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A question about bolts

U

ugly_blazer

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If I had two bolts that were the same size, only was one fine thread and one coarse thread, and using a torque wrench I applied the same amount of torque to each bolt would the clamping force of the bolts be the same or would one be more?
 
/forums/images/graemlins/thinking.gif using that philosophy, would the aging of the torque wrench have an effect on the over all exactness of said wrench, there for yielding an erroneous outcome?
 
Anything is possible. /forums/images/graemlins/thumb.gif

I was just wondering, because if fine thread bolts clamp tighter I may use then to attach some stuff that I don't want to move (fall off).
 
I think that the clamping load would be exactly the same.

You'd be shocked how much clamping load a bolt can create though.

Why not just use larger bolts?
 
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Why not just use larger bolts?

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It's not a lot of fun drilling holes larger than 1/2" in my frame. I'm probably being overcautious, but it would be embarrassing if I went to pull someone and my bumper fell off.
 
1/2" is what I had in mind. A 1/2" bolt will provide a tremendous amount of clamping force. I can't imagine you needing more clamping force than a 1/2" bolt is capable of providing.

1/2" bolts are holding my trailer hitch and 5th wheel hitch in my tow rig just nicely. /forums/images/graemlins/thumb.gif
 
Ya, I guess you're right. I have never had a hitch break off that was using 1/2" bolts.
 
The surface area of the load would be different, I think. It seems that area the load would be spread across (# of threads) is larger in a fine thread as opposed to a coarse thread. With this in mind, the accuracy of the torque reading would be greater? /forums/images/graemlins/dunno.gif Most torque wrenches are calibrated within about 3% of actual, so I don't how much of a difference that would make. If you don't want a bolt to come loose, use Loc Tite or Nyloc nuts. Most places you find fine thread bolts are on mechanisms that require a tight fit with very little tolerance. Engineering gurus, is this accurate?

John
 
dunno about "clamping force", but fine threads = more surface area and therefore more friction...

j
 
on the jet we dont often use ny-lock's or loc-tite, we use nust that have been made out of round and those donr coem off, even on a crazy shakin jet on the 'cat. /forums/images/graemlins/waytogo.gif
 
not to hi jack or anything, but i heard something about grade 5 bolts are better than grade 8's because the g5's bend and the g8' break, is this true?
 
1/2 bolt flat washer lock washer lock nut, your all set.
if your really really really really worryed, find some grade 9 airospace bolts. would hate to think of the cost though /forums/images/graemlins/ignore.gif
 
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not to hi jack or anything, but i heard something about grade 5 bolts are better than grade 8's because the g5's bend and the g8' break, is this true?

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no.

j
 
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not to hi jack or anything, but i heard something about grade 5 bolts are better than grade 8's because the g5's bend and the g8' break, is this true?

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No, because yet though a grade 5 may be more mallible (bendable) it still has less tensile strength than a grade 8, and will therefore fail sooner (i.e. with less of a load) than a grade 8.

John
 
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not to hi jack or anything, but i heard something about grade 5 bolts are better than grade 8's because the g5's bend and the g8' break, is this true?

[/ QUOTE ]

I forget where I heard/read this, but someone said that if you use grade5 bolts in the right place, they can be better than grade8's... the example is for a snowplow, you;d rather bend a bolt, that can still limp the plow home, than to have a grade 8 break, and leave the plow there...
 
This may be true--I have broken a few grade 5 and 8 bolts on my plow(the pins that hold the plow to the plow frame)and all I could get at that late hour was cheap grade 2 bolts at home depot--I hit a few obsructions during the duration of the storm,and I thought sure the bolts would snap(they were 3/4 inch x 6 inch)but the next day I checked them--they looked like banannas,but they didnt crack or break!I know stainless steel bolts are not good for a lot of automotive applications,they dont rust but they seem to be brittle,and dont like heavy shock loads,I tried stainless steel studs in my exhaust manifolds once thinking I;d never have to change them again--WRONG! the next time I went to loosen them,they snapped off like peanut brittle,I had to pull the manifold and have them removed at a machine shop with an end mill--none of my drills would even scratch them /forums/images/graemlins/angryfire.gif. I use cheap carriage bolts or threaded rod for exhaust studs now--they wont be useable again anyway,gaurenteed to break off,but at least they drill out easy. I also put a new front suspension crossmember in a friends corvair,he pirated all stainless bolts from his workplace,we snapped 3 of them just tourqing them into place--we decided they werent the hot setup for shock mounts and suspension bolts,and ended up buying grade 8 bolts from the hardware store.I have noticed that grade 5 and 8 bolts corrode much slower that the cheap grade 2 stuff--maybe better coatings on them,or just better steel?. /forums/images/graemlins/crazy.gif
 
A fine thread and a corse thread bolt of the same size, material, plating, and lubrication will provide the same ammount of clamping force with the same torque.

What you are missing is that a fine thread bolt can be torqued to a higher rating then a corse thread bolt (all else being the same). The higher torque is what will give it more clamping force.

The same is true for grade 5 vs grade 8 (FWIW SAE grade 9 doesn't exist!). Because a grade 8 is made from a stronger material it can be torqued to a higher value then a grade 5 bolt. This will give the grade 8 more clamping force.
 
Ok, thanks. I have always wondered how that worked, thinking that maybe a fine thread would be like a lower gear ratio, more power from less work. Guess not, thanks.
 
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