Determining the exact shear bolt

[nomad]

I said somethings in Confirmed Grade 8 thread about this, but thought this should be a new topic.

Shear bolts which are ductile medium carbon steels (Grade 8 is an alloy) are under normal conditions the weakest point in a new or in a normal/standart quality system (gearbox+pto system+engine+attachment.) Therefore, under normal conditions, even Grade 8 bolt is expected to fail first. But is this really so? No. Because either gearbox/pto/engine/etc is low quality or one of them components is old/ill. So, what to do? You need to make it the shear bolt the weaker than any component in this combined system. But, not much weaker as you will not want the bolt broken frequently even when it hits a small stone. Since your old/ill system is special it will require a certain amount of shear load which Grade 2 or 5 or 8 will not match exactly. Then, what to do? I say Start with Grade 8 bolt and adjust its shear load capability by adding a certain size notch in your bolt. You can make a few experiements by changing the size of that notch in the bolt until you find exact shear load for your special system (it's special because your system isn't new anymore.) Your this special bolt with a certain notch will be somewhere between, say, Grade 2 and Grade 3 or between Grade 5 and 8. Happy shearing.

 

[normde2001]

"I say Start with Grade 8 bolt and adjust its shear load capability by adding a certain size notch in your bolt. You can make a few experiements by changing the size of that notch in the bolt until you find exact shear load for your special system"

So, you are saying we should start with grade 8 and work down to grade 2 as we are destroying our already low quality equipment, until we arrive at a grade that will shear. Wish I had thought of that. /forums/images/graemlins/confused.gif(oops, forgot to put the emoticon in there)

 

[PineRidge]

Seems it would make better sense to start with the softest shaer bolt and work the other way till you find a medium that won't break too often. That way no damage is done to the tractor itself.

 

[Junkman]

The problem that I see with your method is that you don't know at what point the bolt should shear. If you start off with a known factor such as a grade 8 bolt and it doesn't break, then you make a cut in it..... It still doesn't break, and you make the cut deeper.. Then it breaks too quickly. All this time, you are taking a toll on the equipment that is unnecessary. I would rather start off with a softer bolt and then work my way up toward the harder bolt knowing all the time, that the only thing that is happening is my time is being take up with bolt replacement. Not having my gear box subjected to undue stress is more important to me. Using your method, I have a feeling will result in more damage than just a sheer bolt breaking... Personally, I think that it is ill advised to experiment with expensive equipment when the correct part is readily available from most equipment dealers...

 

[Villengineer]

I posted this on the other thread and I thought it would be good to post here. I know that some of this has been covered above already.

</font><font color="blue" class="small">( DO NOT TRY THIS UNLESS YOU WANT TO FIND THE WEAKEST POINT THAT ISN'T THE SHEAR PIN. If you do not get the notch in the shear area of the mechanism you are still trying to shear the full diameter of the Gr8 bolt. If you want to use trial and error method then start with a Gr2 and if it fails under normal use then step up a grade, don't work the other way. Plus why spend more money initially on Gr8 bolts and then weaken them, which requires your time and my time certainly isn't free. It would be vary rare for a manufacturer to use a Gr8 as a shear bolt if for no other reason than they cost the manufacturer more $ than the lower grades. The only reason that I can think of for using a Gr8 as a shear pin would be if there simply wasn't room to use the appropriate diameter Gr2.)</font>

 

[RobS]

I wouldn't use a grade 8 for shear protection even if that's what was specified. In fact, as was mentioned elsewhere a grade 8 is unlikely to be specified due to the higher cost.

A lower grade bolt will give you a "kindler, gentler shear" which will be easier on all the equipment. Grade 8 will take more load but being more brittle will fail with more impact/jolt to the system.

My cutter specifies a grade 2 (metric equivalent). It works fine for me /forums/images/graemlins/smile.gif

 

[HayDR]

Since Nomad does not have his gearboxes yet, how can he know the shear load needed? What size shear bolt, it's hardness, the PTO, the torque needed for the given implement are all questions needs to answer. Looks like KK may have more engineering that Nomad realizes. What about the PTO will the PTO shafts have both CE and OSHA safety approval? To just import into the USA may not be as easy as placing an order and shipping. What about product liability? How much product liability does Nomad have? Nomad may be able to produce a cheaper product but where is the testing, engineering, liability, and parts support coming from? These are questions American importers and manufacturers all realize must be do before any product is released and sold in the USA market. Are these units Nomad is posting pictures of, prototypes or serial production? These are questions every responsible importer answers every day.

 

[Junkman]

</font><font color="blue" class="small">( Since Nomad does not have his gearboxes yet, how can he know the shear load needed? ......... )</font>

I am wondering what kind of tractor he has... his profile is a blank page..... He speaks with authority, but is he an engineer ???? Why don't people fill in their profiles before they post??? /forums/images/graemlins/confused.gif

 

[Deerlope]

Junkman
I often wonder the same thing about one's profile. It is nice see where someone live's and what equip they have also what their occupation is. I guess some just want to keep the rest of us in the dark.

 

[CTyler]

Is there any application using a CUT sized tractor where a grade 8 would be used for a shear bolt???

 

[nomad]

</font><font color="blue" class="small">( Grade 8 will take more load but being more brittle ...)</font>

RobS, as far as I know about this standart grade, it isn't more brittle as it's a ductile material. Brittleness is a thing, shear/tension capability is another thing. Brittle materials don't follow plastic deformation much unlike these ductile alloy steels like Grade 8.

Villengineer, the question of this thread is 2 folds;
1. What's the optimum Grade for shear bolt for a specific (unknown) attachment system (including tractor, etc etc)?
2. How to find that optimum grade bolt?

Lets start that way;
Lets name the optimal shear bolt for a specific system is GradeX. This GradeX will usually lie somewhere in between

Grade2 ......... GradeX ..............Grade8.

A farmer might have already found his/her GradeX position with some lucks and he/she is shearing the bolt rarely and without giving any damage to any component in his/her system. I see that most of farmers chose the simplest way which is to use Grade2. But they are also breaking many bolts which also costs them time that makes them angry. I also seen some farmers using Grade5 without any problem.

So, their GradeX specific to their own special systems is to be determined here and this should be done by each of farmer because each of their system is a special (with ages/component qualities/etc.) Okay, Grade2 is always solution, but this determination of GradeX too is worth to talk about, isn't it? I think everybody is agreeing with me in that. Now, the next is how to determine GradeX.

I'll rewrite that;
Grade2 ......... GradeX ..............Grade8.
(GradeX can be Grade2.5 or Grade5.7 or Grade 7.1 and so on)

Trial-error method has always a cost. Going from Grade8 to Grade2 to find GradeX is a risk and going from Grade2 to Grade8 is another risk. Which risk to be taken? Is there another method (other than trial-error) that a farmer can do? All these are to be talked about here. But before answering these, first, we need to agree about that we really have to find our own GradeX for our own attachment system? Answer to this should be fixed to this first. Those farmers who are interested in knowing their own GradeX can tell their idea/experiences.

Ps: Normde2001, I visited your web pages and really liked your art works. Congrats. We share that interest of art hobby. I have a hobby web site dedicated to weaving and wooden art. www.halikilimci.com (the Moderator can delete this link if it's not permitted.)

 

[nomad]

a little info about deformations&fracture&brittleness;

a shear pin, when applied a force (a combined of tension+shear), follows an elastic deformation first, then after a certain limit, its deformation type becomes plastic until it fractures. Ultimate shear/tension stress is usually reached before the fracture occurs and plastic deformation continues until the fracture occurs. (Sometimes, the fracture occurs early even after a short time of elastic deformation. Such materials can be called the brittle and a good example is the glass.) This isn't a case in our Grade2 to Grade8 pins/bolts, they aren't brittle.

 

[normde2001]

"Ps: Normde2001, I visited your web pages and really liked your art works. Congrats."

Thanks, nomad. I like yours too, and I must say, you certainly are one busy and talented guy.

 

[MossRoad]

<font color="blue">Since Nomad does not have his gearboxes yet, how can he know the shear load needed? What size shear bolt, it's hardness, the PTO, the torque needed for the given implement are all questions needs to answer. Looks like KK may have more engineering that Nomad realizes. What about the PTO will the PTO shafts have both CE and OSHA safety approval? To just import into the USA may not be as easy as placing an order and shipping. What about product liability? How much product liability does Nomad have? Nomad may be able to produce a cheaper product but where is the testing, engineering, liability, and parts support coming from? These are questions American importers and manufacturers all realize must be do before any product is released and sold in the USA market. Are these units Nomad is posting pictures of, prototypes or serial production? These are questions every responsible importer answers every day. </font>

How do you go about determining what strength shear bolts to use in your products?

 

[MossRoad]

<font color="blue">I am wondering what kind of tractor he has... his profile is a blank page..... He speaks with authority, but is he an engineer ???? Why don't people fill in their profiles before they post??? </font>

Junkman, your profile is pretty sparse, too. /forums/images/graemlins/smile.gif Retired, old cars, CT and a BX with a york rake isn't much for me to make a mental picture of you, either.... your bio is also blank. /forums/images/graemlins/smirk.gif

 

[Villengineer]

</font><font color="blue" class="small">( What's the optimum Grade for shear bolt for a specific (unknown) attachment system (including tractor, etc etc)? )</font>
First, for most individuals on this site it would be whatever the manufacturer recommends. If an apparent error occurs as was the case in the thread that started this I would default to Gr2 b/c that's basically an unwritten standard. As an engineer I would try to use the most commonly available shear pin available. Now I don't know this for a fact, but I'm guessing that attachments which have higher HP ratings, and higher HP requirements, use clutch systems rather than shear bolts. For two reasons, 1) They are almost always higher priced and therefore easier to justify the expense and 2) It is much easier to set the ideal torque limit useing clutch packs.

</font><font color="blue" class="small">( How to find that optimum grade bolt? )</font>
Like I stated above, I would try and design around the most commonly available shear pin. If you are designing the attachment, you should know what the drive system will take and you will be specifying a HP range for the tractor to be used with the attachment. Now it's just a matter of how much torque you are going to allow the tractor to transmit into the attachment.

 

[nomad]

MossRoad, he Junkman opened a thread in Related Forums and I already answered him. Lets back to the topic; There are some people like RobS, Villengineer in this thread who have different engineering experiences in their backgrounds. Added farmers experiences, I am interested in how to find GradeX or is it really necessary to determine such a GradeX that I mentioned in my last posts above.

Ps: I just saw now the post of Villengineer and am going to read it after making a cup of coffe;-)

 

[Junkman]

</font><font color="blue" class="small">( Junkman, your profile is pretty sparse, too. /forums/images/graemlins/smile.gif Retired, old cars, CT and a BX with a York rake isn't much for me to make a mental picture of you, either.... your bio is also blank. /forums/images/graemlins/smirk.gif )</font>


As Boondox most appropriately put it........

</font><font color="blue" class="small">( ( Junkman -- I see you take the minimalist approach in your own profile! /forums/images/graemlins/grin.gif

Seriously, yours is a perfect example of protecting your privacy, while giving respondents enough information about your tractor etc so they can provide meaningful answers to your questions. Sometimes I start a reply, but check the profile to try to better tailor it to the poster's situation. But finding nothing there I don't even bother!

Pete )</font>

so you may verify that he said what I have posted.


Name - Paul M.

Occupation - l retired.... definition of occupation - the principal business of one's life.

Bio - Hey, I live in far North East Connecticut. Have a large yard with about an 2 acres of lawn that I mow. Have another 13 acres of forested land that I hope no one will ever build on , have a wife and 2 dogs.

If you would like my blood type??..... A Neg
My cholesterol level?? 179
My blood pressure?? - 120/70

Sorry if I don't own a bunch of accessories for my BX22, but I will post them as I obtain them. I don't know how much more information about my tractor I could put other that that which is already there...... You called it a BX, but it clearly shows it to be a Kubota BX-22.... I guess that I could add the year of manufacture..... 2003. You want me to list the old cars that I own??? 1964 Chevrolet Corvair Spyder Factory Built Show Car for the New York Worlds Fair, 1964 Chevrolet Corvair Greenbriar, custom built ambulance, 1962 Corvair Monza Convertible with factory installed air conditioning, and the list goes on... Do you have a mental picture now?????? Are you or some other moderator going to delete this post even though I have properly and civilly answered you????

 

[BillG_in_TX]

<font color="blue">My blood pressure?? - 120/70 </font>

Was that before or after this post? /forums/images/graemlins/grin.gif

 

[Inspector507]

I love the Corvairs myself.....perfer the '65 and up though /forums/images/graemlins/grin.gif