Universal joint and method of making

A novel universal joint is made by forming a pair of elongated members, finishing the ends of said members to form bearing surfaces which are hard and smooth, and rigidly interconnecting the members between their ends to form a substantially cruciform spider structure which is subsequently assembled with the bearing surfaces of one member pivotally connected to the jaws of one clevis and with the bearing surfaces of the other member similarly connected to the jaws of another clevis, thereby completing a universal joint.

This invention relates to universal joints as commonly used, for example, 
in steering mechanisms and power drive shaft connections and other 
industrial applications. 
According to prior art practice, such a joint has been made by forging a 
one-piece cruciform or spider member, then heat treating and grinding the 
ends of the member to form cylindrical bearings, and then pivotally 
mounting one pair of coaxial spider bearings in needle bearings within 
complementary openings of a clevis and mounting the other pair of coaxial 
spider bearings in needle bearings within complementary openings of 
another clevis to complete the universal joint. 
A major disadvantage of this prior art practice has been the expensive step 
of using a one-piece cruciform forging. According to the invention, it has 
been discovered that the cost of such a spider can be minimized by 
machining or cold heading a pair of elongated members from low carbon, 
soft steel bar stock, heat treating the ends of the members to case harden 
the ends, grinding the ends to form smooth, hard bearings, and rigidly 
interconnecting the members between their ends to complete the spider the 
bearings of which are subsequently pivoted to a pair of clevises to 
complete a universal joint. 
Accordingly a primary object of the invention is to minimize the cost of 
such a universal joint without any sacrifice in strength or dependability 
in service. 
Another object of the invention is to form coaxial bearings on the ends of 
each of a pair of elongated members and rigidly interconnect the members 
with the bearing axes coplanar and with the bearing axis of one member 
perpendicular to the bearing axis of the other member.

Describing the invention in detail and referring first to FIG. 1, a 
preferred embodiment of the invention comprises a novel cruciform 
structure 20, commonly known in the art as a spider, including a pair of 
elongated male and female members 22 and 24 rigidly interconnected 
intermediate their ends at 26 as hereinafter described. 
The member 22 is preferably a carburized steel bar and comprises a pair of 
coaxial bearings 28 and 30 ground to smooth cylindrical form. 
The female member 24 is also preferably a carburized steel bar and 
comprises a pair of coaxial bearings 32 and 34 also ground to smooth 
cylindrical form. 
When the spider 20 is assembled as shown in FIG. 1, the longitudinal axes 
x-x (FIG. 5) and y-y (FIG. 2) of the members 22 and 24, respectively, and 
of the bearings 28, 30, 32 and 34 are coplanar, and the longitudinal or 
bearing axis x-x of male member 22 is substantially perpendicular to the 
longitudinal or bearing axis y-y of the female member 24. 
The bearings 28 and 30 are mounted by conventional needle bearings 36 (FIG. 
1) in complementary openings of a clevis 38 and the bearings 32 and 34 are 
similary mounted in such needle bearings in complementary openings of a 
clevis 42 which is preferably substantially identical in form to the 
clevis 38. 
Referring again to FIGS. 2-4, it will be seen that female member 24 has a 
central cylindrical opening 52 the axis of which is normal to longitudinal 
axis y-y of member 24 from which the bearings 32 and 34 are struck. 
The male member 22, as shown in detail in FIG. 5, has a central cylindrical 
bearing 54 coaxial with the bearings 28 and 30 which are also coaxial with 
longitudinal axis x-x of the member 22. The bearing 54 is also preferably 
ground to smooth cylindrical form to afford a tight fit in opening 52 into 
which the bearing 54 is forced by pressure of a value required to retain 
members 22 and 24 in a rigid cruciform spider structure or assembly 20 
shown in the assembly view of FIG. 1. 
The male member 22 may have a pair of grooves 56 coaxial with axis x-x and 
formed and arranged to define the axially inner ends of bearings 28 and 
30. 
Similarly the female member may have a pair of grooves 58 coaxial with axis 
y-y and formed and arranged to define the axially inner ends of bearing 32 
and 34. 
In fabricating the novel spider 20, the male and female members are 
preferably formed as by machining or cold heading from low carbon, mild 
steel bar stock which has not been heat treated. These members are heated 
to above their critical temperature in a carburizing atmosphere, for 
example, by induction heating or by burning gas to develop both the heat 
and the carburizing atmosphere. The members are then quenched to case 
harden them and their ends, as well as the bearings 28, 30, 32, 34 and 54 
are then ground to finished form. The hole 52 is drilled through the 
female member 24 before carburizing. The bearing 54 of male member 22 
after grinding is press-fitted into the hole 52 by pressure as required to 
hold members 22 and 24 together to define the spider structure 20, 
preparatory to its assembly with clevises 38 and 42. 
The commonly used methods of case hardening are carburizing, nitriding and 
cyaniding. Carburizing may be done by pack carburizing, gas carburizing or 
liquid carburizing, the latter involving the use of calcium cyanide. In 
the present invention, gas carburizing is preferred for reasons of speed 
and economy and a better gradation of the case. 
In gas processing natural gas or propane may be introduced into a heated 
chamber in which the members 22 and 24 are continuously tumbled at a 
temperature above the critical temperature of the case as, for example, by 
rotating the chamber. A direct quench from the chamber is preferred, 
although, if desired, a double heat treatment may be employed to obtain 
optimum properties of both the case and the core. For example, the member 
22 or 24, after cooling from the chamber temperature, may be reheated to 
above the critical temperature corresponding to the low carbon core and 
suitably cooled to refine its structure. The member may then be reheated 
to just above the critical temperature of the case and then quenced. Or, 
if desired, a single reheating from the chamber temperature and quench 
from above the critical temperature of the case may be employed. 
If desired the larger-diameter central portion 51 of the female member 
through which the opening 52 is drilled may be protected from 
carburization, as, for example, by plating the central portion with a 
coating of copper before heating in the chamber. This causes the central 
portion 51 to remain ductile, thereby avoiding any possibility of cracking 
as the male member bearing 54 is press-fitted into the hole 52 which may 
be formed either before or after the copper plating is applied and either 
before or after the female member 24 is heat treated for carburization, as 
heretofore described. 
If desired, the central portion 51 of the female member may be protected 
from hardening by heating only the bearings 32 and 34 axially outwardly of 
the grooves 58 as, for example, by induction heating. 
Also, if desired, the bar stock from which the members 22 and 24 are formed 
may contain enough carbon so that case hardening may be achieved by merely 
heating the members to a temperature above their critical temperature and 
then quenching them. In such a process the heating need not be in a 
carburizing atmosphere. 
After the members 22 and 24 have been assembled, they may be brazed 
together in the hole 52, in which case heat treating and grinding follow 
brazing. 
FIGS. 8 to 10 show a modification of the novel spider 20 wherein parts 
corresponding to those of FIGS. 1-7 are identified by corresponding 
numerals. In this modification the members 22 and 24 are not formed as 
male and female members but instead are substantially identical in form 
with each having a flat central portion 60 notched as at 62 so that the 
notches can be mated as shown in FIGS. 8 and 9 and the members 22 and 24 
may be brazed together at 64 within notches 62 in the position of FIGS. 8 
and 9. 
In this modification, the members 22 and 24 are formed of mild steel and 
are brazed as at 64 to complete the spider 20 prior to heat treating and 
grinding and subsequent assembly with the clevises 38 and 42. 
FIGS. 11-13 show another modification of the novel spider 20 which is 
similar to that of FIGS. 8-10 except that the members 22 and 24, which are 
substantially identical, are round in cross-section and heat treated and 
ground smooth from end to end thereof except for the notches 62, and parts 
of FIGS. 11-13 corresponding to those of FIGS. 8-10 are identified by 
corresponding numerals. Also the modification of FIGS. 11-13 is produced 
by the same method as that of FIGS. 8-10. 
FIGS. 14-16 show still another modification of the novel spider 20 which is 
identical to that of FIGS. 1-7 except that the male member 22 is of 
uniform round cross-section, heat treated and ground smooth from end to 
end thereof. All other parts of this modification are identical to those 
of FIGS. 1-7 and are identified by corresponding numberals. Also the 
spider of the modification of FIGS. 14-16 may be produced as described in 
connection with FIGS. 1-7. 
FIGS. 17-19 disclose yet another modification of the invention wherein 
parts corresponding to those of FIGS. 1-7 are identified by corresponding 
numerals. The spider 20 of FIGS. 17-19 is identical to that in FIGS. 1-7 
except that the male member 22 is provided with threads 65 mated with 
threads 66 in the opening 52 of the female member. The threads 65 of the 
male member 22 preferably include a few deformed threads so that a 
predetermined minimum torque force is required to thread the male member 
22 to the position of FIG. 17. The torque force may be predetermined to 
any value required by a particular application, and the torque force 
required to unthread the male member from the opening is approximately the 
same value to prevent accidental disassembly of the spider 20 in service. 
This is commonly known in the thread art as an interference threaded 
engagement. 
The modification of FIGS. 17-19 is produced by forming the male and female 
members 22 and 24 respectively, then drilling and tapping the hole 52 in 
the female member and threading the male member at 65, then heat treating 
the male and female members, and then grinding as heretofore described. 
Finally, the male member 22 is treated into the hole 52 of the female 
member to form the cruciform spider 20 shown in FIG. 17. The spider may 
then be assembled with clevises 38 and 42 to complete the universal joint 
shown in FIGS. 1 and 2. 
If desired, during heat treating of the male and female members 22 and 24 
of this modification, the threaded portions of these members may be 
protected from case hardening as, for example, by copper plating these 
portions including the threads or by induction heat treatment of the 
bearing portions only. Also, if desired, when such portions are protected 
from case hardening, the hole 52 may be drilled and/or tapped after heat 
treating and the male threads 65 may be formed before or after heat 
treating. 
Referring now to FIGS. 20-22, another modification of the novel spider 20 
is shown wherein parts corresponding to those of FIGS. 1-7 are identified 
by corresponding numerals. In this modification, the male member 22 is 
slideably fitted within female member 24 and is positioned as shown in 
FIG. 22. A pair of punches 68, one of which is shown in FIG. 21, are then 
actuated to indent the female member 24 as at 70 into interlocking 
engagement with the male member 22 as shown in FIG. 21. Preferably, prior 
to the punching step the bearings 28, 30, 32 and 34 are heat treated and 
ground as heretofore described, so that after the punching step, the 
spider 20 is ready for assembly with clevises 38 and 42 to complete the 
universal joint of FIGS. 1 and 2. The central portions of members 22 and 
24 of this modification are protected from the heat treatment as 
heretofore described. If desired, the punching step may precede heat 
treatment and grinding, in which case such protection from heat treatment 
is unnecessary. 
It should also be noted that in this embodiment, as well as in previous 
embodiments, the bearings 28, 30, 32 and 34 are shown as complete 
cylinders, however it will be understood by one skilled in the art that, 
if desired, any one or all of these bearings may be formed with one or 
more flat areas dividing the bearing into spaced parti-cylindrical 
segments struck from the same axis. 
Referring again to FIG. 1, it will be understood that after the needle 
bearings are assembled they are interlocked with the clevises 38 and 42, 
as, for example, by indenting flanges 37 of the needle bearings into 
interlocking exgagement with the surrounding portions of the clevises.