Method of and apparatus for finish-grinding a camshaft

A rough-ground camshaft has a shaft extending along and defining an axis and carrying a plurality of axially spaced cams each having a cam surface. This camshaft is finish-ground in system wherein for each cam there is a respective coarse prefinish tool and a respective fine finish tool. Every other cam surface is engaged in one diametrial direction by the respective coarse prefinish tool and in the opposite diametrical direction by the respective fine finish tool, and vice versa for the remaining cams, so that the prefinish tools, like the finish tools, alternate to opposite side of the camshaft axis. The camshaft is rotated about its axis and to start with all of the tools are urged against the respective cams, so that each cam is engaged in one diametrical direction by the respective prefinish tool and in the opposite direction by the respective fine finish tool. This shapes the tools, whereupon the fine finish tools are retracted for prefinishing of the cam surfaces. Then the prefinish tools are retracted and the fine finish tools are engaged with the cams for fine-finishing.

FIELD OF THE INVENTION 
The present invention relates to a method of and apparatus for 
finish-grinding a rough-ground camshaft. more particularly this invention 
concerns such a method and apparatus wherein the finish-grinding entails a 
prefinishing with coarse prefinish tools and a subsequent fine finishing 
with fine finish tools. 
BACKGROUND OF THE INVENTION 
It is standard procedure in the manufacture of a camshaft, particular the 
type used in an automotive vehicle to open and close the valves of the 
internal-combustion engine thereof, to rough-grind the casting serving as 
the blank for the camshaft. Such rough-grinding is normally conducted by 
rotating the camshaft about its axis between centers, lathe-fashion. 
Meanwhile a driven grinding wheel operated off a master cam performs on 
the camshaft a grinding operation that gives it the basic shape at the cam 
and bearing surfaces. Normally several such driven grinding heads are 
employed at the same time on the camshaft, being driven radially against 
it in one direction under the guidance of the afore-mentioned master guide 
cams. 
Subsequently the coarse-ground cam surfaces and prefinished by means of 
coarse prefinish tools, and then finish-ground be means of fine finish 
tools. These tools are normally either constituted by appropriately shaped 
ceramic blocks of the appropriate grit, or by synthetic-resin blocks in 
which the appropriate grit has been embedded. A roughness of about 0.2 
microns is normally desired at the end of the prefinishing, and a 
roughness of about 0.1 microns is desired at the end of the fine-finishing 
operation. 
Typically this is done simply by urging the appropriately shaped tools 
radially against the camshaft with a predetermined force while rotating 
the camshaft. The tools will smooth out the coarse-ground surfaces, which 
smoothing out is sometimes aided by slight axial reciprocation of the 
camshaft as it is rotated. First the coarse finishing operation is carried 
out, then the coarse finish tools are removed and the fine finish tools 
are urged against the cam surfaces. 
It is absolutely essential that the cam surfaces be perfectly smooth and 
perfectly formed. The above-described procedure produces a good product. 
Nonetheless a more finely finished cam surface will result in 
substantially descreased wear and correspondingly longer engine life. 
OBJECTS OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
method of and apparatus for finish-grinding a rough-ground camshaft. 
Another object is to provide such a method and apparatus which produce a 
camshaft that is better finished and formed than those produced according 
to the prior-art system. 
SUMMARY OF THE INVENTION 
These objects are attained according to the instant invention in a method 
of the above-described general type wherein each cam surface is associated 
with a respective tool. According to this invention the camshaft is 
rotated about its axis and against every other cam surface the respective 
tool is urged with a predetermined pressure and in a predetermined radial 
direction while simultaneously the remaining tools are urged against the 
respective cam surfaces with substantially the same pressure but in the 
opposite radial direction. 
It has astonishingly been found according to the instant invention that one 
of the principal causes of untrue surfaces on a camshaft was that the 
camshaft was normally bowed in one direction while being finished. 
Normally all of the grinding or finishing tools were urged in one radial 
direction against the respective cam surfaces at the same time, so that 
obviously the camshaft would be subjected to considerable radial pressure 
tending to deform it slightly. The result was that all of the surfacees 
were made slightly frusto conical, tapering outward from the center. As 
attempts were made under the prior-art system to obtain higher operating 
speeds, the inevitable answer was always to merely press the abrasive 
tools against the camshaft with greater pressure, thereby increasing the 
bowing effect. According to the instant invention this is overcome by 
directing alternate tools in alternate directions against the camshaft. 
Thus any radially effective force is only going to exist from one cam 
surface to the next where it will be countered by an opposite force. There 
will be no net radially effective force effective on the camshaft between 
its ends. 
This is most easily achieved according to the instant invention by 
providing the coarse and fine finish tools directly opposite each other, 
that is to diametrically opposite sides of the camshaft axis. In addition 
the fine finish and coarse finish tools are on alternate sides of the aixs 
on the diametrical plane on which all of the tools lie. Thus it is 
possible to shape the tools by first engaging all of them against the 
rotating camshaft, and thereafter to pull away only the coarse prefinish 
tools, leaving the fine finish tools in engagement with the camshaft to 
finish the operation. 
The above-described system not only has the advantage of producing a much 
truer surface, formed of a family of lines parallel to the axis of the 
camshaft, but it also allows higher operating speeds to be obtained by 
allowing the abrasive tools to be urged with considerable force against 
the camshaft. Since the forces cancel each other out there is no worry 
about pushing the camshaft out from between the lathe centers on which it 
is rotated, or about damaging the bearings of the headstock and tailstock. 
According to the instant invention each of the tools is mounted on a 
respective lever pivoted about an axis parallel to the camshaft axis and 
operated by a respective fluid-powered cylinder. These cylinders exert 
during engagement of the respective tools with the respective cam surfaces 
a constant force via the respective tools on the respective surfaces so 
that even as the respective tools must move radially inwardly and 
outwardly to follows the ups and downs of the rotating cam surface, the 
engagement force remains the same. 
In accordance with a particular procedure of the instant invention, the 
coarse prefinish tools and the fine finish tools are all urged to start 
with against the cams, with the respective prefinish tools engaging each 
cam surface in one radial direction and the respective finish tools 
engaging in the radial opposite direction, but of course with the tools of 
the same type alternating on opposite sides of the axis. After a brief 
period in which both tools act on the cam surfaces the prefinish tools 
only are retracted radially away from the cam surfaces so that the final 
smoothing is carried out only by the fine finish tools. Such a procedure 
has been found to work extremely well, with no bending of the camshaft 
whatsoever so that if the cam surfaces are slightly frustoconical for the 
reasons described above they will be rendered cylindrical. This system 
according to the instant invention also allows the tools to be pressed 
with considerable force against the surfaces they are machining, so that 
higher production rates can be achieved.

SPECIFIC DESCRIPTION 
As seen in FIG. 1 a camshaft 2 has a shaft 12 on which are carried a 
succession of axially spaced valve-lifting cams 1 and several bearing 
surfaces 6. The cams 1 have as seen in FIGS. 4A-4C outer surfaces 1' that 
are not centered on the axis 9, but the outer surfaces 6' of the bearing 
surfaces 6 are centered on the axis 9. This camshaft is mounted on centers 
between a driven headstock 3 operated by a motor 13 and a tailstock 3a so 
that the camshaft 1 is during the below-described finishing operations 
always rotated at a generally constant speed about its axis 9. 
According to this invention there is associated with each cam 1 a coarse 
prefinish tool or stone 4 and a fine finish stone 5, the former being 
shown for illustration's sake with a simple diagonal hatching and the 
latter with cross hatching. These tools 4 and 5 are carried as seen in 
FIG. 3 on lone first-class levers 7 pivoted at 10 about axes above and to 
either side of the axis 9 and each associated with a respective 
fluid-operated cylinder 8 of the double-acting type so that the tools 4 
and 5 can be moved into and out of radial engagement with the respective 
cam surfaces 1'. FIG. 1, which is a top view, shows how the prefinish 
tools 4 are staggered to opposite sides of the axis 9, as are the finish 
tools 5. 
The system according to the instant invention has been found particularly 
useful in eliminating a common deformation such as shown in 11 of FIG. 2. 
Thus the cam 1 shown in FIG. 2 has an outer surface which is not formed by 
a family of lines parallel to the axis 9, but instead by a family of lines 
that all converge toward and meet the axis 9. This out-of-true condition 
is the result of a rough grinding that is executed with such force that 
the entire camshaft 2 is bent to one side, so that from the middle out all 
of the surfaces 1' taper outward. 
With the system according to the instant invention at first as shown in 
FIG. 4A both tools 4 and 5 for each cam surface 1' are uged into radial 
contact in opposite directions relative to a plane P including the axis 9 
with the respective cam surface 1'. During this operation the tips of the 
tools 4 and 5 are formed somewhat. These tools 4 and 5 may be formed of 
ceramic blocks of appropriate grit, or of synthetic-resin blocks in which 
the apropriate grit is embedded. 
Thereafter as shown in FIG. 4B the fine-finish tools 5 are withdrawn and 
only the coarse prefinish tools 4 are urged against the cam surfaces 1. 
Since the prefinish tools 4 as seen in FIG. 1 also alternate to opposite 
sides of the axis 9 there will be no measurable bending of the camshaft 2. 
This feature therefore allows considerable pressure to be exerted by the 
tools 4 against the surfaces 1'. 
Subsequently as shown in FIG. 4C the tools 4 are withdrawn and the tools 5 
are all engaged with the respective cams 1. Again since these tools 5 are 
staggered to opposite sides of the axis 9 they can also exert considerable 
force. 
It is also possible according to the instant invention to skip the step as 
shown in FIG. 4B and go directly from the step of FIG. 4A to the step FIG. 
4C. Thus during the prefinishing both tools 4 and 5 will engage each cam 
surface 1'. Toward the end of the operation only the prefinish tools 4 are 
withdrawn from the cams 1 so that the final smoothing is effected by the 
tools 5 alone. 
It is noted that during the above-described operation it is possible to 
axially slightly reciprocate the camshaft 2 while rotating it about its 
axis 9. Furthermore it should be noted that the forces exerted by the 
tools 4 and 5 against the surfaces 1' are always equal. At the very least 
the forces exerted by the tools 4 should all be equal and the forces 
exerted by the tools 5 should all be equal. Normally the forces exerted by 
all of the tools are equal to one another.