SAE Grade-8 bolt snapped @135ft/lbs

I'm dealing with a critical application. If these fasteners fail, the
results could potentially be fatal. I need maximum security. I've been
torquing 1/2" grade-8 bolts to 135ft/lbs. Tonight, one of the bolts
snapped in half while torquing. This made me rethink all the other
bolts that I've been torquing to this spec. First, shouldn't a 1/2"
grade-8 bolt withstand far more than 135ft/lbs??? If not, I need a
general torque spec that will ensure proper bolt tension. Remember, if
these bolts fail or come loose, the results will not be pretty....

First of all, check this website
http://www.rockcrawler.com/techrepor...que/index.asp# and
check out their torque calculator. From what it is saying, a 1/2"
Grade 8 bolt should be torqued to 145 ft-lbs dry. I'm not sure why
your bolts would be snapping in half since normally the head would come
off from over-torquing. Of course you didn't say what application you
were using the bolts for, but I can tell you that you need thread
length engagement of 2.5 times the bolt diameter to ensure maximum
holding capacity. Any longer than that has no additional effect.
Remember also, that these bolts are made by the millions so it is
entirely possible that a bad one could have slipped through. Also, if
you are using nuts, make sure these are properly graded as well...

On 8 Mar 2005 19:13:07 -0800, "Keith" > wrote:

>First of all, check this website
>http://www.rockcrawler.com/techrepor...que/index.asp# and
>check out their torque calculator. From what it is saying, a 1/2"
>Grade 8 bolt should be torqued to 145 ft-lbs dry. I'm not sure why
>your bolts would be snapping in half since normally the head would come
>off from over-torquing. Of course you didn't say what application you
>were using the bolts for, but I can tell you that you need thread
>length engagement of 2.5 times the bolt diameter to ensure maximum
>holding capacity. Any longer than that has no additional effect.
>Remember also, that these bolts are made by the millions so it is
>entirely possible that a bad one could have slipped through. Also, if
>you are using nuts, make sure these are properly graded as well...


I'm not following the 2.5 x dia engagement length statement. If you
used 1/2" bolts and normal sized nuts the engagement length in the nut
would only be around 1/2" - 3/4" for typical nuts. How would you
ever use a bolt and nut where you could get 2.5 x dia engagement? I
can see it for putting head bolts or main caps on, they have drilled
and tapped holes of decent length.

> How would you ever use a bolt and nut where you could get 2.5 x dia
engagement?

A jam-nut?

"ultralight" > wrote in message oups.com...
: I'm dealing with a critical application. If these fasteners fail, the
: results could potentially be fatal. I need maximum security. I've been
: torquing 1/2" grade-8 bolts to 135ft/lbs. Tonight, one of the bolts
: snapped in half while torquing. This made me rethink all the other
: bolts that I've been torquing to this spec. First, shouldn't a 1/2"
: grade-8 bolt withstand far more than 135ft/lbs??? If not, I need a
: general torque spec that will ensure proper bolt tension. Remember, if
: these bolts fail or come loose, the results will not be pretty....
:

I looked at:
http://www.boltdepot.com/fastener-in...ded-Torque.htm
and it says you're overtorqueing by quite a bit.

Whatcha usin' it for? Curiosity got me.

Dave

Well, he never did say what his application was, and if he was using
nuts or not. I was just adding the 2.5 times diameter rule just for
his general knowledge... Although I'm sure everyone already knows that
anyway. It's also better to torque in stages when using a higher
torque amount. Either way, for maximum security, I would get a bolt
with a rolled thread made from material that has been certified and NDT
tested. It would add a few bucks to the cost, but you can guarantee
the bolt will be harder to snap than any 10 cent hardware store Grade-8
"Made in China" bolt. This website explains the difference:
http://www.lancasterthreaded.com/docs/tensile.htm

A grade 8 bolt is only a grade 8 bolt if you know who made it. There
has always been a problem in my lifetime of counterfeit and cheap
import bolts that are marked as one grade, but don't make the grade. In
mission critical applications (aircraft, bridges, etc), the
manufacturer of the equipment does independent testing of random
samples of the fasteners.

As others have noted, buy from a quality manufacturer of rolled-thread
bolts. Tables I have in my shop show 90 ft/lbs for plated grade 8 (the
common yellowish ones), 115 ft/lbs for unplated. There are also grades
above 8, like 8.2 and ASTM A490. You probably don't need this though, a
snap a 135ft/lbs indicates that you're most likely the victim of a
sub-standard import bolt.

-Adam

On Thu, 10 Mar 2005 04:56:36 UTC wrote:

> A grade 8 bolt is only a grade 8 bolt if you know who made it. There
> has always been a problem in my lifetime of counterfeit and cheap
> import bolts that are marked as one grade, but don't make the grade. In
> mission critical applications (aircraft, bridges, etc), the
> manufacturer of the equipment does independent testing of random
> samples of the fasteners.
>
> As others have noted, buy from a quality manufacturer of rolled-thread
> bolts. Tables I have in my shop show 90 ft/lbs for plated grade 8 (the
> common yellowish ones), 115 ft/lbs for unplated. There are also grades
> above 8, like 8.2 and ASTM A490. You probably don't need this though, a
> snap a 135ft/lbs indicates that you're most likely the victim of a
> sub-standard import bolt.

There's also a question of fatigue if the bolt had been used at max
torque before. I had one head where the grade 8 bolts used to hold
the cam assembly were specified for one time use only. Being a bit
skeptical, I played it with and sure enough the darned bolts would
begin to stretch, neck down and finally break after 5-6 cycles if I
let them set for a day or so between removals.

--
Will Honea

ultralight wrote:
>
> I'm dealing with a critical application. If these fasteners fail, the
> results could potentially be fatal. I need maximum security. I've been
> torquing 1/2" grade-8 bolts to 135ft/lbs. Tonight, one of the bolts
> snapped in half while torquing. This made me rethink all the other
> bolts that I've been torquing to this spec. First, shouldn't a 1/2"
> grade-8 bolt withstand far more than 135ft/lbs??? If not, I need a
> general torque spec that will ensure proper bolt tension. Remember, if
> these bolts fail or come loose, the results will not be pretty....

135 ft-lbs to too high a torque for a 1/2" grade 8 bolt. I
assume you are torquing them dry. If you are lubricating the
bolts, then 135 ft-lbs is way to high.

http://www.futek.com/boltcalc.asp
http://www.assemblymag.com/CDA/Artic...,99794,00.html
http://dodgeram.org/tech/specs/bolts/SAE_bolts.html
http://www.boltdepot.com/fastener-in...ded-Torque.htm
http://www.boltdepot.com/fastener-in...ade-Chart.aspx
http://www.futek.com/files/Pdf/Manua...0Equations.pdf

Ed

Please tell me you are useing a CALIBRATED torque wrench.

Matt