What shear bolt grade would you recommend?

[Henri88]

New to brush cutting. I have a new to me Howse 4' rotary cutter and a 2305 JD with 18hp pto. The Howse manual recommend grade 5 or lower so my choice is either 5 or 2. I am leaning more towards the grade 2 but I'm worry that the shear bolt would be prone to shear easily. Your thoughts.

I will be using it on a 1 1/2 acre with mostly grass, but we did cut some Hawthorn and apple trees. I also know all about the slip clutch but would like to stick with the shear bolt if possible.

Henri

 

[arlen4720]

New to brush cutting. I have a new to me Howse 4' rotary cutter and a 2305 JD with 18hp pto. The Howse manual recommend grade 5 or lower so my choice is either 5 or 2. I am leaning more towards the grade 2 but I'm worry that the shear bolt would be prone to shear easily. Your thoughts.

I will be using it on a 1 1/2 acre with mostly grass, but we did cut some Hawthorn and apple trees. I also know all about the slip clutch but would like to stick with the shear bolt if possible.

Henri

I would start with the safe bet, and use a grade 2. If it proves to be unworkable, then go to a grade 5.

 

[RickB]

I would start with the safe bet, and use a grade 2. If it proves to be unworkable, then go to a grade 5.

Good plan.

 

[Henri88]

Tx guys! Does shearing a bolt while bush cutting a common thing. Sorry but I am completely green to this activity.

 

[newbury]

I just faced that with my Agrisupply PHD. The manual says grade #5. I bought a handful of #2's. I figure break $5 worth of bolts is better than $100 of PTO or $300 of PHD.

 

[ARCKING]

I wouldn't be worried about running grade 5 bolts. At CNH (and I would assume Howse is the same) components are engineered based on grade 8 shear bolts with the assumption that someone will attempt it. I'm used to property where shearing bolts on plows and bush hogs is common, so I'd vote grade 5.

 

[catdozer]

What i have done also is if a grade 2 is to soft, get a grade 5 one size smaller.

 

[Henri88]

I'm not to worry about the implement, it is the pto on the tractor that worry's me the most. As mention above, I'm going with grade 2, but I just don't know how frequent a shear bolt will brake under normal (brush cutting) use. Maybe I'm over worrying here, but I was kind of hoping that someone with pretty much the same set-up would chime in. Maybe I should've ask my question on the JD forum since it is not the implement but mostly the tractor that I worry about.

Arcking, what size is your cutter and tractor? Tx

Henri

 

[ARCKING]

Arcking, what size is your cutter and tractor? Tx

I usually break things with a 55hp tractor and 10ft bushog...a little different scale than you're talking. I've never sheared a PTO bolt other than on a round baler though - usually it's the rough ground that shears other bolts. Not saying it isn't rough on the equipment, but if I were to use lower grade bolts I'd never get anything done.

 

[Henri88]

Tx Arcking!

 

[Gary Fowler]

I would use the grade 5 as recommended. My BIL has a shear bolt 6 foot hog and with even a grade 5 bolt it will shear if he forgets to idle down his tractor before hitting the electric engagement button. I DO NOT LIKE those things as there is no way to feather in the PTO using the clutch. That is likely the worst invention that they ever put on a tractor.

 

[RickB]

I wouldn't be worried about running grade 5 bolts. At CNH (and I would assume Howse is the same) components are engineered based on grade 8 shear bolts with the assumption that someone will attempt it.

That right there is a dangerous assumption coupled with an uninformed opinion.

 

[Soundguy]

ditto.

I'd start soft and go from there.

better to shear a cheap pin and know you need a little harder.. than to repair a driveline or gearbox due to starting at the top end..

 

[hosspuller]

Another point. Always engage the PTO at idle speed, then increase to operating speed. It'll be less wear on the PTO clutch, driveline, and your wallet.

 

[ARCKING]

That right there is a dangerous assumption coupled with an uninformed opinion.

I don't think it's a dangerous 'assumption' to use the bolts recommended by the manufacturer. I wouldn't suggest using anything with a greater shear strength than what the manufacturer recommends, but considering it's likely designed with a factor of safety, so I wouldn't be concerned running a bolt on the higher end of what is recommended. As for an uniformed opinion, I'm not sure where comes from - I make no claims to being an expert.

I'm with the others though - start soft and work your way up.

 

[Henri88]

Again, tx for all the good info. As for what the manufacture recommend, I suspect it to be more for the protection of the implement and not for the pto drive of the tractor.

Henri

 

[RickB]

I don't think it's a dangerous 'assumption' to use the bolts recommended by the manufacturer. I wouldn't suggest using anything with a greater shear strength than what the manufacturer recommends, but considering it's likely designed with a factor of safety, so I wouldn't be concerned running a bolt on the higher end of what is recommended. As for an uniformed opinion, I'm not sure where comes from - I make no claims to being an expert.

I'm with the others though - start soft and work your way up.

You made claims about design standards for machines manufactured all over the world by dozens of engineering groups who work independently under the CNH umbrella and as vendors to CNH, saying those machines are designed to use grade 8 shearbolts without causing collateral component failure.
I very much doubt that you can verify that.

 

[ARCKING]

You made claims about design standards for machines manufactured all over the world by dozens of engineering groups who work independently under the CNH umbrella and as vendors to CNH, saying those machines are designed to use grade 8 shearbolts without causing collateral component failure.
I very much doubt that you can verify that.

I don't want to take over Henri's thread defending an assumption, so let me say to anyone that may read this later and take up arms that's there's no guarantee that all machines are design to handle a shearbolt above manufacturer's specs. I'm sure that there are machines that due to cost or weight reduction/etc, are running with much smaller factors of safety. I know that some CNH platforms design for grade 8 bolts from talking to engineers in New Holland - it's good engineering design to keep that possibility in mind.

 

[Gary Fowler]

Again, tx for all the good info. As for what the manufacture recommend, I suspect it to be more for the protection of the implement and not for the pto drive of the tractor.

Henri

I think you are wrong on that assumption. The shear bolt is to protect the drive line in its entirety from tractor to implement. I totally doubt that a 3/8" bolt ( 3/8" is about a standard shear pin diameter for a 6 foot BH, yours may be smaller) of any grade is going to hold solid and not shear prior to damage happening to your 1 3/8" drive line on your tractor. The drive line on your tractor should stall the engine before damage happens. The shear pin is to protect it from sudden impact like hitting large immovable objects that immediately stop the blade rotation. Some times these shear pins fail prematurely without hitting any objects because the safety factor is so high that normal work cant be done without shearing the pin. Those times, the operator needs to get a harder pin.
So the suggestion on starting with a grade 2 and if that fails too easily, go to a grade 5 and even a grade 8 if needed is a good one. I don't think you would damage your tractor any with any grade as long as the size is the same. As for using a smaller bolt, I wouldn't do that for sure as you will be shearing them all the time and the slack allowed in the hole would make it super easy to do. Keep the shear bolt hole filled with the proper size bolt and idle down before engaging or disengaging the PTO.

 

[jenkinsph]

Henri,
I would buy both grade 2 and 5 shear bolts, few of each as the trip to town cost alot more than the bolts. With the 2305 I would agree to try the grade 2 first and see how these hold up for you. Hard to know what to expect because conditions vary so much but I have used some shear bolts for 15 minutes and others that lasted longer than I could remember. If I was constantly changing the grade 2 then I would resort to the grade 5 but recognize that if you hit something out of the ordinary the shearbolt should break, that is its purpose.