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Old 24-06-2007, 23:29   #16
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The industry standard is the one you describe, for which I have provided the link.
Andy, with all due respect, this practice maybe done, but it is NOT industry standard. Even in Dels original diagram, "b" even states in the last sentance that "this form of securing is questionable".
Maybe Michigan wheel use the technique you describe, but that doesn't automaticly make industry standard. There may or may not be a valid reason for them to do it in the way they do. But I can assure you that my version is the more common industry standard. And for the reason I stated. The "big" nut takes the torsional force, the "small nut" is simply there for locking.
By the way, those Nord-Locks are simply magic.
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Old 24-06-2007, 23:47   #17
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Remember guys this is the marine industry. Standards? Everyone has one. LOL
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Old 25-06-2007, 00:10   #18
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There are many arguments both ways, the arguments that say the thin nut goes first make a lot of sense to me.

When you tighten the second nut, it loads up its threads and by pushing down on the lower nut it UNLOADS those threads. The thread on the inner nut must be loaded DOWN toward the prop, otherwise it would not serve its locking purpose. Assuming that thread loading is the key, then the thicker nut should have the higher thread loading in normal use and be the outer nut.

But in the real world it doesn't matter. some people do it one way, some do it the other. I have never heard of a prop coming off because the threads on the shaft were over loaded and stripped.

The whole argument would seem to be a tempest in a teapot from a practical standpoint. Either approach works to jam the nuts against backing out, and that, rather than thread loading, seems to be the key.
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Old 25-06-2007, 00:49   #19
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Originally Posted by fstbttms
A quick Google search comes up with illustrations refuting your position:



LOCKING DEVICES, KEYS, SPRINGS, RIVETS AND WELDING

However, there seems to be more literature supporting the "jam nut first" theory. I will contact my favorite propeller repair shop tomorrow and ask which they recommend. I will post their response here.
Did you happen to notice where your link is from
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Old 25-06-2007, 01:22   #20
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Quote:
Originally Posted by GreatKetch
The whole argument would seem to be a tempest in a teapot from a practical standpoint. Either approach works to jam the nuts against backing out, and that, rather than thread loading, seems to be the key.
Apathy! There is a reason for specified torques. So people without good mechanical knowledge don't over/under tighten fasteners. Ever seen a perfectly good wheel/tire laying along the freeway and then the car farther up the road?

The problem being when you load the narrow nut the threads in the nut become distorted.

If one tightens the narrow against the long nut, the narrow can work loose, in turn, leaving the long nut to fend for itself.

When one tightens the long nut against the narrow nut, it preserves it and they both work together.


So, why not use two long nuts??? You can! if you want all that extra hanging out there, and there's no distortion in the thread, just making it longer nut thats just a little extra tight.

Besides, have you ever seen a long nut's face precisely perpendicular to the threads. NOT! Put one on a piece of all-thread and spin it in a lathe.

A jam nut (narrow) will straighten itself out because the threads do distort. Then the long nut follows suit the best it can. Read the first post very carefully!

Engineers have been working on this for many years and the theory still stands today. See my first post (1943)
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Old 25-06-2007, 01:35   #21
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There is another point missing in this discusion. I missed it at first, my mistake. I was not thinking of a Prop being held on, but rather using it to tension a bolt. In bolt tensioning, the required torq is not just protecting the thread of either Bolt or Nut, but it is protecting the tensional force of the bolt. It is stretching the bolt a required amount.
In the case of the propellor scenario, we are not interested in stretching the shaft in anyway, mearly protecting the threads, especially if they are softer Brass Nuts.
For me, I use a nut with a Pin through it on my shaft.
If I was using a a dual nut system, I would probably still use some thread lock.
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Old 25-06-2007, 02:01   #22
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Interesting subject - I have alway installed the jam nut outside the large nut.

BTW - Did anyone read the text of Delmarrey's posted page - "Theoretically, the locknut should be placed as shown in the figure. In practice, it is usually placed on the outside so it can be manipulated more easily."

My question regarding the theory of the case is do the threads on the shaft/bolt stretch or do the threads on the nut stretch. You would think you want the nut to be sacrificial as prop shafts might be a little more expensive to replace. Then in a high torque environment do I want the 20 threads of the thick nut taking the initial torque or the 10 threads of the jam nut?

As an FAA licensed mechanic I went to AC43.13 (the FAA bible on hardware) and it mentions jam nuts but doesn't mention how to use them. In reality aircraft use fibre or metal lock nuts or castellated and cotter pined.

So I'd go with the standard answer. If the installation comes with a manual - follow that. If not use your best engineering judgement. In any critical joint I would avoid a jam nut as my safety locking device at any cost and I suspect all prop installations have a cotter pin backing up the whole shebang anyway.

Not to say I'm unwilling to learn new tricks but baring any definitive answer, I'll keep putting it together as I was taught in A&P school 30 years ago. Jam nut on top.
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Old 25-06-2007, 08:16   #23
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Originally Posted by Terra Nova
you'll have to do better than a phone call to your local repairman to convince anyone here. While you're Googling, try ANY other marine propeller manufacturer if you won't believe Michigan Wheel.
Not interested in convincing anyone here. And the "local repairman" I trust is one of the largest propeller repair facilities on the West Coast. So I'll take their word as gospel, "yo".
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Old 25-06-2007, 08:22   #24
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Quote:
Originally Posted by delmarrey
Did you happen to notice where your link is from
Yes, I did notice where the link is from. What're you saying? Hmmm...?
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Old 25-06-2007, 09:02   #25
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Wait! I need more popcorn.
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Old 25-06-2007, 13:30   #26
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I spoke with Jeff at Bay Propeller in Alameda today. He confirmed that the correct assembly is jam nut-first. He also said that they have had many arguments with customers over the correct order of the nuts and will install them big nut-first if the customer insists. For myself, I will begin installing the jam nut against the prop.
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Old 25-06-2007, 13:34   #27
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Did he say why????
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Old 25-06-2007, 13:37   #28
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Quote:
Originally Posted by Alan Wheeler
Did he say why????
He said that many customers are firm in their belief that the jam nut goes on last and will not be dissuaded. It's the customer's dime, so they get what they want.
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Old 25-06-2007, 13:47   #29
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Sorry, I meant to say, why do they use the other method? Did they have a particular reason? or was it just the way they had always done it or or or??
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Old 25-06-2007, 13:50   #30
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Quote:
Originally Posted by Alan Wheeler
Sorry, I meant to say, why do they use the other method? Did they have a particular reason? or was it just the way they had always done it or or or??
Jeff said something about "unloading" the inner nut and not stretching the threads. I didn't ask him to go into detail but he indicated that there is good science behind having the jam nut on first. It wasn't arbitrary on their part.
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