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???