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SAE Grade-8 bolt snapped @135ft/lbs
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Dave Danger
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- Joined
- Mar 14, 2005
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- 5
SAE Grade-8 bolt snapped
After reading all the above, it is obvious that for whatever reason, the originator has a reason that he'd rather use grade 8 (hardware store) bolts than something that may have more than enough tensile strength. "Shrug the shoulders" and go sideways around the tree. Use more of them (bolts) for the application that he's after. Assuming the application will allow it, use 2 or even 3 bolts instead of 1 to do whatever the job is. Less torque will be required as the load will be shared.
Think outside the box a bit.
Dave Danger
After reading all the above, it is obvious that for whatever reason, the originator has a reason that he'd rather use grade 8 (hardware store) bolts than something that may have more than enough tensile strength. "Shrug the shoulders" and go sideways around the tree. Use more of them (bolts) for the application that he's after. Assuming the application will allow it, use 2 or even 3 bolts instead of 1 to do whatever the job is. Less torque will be required as the load will be shared.
Think outside the box a bit.
Dave Danger
Dave Danger said:
You cannot compare SAE fasteners to just any "hardware store" bolt. The truth is, each SAE grade is manufactured to meet certain tolerances. That's why these fasteners are widely used in the automotive industry to hold critical parts together. If they weren't made to specific tolerances, the auto manufactures wouldn't risk billions of dollars in lawsuits by using them.
The reason many people claim that SAE grades do not meet specific tolerances, is because sometime in the 1980's a very large volume of hardware was imported into the united states with false SAE markings. It remains a problem to this day. Regardless, if the appropriate paperwork can be furnished with purchase of SAE fasteners, they WILL meet specific tolerances. In the case of grade-8 hardware, it is a 150,000psi tensile-strength.
SAE provides "standards," but there is no quality control nor consistency in the parts. The FAA has put out numerous warnings about the use of Grade 8 hardware...weather or not one chooses to use this hardware on aircraft is beside the point; the warning is valid. The parts do not show consistency, which is why they're not approved for use on aircraft. If tensile strength were the only issue, they'd be fine, but there is no quality assurance in grade 8 hardware.
Again, do what you will for the critical operation upon which your life depends. Don't however try to hold out automotive standards as some high level of quality, because they're not. Automotive parts are made based on economy, and it's far easier to replace a defective cheap part in the automotive industry than manufactur higher quality equipment. Automotive standards are rough, often not overly exact. Rather than build a quality part for a car, usually the part is just built bigger.
Most of your hardware store bolts (or automotive store bolts, if you prefer) have tensile strengths closer to 60,000 PSI or less, with Grade 8 at a shear value of 91,000 psi and 150,000 ultimate (in theory), while AN bolts are 125,000 psi. Hardware store SAE bolts are mostly not corrosion resistant, and bend easily. AN bolts are nickle alloys, while SAE Grade 8 bolts are mild steel. AN bolts are more ductile, while SAE Grade 8 are more brittle. AN hardware and SAE hardware have very different thread load bearing properties and capabilities. AN, NAS, and MS bolts (aircraft grade hardware) are consistent in properties, qualities, and standard from lot to lot. SAE Grade 8 hardware is NOT. AN bolt threads are rolled after heat treating, whereas SAE are cut afterward.
All AN hardware has the same properties. Grade 8 hardware has vastly different properties that vary with manufacturer and lot number. Where the AN hardware is rolled, often the SAE Grade A threads are cut, and that's one of two places the bolts tend to break. Yours twisted off with torque, I believe. Did it twist off in the threads? The other place these tend to break is the head, owing both the britleness,and the inconsistency in radiusing the head and shank.
You'll note I listed alleged tensile strengths. Tensile strengths for SAE Grade 8 can only be approximated, due to the variance between lots. This is not the case for NAS, MS, or AN hardware, and that's a very important distinction.
You mumbled something about not confusing SAE hardware with hardware-store hardware. I don't want to burst your bubble (actually, I do), but hardware store hardware IS SAE. It may nor may not be Grade 8, as numerous grades exist, but all the standard bolts and sizes you find are SAE bolts...just with varying degrees and qualities of production. Grade 5 is SAE. So is Grade 8. Grade 5 has lower tensile strengths, but tends to bend more, is less brittle, and may actually do better than the Grade 8 in many cases. Of course, you need to specify weather you're after actual tensile strength (as in holding the threads or headof the bolt on) or shear strength. In either case, test out several examples purchased from different sources in the SAE, and you'll find numerous different failure points...showing clearly the lack of consistency in production.
Actually yes, the hardware store bolts are SAE bolts. Not all grade 8, but still SAE...unless they're metric.
If they weren't made to specific tolerances, auto manufacturers wouldn't take the risk? No? Why do you suppose the FAA doesn't permit or authorize their use? Think about that a little before you reply.
Again, do what you will for the critical operation upon which your life depends. Don't however try to hold out automotive standards as some high level of quality, because they're not. Automotive parts are made based on economy, and it's far easier to replace a defective cheap part in the automotive industry than manufactur higher quality equipment. Automotive standards are rough, often not overly exact. Rather than build a quality part for a car, usually the part is just built bigger.
Most of your hardware store bolts (or automotive store bolts, if you prefer) have tensile strengths closer to 60,000 PSI or less, with Grade 8 at a shear value of 91,000 psi and 150,000 ultimate (in theory), while AN bolts are 125,000 psi. Hardware store SAE bolts are mostly not corrosion resistant, and bend easily. AN bolts are nickle alloys, while SAE Grade 8 bolts are mild steel. AN bolts are more ductile, while SAE Grade 8 are more brittle. AN hardware and SAE hardware have very different thread load bearing properties and capabilities. AN, NAS, and MS bolts (aircraft grade hardware) are consistent in properties, qualities, and standard from lot to lot. SAE Grade 8 hardware is NOT. AN bolt threads are rolled after heat treating, whereas SAE are cut afterward.
All AN hardware has the same properties. Grade 8 hardware has vastly different properties that vary with manufacturer and lot number. Where the AN hardware is rolled, often the SAE Grade A threads are cut, and that's one of two places the bolts tend to break. Yours twisted off with torque, I believe. Did it twist off in the threads? The other place these tend to break is the head, owing both the britleness,and the inconsistency in radiusing the head and shank.
You'll note I listed alleged tensile strengths. Tensile strengths for SAE Grade 8 can only be approximated, due to the variance between lots. This is not the case for NAS, MS, or AN hardware, and that's a very important distinction.
You mumbled something about not confusing SAE hardware with hardware-store hardware. I don't want to burst your bubble (actually, I do), but hardware store hardware IS SAE. It may nor may not be Grade 8, as numerous grades exist, but all the standard bolts and sizes you find are SAE bolts...just with varying degrees and qualities of production. Grade 5 is SAE. So is Grade 8. Grade 5 has lower tensile strengths, but tends to bend more, is less brittle, and may actually do better than the Grade 8 in many cases. Of course, you need to specify weather you're after actual tensile strength (as in holding the threads or headof the bolt on) or shear strength. In either case, test out several examples purchased from different sources in the SAE, and you'll find numerous different failure points...showing clearly the lack of consistency in production.
Actually yes, the hardware store bolts are SAE bolts. Not all grade 8, but still SAE...unless they're metric.
If they weren't made to specific tolerances, auto manufacturers wouldn't take the risk? No? Why do you suppose the FAA doesn't permit or authorize their use? Think about that a little before you reply.
Avbug,
There is no doubt that aircraft-class fasteners are superior. I never doubted that. All I'm contesting is that SAE grade-8 hardware will suffice for my particular application. Just as someone else said, I am using multiple fasteners at any given point of attachment. The failure of one fastener will not result in carnage, and the problem can be noted before the results are catastrophic.
I value your input, and trust in everything you say. But understand that I'm working on a truck suspension, not a Boeing 777 wing spar. Above all, I wouldn't do anything that might potentially become a hazard to myself or others. Trust in my judgment, and sleep at night knowing that I'm not building an airplane.
There is no doubt that aircraft-class fasteners are superior. I never doubted that. All I'm contesting is that SAE grade-8 hardware will suffice for my particular application. Just as someone else said, I am using multiple fasteners at any given point of attachment. The failure of one fastener will not result in carnage, and the problem can be noted before the results are catastrophic.
I value your input, and trust in everything you say. But understand that I'm working on a truck suspension, not a Boeing 777 wing spar. Above all, I wouldn't do anything that might potentially become a hazard to myself or others. Trust in my judgment, and sleep at night knowing that I'm not building an airplane.
Clutch_Cargo
Well-known member
- Joined
- Feb 21, 2005
- Posts
- 242
belchfire
unpredictable member
- Joined
- Sep 2, 2003
- Posts
- 27,772
Avbug,
I wish to point out to you that construction
of things like skyscrapers are engineered
and built with SAE grade hardware. So are
American cars (excepting special applications).
There are standards, the bolted joints are
designed around the limitations of the minimum
standards for the sae bolts. They are also
avalible with different kinds of corrosion
protection from none to galvanized.
Unanswered...I seem to recall something about
a suspension project some months back. You
must be getting along with it.
Did you lube the bolts/threads??? Look back
at the chart. The waxed bolts only took about
45% of the torque of the dry bolts!
Is the bolted joint properly designed? (Is it
putting the bolts in shear rather than tension).
Were you using self locking nuts? The drag on
self locking nuts changes the torque value.
Are the bolt holes round, true and properly
aligned?
I bring these things up because a poorly designed
or built joint will fail even if you use Avbug's best
NAS close-tolerance high strength bolt.
Oh yeah...try to find a retailer that can provide
US manufactured hardware. That crap that is
getting over here from the people's enslavement
camp of China is not worth a rat's a$$
I wish to point out to you that construction
of things like skyscrapers are engineered
and built with SAE grade hardware. So are
American cars (excepting special applications).
There are standards, the bolted joints are
designed around the limitations of the minimum
standards for the sae bolts. They are also
avalible with different kinds of corrosion
protection from none to galvanized.
Unanswered...I seem to recall something about
a suspension project some months back. You
must be getting along with it.
Did you lube the bolts/threads??? Look back
at the chart. The waxed bolts only took about
45% of the torque of the dry bolts!
Is the bolted joint properly designed? (Is it
putting the bolts in shear rather than tension).
Were you using self locking nuts? The drag on
self locking nuts changes the torque value.
Are the bolt holes round, true and properly
aligned?
I bring these things up because a poorly designed
or built joint will fail even if you use Avbug's best
NAS close-tolerance high strength bolt.
Oh yeah...try to find a retailer that can provide
US manufactured hardware. That crap that is
getting over here from the people's enslavement
camp of China is not worth a rat's a$$
The chinese and the mexican hardware seems to be the worst. A lot of our hardware is Japanese and generally that's a good product and up to snuff.
Actually, a lot of large consutruction is welded, and often hardware other than SAE is used. To stipulate that SAE grade is used is rather simplistic, given that 8 different grades are in use, each with very different strengths and properties.
Most American cars use metric fasteners and threads, not SAE.
While true that many joints are designed to be secured by bolts manufactured to SAE standards, the truth is that many SAE "standard" parts are very inconsistent from lot to lot, and don't hold up. I've seen more than a few twist right off on automobiles...if you've worked around cars much, you'll know this, too.
Lube Torque is always a critical consideration in any torque application. The publications detailing the particular installation should always specify if the torques are applied wet, or dry, and generally what is to be used for the lube torque.
Actually, a lot of large consutruction is welded, and often hardware other than SAE is used. To stipulate that SAE grade is used is rather simplistic, given that 8 different grades are in use, each with very different strengths and properties.
Most American cars use metric fasteners and threads, not SAE.
While true that many joints are designed to be secured by bolts manufactured to SAE standards, the truth is that many SAE "standard" parts are very inconsistent from lot to lot, and don't hold up. I've seen more than a few twist right off on automobiles...if you've worked around cars much, you'll know this, too.
Lube Torque is always a critical consideration in any torque application. The publications detailing the particular installation should always specify if the torques are applied wet, or dry, and generally what is to be used for the lube torque.
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