Which SAE Grade Hex Bolt Do I Use?

rancar · Mar 6, 2003

Thanks everyone. Just got back from a lunch errand where I thought I'd visit a nice old fashioned hardware store near my worksite that I used to go to in the early 1990s before the Home Depots came into my area. And yep....I found the Grade 8s along with a few other things that Home Depot doesn't carry. I'm going to have to visit these old line establishments more frequently..... /forums/images/graemlins/smirk.gif /forums/images/graemlins/smirk.gif

rancar · Mar 6, 2003

Steve....

"McMaster Carr has...."

You certainly are a treasure trove of good information. /forums/images/graemlins/laugh.gif Thanks for this website. I wish I knew about it a long time ago for other things I was searching for. Thanks!!

....Bob

Hoeman00 · Mar 6, 2003

2,500#/4 bolts / .196in^2 (xsection area) = 3,000 psi shear stress. Grade 5 or 8 will do nicely.

What about that ground hog hole he doesn't see w/ 1000bf log on the carrier /forums/images/graemlins/wink.gif
The shank of the bolts should extend thru the plates because of reduced diameter where the threads are(less than 27/64" diameter) then if u have too cut excess threaded part off.

hazmat · Mar 6, 2003

What about that ground hog hole he doesn't see w/ 1000bf log on the carrier 

Ahh yes, the dynamic loading. /forums/images/graemlins/blush.gif Lets assume the bolt can hit 75,000 psi in shear B4 failure, Bob would have to have a 25G hit to reach that.

You are correct, it is best to be on the "shoulder" of the bolt, not the threads. The xsection area at the thread is .14 -> 4,400 psi stress.

I assume since the bolt is 3.5" long, it is going thru a tube, in which case it may be in double shear (depending if the bracket is on one side or both sides of the tube). Double shear (bracket on both sides) is better (less stress on the bolt) /forums/images/graemlins/grin.gif

rancar · Mar 6, 2003

Steve....

"...Bob would have to have a 25G hit to reach that..."

/forums/images/graemlins/confused.gif Does this mean I have to look out for those real big woodchuck holes? /forums/images/graemlins/tongue.gif I think I understand the gist of what's being discussed here and I'm certainly going to watch out for the chuck holes but will Grade 8 bolts even survive this shock? Will a potential shear occur even if I hit a monster chuck hole or two?.....or should I go the other route and think of going with welds to prevent the brackets and a lower lift pin from potentially shearing off while in transit?

"...I assume...it is going thru a tube, in which case it may be in double shear (depending if the bracket is on one side or both sides of the tube). Double shear (bracket on both sides) is better (less stress on the bolt)..."

Yes, the bracket surrounds the tubular framing on two sides and the Grade 8 bolt will go through two ends of the bracket and two sides of the tube.

So.....you think Grade 8 will suffice, even with a full load of logs on the back and assuming I hit a chuck hole every now and then?

....Bob

hazmat · Mar 6, 2003

Will a potential shear occur even if I hit a monster chuck hole or two?.....or should I go the other route and think of going with welds to prevent the brackets and a lower lift pin from potentially shearing off while in transit?


I'd stick with the bolts. Contrary to popular belief, welding isn't necessarily any stronger than bolting. It is very design specific, ie, what size bolt vs. how many inches of weld. From an engineering perspective, it is easier to predict the strength of a bolted joint, because there are fewer variables & it is not a high skill assembly process. That said, the perfect weld has the potential to be as strong as the joined parts.

Since you do have a double shear load, the bolts can withstand twice the force, ie 50g shockload. That is an extremenly high number, especially considering you are driving a rubber tired vehicle on dirt!

If you manage to find a woodchuck hole capable of delivering 50g shock load, I'd venture that you'll find several of your tractor's weakest links /forums/images/graemlins/crazy.gif The carryall breaking would be the least of your worries.

Soundguy · Mar 6, 2003

Nice calc's...

50 gs'' hmm..Yep.. I imagine a 10' freefall and then deadstop at the ground will be a decent stresstest on the front/rear axles as well as the tranny/frame union... ( Ironicaly carryall would probably survive unless half of the tractor carcass rolled back on it...
/forums/images/graemlins/shocked.gif
Soundguy

rancar · Mar 6, 2003

"...I imagine a 10' freefall and then deadstop at the ground will be a decent stress test on the front/rear axles as well as the tranny/frame union..."

Geez Chris....we're talking only about a large woodchuck hole.....not a sinkhole like you guys in Florida get from time to time. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

"...Ironicaly carryall would probably survive unless half of the tractor carcass rolled back on it..."

Having said that.....you guys have convinced me. Grade 8 bolts are the way I'm going and this carryall then will be built like a tank. /forums/images/graemlins/wink.gif Thanks again everyone for your help.

....Bob