Threaded Bolt Lead Entry Geometry to Prevent Cross-Threading
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional fastener systems often experience cross threading due to initial contact between the bolt thread crest and nut thread root, exacerbated by slight misalignment of the bolt and nut axes, leading to jamming and restricted axial movement.
Innovation Solution
The fastener system employs lead entry threads with a higher pitch, approximately 1.40 to 1.60 times the body thread axial pitch, to accelerate axial movement and align the nut and bolt axes, preventing cross threading by increasing the helix angle and reducing interference at the thread contact zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional constant pitch threads are used, then manufacturing is simple and standard, but cross threading occurs due to initial contact between bolt thread crest and nut thread root
Solution Approach 1:
The patent applies parameter changes by varying the thread pitch along the bolt length. The lead entry portion has a first pitch while the body portion has a second pitch, creating different helix angles that prevent cross threading during initial engagement while maintaining proper thread engagement for the body portion.
2Ease of operation
If lead entry threads with higher pitch are used, then cross threading is prevented and axial alignment is improved, but manufacturing complexity increases
Solution Approach 1:
The bolt is segmented into two distinct threaded portions: a lead entry portion with first pitch and a body portion with second pitch. This segmentation allows each portion to perform its specific function - the lead entry portion guides alignment and prevents cross threading, while the body portion provides secure engagement.
Solution Approach 2:
Different thread pitch characteristics are applied to different locations of the bolt. The lead entry portion has optimized pitch for alignment and cross-threading prevention, while the body portion has pitch optimized for engagement strength and load bearing.
3Adaptability or versatility
If standard thread proportions are used, then compatibility with standard nuts is maintained, but cross threading jams the threads and restricts axial movement
Solution Approach 1:
The patent changes the pitch parameter along the bolt length to resolve the contradiction. The lead entry portion uses a pitch that creates a helix angle facilitating smooth entry and alignment, while the body portion uses standard pitch proportions for compatibility and strength.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A threaded fastener system, incorporating a bolt and a nut assembly, wherein the bolt has a threaded lead entry point 22 whose pitch 39 and helix angle are of a higher magnitude than that of those on the body/shank 21 of the bolt.