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Old 01-26-2009, 01:40 AM   #1
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Ok, so, I'm casually flipping through Mr. Bell's Maximum Boost, and he mentions fasteners in order of preference:

1) Bolt with a nut
2) Stud threaded into receiver on one end, nut on the other
3) If unavoidable, a bolt threaded into receiver - garunteed to fall out.

So, folks who studied ME... WHY? I don't get it. It seems a stud has two places to slip, threads in receiver, and threads in the nut.

A bolt with a nut seems ok, though if either the nut or the bolt turns, it could loosen.

But a bolt into a receiver is all one big solid piece, it's hard to imagine better. There's only one place you have to lock... Anyway, I don't get it. Does someone here have a better way to look at it?
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Old 01-26-2009, 01:55 AM   #2
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Studying ME, so take it FWIW...

When a stud is installed properly, it "pushes" down on the metal it screws into, putting the metal in compression. Then, when you tighten the nut, it pulls on the stud, putting the surface in tension. The net result is the metal the stud screws into is less deformed as some of the tensile load is canceled out by the compressive load.

Bolts are bad about backing out in a high vibration environment. IE-turbo to manifold bolts. However, you could drill the heads of the bolts so you could wire them together, preventing them from backing out.

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Better would be studs w/ nuts though, but this was way easier.
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Old 01-26-2009, 03:06 AM   #3
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Im a freshman engineer so cant contribute much, all I know is after working with nord-lock nuts on the FSAE car, they ****** rock. Even just bolts wont back out with those suckers.
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Old 01-26-2009, 09:47 AM   #4
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Quote:
Originally Posted by cardriverx View Post
Im a freshman engineer so cant contribute much, all I know is after working with nord-lock nuts on the FSAE car, they ****** rock. Even just bolts wont back out with those suckers.
They've failed by people on this site. If my 10mm studs don't hold, I'm going the same route as Pat. I drilled my studs and nuts for safety wire, but couldn't get to the 4th (disco-potato), but I guess I could wire 3 and check the 4th on occastion. OK, I know what I'm doing this weekend.
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Old 01-26-2009, 11:13 AM   #5
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Pat is correct, Studs offer more surface tension among other things. I have only briefly studied this subject in mechanics of materials and we really never got to the chapter on screws.

Stay tuned: i just started my machine design class.
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Old 01-26-2009, 11:58 AM   #6
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I'm going to answer from a strength standpoint.

with a nut/bolt, you can hold the bolt and turn only the nut which means you are less likely to torque the bolt itself.

with a stud/nut you can't hold the stud but you are still turning the nut which means less torque on the stud. still, it adds a point of failure because you have two threaded interfaces.

with a bolt in a threaded hole, you turn the whole bolt which will torque and stretch thus reducing its ultimate strength. in addition, as you tighten the bolt down, you're working against the forces generated by the clamping at the head and will not get a true thread torque value.
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Old 01-26-2009, 12:50 PM   #7
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Old 01-26-2009, 02:28 PM   #8
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Ok, all good answers, food for thought :-)

Quote:
Originally Posted by hustler View Post
They've failed by people on this site. If my 10mm studs don't hold, I'm going the same route as Pat. I drilled my studs and nuts for safety wire, but couldn't get to the 4th (disco-potato), but I guess I could wire 3 and check the 4th on occastion. OK, I know what I'm doing this weekend.
Oh yeah - I have had a bunch of nordlocks fail - I thought maybe it was because they were the cheaper ones, and they would squish. I think Stainless Steel is a requirement for this...

I don't know what Pat did, but on my own, I just put in the next bigger stud. I also got steel spring lock nuts for it. It wasn't really very cheap - moreso since I bought extras in nearby sizes to make sure I had my bases covered. What I found with the original GT28 studs is you had two choices: Loose enough to fall out, or tight enough to break.

The bigger studs and high quality lock nuts have worked 100% - not only better than I expected, but better than I thought possible.

AbeFM : photos : Drilling Exhaust Housing on Turbo for Big Studs- powered by SmugMug

Quote:
Originally Posted by patsmx5 View Post
Studying ME, so take it FWIW...

When a stud is installed properly, it "pushes" down on the metal it screws into, putting the metal in compression. Then, when you tighten the nut, it pulls on the stud, putting the surface in tension. The net result is the metal the stud screws into is less deformed as some of the tensile load is canceled out by the compressive load.
It's certainly the "way easier" which leads me to want to use bolts. :-)

See, the explanation sounds good - I think it's "the" answer. What bothers me is I have often heard people say not to tighten studs in very hard. From what you are saying, I would think those people are just plain wrong.

Just to make sure I'm clear on this, you're saying you can have higher force on the threads in the nut than you do on the threads the other end of the stud threads into, right? Is there anything special you do to the top of a hole that you just tapped for a stud, then?


Quote:
Originally Posted by y8s View Post
I'm going to answer from a strength standpoint.

with a nut/bolt, you can hold the bolt and turn only the nut which means you are less likely to torque the bolt itself.
That weirds me out a bit - the torque on the bolt should be the same throughout, except when accelerating.

Quote:
with a bolt in a threaded hole, you turn the whole bolt which will torque and stretch thus reducing its ultimate strength. in addition, as you tighten the bolt down, you're working against the forces generated by the clamping at the head and will not get a true thread torque value.

Hmmm, I may expand this later, I'm trying to decide if I should use through screws on a project coming up with a nut on each end or not. No temperature extremes, but high reliability is a must.


BTW: These are the nuts I used:



Note: A side effect of these is that it's damned near impossible to get a wrench on it, even compared to what you used to think was impossible. I ground the turbo to make wrench room with a dremel. The upside is, tighten it once, right, off the car, and you'll never have to do it again.
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Old 01-26-2009, 02:28 PM   #9
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I think it's what Y8s said. I doubt it has much to do with which ones will come loose and more to do with which ones provide better loading. I haven't technically graduated yet, but I have already taken my machine design class.
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Old 01-26-2009, 02:32 PM   #10
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Quote:
That weirds me out a bit - the torque on the bolt should be the same throughout, except when accelerating.
Not necessarily, because there will be friction all along the length of the bolt.
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Old 01-26-2009, 03:18 PM   #11
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I believe what y8s was saying is that you are less likely to put twist(torque) into the bolt shank as it is more of a straight pull when you are tightening just the nut. same goes with a stud, it's just there is nothing to realy capture one end of it.

tightening a bolt from the head puts a lot of twist in the shank of the bolt and with heat cycles accompanied by vibrations can make them "spring" back to their natural state effectively loosening the bolt.

I think some people don't think about the difference between torque and torque if you catch my drift.
meaning that with a stud you put more stretch in the stud by the amount of torque you apply to the nut via a wrench resulting in more clamping force.

by tightening a bolt from the head you loose some clamping force because you are introducing more torque(twist) to the bolt itself, thus requiring more torque at the wrench to create the same clamping force. by that time though it is usualy to much and has weakend the bolt. this is why on some vehicles the manual recomends tightening head bolts to a certain spec, then back off and retorque(at the wrench) to remove some of the torque(twist) from the bolt itself.
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Old 01-26-2009, 05:03 PM   #12
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Quote:
Originally Posted by dynokiller90 View Post
I believe what y8s was saying is that you are less likely to put twist(torque) into the bolt shank as it is more of a straight pull when you are tightening just the nut. same goes with a stud, it's just there is nothing to realy capture one end of it.

tightening a bolt from the head puts a lot of twist in the shank of the bolt and with heat cycles accompanied by vibrations can make them "spring" back to their natural state effectively loosening the bolt.

I think some people don't think about the difference between torque and torque if you catch my drift.
meaning that with a stud you put more stretch in the stud by the amount of torque you apply to the nut via a wrench resulting in more clamping force.

by tightening a bolt from the head you loose some clamping force because you are introducing more torque(twist) to the bolt itself, thus requiring more torque at the wrench to create the same clamping force. by that time though it is usualy to much and has weakend the bolt. this is why on some vehicles the manual recomends tightening head bolts to a certain spec, then back off and retorque(at the wrench) to remove some of the torque(twist) from the bolt itself.
you're on the same track I am. it's all about keeping torsion out of the bolt.
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Old 01-26-2009, 05:14 PM   #13
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Yeah that makes sense. Oh well, bolts were easier for me. FWIW, I taped the manifold 3/8-16 and torqued the bolts to probably 20 ft*lbs. So far, they're working.
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Old 01-28-2009, 04:29 AM   #14
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Quote:
Originally Posted by y8s View Post
you're on the same track I am. it's all about keeping torsion out of the bolt.
That the torsion is released by slight slipping of the threads at the "fixed" end of the stud?

That does sound reasonable, the whole thing. I'm glad I asked. :-)
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Old 01-28-2009, 11:27 AM   #15
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I'm thinking more that the nut spins on the stud = less torsion on the threads of the stud.
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Old 01-28-2009, 02:07 PM   #16
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So, I have a bolt, one end is not moving, the other has a nut on it on which you apply 20 ft-lbs.

Now I have another, it's end (the same distance, diameter away, etc) is also not moving, with an identical nut on it which you apply the identical 20 ft-lbs.

Can you tell me which one has less torsion on it? Can you tell me which is held due to threads in a hole and which has a bolt head on it? What if I locked two nuts on it, or screwed in the stud but then welded it in place? Would any of these change the torsion on a bolt with certain conditions on one end, and held rigidly on the other? It seems all an element in the middle of the shaft would know is what the parts next to it are doing (i.e. moving or not moving, under stress or not)

I'm confused again. :-)
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Old 01-28-2009, 02:34 PM   #17
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Maybe it's just me, but I can't see much torsion being in the shank of the bolt or stud. I mean, maybe a little bit, but not much. What if I tap the heads of the bolts with a hammer after I torque them? That would probably release any torsion. Better question: Does the torsion in the bolt/stud matter? I mean, it's not like it winds up 1/4 turn or something. We're probably talking 1/2* or something for a 1" long bolt right?
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Old 01-28-2009, 07:07 PM   #18
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you'd be surprised at how much torsion you can put in a bolt. of course there are many factors that can contribute to it. Diameter, grade, thread taper, torque(at the wrench) and so forth. but yes a short bolt won't twist as much as a long one. It does however put just as much strain on the bolt.

two bolts being equal in all dimensions and grade aside from length will twist the same amount per unit of length measure. so a bolt twice as long will show twice as much measureable twist from one end to the other, but that doesn't mean that it is twisted more. So the same amount of stress is present in both bolts. A shorter bolt will fail at a lesser degree of angle than a longer bolt, but the same amount of stress has to be applied to each to reach the failure point. so in short just because the torsion appears to be a small amount on a shorter bolt the stress that is induced could be at or close to a critical point.

here's an anecdotal experience that we've all come across. think back about that rusty bolt you were removing. you had to get the breaker bar out and the wd40. as you are turning it, it pops and creeks at it twists right? that right there is the torsion we're talking about and you can feel it in your hands. If you watch closely you can even see it happening.
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