Whats got the highest shear strength? Something stronger than a grade 8 bolt, maybe a grade 9, or some kind of hardend tool steel?

Its got to be a 3/8" diamater

Im just afraid to ask Why

Yup, Grade 9. I picked up a couple 1 x 8" Grade 8s, a couple days ago, and am already thinking of going up to Grade 9

what in the HELL are you guys building that you need grade 9 bots.

Grade 8 bolts hold our 30 ton press into place.......

Im just afraid to ask Why

I'm asking for a guy I know to try and give him some ideas.
Heres what hes got. There is a keyway on a 1.5" shaft, then a yoke on that. Problem is that keyway is supposed to be the designed in weak link, and when it strips, its a 2 hour jub to replace it. We removed the keyway and drilled a 3/8" hole through the yoke and the 1.5" shaft to run a bolt through, so when it shears off, all we gotta do is line the hole back up, tap the sheared bolt out, and put a new one in. Grade 5 bolts were shearing off easilly, then the grade 8 was a little stronger, but we need something stronger yet to keep the shearing off to a minimum. I know it won't be as strong as the keyway, but its got to be a 1 minute fix when it happens and with the keyway it takes hours.
He was thinking about drilling the hole out to 7/16", but the bigger that hole gets, the weaker the shaft gets, so if we can get away with using a 3/8" pin it would be best.
So if theres anything stronger than a grade 9 bolt, we will try it and see how it works. If it doesn't, maybe step up to a 10mm or a 7/16"

what in the HELL are you guys building that you need grade 9 bots.

tire carriers. I've decided to go a different route with these, and use 1" bolts, for the hinge, and allow me to create a double shear with the mounts... MUCH stronger than the roller bearing hinges I've been using



Mike, how long has the guy been running the 3/8" Grade 8 bolt? if it hasn't been too long, I'd go ahead and abuse it, and see if the Grade 8 fails in the same condition that the keyway did. If it fails sooner, then consider the Grade 9. You know you still want the bolt to fail first, rather than finding a stronger bolt, and take a chance on destroying the shaft

Mike what is this on? A truck?

Do you have to use a bolt? Is it shearing at the threads? The shearpoint would be more precise/repeatable if you could use a pin with a LPF. That way you could control the OD and surface finish. It could be pressed in/out. If you can do that, then the options open up for material. 300M may have the properties you need and can be purchased centerless ground in various lengths. I would have to browse my Machinery's Handbook to be sure.

Grade 8 bolts are commonly made of 4140. If the 3/8 bolt is close, you could make a 4140 pin .010" larger in OD, heat treat it to grade 8 specs and possibly hit the sweet spot. Can you get any specs on the shear point from the manufacturer? If so, I could calc the ideal size pin.

Do you have to use a bolt? Is it shearing at the threads? The shearpoint would be more precise/repeatable if you could use a pin with a LPF. That way you could control the OD and surface finish. It could be pressed in/out. If you can do that, then the options open up for material. 300M may have the properties you need and can be purchased centerless ground in various lengths. I would have to browse my Machinery's Handbook to be sure.

Grade 8 bolts are commonly made of 4140. If the 3/8 bolt is close, you could make a 4140 pin .010" larger in OD, heat treat it to grade 8 specs and possibly hit the sweet spot. Can you get any specs on the shear point from the manufacturer? If so, I could calc the ideal size pin.

I agree with that but i am also thinking something else.

If he is shearing the original keyway, the motor or whatever driving the shaft may be oversized for what he is powering.

Normally if i start shearing keyways on an AC drive it work, there is more to the problem than the keyway. Something isn't correct in the application because that key was engineered to that motor and drive system. If he put something together and it's shearing the key, and grade 8 bolts, he may be oversized when it comes to the power of the motor, a smaller drive unit may be necessary.

here u go Grade 9 bolts http://www.f911.com/fore2.html

i used these on my trac bar

Mike what is this on? A truck?
Its on a pulling sled.
http://www.supermotors.net/getfile/449949/fullsize/100_2072.jpg
Its on old homemade one built with parts off of I don't know what, so its not like everything was originally designed with this type of use in mind. You can't really see it, but at the very front of the sled theres a gearbox with a sprocket that pulls the chain and weight box up the sled. Theres a driveshaft that goes up to it from some truck transmissions, and the yoke where the keyway is at is on the input shaft of the gear box that drives the chain.
I should have goten a pic of the yoke and gearbox yesterday, I didn't think about it when I was there.




Mike, how long has the guy been running the 3/8" Grade 8 bolt? if it hasn't been too long, I'd go ahead and abuse it, and see if the Grade 8 fails in the same condition that the keyway did. If it fails sooner, then consider the Grade 9. You know you still want the bolt to fail first, rather than finding a stronger bolt, and take a chance on destroying the shaft
Yesterday was the first time. The bolts are failing much sooner that what the keyway was failing at. I would say the grade 5 was failing at 40%, and the grade 8 maybe 50%.
With normal use the bolts don't fail, its when it gets a big shockload, or someone leaves the gear box in gear and backs up when the weight box is already in the full back position. Its got gear reduction upon gear reduction upon gear reduction.....so it shears off the keyway like it was nothing. The bolts were shearing off anytime the sled got jerked hard, or maybe every 10 runs with the high horsepower trucks. The keyway didn't shear off with any of that, but it did shear off anytime someone accidently left one of the boxes in gear and backed up with the weight box all the way down in the far back position. I think if it were my sled, I would just be sure everything was out of gear before backing up and use the keyway. But the guy that owns it is worried about it happening again so he wants a 1 minute fix for it if it should happen again. When the keyway sheared off last time, we were done for the night. Thats why hes expermienting with what size pin will work, and still having it as small as possible



Do you have to use a bolt? Is it shearing at the threads? Its shearing the shank of the bolt. The input shaft on the gearbox is 1.5", the outside diamter of the yoke where it fits over the input shaft is probably 2.25", so the yoke has got a 3/8" wall, and we were putting a 4" bolt through it. The threads were all the way through it so all the force was on the shank

The bolts are failing much sooner that what the keyway was failing at. I would say the grade 5 was failing at 40%, and the grade 8 maybe 50%.
...
Its got gear reduction upon gear reduction upon gear reduction.....so it shears off the keyway like it was nothing.
...it did shear off anytime someone accidently left one of the boxes in gear and backed up with the weight box all the way down in the far back position.
...he wants a 1 minute fix for it if it should happen again.So he wants to go from shearing a $1 bolt to either shearing a $3 bolt or what? A $100 chain? A $300 gearbox?

I think he's going about this all wrong - I think he needs either a 1-way drive or a viscous coupling somewhere in the drivetrain (or both).

So he wants to go from shearing a $1 bolt to either shearing a $3 bolt or what? A $100 chain? A $300 gearbox?

I think he's going about this all wrong - I think he needs either a 1-way drive or a viscous coupling somewhere in the drivetrain (or both).

I kind of have to agree with Steve.

If he does get the bolt/keyway/whatever to stop shearing, what's going to shear next?

Why does it have to be a single bolt? Why not increase the number of shear pins so the shear stress is over a much larger area?

I kind of have to agree with Steve.

If he does get the bolt/keyway/whatever to stop shearing, what's going to shear next?

X2

So he wants to go from shearing a $1 bolt to either shearing a $3 bolt or what? A $100 chain? A $300 gearbox?
The problem is if anything like that breaks it would take too long to fix. He wants to be able to fix it within a minute, so thats why hes using the bolt as a weak link. If we could get it to work right it won't be a problem either. Just need to find something with a higher shear strength than a 3/8" grade 8 bolt.



I think he's going about this all wrong - I think he needs either a 1-way drive or a viscous coupling somewhere in the drivetrain (or both).
Viscous coupling wouldn't work. A one way drive might, because that would eleminate the backing up problem, and since that was the only thing that was shearing the keyway off, we could go back to using the keyway since the chances of it breaking then are slim to none. The bolts were shearing every once in a while when the sled was jerked hard, which the keyway didn't have a problem with. The thing is he is just afraid of the keyway doing it again and having to take 2 hours to fix it while everyone waits around.
If we could come up with a bolt or pin like were using now, and have it be as strong as the keyway or at least 75% as strong without weakening the input shaft too much that would be prefect. Then it would shear off only when it was supposed too, and no false alarms. And if it did, it could be fixed in a minute, which teh keyway can't be
Were just afraid if we drill the bolt out to 1/2", that will make the bolt strong enoufgh, but then did we take too much meat out of the center of input shaft so thats whats going to snap instead of the bolt?








If he does get the bolt/keyway/whatever to stop shearing, what's going to shear next?
Probably break the gear box, or maybe a U-joint on the last shaft where its geared down the most, but the bolt is shearing way too easilly, before it needs too. Thats the problem. The only thing that shaft and gear box control is the movement of the weight box, which is 22,000 pounds. I'd say the gearboxes and driveshats being used are way undersized for the job, especially with the gear reduction, but thats what hes got right now and nothing else to work with really.

Why does it have to be a single bolt? Why not increase the number of shear pins so the shear stress is over a much larger area?

Thats what I wanted to do, but the shaft only goes in to the yoke 1"

Well here is part of the problem Mike

The Shear strenght of a simple bolt, any grade isn't measured left to right.


It's measured as though you're pulling up on the head of the bolt, not pushing on the side of the bolt. Shear strength isn't for side to side movement, it's for up and down movement. That's why you're shearing grade 8 bolts so fast. I'd imagine that your going to shear grade 8's faster than grade 5's more or less because they are more brittle from the strenght treatment than anything else. In David's application, they more than likely won't shear, he is stressing the right motion on the bolt.

A bolt isn't what you need, you need to have some 316 stainless steel pins machined. Or some type of pin that is engineered for side to side motion strength.

just weld it you *****s :flipoff:

Well here is part of the problem Mike

The Shear strenght of a simple bolt, any grade isn't measured left to right.


It's measured as though you're pulling up on the head of the bolt, not pushing on the side of the bolt. Shear strength isn't for side to side movement, it's for up and down movement. That's why you're shearing grade 8 bolts so fast. I'd imagine that your going to shear grade 8's faster than grade 5's more or less because they are more brittle from the strenght treatment than anything else.
I thought that IS shear strength, and what you're talking about is tensile strength?


A bolt isn't what you need, you need to have some 316 stainless steel pins machined. Or some type of pin that is engineered for side to side motion strength.
Thats exactally what I was asking. Do you know if they really are stronger than a bolt in this situation?

Thats exactally what I was asking. Do you know if they really are stronger than a bolt in this situation?

It looks like stainless steel or titanium pins are the way to go.

http://en.wikipedia.org/wiki/Tensile_strength#Typical_tensile_strengths

You'd probably want to use something like this:


http://www.mcmaster.com/

Edit: SHIT!

Go here and put this part # in the search box: 95165A085

End Edit

That pin has a shear strength of 10,300 lbs, that's five tons of force. That beats most grade 8 bolts.

But i still think you need to rethink the design before you break something else.

It looks like stainless steel or titanium pins are the way to go.

http://en.wikipedia.org/wiki/Tensile_strength#Typical_tensile_strengths

You'd probably want to use something like this:


http://www.mcmaster.com/

Edit: SHIT!

Go here and put this part # in the search box: 95165A085

End Edit

That pin has a shear strength of 10,300 lbs, that's five tons of force. That beats most grade 8 bolts.

But i still think you need to rethink the design before you break something else.
Brush up on your terms before dispensing technical advice. Shear is the force acting in opposite directions perpendicular to the axis of the fastener. Tensile strength is the force pulling apart a fastener along its axis.

The problem with using a screw is that for a 3/8" hole, you're using a 3/8" screw with a minor dia of .300 inch which is 80% of what you would've had with a full 3/8" rod.

Mike, what about hitch/lynch pins?

A bolt isn't what you need, you need to have some 316 stainless steel pins machined. Or some type of pin that is engineered for side to side motion strength.


I disagree on the 316SS or Titanium. Do a comparison with 4140. You'll want to select another tool grade steel. I know W1 is very tough, but I do not know whether or not the tensile strength or shear is higher/lower than the 4140. If I get a chance in the morning, I'll search when I've got my resources available.

Okay.

But i know a bolt ain't what he needs.

And i still think they should look at the entire set-up prior to trying to make that pin/keyway/bolt not snap. If they make the weakest link the strongest, it's going to cause damage further down the line.

Okay.

But i know a bolt ain't what he needs.

And i still think they should look at the entire set-up prior to trying to make that pin/keyway/bolt not snap. If they make the weakest link the strongest, it's going to cause damage further down the line.

I agree 100% with that. There has to be some other issue.......in other words, something is causing/creating more resistance now than it once did. I think a little root cause analysis would go a long way. Was the sled "upgraded" at some point? Did it carry less weight in the past?

Sounds to me more like it's the impact/shock loading going into the system that's breaking stuff. I'm betting, now that they have a sled to use as a standard, the trucks are all being improved, beyond what the sled can handle.

I still think a viscous coupling (like in the d'shaft of a Land Rover Freelander) would do wonders for this problem. Or anything that dampens the impact of the trucks launching. Hell: use some really heavy compression springs (like the rear clamps for an aluminum boat trailer, but MUCH stronger) to connect the chain to the weight.

And i still think they should look at the entire set-up prior to trying to make that pin/keyway/bolt not snap. If they make the weakest link the strongest, it's going to cause damage further down the line.

They're not trying to make the bolt any stronger than the keyway. All they want to do is make it as strong, or at least 75%






Sounds to me more like it's the impact/shock loading going into the system that's breaking stuff.
Thats exactally what was shearing the bolt.

I'm betting, now that they have a sled to use as a standard, the trucks are all being improved, beyond what the sled can handle.

the real sleds don't have any trouble with it. This is an old home made sled built from a line of truck transmissions and the other gearboxes that were originally designed for other things. So the standard froces seen here were not taken in to account when the parts were designes.


I still think a viscous coupling (like in the d'shaft of a Land Rover Freelander) would do wonders for this problem. Or anything that dampens the impact of the trucks launching. Hell: use some really heavy compression springs (like the rear clamps for an aluminum boat trailer, but MUCH stronger) to connect the chain to the weight.
That would probably keep anything from breaking, but a viscous coupler would allow the shaft to slip, so it would be possible to move the sled forward and gain distance, while the weight does not move. Sure if its just a shockload it wouldn't make much of a difference, if any at all, but if someone looses first place by a tenth of an inch the're going to be bitching about it.

Thats exactally what was shearing the bolt..Then you don't need a "stronger" shear pin; you need a "tougher" one. But since toughness isn't a design spec of any off-the-shelf shapes or products (AFAIK), there will be no telling what the toughness of one pin is compared to another "identical" one. IOW: you can't base the design on a specific toughness - you must redesign for the proper strength based on the loads (shock or otherwise)....if someone looses first place by a tenth of an inch the're going to be bitching about it.More or less, do you think, than they bitch about the day being wasted after the sled breaks? As long as they lost using the same sled as the guy who wins, they have NOTHING to bitch about. But if they spent time & money to come up there, and they can't even race, they won't be back.

Then you don't need a "stronger" shear pin; you need a "tougher" one. But since toughness isn't a design spec of any off-the-shelf shapes or products (AFAIK), there will be no telling what the toughness of one pin is compared to another "identical" one.

Off the shelf, correct, but steels (mostly tool steels) are rated for toughness.


Mike - Here are some numbers to give you a comparison. All of these materials are at the top end for strength.

4140 - in a normalized state has a tensile strength of 148,000 lb/in.(squared) and 95,000 yield
4140 - HT and tempered at 400dgr is 257,000/238,000
8640 - HT and tempered at 400dgr is 270k/242k (This is the material of the bolts that Chris85XLT suggested)
8650 - For ultimate strength, this may be the grade you're looking for, because of it's high yield in shear, but I don't have enough data readily available to make a good call on it.
9255 - tempered at 400dgr is 305K/297K; however, you would want to verify it's resistence to shear.


An 8640 (F911) bolt would be the quickest way to see if you're in the ballpark for yield. If you don't see any significant improvement with that, I would consider increasing the diameter and stick with 4140, because it's readily available at steel stores.

One other very important thing to keep in mind. If the clearance between the bolt and ID is substantial, the increase in shock load will be tremendous. It should have a light press fit for best results.

I dunno, maybe these would work...
http://users.mo-net.com/mcruzan/images/bolts.jpg
...bolts off the Minuteman III nuclear warhead assembly; I got maybe half a dozen left...

how long does the pin have to be? find a 3/8" drill bit that is blank for the correct length you need, and then cut off the fluted portion of the bit. presto chango, you have a tool steel roll pin.

grainger and mcmaster have tons of bits, you should be able to find one that works.

http://www.i-car.com/graphics/about_icar/current_events/advantage/2006/advantage_online_0612/full_size/fig_03.gif

MART: Martensitic Steel - Too brittle for your application.
HSLA: High Strength Low Allow - May be ideal?

Can't recall what some of these other abbreviations are. Tool Steel would be ideal. Try out Squatty's idea.

use a grade 8 fine thread bolt.
it'll be stronger than the coarse thread bolt, yet pretty easy to get your hands on.

use a grade 8 fine thread bolt.
it'll be stronger than the coarse thread bolt, yet pretty easy to get your hands on.

If he is breaking a grade 8 coarse thread, why wouldn't he break a grade 8 fine thread? The only difference is the thread count.

use a grade 8 fine thread bolt.
it'll be stronger than the coarse thread bolt, yet pretty easy to get your hands on.

Wouldn't matter in this case because all we are using is the shank of the bolt. The threads came clear out the other end






More or less, do you think, than they bitch about the day being wasted after the sled breaks? As long as they lost using the same sled as the guy who wins, they have NOTHING to bitch about. But if they spent time & money to come up there, and they can't even race, they won't be back.

Thats why he is trying to perfect the bolt and get it to work fairly reliably. So if/when it does break, it only takes a minute to fix.





Off the shelf, correct, but steels (mostly tool steels) are rated for toughness.


Mike - Here are some numbers to give you a comparison. All of these materials are at the top end for strength.

4140 - in a normalized state has a tensile strength of 148,000 lb/in.(squared) and 95,000 yield
4140 - HT and tempered at 400dgr is 257,000/238,000
8640 - HT and tempered at 400dgr is 270k/242k (This is the material of the bolts that Chris85XLT suggested)
8650 - For ultimate strength, this may be the grade you're looking for, because of it's high yield in shear, but I don't have enough data readily available to make a good call on it.
9255 - tempered at 400dgr is 305K/297K; however, you would want to verify it's resistence to shear.


An 8640 (F911) bolt would be the quickest way to see if you're in the ballpark for yield. If you don't see any significant improvement with that, I would consider increasing the diameter and stick with 4140, because it's readily available at steel stores.

One other very important thing to keep in mind. If the clearance between the bolt and ID is substantial, the increase in shock load will be tremendous. It should have a light press fit for best results.

Passing the information on. Thanks guys

...It's measured as though you're pulling up on the head of the bolt, not pushing on the side of the bolt. Shear strength isn't for side to side movement, it's for up and down movement. That's why you're shearing grade 8 bolts so fast. I'd imagine that your going to shear grade 8's faster than grade 5's more or less because they are more brittle from the strenght treatment than anything else. In David's application, they more than likely won't shear, he is stressing the right motion on the bolt.

A bolt isn't what you need, you need to have some 316 stainless steel pins machined. Or some type of pin that is engineered for side to side motion strength.

:scratchhe Not sure where you're getting that idea. Two things -- bolts are primarily used in shear applications, for one. Second, Mike's correct in that this is a shear application versus tension. Incidentally, the pure shear application is actually easier to deal with numerically.

use a grade 8 fine thread bolt.
it'll be stronger than the coarse thread bolt, yet pretty easy to get your hands on.

If he is breaking a grade 8 coarse thread, why wouldn't he break a grade 8 fine thread? The only difference is the thread count.

When loaded in shear or tension in the thread area, a fine thread bolt is stronger than a coarse thread bolt. The threads are all proportioned the same, so for the same outside diameter (a.k.a. major diameter), a fine thread bolt will have a larger diameter at the root of the threads (minor diameter) because the threads aren't as deep.

This doesn't matter, because in Mike's case the threads aren't in the shear zone. No difference.

What I don't really have handy right now is actual, useful information. Don't have any of my stuff with me, and about to run out the door. Sorry, man! :duh