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Bolt torque resources (especially nylock)

proFeign

Cast Iron
Joined
Oct 2, 2007
Location
Santa Barbara, CA
I have been looking with very little luck for a comprehensive bolt torque standards table that includes nylock nuts and bolts. What little I could find had some vague notes about adding 5 in-lbs for nylocks but I would think that this is not perfect advice given that the prevailing torque for nylocks seems to be much greater for larger diameter fasteners.

I have a machinery's handbook (latest ed.) and the "Fastener Black Book" which only has torque values for plain fasteners...

Any suggestions? The FBB mentions something called a Skidmore-Wilhelm device for measuring fastener installations - has anyone used one of these?

Nylock resources greatly appreciated!
 
Pro, get a copy of AC 43.13, "Aircraft Inspection and Repair-Acceptable Methods, Techniques, and Practices", which every certified aircraft mechanic and homebuilder will have. It will be available from any aircraft bookstore or Aircraft Spruce and Specialty, try their website. Kind of a smaller "Machinery's Handbook" for folks working on airplanes. You will have to learn some AN numbers for the various nuts, but you can impress your friends afterward when you tell them that a bolt sticking thru a nyloc nut is not airworthy unless 1 to 1 1/2 complete threads are showing! Bill S.
 
If I were using a nylock nut I would use a torque wrench to see how much drag the nylock has and then add that to the final torque value.

I would do the same for the bolt with the nylon button in the thread.

Why would you need a chart?
 
There are way too many potential variables for a concise (truly useful) chart. Plating, surface finish, contact area, locking element hardness, the list goes on. Each situation has to be evaluated on its own merit.
 
Make your own chart. Take the bolt to which you will be adding a nyloc to, measure its lenght with a mic, install and torque plain nut, measure its lenght again. Now install nyloc, and tighten until the bolt is the same lenght as with the plain nut, thats as close as you can get with nyloc's. They are not very good for torquing, the second time a nyloc is torqued will be different than the first time, the third time a different value again.
 
If I were using a nylock nut I would use a torque wrench to see how much drag the nylock has and then add that to the final torque value.

I would do the same for the bolt with the nylon button in the thread.

Why would you need a chart?

Indeed! The check with a torque wrench and add the prevailing torque method has been what I've been doing.

If it were just me I have had a great deal of luck with my wrist alone, but there is an initiative at my place of business to try to standardize around a generally accepted group of specs and I'm trying to find all the resources I can to see how much of a "standard" is practical...
 
Pro, get a copy of AC 43.13, "Aircraft Inspection and Repair-Acceptable Methods, Techniques, and Practices", which every certified aircraft mechanic and homebuilder will have. It will be available from any aircraft bookstore or Aircraft Spruce and Specialty, try their website. Kind of a smaller "Machinery's Handbook" for folks working on airplanes. You will have to learn some AN numbers for the various nuts, but you can impress your friends afterward when you tell them that a bolt sticking thru a nyloc nut is not airworthy unless 1 to 1 1/2 complete threads are showing! Bill S.

Thanks! I'm looking for that standard now...
 








 
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