Double nutting?
Double nutting?
(OP)
I've never seen anything that I would consider official (pro or con) on the subject of using double nuts, but I've never been a fan for some reason. It just doesn't seem like a proper engineering approach to me; however, I wouldn't mind being able to make an educated decision. I'm not really sure the exact problem double nuts are intended to solve, though it seems to be suggested when people want a higher degree of confidence that a fastener is not going to back off. Does it really accomplish anything? If anybody can point me in the direction of where I can read up on this in order to speak more intelligently on the subject, I'd sure appreciate it.





RE: Double nutting?
jam nuts. You might want to search on jam nuts.
I am rather certain that the conclusion was that they
do very little good. But check it out.
RE: Double nutting?
You can find more information in Handbook of Bolts and Bolted Joints edited by Bickford and Nassar, and NASA RP1228 Fastener Design Manual.
Regards,
Cory
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Double nutting?
http://www.du.edu/~jcalvert/tech/jamnut.htm
RE: Double nutting?
Jam nuts. These nuts are normally "jammed" together
as shown in figure 7, although the "experts" cannot agree
on which nut should be on the bottom. However, this type
of assembly is too unpredictable to be reliable. If the innernut is torqued tighter than the outer nut, the inner nut will yield before the outer nut can pick up its full load. On the other hand hand, if the outer nut is tightened more than the inner nut, the inner nut unloads. Then the outer nut will yield before the inner nut can pick up its full load. It would be rare to fet the correcto amount of torque on each nut. A lock nut is a much more practical choice than a regular nut and a jam nut. However, a juam nut can be uses on a turnbuckle, where it does not carry any of the tension load.
Figure 7 shows the jam nut next to the mounting surface with the thicker nut on top.
Not certain if this applies fully to double nutting.
I know they use double nuts in many structural applications
where the loads are basically static. I see them all the time on monopole designs.
RE: Double nutting?
RE: Double nutting?
Regards,
Cory
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Double nutting?
RE: Double nutting?
The only cases where I have had to use double nutted bolts is when they are going to subjected to intense vibration loads for an extended amount of time. For this use, I was able to use special bolts where they had UNC Right hand threads and UNF Left hand threads. This allowed for everything to be cinched tight.
RE: Double nutting?
They were used to set the 'plunge' height of the drill.
I used to have a list of approved fastening techniques for on UK military A/C, but can’t remember if jam nuts were on there.
I’ve certainly used them at home in situations where there is rotation or vibration(when I didn't have a nyloc or similar to hand), how well they work seems to depend on how well I manage to torque them against each other!
The thing I have used at work and seen used more is where you have a ‘screw’ that adjusts up and down in a threaded hole and then has a locking ring to set whatever displacement you come up with. I’ve used it on items subject to rotation with some success. I’ve seen it used on things like flow valves too. It’s the same basic principle but instead of 2 nuts you have a threaded hole and a nut.
RE: Double nutting?
If I was at home, if I was working on my car, or if I was in the middle of the ocean and needed to lock a fastener and had no other choice available, I'd use two nuts. In a heartbeat. I know will work to a certain extent. I'm trying to determine the engineering behind the use of jam nuts.
I'm not sure what help anecdotal evidence would be if I was trying to present an argument for or against. I was really looking for reasons why a jam nut would be chosen and the mechanism by which it works. If I know those two things, I'll understand when and why it should be used.
I do appreciate the response. It certainly doesn't seem like there's any consensus, but at least I know that generally, I'm not alone in my skepticism.
RE: Double nutting?
For Nyloc, or for that matter thread lock, is there any compatibility issues between them and the diesel or other chemicals present?
My materials/chemistry is a bit rusty but I'd want to be sure that the diesel or any contaminants or solvents used when cleaning the tanks etc, wouldn't degrade the nyloc/threadlock.
If compatibility is an issue you could still look at all metal 'stiff nuts' or even something like wire locking or castellated nuts & split pin etc instead of jam nuts.
The link unclesyd gives explains how they work, essentially they 'pre-load' each other so they are less likely to become loose from vibration.
Thinking about it variations on the theme were used on aircraft stores as I recall. They were used on fuze pockets and the like I think. They were more like locking rings than actual nuts but used the same principle. However it was several years ago I was looking at such things and I can’t recall for sure.
htt
thread311-164764: Jam Nuts
thread725-167507: Jam Nut with insufficient thread
ht
Several of them reference the same link as unclesyd.
RE: Double nutting?
Our extensive monorail system has all the support rod double nutted.
RE: Double nutting?
If I asked how to determine the proper torque on a bolt, would anybody think an example of how a bolt was torqued would be a good answer? Or that providing an example of a situation in which a bolt required torqueing would be of any help? None of that presents a compelling argument for their use. I understand they have worked or were used in this or that situation. That's not what I would consider engineering rationale for use anywhere else. Isn't the point of engineering to determine what's happening and why so that those lessons can be applied to other situations totally unrelated? That's always been my approach.
I have yet to see two references that are in agreement. There appears to be disagreement on the torqueing sequence and even the order of the nuts. I would like to see the "Handbook of Bolts and Bolted Joints" but I don't have access to it. I was hoping to find what I needed here, but I don't believe I'm getting anywhere.
I really appreciate all the well intentioned input. Thanks guys.
RE: Double nutting?
RE: Double nutting?
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I talked with my neighbor, ex-NASA employee and he stated that NASA did use quite a lot of jam nuts on ground applications. He mentioned one reason that they might not be considered for launch vehicles was the weight consideration.
RE: Double nutting?
RE: Double nutting?
RE: Double nutting?
for the different types of locking methods, the double
nut bolts did better than the others but soon vibrated
loose. It was in the Nordlock Washer Video sited earlier.
I assume this was not all a Sales pitch by Nordlock.