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'[OT] Mechanical Strength of a Bolt'
> Sorry if I already posted this...
When I saw that, you hadn't, at least in my part of the space-time
But the "initial" post arrived 3 minutes after its successor.
Such things happen here out at the beginning of time.
Here it's sunrise on Wednesday February 1st.
Or would be if it wasn't raining and therefore extremely probably
cloudy and therefore still rather dark.
For most reading this, or wisely not reading it, it's somewhat after
sunrise on the day before :-)
Back to work ...
Gotta love these one off pro bono lashups.
Where are the 7812s. Aaagh. No 7812's. OK LM317. Which pin is adjust.
OK. What's the recommended output to adj resistor. 240. 240?. 240!
Don't they know about E12 series. Or E6. Or E1 for that matter. Hmm.
100's a bit low. 1ks a bit high. OK ok 270 then. Lessee -
(12-1.25)/1.25*270 = . Where's the calculator. A real man could do
that in his head. And a real engineeer... . But an unslept engineer's
been known to do silly things, even on something so simple. OK then.
Use C. No not C, C.COM. Good old DOS. 2322. 2200? 2200/270*1.25+1.25 =
? C. 11.43. Bit low. Not that it matters really. Just to drive a 12v
CCFL. Could add a series diode. nasty. Still. 2700s gotta be too high
though. c 2700/270 - OK - even I can do that on no sleep * 1.25 + 1.25
= 13.75. Yep. A bit low is better. Could use parallel resistors. Nah.
Not worth the hassle here. Now. Caps. Do I REALLY have to decouple
the reference divider? What a pain. Noise is hardly an issue here. Is
it? What about protection diodes. Nah - no real energy to feed back.
Another 317 for 5v? But then I'd have to calculate the divider again
:-). OK - LM340s we have. There IS a place for LM340s after all. But
not a very big one. Caps? Pretty unimportant AFAIR. Better check the
book just in case. Boo? Yep book. 1982 National. Not even NatSemi back
then. Even quicker than looking on the PC. Is the 317 really that old?
Apparently. Where was I. Oh yes, caps. Just feeding some switches. Not
critical. But an oscillating switch feed would be 'interesting'. OK.
That's the caps sepcd. Looks like time for a coffee. Shame caffeince
doesn't affect me at all. Just as well :-). It's the ritual I guess.
Even if it's decaf. Maybe some Uncle Toby's porridge. No - a bit early
yet. Back to work ...
See, I should have had some sleep :-)
And an interesting (to me) observation.
When I replied to this it deleted the [OT].
It was originally [OT]: - the : being optional these days.
I went back and tried a few others.
Anything original with a trailing colon after the ] deletes the tag.
But replying to a Re ... with or without : or a new post without : is
I'm using OE6.
Will be interesting to see how many others end up with tag deleted.
I reckon Russell is developing some kind of brain/PS2 interface so he just thinks stuff into his email client...
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On Tue, Jan 31, 2006 at 06:16:53PM -0000, Michael Rigby-Jones wrote:
>critical. But an oscillating switch feed would be 'interesting'. OK.
> >That's the caps sepcd. Looks like time for a coffee. Shame caffeince
> >doesn't affect me at all. Just as well :-). It's the ritual I guess.
> >Even if it's decaf. Maybe some Uncle Toby's porridge. No - a bit early
> >yet. Back to work ...
> I reckon Russell is developing some kind of brain/PS2 interface so he just thinks stuff into his email client...
I built one of those ages ago actually, but it's hooked up to a timer,
so it only works if I've recently slept for at least 7 hours...
>From the original post
>I need to know the strength of a bolt.
From R. McMahon
>And *NOW* multiply by your safety factor.
>You do have a safety factor, hopefully.
>What is it?
>Invariably YMWV :-) *
Based upon the original post, I assumed the poster wanted to know the failure strength of the bolt (joint), not the joints ability to carry a load with a pre-determined margin of safety ;-) Pmax = Ultimate / 1.5 is pretty standard in the aircraft industry. For tooling, ground handling equipment Pmax = Utimate / 5.0. Hope my 1.9999999999 cents helps.
'[OT] Mechanical Strength of a Bolt'
>Can you please explain this a bit? Does this mean that when >we operate in a range where shearing is an issue, the shear >forces are so strong that the material friction is not >relevant? Is this dependent on the materials in use?
Yes. When operating at the max load carrying capability of a mechanically fastener joint using most structural materials (wood, Al, Ti, steels), the load transfer due to friction is negligible. What's more important, the variability of friction for a joint that will be 'reasonably' manufactured is quite large and thus not reliably predictable. In the case of 'man rated' structure, it is dangerous to assume any beneficial effects of friction.
To help in rationalization of the relative values involved, try not to think about force, but work with stress. Stress, being force divided by area, is a normalized value. I don't want the process to sound all 'spooky and mystical, or even Zen', but it will give you an sort of order-of-magnitude feel about the structure.
One other thing, things get a bit more complicated if the joint involves more than one fastener. That is, it is not valid to take the failure load of a joint with one fastener and double it for a two fastener joint....
Let me know if you need more :-)
mark rewis wrote:
>> Does this mean that when we operate in a range where shearing is an
>> issue, the shear forces are so strong that the material friction is not
>> relevant? Is this dependent on the materials in use?
> Yes. When operating at the max load carrying capability of a
> mechanically fastener joint using most structural materials (wood, Al,
> Ti, steels), the load transfer due to friction is negligible.
This is surprising, and judging by some previous comments, not only to me.
Always good to have someone around who /knows/ rather than assumes :)
> Let me know if you need more :-)
No, not really, at the moment :) Thanks for sharing,
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