Which SAE Grade Hex Bolt Do I Use?

rancar · Mar 6, 2003

OK....here's a question for you machinists and hardware techies .....

I'm rehabbing an old carryall for my JD4710 tractor. I recently had to have new lower lift pins custom made due to the old pin's incompatibility with the ball and socket ends on the lower draft links. The lower lift pins are housed in a bracket assembly that is bolted onto the carryall's frame. Two bolts fasten each bracket assembly to the frame's sides...four bolts total.

The old Hex bolts were 1/2" by 3 1/2". I intend to retain the 1/2" diameter since I don't have the tools to re-drill larger holes in the carryall's frame. The lift capacity on a JD 4710 3PH is 2,500lbs but I don't anticipate carrying anything greater than about 1,500 lbs (new custom made pins were threaded for this load capacity). I'll be using the carryall primarily to haul logs out of the woods and fieldstone out of the hedgerows.

Now, the question:

What Hex bolt SAE grade is recommended for this kind of assembly? I can't bring myself to use the fragile SAE 1 grade products I see in Home Depot due to safety concerns. I don't want to see these bolts snapping off under heavy loads. I've thought SAE 5 grade would be sufficient. SAE 8 grade sounds like overkill and are quite expensive possibly requiring me to buy a whole box of these which I don't need.

Anyone have any thoughts on this issue? Thanks for any input.

....Bob

Hoeman00 · Mar 6, 2003

I'd go w/ the best available, at least gade 8, u aren't looking at the shock load that these could be subject too.
U don't have any one local like a bolt house or ? that sells in less than box lots?

Anonymous Poster · Mar 6, 2003

Bob,
Tractor Supply Company (TSC) sells Grade 8's individually (by weight.) Might give you the strongest bolt with the least cost.

cowboydoc · Mar 6, 2003

I just bought some grade 8's, metric 14x1.5 and they were $1.20 per bolt.

herbenus · Mar 6, 2003

I'd only go grade 8. I wouldn't buy bolts for this from home depot. You should be able to find a place that sells a few. I didn't know about Tractor Supply. I'll keep that in mind for future projects.

rancar · Mar 6, 2003

"...U don't have any one local like a bolt house or ? that sells in less than box lots?...

I'm finding it difficult to find Grade 8 at local hardware stores around me. They go to grade 5. I can get Grade 8 online but they sell them in boxes of 3-4 dozen or thereabouts. I can likely get what I'm looking for in local machine shops but these guys don't sell retail. I'll check out TSC though. Thanks for the tips gentlemen.

....Bob

hazmat · Mar 6, 2003

Bob,

When designing/building in small quatities (eg 1) you waste more "money" thinking about it than just buying the better bolt.

McMaster Carr has Grade 8 1/2-13 X 3.5" for $7.95 /box of 10 (plus shipping). You could probably get them at a local hardware store or look under "industrial supply" in the yellow pages. Like the commercial used to say, call ahead.

For fun here are the calcs you would do.

Grade 8 has a min tensile (pull) strength of 150,000 psi, grade 5 is 120,000 psi.

Sounds like you are loading them in shear (bolts are weaker in shear than tension).

Assume that bolts are directly in line with lift pins, if they are offset, then we need to do some moment (torque) calcs.

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

hazmat · Mar 6, 2003

Forgot the "cost" calc.

10 minutes for me to write the previous post. They bill me out at $105 / hour = $17.50 = more than the bolts cost.

PS the p/n of the bolt at Mcmaster is 91286A339

hazmat · Mar 6, 2003

I'm finding it difficult to find Grade 8 at local hardware stores around me.

try the aforementioned "industrial supply" or NAPA.

NY_Yankees_Fan · Mar 6, 2003

I know my Sears Hardware Store carries grade 8, have any around?

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