Locking fastener

Abstract

A vibration-resistant prevailing torque fastener combination comprising a conventional first element having a standard thread form with first flank angles and a modified second element having a thread form characterized by second steeper flank angles over the entire length thereof, and a truncated root caused by foreshortening of the flanks over a portion of the thread length to produce a helical flat which firmly engages and typically deforms the crest of the first element when threadedly engaged therewith. A difference in flank angles provides longitudinal clearance to receive the deformed material during the threaded engagement. Tapping tools are disclosed.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. In a prevailing-torque fastener combination; a first element having a helical thread form with leading and trailing flanks which lie at respective first angles to the thread axis and which, before threaded engagement with another element, .[.intersect.]. .Iadd.converge .Iaddend.to define a crest of substantially constant diameter over the working length of said element;   a second element having a helical thread form with leading and trailing flanks which lie at respective second angles relative to the thread axis and which are .[.truncated.]. .Iadd.foreshortened .Iaddend.to define a root surface;   the first and second elements being conjugally threadable with one another;   at least a portion of the second element having a thread depth of lesser dimension than the thread depth of the first element thereby to cause firm radial engagement between the crest of the first element and the root surface when said elements are at least substantially fully threaded together;   .[.the threads of said elements being configured.]. .Iadd.at least one of said second angles being greater than the corresponding one of said first angles by an angle of no greater than about 15° .Iaddend.to create longitudinal clearance between the flanks adjacent the engaging crest and .[.truncated.]. root sufficient to receive deformed material from said engaging crest when threaded together.   
     
     
       2. The combination defined in claim 1 wherein the first angles are the same and the second angles are the same such as to produce symmetrical thread forms in each of said male and female elements. 
     
     
       3. In a prevailing torque-fastener combination: a male element having a helical thread form with leading and trailing flanks which lie at respective first angles to the thread axis and which .[.intersect.]. .Iadd.converge .Iaddend.to define a crest of substantially constant diameter over the working length of said element;   a female element having a helical thread form with leading and trailing flanks which lie at respective second angles relative to the thread axis and which .[.intersect.]. .Iadd.converge .Iaddend.to define a root;   the first and second elements being conjugally threadable with one another;   at least a portion of the female thread form root being of lesser diameter than the male crest to cause firm radial engagement therebetween when said elements are at least substantially fully threaded together;   .Iadd.at least one of .Iaddend.the second angles being greater than the corresponding first .[.angles.]. .Iadd.angle .Iaddend.to create longitudinal clearance between the flanks adjacent the male crest and female root sufficient to receive deformed material from one of said elements when threaded together.Iadd., the difference in flank angles being on the order of about 15°.Iaddend..   
     
     
       4. The combination defined in claim 3 wherein the root of the female element is truncated to form a helical flat. 
     
     
       5. The combination defined in claim 4 wherein the helical flat is substantially parallel to the thread axis. 
     
     
       6. The combination defined in claim 4 wherein said female element exhibits a crest of constant diameter and a root of varying diameter such that at least partial threaded engagement between the male and female elements can be achieved before radial engagement between the male crest and the female root occurs. 
     
     
       7. The combination defined in claim 2 wherein the first angles are the same and the second angles are the same such as to produce symmetrical thread forms in each of said male and female elements. 
     
     
       8. For use in combination with a male threaded element having angled flanks and a constant thread diameter; a female threaded element, .Iadd.at least one of .Iaddend.the flanks of which .[.lie.]. .Iadd.lies .Iaddend.at a greater angle relative to the thread axis than the corresponding .[.flanks.]. .Iadd.flank .Iaddend.of the male element to provide longitudinal clearance between the flanks adjacent the crest of the male element and the root of the female element when the two elements are engaged, .Iadd.said flanks being substantially uniplanar and lying at angles of no greater than about 75° from the longitudinal thread form axis, .Iaddend.and a helical surface of truncation formed over at least a portion of the female root and which is of lesser diameter than the diameter of the male crown so as to produce firm radial engagement between said elements when substantially fully threadedly engaged.Iadd., the difference in flank angles being on the order of about 15°.Iaddend..   
     
     
       9. Apparatus as defined in claim 8 wherein the female element is characterized by a constant diameter crest and a varying diameter root, the greater root diameter being contiguous to one end of the thread form to permit a free-running starting engagement. 
     
     
       10. The apparatus defined in claim 8 wherein the angles of the flanks are equal and opposite so as to create a symmetrical thread form.