Horizontal external broaching machine

A horizontal external broaching machine has a horizontally movable tool slide disposed on a horizontal machine frame. The tool slide, which serves to receive a broaching tool, is supported laterally and vertically, by means of guide surfaces, on guide surfaces of the machine frame. The tool slide is provided with a toothed rack which extends in the direction of movement of the tool slide. A driving pinion, provided with corresponding teeth, meshes with the rack, the pinion being adapted to be driven via a shaft by a drive motor. The center of gravity of the tool slide and of the rack together with the associated drive pinion are disposed on one side of the guide surfaces. The drive pinion is arranged vertically above the rack, the rack and the drive pinion being provided with helical teeth which, during driving in the broaching direction, are acted on by a force directed in the direction of the shaft of the drive pinion and intensifying the bearing forces acting on the guide surfaces for the tool slide.

BACKGROUND OF THE INVENTION 
This invention relates to horizontal external broaching machines having a 
horizontally movable tool slide or carriage disposed on a horizontal 
machine frame, in which the tool slide, which serves to receive a 
broaching tool, is supported laterally and vertically by means of guide 
surfaces on guide surfaces of the machine frame, and in which there is 
disposed, on the tool slide a toothed rack which extends in the direction 
of movement of the tool carriage and in which a driving pinion provided 
with corresponding teeth meshes and is adapted to be driven by means of a 
shaft of a drive motor. 
A horizontal external broaching machine of this kind is known, for example, 
from a leaflet of THE LAPOINTE MACHINE TOO COMPANY, entitled "SRHE 
LAPOINTE Horizontal Broaching Machine", in which the tool carriage is 
supported in relation to the machine frame on the one hand by two lower 
guide surfaces, which are inclined in relation to the vertical and in 
relation to the horizontal, and by an upper guide surface which is 
likewise inclined in relation to the vertical and to the horizontal. The 
rack is disposed on the underside of the tool slide or carriage with its 
teeth lying at the bottom. A drive pinion, which like the rack is provided 
with herringbone teeth, is disposed below the rack. Despite the extremely 
heavy construction of this machine, manufacturing accuracy in the range of 
a few .mu.m is not possible with its aid. 
SUMMARY OF THE INVENTION 
It is the principal object of the present invention to provide a horizontal 
external broaching machine of the kind first described above by which 
extremely great machining accuracy can be achieved. 
According to the present invention there is provided a horizontal external 
broaching machine having a horizontally movable tool slide disposed on a 
horizontal machine frame, the tool slide, which serves to receive a 
broaching tool, being supported laterally and vertically, by means of 
guide surfaces, on guide surfaces of the machine frame, and in which the 
tool slide is provided with a toothed rack which extends in the direction 
of movement of the tool slide and in which a driving pinion provided with 
corresponding teeth meshes. The pinion is adapted to be driven via a shaft 
by a drive motor. The center of gravity of the tool slide and of the rack 
together with the associated drive pinion are disposed on one side of the 
guide surfaces, the drive pinion being arranged vertically above the rack. 
The rack and the drive pinion are provided with helical teeth which during 
driving in the broaching direction, are acted on by a force directed in 
the direction of the shaft of the drive pinion and intensifying the 
bearing forces acting on the guide surfaces for the tool slide. 
As a result of the above-mentioned arrangement of the guides of the tool 
slide and of the tool slide drive in relation to one another, it is 
ensured that the forces acting on the guide surfaces and resulting on the 
one hand from the dead-weight of the tool slide and on the other hand from 
the driving forces acting on the rack will be in the same direction. This 
has the consequence that the bearing forces acting on the guide surfaces 
through the dead-weight of the tool slide are still further increased 
during the drivinging of the tool slide in the broaching direction. The 
guide surfaces are therefore not relieved of load, so that it is reliably 
ensured that the tool slide will not perform any relative movement in 
relation to the guide surfaces, which in practice otherwise leads to the 
manufacturing inaccuracies mentioned. Due to the fact that the rack and 
consequently also the drive pinion are provided with helical teeth, during 
the driving of the tool slide in the broaching direction, an additional 
force similarly directed to the previously mentioned forces acts on the 
guide surfaces. In addition, horizontal stabilization of the tool slide is 
also thereby achieved. 
In a particularly simple preferred aspect of the present invention, the 
center of gravity of the tool slide and the rack together with the 
associated drive pinion is disposed on the opposite side of the guide 
surface, with respect to the broaching tool. 
Furthermore, it is particularly advantageous for the two guide surfaces of 
the machine frame, which are disposed in a common vertical plane, to be 
provided to take the horizontal forces. Moreover, it has been found 
advantageous for a machine frame guide surface which is inclined in 
relation to the vertical and in relation to the horizontal to be provided 
to take the vertical forces and to be associated with a web which is 
provided in the tool slide and extends between the rack and the guide 
surface. The forces emanating from the rack are thus transmitted without 
bending loads to the associated guide surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown particularly in FIGS. 1 and 3, an exemplary horizontal external 
broaching machine according to the present invention includes a 
horizontally disposed machine frame 1, on which a tool slide 2 is mounted 
for reciprocal horizontal sliding in accordance with the double 
arrow-headed line 3 showing the directions of movement. At the side of the 
machine frame 1 is disposed a so-called angle table 4, which carries a 
cradle table 5 which is pivotable on a circular arc path defined by 
surface 6 lying in a vertical plane. On the cradle table 5 is disposed a 
circular dividing table 7 which is rotatable about its center axis 8. The 
center axis 8 also extends through the center point 9 of the circular arc 
path defined by surface 6. At the foot of the machine frame 1 is provided 
a coolant container 10. 
On the tool slide 2 is fastened a tool holder 11, to which in turn a 
broaching tool 12 is fastened by means of an intermediate holder 13, as 
shown in FIGS. 4 and 5. 
The tool slide 2 is guided and supported in relation to the machine frame 1 
by means of two guide bars 14, 15 lying in a common vertical plane. The 
upper guide bar 14 and the lower guide bar 15 both have a vertical guide 
16 and 17 respectively, these two guide surfaces 16, 17 also lying in a 
common vertical plane. These two guide surfaces 16, 17 are open in the 
direction of the broaching tool 12, which is disposed laterally of the 
tool slide 2, or in the direction of the angle table 4. The two guide bars 
14, 15 are mounted on a particularly sturdy and torsionally stiff vertical 
wall 18 of the machine frame 1, which wall is braced against the machine 
frame 1 by means of stiffening webs 19. 
The tool slide 2 is provided with guide surfaces 20, 21 which are 
associated with the two guide surfaces 16, 17 and likewise lie in a common 
vertical plane, and which bear against the respective guide surfaces 16, 
17. 
On the lower guide bar 15 is also provided a guide surface 22 which is 
inclined in relation to the horizontal and to the vertical and which is 
situated on the side of the lower guide bar 15 remote from the broaching 
tool 12 or angle table 4. On the tool slide 2 is in turn provided a guide 
surface 23 which is associated with and lies against the said guide 
surface 22. In the region of the bottom end of the upper guide bar 14 and 
of the upper end of the lower guide bar 15 there are provided respective 
recesses 24 and 25 (FIG. 5) in the tool slide 2, in order to ensure that 
the mutually associated guide surfaces will lie correctly against one 
another without edge pressure. 
On the upper face of the tool slide 2, on the opposite side of the guide 
bars 14, 15 with reference to the broaching tool 12, a corresponding 
recess 26 in the tool carriage 13 contains a toothed rack 27 which extends 
in the direction of movements indicated by the line 3 and which on its 
upper face is provided with helical teeth 28. This rack lies at each of 
its two end faces against a stop surface 29 and is fastened by means of 
screws 30 in the bottom of the recess 26. A drive pinion 32 provided with 
corresponding helical teeth 31 meshes from above with the inclined teeth 
28 of the rack 27, the pinion 32 being adapted to be driven via a shaft 
33, disposed horizontally and perpendicularly to the direction of movement 
3, by an electric drive motor 34, fastened on the machine frame 1, by way 
of reduction gearing 35. At its free end and in the proximity of the 
reduction gearing 35 the shaft 33 is radially mounted by means of cylinder 
roller bearings 36, 37 respectively, and in the proximity of the drive 
pinion 32, it is mounted radially and axially by means of two tapered 
roller bearings 38 in an X arrangement. As can be seen in FIG. 4, the 
bearings are fastened in the usual manner. 
The tool slide 2, which is in the form of a hollow box, has a diagonnaly 
extending rib 39 which extends from the rack 27 to the guide surface 23 
and in its longitudinal direction is substantially at right-angles to the 
guide surface 23. The center of gravity 40 on the tool slide 2 lies on the 
opposite side of guide surfaces 16, 17, 20, 21, 22, 23, with reference to 
the broaching tool 12. In addition, as can be seen in FIG. 5, the center 
of gravity 40 lies on the horizontal center longitudinal plane 41 of the 
tool slide 2, in which the broaching tool 12 also lies and which is 
symmetrical to the guide bars 14, 15. 
In FIG. 5 the forces occurring during operation are shown. The force G, 
which is directed vertically downwards and is produced by the weight of 
the tool slide 2 and that of the broaching tool 12 fastened on the latter, 
acts at the center of gravity 40, and because of the previously explained 
position of the center of gravity 40 relative to the guide surfaces 16, 
17, 20-23, leads to the partial forces G.sub.16, G.sub.17, and G.sub.22, 
which are likewise shown in dashed lines in FIG. 5 and each of which is 
directed at right-angles to the respective guide surfaces 16, 17, 22 of 
the guide bars 14 and 15. In other words, this means that because of the 
above mentioned position of the center of gravity 40 the tool slide 2 is 
always pressed with its guide surfaces 20, 21, 23 onto the associated 
guide surfaces 16, 17, 22 of the guide bars 14, 15. 
Because of the helical teeth of the rack 27 and of the drive pinion 32 a 
force P.sub.H, which is directed horizontally and perpendicularly to the 
broaching direction 42 and also to the vertical guide surfaces 20, 21 of 
the guide bars 14, 15, acts on the tool slide 2 during broaching, that is 
to say during the travelling of the tool carriage 2 in the broaching 
direction illustrated by the arrow-headed line 42 (FIG. 1). Due to the 
fact that forces pressing them apart act on two teeth when the latter roll 
on one another under load, in the corresponding rotary drive of the drive 
pinion 32 for moving the tool slide 2 in the broaching direction 
designated by the line 42, the tool slide 2 is acted on by a force P.sub.V 
which is directed vertically downward and which together with the force 
P.sub.H forms the resultant force P.sub.R which is likewise shown as a 
dotted line. The resultant bearing forces acting on the guide surfaces 16, 
17 22 on the one hand through the weight of the tool slide and of the 
broaching tool 12 and on the other hand through the drive are shown in 
FIG. 5 in solid lines as resultant forces R.sub.16, R.sub.17, and 
R.sub.22, while it may be added that the forces P.sub.22 and G.sub.22 and 
thus the resultant force R.sub.22 on the guide surface 22 extend in the 
direction of the web 39 and are therefore transmitted by the latter 
without bending forces. 
As can be seen in FIG. 6, the helical teeth 28 of the rack 27 are inclined 
at an angle .beta., which may be about 10.degree., in relation to the 
direction perpendicular to the broaching direction 42. The previously 
mentioned laterally directed force component P.sub.H is thereby produced. 
Since during the return travel of the tool slide 2 oppositely to the 
broaching direction designated by the line 42, the helical teeth of the 
rack 27 and drive pinion 32 have the consequence that the tool slide 2 is 
acted on by a force which is oppositely directed to the force P.sub.H and 
which applies a torque tending to lift the tool slide 2 off the guide 
surfaces 16, 17, 22, an additional auxiliary guide surface 43 is also 
provided on the guide bar 14, this surface 43 being associated with a 
corresponding auxiliary guide surface 44 on the tool slide 2. These 
auxiliary guide surfaces 43, 44 are arranged with mirror-image symmetry to 
the guide surfaces 22, 23, referring to the center longitudinal plane 41. 
It may be emphasized that accuracy of guidance of the tool carriage 2 when 
not loaded, that is to say during its return to the starting position, is 
not important. 
In FIG. 7 is shown the angle of action .alpha..sub.t between the helical 
teeth 28 pf the rack 27 and the helical teeth 31 of the drive pinion 32, 
which angle is the cause of the force P.sub.V. 
It may also be added that the shaft 33, and accordingly the rack 27 and the 
drive pinion 32, may also be inclined in relation to the horizontal, so 
that, for example, the force P.sub.V acting as the result of the angle of 
action .alpha..sub.t extends approximately in the direction of the force 
P.sub.R in FIG. 5. In this case the torque pressing the guides of the tool 
slide 2 onto the guides on the machine frame 1 becomes even greater. In 
such a case however the drive pinion 32 is also disposed above, although 
not necessarily vertically above, the rack 27. 
On the circular dividing table 7 is fastened a workpiece 45 shown in 
phantom, for example a turbine wheel, in whose peripheral surface it is 
desired to broach recesses, for example so-called fir-tree profiles.