How many threads
How many threads
(OP)
How many threads have to catch in a 1/4-20 bolt to get the full rated bolt strength? I can not find it anywhere. I vaguely remember that 4 threads is all you need. right/wrong?
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RE: How many threads
thread404-149977: Minimum thread depth
Learn the rules,so you know how to break them properly.
Dalai Lama
_____________________________________
RE: How many threads
If you are "blind tapping" into a hole, the last 1.5 thread turns are NOT "good threads" for strength.
For nuts, the bolt or studs should be visible (extend past the end of the nut) by at least 1-1/2 threads. Of course, that's a generic requirement to develope the "full strength" of the male threads in the bolt and female threads in the nut.
RE: How many threads
http://www.boltplanet.com/ has a calculator that can be usefull to play around with, but as it's free & on the internet - buyer be ware.
I've seen the 'well only 3 threads are doing all the work' argument used in tight situations. However, usually 1 X diameter is a good target.
When you say 1/4 bolt do you mean into an appropriate nut?
The properties of the female half of the joint also affect it. A 1/4 bolt into modelling clay wont give you the same result as 1/4 bolt into 303 SST nut etc.
I believe rated values are given for going into a nut of a comparable grade but I don' know for sure.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: How many threads
RE: How many threads
Female thread shear area calculation requires engaged thread length, minimum major diameter of external threads, maximum pitch diameter of the internal thread, and thread pitch. These are often found in tables as An/mm (area per unit length) where the length is the engaged thread length.
Male bolt screw thread tensile area is available directly from tables.
Strength is found by using yeild or proof stress of each material (bolt material and female thread material) together with the tensile/shear areas found above.
Also consider the type of loading the connection will experience, and choose a conservative factor of safety.
RE: How many threads
The first thread in the nut(bearing face end)sustains a stress level 231%(fine thrd),179%(coarse thrd) of applied load.
This tapers back to a much lower level.
Engaging less threads than in a typical nut raises first thrd stress level higher.
Using a nut one grade lower than the bolt distributes
thread loads more evenly.
I still have not answered your question.
RE: How many threads
Dan
www.eltronresearch.com
Dan's Blog
RE: How many threads
The point is that you need to push on the pencil and do a proper analysis for your situation. Professional conduct and skilled practice are two concepts that come to mind.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: How many threads
The is also a more detail analysis of the problem in the Unbrako Fasteners Handbook.
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