Bolt Torque Coefficients
Bolt Torque Coefficients
(OP)
Hi All-
Does anyone know of a good resource for bolt torque coefficients? I need to determine the axial preload, given the installation torque, on a copper fitting being screwed into an acetal housing.
Thanks for the help!
Does anyone know of a good resource for bolt torque coefficients? I need to determine the axial preload, given the installation torque, on a copper fitting being screwed into an acetal housing.
Thanks for the help!





RE: Bolt Torque Coefficients
For normal materials, it will be possible to find a reference with pretty much whatever value you want.
You really should test your materials and your application.
For uncommon materials you probably have no choice but to test it yourself.
RE: Bolt Torque Coefficients
Have you tried machineries handbook or Matweb
RE: Bolt Torque Coefficients
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Bolt Torque Coefficients
ISZ
RE: Bolt Torque Coefficients
Lastly, fluid carrying joints rarely require preload. Rather, they need to be leak resistant, hence the use of thread tape, flares, gaskets, etc. Usually hand tight plus 90 degrees rotation is good. If the joint isn't sealed, advance another 90 degrees. Use some extra parts in the beginning to learn the amount of angle that begins deformation/fracture, and use a value below this (using a safe margin).
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Bolt Torque Coefficients
Section N, Technical Data
Industrial Fasteners Institute
1505 East Ohio Building
Cleveland, Ohio 44114
From Fastener Standards as follows:
Equation:
T=KDW
Where:
T=torque (lb-in)
K=Torque Cofficient (not to be confused with coefficent of friction)
D=Nominal bolt size (in)
W=Bolt Tension (lb)
Arbitrary values for K are often assigned in non-critical applications as follows:
K=0.20 for nonplated steel fastners
K=0.15 for plated fasteners
In applications where additional lubricants, such as greases, oils, and waxes, are applied to the fasteners, K may be assumed to be as low as 0.12.
Generally, the above K values are conservative, and the actual preload induced by a given torque is slightly less than calculated.
A more exact value for K is expressed by the following equation....This is where I stop... you need to read the entire section if it is a critical fastener and you can't use the values listed above for K. The book has a table for torque cofficient K for bolt sizes 1/4-20 thru 1-14.
RE: Bolt Torque Coefficients
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RE: Bolt Torque Coefficients
RE: Bolt Torque Coefficients
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Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Bolt Torque Coefficients
Thanks for saying that!
Do you really think that the handbook you sort will list a value for this particular combination?
RE: Bolt Torque Coefficients
trying to calculate this is pretty much just an exercise because you will never retain that clamp in an acetal nut member.
RE: Bolt Torque Coefficients
No the handbook doesn't have anything like this, but it does have the most permutations I have seen in a single publication.
Good comments from Screwman. I bet this is an NPT joint that doesn't need preload, so why bother. Also, if a minimum gasket force is necessary, it still would be better to use angle control.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Bolt Torque Coefficients