OT - Torque the Nut or the Bolt?

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mike wrote: ...

Sorry, but even if you can _TEMPORARILY_ counteract the force, you can't always keep it from returning (external side load, for example).
If you think that isn't so, I reiterate you simply haven't worked on enough stuff.
Have a nice day and hope all your assemblies are so simple...
--
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Unless I'm not understanding your use of the word "squeezing", I don't agree.
As I said previously, certain combinations of bolt and object allow for a "drop right in" situation, other combinations require turning/ pushing to get the bolt in.
Here is an example bolt in question:
http://www.cometkartsales.com/store/chassis/cpa/images/margayparts/markpbolt.jpg
The diameter of non-threaded portion of the bolt, as well as the diameter of the hole it goes through, can be significantly different - relatively speaking. If the hole happens to be in a 3/4" thick piece of steel sitting on top of a 1" steel bushing, these different diameters cold make a significant difference in side load.
There is also the issue quality control where it is possible that any given hole might not be perfectly perpendicular to the faces. While this will not only impact the sideload on the bolt, it introduces all sort of other problems in the final product that I don't need to go into here. Picture a bolt held straight by the bushing and then being inserted into a 3/4" hole that is not perpendicular to the bushing. I see significant sideload being introduced in the last 3/4".
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mike wrote: ...

_Drift_ punch in the hole, not on the bolt, silly...
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If you use tapered rods in neighboring holes to line things up... then there is no side load on your bolt! It drops right in.
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mike wrote:

That "tapered rod" is a drift punch.
> ... then there is no side load on your bolt! It drops right in.
Sometimes yes, sometimes not so much.
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re: If you use tapered rods in neighboring holes to line things up... then there is no side load on your bolt! It drops right in.
Not so. In my application, the non-threaded portion of any given number of bolts are known to be of varying diameters, as are the holes of any given number of the object being fastened. There are times when the bolt needs to be pressed while turned to insert or remove and there are times when the bolt just drops right in. Since we are required to obtain both the object and the bolts from a single source we are stuck with what we get.
We prefer the tightest fit possible, which is why I concluded that torqueing the nut is the correct method for us to use. If, in our ideal situation, we have a very tight fit, then the side load on a "big bolt/small hole" combination would impact our torque readings considerably.
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DerbyDad03 wrote: ...

Most definitely, tight tolerances are a prime example of where the side pressure doesn't go away and where definitely for consistency from assembly to assembly you would want to use the nut end.
"Mike" is simply too inexperienced apparently to have run into "real world" complications to the theoretical descriptions he finds on the web... :(
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wrote:

re: If you use tapered rods in neighboring holes to line things up... then there is no side load on your bolt! It drops right in.
Not so. In my application, the non-threaded portion of any given number of bolts are known to be of varying diameters, as are the holes of any given number of the object being fastened. There are times when the bolt needs to be pressed while turned to insert or remove and there are times when the bolt just drops right in. Since we are required to obtain both the object and the bolts from a single source we are stuck with what we get.
We prefer the tightest fit possible, which is why I concluded that torqueing the nut is the correct method for us to use. If, in our ideal situation, we have a very tight fit, then the side load on a "big bolt/small hole" combination would impact our torque readings considerably.
(end of transmission)
You may refer to my previous posts and applaud now.
Steve
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re: You may refer to my previous posts and applaud now.
If I wasn't so tired from reviewing this long thread, I'd stand up too. ;-)
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wrote:

re: You may refer to my previous posts and applaud now.
If I wasn't so tired from reviewing this long thread, I'd stand up too. ;-)
Thank you. At least most of the usual suspects have agreed that 99% of the time, it don't matter. And that was stated by, IIRC, all. The discussion came about in circumstances that involve the other 1%, which is what I am interested in. I know what happens when things go right. What I'm interested in is those other times, because they are the ones that make it interesting and labor intensive. ............. ez outs ......... drilling .......... broken ez outs ............ torches ............ application of heat, cold, penetrants, etc ................ learning new cuss words ........... getting out the first aid kit .........
need I go on?
Steve
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Holy shit it doesn't matter. If you can reach both the bolt head and the nut I'd have thought you'd have torqued 'em both and figgered it out. .

I doubt that.

Good luck with that.

Fail... when?

Yeah, but there's only one "real" answer among "everything that has been said in this thread"- Don Young's.

I hope this isn't a spacecraft. -----
- gpsman
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gpsman wrote: ...

Don's is precisely correct in what it deals with, but if there is a tight fit of the bolt in the hole and one torgues the bolt and not the nut, the reading of the torque wrench will include the resistance of the bolt and the resulting applied torque will be low by that amount as compared to what would be applied if torqued the nut.
That's all, no more, no less...
That the torque spec is an approximation and all that is certainly true, but the real world still intrudes on what one will measure in different circumstances.
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Your boat is too big for you ho. -----
- gpsman
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gpsman wrote: ...

The question that started it off had tolerances that created the situation. By some design standards that's so, but real world strikes again...
And also there's the place where the bolt functions as a load-carrying member, etc., etc., etc., ...
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I don't care which world. How are you going to get your bolt *through* hole and still retain enough friction between the two surfaces to affect the torque wrench reading? -----
- gpsman
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gpsman wrote:

Sometimes it's easy, sometimes it isn't...I've already gone thru it enough times I no longer care.
OP's occasionally driving or pressing them, apparently, as I read his post...
My practical problems tend to have weighted loads that aren't easy to control in repair situations so one can manage to get the sucker in there, but as soon as let go of the drift, it'll close up hard...
If that doesn't float your particular boat, so be it...
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dpb wrote: ...

...
Actually, it would be easy enough for him to test how significant it is in his case--take one of his tightest-fit examples and torque it from the bolt side, then check the nut end. If the drag is significant, he'll find he can torque it further; if it only seems tight getting it in the hole but isn't _that_ tight, it won't make a noticeable difference.
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I have had cases where the bolt/hole combination has been *extremely* tight. It required turning and tapping to insert the bolt. Now I think I've got my ideal case, right?
Then I grab the toruque wrench and before I reach my desired setting, the bolt snaps just below the threads. (The threads are, of course, narrower than the shaft, so there is no friction between the threads and the hole.) This raises the question of what caused the failure.
Was this bolt weaker than the others or did the fact that the bolt could not twist/stretch in the hole cause to snap at a lower torque than it could normally handle? Since most failures seem to occur with the tighter bolts, either the larger bolts are weaker or the friction prevents the stretching.
I'll vote for the friction.
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re: I hope this isn't a spacecraft.
Why would anyone ask a spacecraft related question in a home repair forum? Jeez.
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DerbyDad03 wrote: ...

Heck, somebody asked about nuclear power plants just the other day... :)
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