite shaft 10 and likewise in eccentric manner, on which pin a 
disc-like cam 16 is fixedly attached to the gear wheel 7 concentrically of 
the pin and extending around the shaft 8. A counter-weight 17 extends 
around the cam 16. The counter-weight is provided with a recess 18 to 
provide space for the carrier 12. 
An impact ridge 19 is arranged on top of the counter-weight 17. 
Both guide members 13, 14 are formed by two flat plates 20, 21 which are 
mutually joined by means of a long shaft 23, which in addition to 
extending through the housing also extends through the plates 20, 21, and 
by a short shaft 25 which only extends through both flat plates 20, 21. 
Both shafts 23, 25 are fixedly connected to both plates 20, 21. A guide 
roller 24 is arranged rotatably on the long shaft 23. A roller 26 is 
arranged rotatably on the short shaft 25. 
As a result of this construction, the upper roller 24 is mounted rotatably 
but fixedly in the housing 2, while the shaft 25 of the lower roller 26 is 
rotatable on the shaft 23. The carrier 12 extends between both rollers 24, 
26. To bring the lower roller 26 into contact with the carrier 12 a spring 
27 is arranged between housing 2 and guide member 13. 
The construction of the other guide member 14 will now be discussed. Guide 
member 14 comprises two flat plates 28, 29 connected by a short shaft 31 
on which a roller 32 is arranged for rotation; and along shaft 33 on which 
a roller 34 is arranged for rotation. 
The long shaft 33 is mounted on either side in a sub-frame 35 that is 
formed by a first plate 36 and a second plate 37. The long shaft 33 
extends through both plates 36, 37 of the sub-frame. The sub-frame is 
fixed for reciprocating in its entirety in the direction transversely of 
the direction of movement of the carrier in the housing 2. 
By means of a spring 38 arranged between the upper part of housing 2 and 
the sub-frame 35 the latter is constrained downward. In the sub-frame 
between both plates 36, 37 is again arranged a shaft 39 on which a roller 
40 is mounted. The shaft 39 herein extends through slots 41, 42 arranged 
in the plates 36 and 37 respectively. The shaft 39 with the roller 40 
fixed thereto is thus movable in the direction defined by the slots 41 
respectively 42. A spring 43 is further arranged which exerts a force on 
the guide member 14 such that the roller 32 is urged into contact with the 
carrier 12. A spring 49 arranged between the housing 2 and the roller 40 
urges the roller to a preferred position located as far downward as 
possible. 
An eccentric 44 is arranged to adjust the stroke of the sub-frame 35. The 
eccentric 44 is formed by a shaft 45 which extends through the housing 2 
and to which is fixed a lever 46. Arranged eccentrically on the shaft 45 
is a thickened piece 47 which can be rotated by means of the lever 46. It 
is thus seen that the rollers 32,34 engage respective upper and lower 
planar surfaces of an offset extension of the carrier 12. Again, these 
parallel planar surfaces are perpendicular to a plane containing the blade 
48. It is herewith possible to limit the stroke of the sub-frame 35 on the 
underside. 
The operation of the present device will now be elucidated. 
The shaft 4, and therewith the gear wheel 7, is set into rotation by means 
of the electric motor 3. The carrier 12 is driven by means of the crank 
mechanism fixed to the gear wheel so that the carrier 12 performs a 
reciprocating movement. As a result a saw-blade 48 attached to the carrier 
12 will likewise perform a reciprocating movement. It is of course 
possible to arrange another tool instead of a saw-blade, for instance a 
filing blade. 
By means of the disc 16 the counter-weight 17 is driven such that it 
likewise performs a reciprocating movement. The phase of the reciprocating 
movement of the counter-weight 17 is opposed to that of the carrier 12 so 
that vibrations in the direction of the reciprocating movement are 
eliminated as far as possible. 
When the workpiece is used an upward oriented force will generally be 
absorbed by the saw-blade 48. 
To absorb this force the roller 24 is fixedly mounted in housing 2 by means 
of the shaft 23. The other roller 26 likewise forming part of the first 
guide member 13 is urged into contact with the carrier 12 by means of the 
spring 27 so that play is prevented. 
As a consequence of the upward directed force absorbed by the saw-blade 48 
the roller 34 will have to absorb a downward directed force. The long 
shaft extending through the roller 34 is mounted in the sub-frame 35 for 
this purpose. The spring 43 ensures that the roller 32 is urged into 
contact with the carrier 12 so that play is likewise prevented in the 
guide member 14. 
As previously stated, the sub-frame 35, which essentially determines the 
position of the roller 34, is mounted in the housing transversely of the 
main direction of movement of the carrier 12. 
In order to provide a "feed" which is particularly important with the 
application as saw, the impact ridge 19 is arranged on the counter-weight 
17. When the impact ridge 19 is moved forward it presses against the 
roller 40 so that the latter, also as a result of the form of the slots 41 
and 42, is pressed upward. That is to say, the sub-frame 35 is mounted for 
reciprocating movement in a plane substantially perpendicular to the axis 
of reciprocation of the carrier 12. The horizontal component of the force 
exerted by the impact ridge prevents the roller 40 being moved upward 
relative to the sub-frame. The sub-frame is thus moved upward counter to 
the force of the spring 38. During the return movement of the 
counter-weight the horizontal component of the force exerted by the other 
side of the impact ridge will cause the roller to move upward, wherein the 
shaft 39 moves obliquely upward through the slots 41. Thus the sub-frame 
then remains at rest, as does the saw-blade. 
This movement of the sub-frame provides, as stated above, the feed of the 
operating member, that is, that at the cam beginning of a work stroke of 
the operating member the operating member is pressed with force into the 
workpiece to make the reciprocating movement of the operating member as 
effective as possible. 
The lowest position of the stroke of the sub-frame 35 can be changed by 
means of the lever 46 so that it is possible to carry the sub-frame to a 
position such that the protrusion 19 no longer comes into contact with 
roller 40.