Abrasive belt machine tool for machining cylindrical bearing surfaces on shafts

Abrasive belt machine tool for machining cylindrical bearing surface on shafts, in particular journals on camshafts or journals and/or crank pins on crankshafts, comprising for machining each bearing surface two opposed jaws 5 mounted on two arms 1 and each having first and second concave application surfaces 6a, 6b having different diameter in at least two different positions. The abrasive belt 9 passes in front of the concave surfaces 6a and 6b of the two jaws 5. The support 2 of the arms is mobile between at least two positions such that in one of said positions the first concave surface 6a can apply the abrasive belt 9 to a bearing surface 8a having a corresponding diameter on a first shaft and in the other of said positions the concave surfaces 6b can apply the abrasive belt 9 to a bearing surface having a corresponding diameter on a second shaft.

The present invention concerns an abrasive belt machine tool for machining 
cylindrical bearing surfaces on shafts, in particular journals on 
camshafts or journals and/or crank pins on crankshafts. 
Prior art machines of this type comprise two arms pivoting in a plane on a 
common support for machining each bearing surface of the shaft which is 
rotated about its axis during machining. Two opposed jaws are mounted on 
said arms and each has a cylindrical segment shape concave application 
surface having a diameter corresponding to the diameter of the bearing 
surface to be machined. Guide means are provided for passing the abrasive 
belt in front of the application surfaces of the two jaws. Means for 
maneuvering the arms apply the abrasive belt to the bearing surface to be 
machined via the concave surfaces of the opposed jaws. 
Prior art machines of the above type are set up to machine bearing surfaces 
on identical shafts. In the field of automobile engines it is increasingly 
frequent for the same engine architecture to be available in a number of 
models or types distinguished by different power ratings, for example. In 
this case it is common for the crankshafts of the various engine models or 
types to have the same length, the same number of journals and the same 
number of crank pins but to have different diameters of the journals 
and/or crank pins. At present using abrasive belts to machine such 
crankshafts requires either a machine dedicated to the crankshafts of each 
engine type or model or stopping the machine and changing the jaws to 
change from a crankshaft for one type or model to another. The same 
problem arises in machining journals of camshafts. 
It would be desirable to be able to change from abrasive belt machining of 
the bearing surfaces of camshafts or crankshafts for one type or model to 
those for another type or model on the same machine tool without needing 
to stop the latter to change the jaws to match the concave abrasive belt 
application surfaces to the various diameters of the bearing surfaces to 
be machined. 
The present invention is precisely directed to a machine tool achieving 
this result in a simple manner subject to minimal additional cost. 
On the abrasive belt machine tool in accordance with the invention at least 
first and second concave application surfaces having different diameters 
are mounted in opposition in at least two different positions on the arms 
so that the abrasive belt passes in front of the concave surfaces of the 
two jaws. The support is mobile between at least two positions such that 
in one of said positions the first concave surfaces having a first 
diameter of the jaws can apply the abrasive belt to a bearing surface 
having a corresponding diameter on a first shaft and in the other of said 
positions the second concave surfaces having a second diameter can apply 
the abrasive belt to a bearing surface having a corresponding diameter on 
a second shaft. 
Accordingly, simply by changing the position of the support for the arms 
carrying the jaws, and with no other operation, it is possible to change 
instantaneously from machining bearing surfaces of a shaft of a first type 
or model to machining corresponding bearing surfaces having a different 
diameter of a shaft of another type or model. 
In the context of the invention, the jaws mounted on the arms can be either 
multiple jaws each having at least two concave application surfaces with 
different diameters or single jaws in which case at least two single jaws 
having concave surfaces with different diameters are mounted at different 
positions on each arm.

The abrasive belt machine tool shown in the drawings constitutes, for 
example, a machine for superfinishing cylindrical bearing surfaces on 
shafts, in particular journals on camshafts or crank pins and/or journals 
on crankshafts. For machining each bearing surface of the shaft it 
comprises a pair of opposed arms 1 mounted on a common support 2 so that 
the two arms, coupled by gears, can be pivoted about pivots 3 by 
manoeuvring means 4 consisting of a hydraulic cylinder. The inside face at 
the free lower end of each arm 1, facing towards the opposite arm, carries 
a double jaw 5 comprising two cylindrical segment shape concave surfaces 
6a, 6b the parallel axes of which are spaced from each other along the 
length of the arms 1. 
The support 2 common to the two arms 1 can be moved vertically by a 
hydraulic cylinder 7 the travel of which is defined so as to bring the 
application surfaces 6a or 6b of the two jaws 5 selectively to either side 
of the bearing surface 8 to be machined of the shaft, which can be held 
between points and rotated about its axis in the manner well known in the 
field of abrasive machining of shaft bearing surfaces. 
The concave surfaces 6a of the two jaws 5 have a radius of curvature 
corresponding to the radius of curvature of a first bearing surface 8a and 
shown in FIGS. 1 to 3 and the concave surfaces 6b of the jaws 5 having a 
radius of curvature corresponding to the radius of a second bearing 
surface 8b shown in FIGS. 5 through 7, the two radii being different. In 
the example shown the radius of curvature of the surfaces 6a (and 
therefore the radius of the bearing surface 8a) is greater than the radius 
of curvature of the surfaces 6b (and therefore the radius of the bearing 
surface 8b). 
Guide means pass an abrasive belt 9 in front of the two concave surfaces 
6a, 6b of each jaw 5. Between two successive machining cycles the belt is 
advanced, in a manner that is known in itself, from a reserve spool 10 
onto a take-up spool 11. 
In FIGS. 1 to 3 the support 2, the arms 1 and the jaws 5 are in a bottom 
position in which the concave surfaces 6a of the jaws 5 are on either side 
of a bearing surface 8a to be machined, the radius of which bearing 
surface corresponds to the radius of curvature of the surfaces 6a. 
Accordingly, when the jaws 5 are clamped up by the cylinder 4, the concave 
surfaces 6a of the jaws 5 apply the abrasive belt 9 to the bearing surface 
8a. 
In FIGS. 5 through 7, however, the jaws 5 are in a top position in which 
the concave surfaces 6b of the jaws 5 are on either side of a bearing 
surface 8b the radius of which corresponds to the radius of curvature of 
the surfaces 6b so that when the jaws 5 are clamped up the concave 
surfaces 6b of the jaws 5 apply the abrasive belt 9 to the bearing surface 
8b. 
It is therefore possible, on the same abrasive belt machine tool, to change 
instantaneously from machining a bearing surface 8a having a first 
diameter of a first shaft to machining a bearing surface 8b having a 
second diameter of a second shaft, and vice versa, without any operation 
other than changing the position of the jaws 5, which is achieved by 
actuating the cylinder 7. 
FIG. 4 shows that the concave surface 6b (like the concave surface 6a) of 
each jaw 5 is not defined directly by the metal jaw 5 itself but by a 
lining 12 of a more flexible material, for example polyurethane, which is 
attached to the jaw 5 to achieve a more regular distribution of the 
pressure with which the abrasive belt 9 is applied to the bearing surface 
to be machined. 
Note also that in the context of the invention the number of concave 
abrasive belt application surfaces with different radii carried by each 
arm 1 can be greater than two, in which case the cylinder 7 can move the 
jaws 5 into more than two different positions, enabling more than two 
bearing surfaces with different diameters to be machined on the same 
machine. 
Finally, FIG. 7 shows in dashed line that each jaw 5, rather than being a 
multiple jaw, in this instance a double jaw having two concave application 
surfaces with different radii, could comprise two single jaws 5a, 5b each 
having one application surface, the two jaws 5a and 5b of each arm 1 
having concave surfaces with different radii and being mounted in 
different positions on the arm 1.