Low tolerance threaded fastener

A threaded fastener is having a raised area or bump on a thread flank. The flank can be positioned on the nut thread or on the bolt thread. The bump forces the mating threads at least on one flank to have near zero tolerances along the pitchline of the threads and thereby eliminating play.

BACKGROUND OF THE INVENTION 
This invention relates generally to threaded fasteners such as nuts and 
bolts and more particularly to threaded fasteners having an improved 
thread and reduced tolerances and improved fastening. 
Threaded fasteners are well known to the art. One goal of threaded 
fasteners, particularly nut and bolt combinations, is to provide such a 
fastener that stays tightened and does not loosen in use. Generally 
accepted matching techniques result in tolerances between the nut an bolt 
threads and there is clearance or play which allows for movement between 
the elements. For example, a fastener or nut and bolt can loosen under 
load or vibration. 
There are several prior art systems that try to remedy this problem. First, 
locknuts are used with a nylon washer locked in at the end of the nut. 
When the nylon washer contacts the bolt, it tightens around the thread and 
locks the nut in position. Locknuts have disadvantages. The nylon portion 
of nut has no load carrying threads. Further, it requires more material to 
make the nut longer and the nylon washer and the nut must be made 
separately and then crimped together. The locknut of this type can be used 
only a few times, is not as resistant to heat and requires chemicals i.e. 
nylon. 
Deformed nuts have been used to overcome the loosening problem. These 
comprise nuts that are deformed out of the circular shape and made into 
rounded-off triangle shape. Then the bolt engages the threads, it contacts 
three points and the nut locks around the bolt. However, only heat-treated 
nuts can be used. To make the deliberate deformation requires an expensive 
manufacturing set-up. Further, the process is very slow. Also, the 
reaction of each individual nut is variable, which makes it difficult to 
predict or guarantee tolerances. Moreover, it can only be used with nuts. 
A spiral lock is a lock thread is a commercially available alternative. 
However, the spiral lock provides an interference on the outside diameter 
of the bolt. It is difficult to control the interference with accuracy. 
The surface of the bolt thread can cause galling of the nut and subsequent 
failure. 
Interference-fit threads are used which include a complete interference of 
the matching parts at the flanks to provide an interference or metal flow. 
However, based upon accepted machining practices, it is very difficult to 
produce, for example, class 5 threads (Federal Standard Screw-Thread 
Standards For Federal Services-Class 5 Interference Fit Screw Threads). 
Examples of prior art fastener technologies are disclosed in the following 
U.S. Pat. No: 1,369,156, to Woodward; No. 2,842,180, to Brown et al; No. 
3,459,250 to Tabor; No. 3,661,194, MacFarlane et al.; No. 3,721,283, to 
Evan; No. 3,850,215, to Orlomoski; No. 3,927,503, to Wilson; No. 
4,023,914, Holmes; No. 4,071,067, to Goldby; No. 4,396,321, Holmes; No. 
4,846,614, to Steinbock; and No. 5,194,214, to Snyder et al. 
It would be advantageous, therefore, to develop a fastener that has close 
tolerances yet is resistant to loosening or play without the disadvantages 
of the prior art designs. 
SUMMARY OF THE INVENTION 
It is among the principal objects of the present invention to provide a 
threaded fastener that is resistant to loosening. 
It is another object of the present invention to provide a threaded 
fastener that has very close tolerances and is resistant to loosening. 
Another object of the present invention to provide a threaded fastener that 
controls thread contact and tolerances along the thread pitchline. 
Another object of the present invention to provide a threaded fastener that 
controls thread contact and tolerances along the thread pitchline and by 
controlling width of contact. 
Still another object of the present invention is to provide such a threaded 
fastener that not only controls the pitch diameter of the respective 
threads to assure correct interference along the thread flank, but also 
controls the width of contact. 
It is still another object of the present invention to provide such a 
threaded fastener that can be manufactured and produced in a broad range 
of sizes. 
It is yet another object of the present invention to provide such a 
threaded fastener that is simple and economical to tool, versatile and 
well suited for its intended purposes. 
In accordance with the invention, a threaded fastener is provided having a 
raised area or bump on the thread flank. The bump forces the mating 
threads at least on one flank to have near zero tolerances along the 
pitchline of the threads and thereby eliminating play.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates a standard thread 1 with clearance C. FIG. 8 also 
illustrates the relationship and play between a normal nut thread 2 and 
bolt thread 3 As will be appreciated, there are significant clearances C 
between the respective threads. FIG. 9 illustrates a normal thread under 
irregular load conditions with significantly increases the clearance C 
between the nut and bold threads. The amount of clearance is determined by 
the tolerances set by the manufacturer. FIG. 2, by comparison, is an ideal 
or perfect thread having full flank contact at points 4 and 5. A perfect 
thread, however, would require the nut and bolt have identical pitch 
diameters without clearance. 
FIG. 3 illustrates one preferred embodiment of the threaded fastener of the 
present invention, indicated generally by reference numeral 10. The 
fastener includes a nut thread 12 and a bolt thread 14 As can be seen, the 
nut thread 12 is tooled with bump 16 on the flank of the thread. As seen 
in FIGS. 10-13, the bump 16 urges the threads to one side so that there is 
full flank contact at point 20. The thread, with the bump, are formed by a 
thread tapping tool. As shown in FIG. 10, the contact area can be varied 
according to holding torque. The size of the bump 16 can be varied to 
increase the contact areas on the flanks, as shown in FIG. 4, which has an 
enlarged or wider bump 16. FIG. 12 illustrates a condition of "zero" play 
between the thread flanks as a result of the size and positioning of the 
bump 16. FIG. 13 illustrates the substantial contact between the flanks of 
the threads due to the positioning and size of bump 16, even under load 
conditions. 
FIG. 5 illustrates another embodiment of the thread of the threaded 
fastener of the present invention including a pair of spaced apart bumps 
16A and 1 8B. 
As shown in FIG. 6, the right flank has 100% contact and at the left 
approximately 15% contact. 
The threaded nuts previously described can be formed by using a tape with a 
complementary indention which will create the desired bump on the thread 
flank when tooled. 
FIG. 7 illustrates another embodiment of the present invention wherein the 
bolt 22 has a bulge 24 formed on the thread flank. This thread is easily 
formed on a thread rolling machine with thread rolling dies in a cold 
forming process. These threads can be formed of a harder material than the 
nut so that the bump can "bite" into the softer metal. The inclusion of 
the bump on the bolt thread causes the threaded fastener to function the 
same way as previously described embodiments, with flush fit on the flanks 
at point 26. 
It will be appreciated from the foregoing that various changes and 
modifications may be made in the threaded fastener of the present 
invention without departing from the scope of the appended claims. 
Therefore the foregoing specification and accompanying drawings are 
intended to be illustrative only and should not be viewed in a limiting 
sense.