What is Effect of Thread Class on Torque & Preload? 2

[Guest102023]

I am wondering what effect thread class has on the ability to effect a preload (accurately) in a machine screw, as indicated indirectly by torque. Specifically, I am looking at several 1" studs from a flange joint; the sloppiness of the nuts prompted my query.
One thought I had is that possibly individual threads have less mutual support, resulting in more local deformation of threads. Of course initial tightening will be somewhat easier when using fingers.

Any thoughts/knowledge on this?

 

[TVP]

There is some discussion of this in Bickford's Hanbook of Bolts and Bolted Joints.

 

[Guest102023]

TVP,
I found that book, but where do I look?

 

[TVP]

The discussion on thread tolerances, etc is on pages 128-134 and 780-793. The following links have some information on thread dimensions, loosening behavior, etc. The first link to Michael Oliver's site has a number of technical articles that are good:

http://sites.google.com/site/olivertestingandconsulting/home/fastener-articles

http://muhendisizbiz.net/uploadlar/12216/three-dimensional_finite_element_analysis_of_threa.pdf

http://www.ewp.rpi.edu/hartford/~pe...0bca982f500602a=0&bcsi_scan_filename=ref4.pdf

https://www.faa.gov/library/reports/media/FASTENER_AUDIT_REPORT.pdf

 

[Tmoose]

Have you done any measurements to identify why the nuts feel "sloppy?"
If the "sloppy" threads still meet a reasonable dimensional standard I would not expect a de-rate.
Would New nuts fix it ?

Note that the tap drill size could influence the " % of thread (height)" and be indetectable as "slop."

http://www.boltscience.com/pages/strength.htm

"Studies have shown that for threaded assemblies of usual proportions, tap-drill size is relatively unimportant so long as the percentage of thread height is greater than 60%."

Here's a case (formed threads) when the threads checked fine with gages, but had very weak threads.

http://machinedesign.com/article/internal-thread-strip-out-tests-yield-surprising-results-0113