Questions about old thread engagement thread

[AaronH]

All,

While researching thread engagement I ran across this old thread:

http://www.eng-tips.com/viewthread.cfm?qid=254805

Mr. Fox eludes to an error in Machinery's handbook. I have been searching the past threads to see if I could find where he spoke more about it in a previous thread, but so far I haven't located it. I have created a spreadsheet of my own and was comparing it to ElectricPete's spreadsheet. Our calcs agree up to the internal thread engagement calc. His formula is significantly different that the one listed in my 24th edition Handbook. I am very curious as to this error in the book. I am hoping someone can give some more details as to which formulas were/are incorrect.

Regards,
Aaron

 

[AaronH]

Also, the U of T-M link seems to be broken from Mr. Fox's post. Anyone know if this information is duplicated elsewhere? I'd like to read it and gain more insight.

Thanks,
Aaron

 

[desertfox]

Hi AaronH

What I remember about this error was that if you had mating threads of different materials one could improve the level of shear stress by increasing the length of thread engagement infinitely, however in practice once the thread engagement reaches a length of about (1.5x diameter of bolt) you are using then there is little or no improvement of the stress on the mating threads.
Have a read of this link:-

http://www.roymech.co.uk/Useful_Tables/Screws/Thread_Calcs.html