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Threading depth.

Threading depth.

Threading depth.

Dear all,

I am looking for a "table" that could relate the screwing depth to the bolt/nut materials (or property class). I encountered only very general observations and "good-practice" advises, but nothing that would tell me, for example, what is the screwing depth necessary to fasten a M24 bolt class 10.9 into a St37 steel plate, using the same tightening torque as if the bolt would be fitted with a nut class 10.

Or let me put it in another way: what is the relation between the number of threads (or the height of the threaded plate or nut) and the percentage of load the first thread is subjected to?

Obviously, this could be calculated, but sometimes there is no time to do it and a quick estimation is necessray  - at an initial stage of a certain design, for example.

Does anybody have an idea?

RE: Threading depth.

dulmant:  I attempted to answer this question in Thread725-35222.  See if it gives you what you need.  It's not a table, but it tells you how to calculate the answer depending on the scenario.  Hope this helps you.

RE: Threading depth.

Forgot to answer your second paragraph.  According to Bickford, Handbook of Bolts and Bolted Joints, Dekker, 1998, p. 790, and another source, Chaddock, 1974, the initial axial thread shear force distribution (%) is as follows.

Bickford:   34, 23, 15, 11, 7, 4.5, 3, 2, 1.3, 0.09.
Chaddock:   34, 23, 16, 11, 9, 7.

However, various sources claim this is only the immediately initial distribution and that it quickly dissipates quite a bit, or evens out somewhat, due to material relaxation (I think), especially in the nut material.  This might be why quite a few sources seem to imply the axial thread shear stress can be roughly approximated in the analysis by assuming a uniform distribution over all threads, though no sources I've found, so far, are all that explicit nor definitive on this topic.  So I currently don't have a definitive answer nor general equation regarding your second paragraph.

RE: Threading depth.

The link vonlueke included above shows two ways to calculate stripping (one from me and one from him), so it is a good one to review.

Regarding thread force distribution, here are some data from Nuclear Engineering and Design 181 (1999) 109-116, A study of the helical effect on the threaded connection by three dimensional finite element analysis :

1" x 8 UNC: 34, 20, 14, 10, 7, 6, 5, 4
1" x 12 UNF: 29, 18, 14, 11, 9, 8, 7, 5
1" x 16 UNF: 24, 18, 14, 12, 11, 9, 7, 5

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