PTO shaft shear bolt strength

[Southernfarm]

Just bought a BX42S chipper at auction. It is new and it is a Wallenstein Chinese copy. Not bad, just be sure to rebuild it before using it. Anyway it came with a PTO shaft. There is a bolt in the shear bolt place. The cheap Chinese bolts probably would break before anything else, but I don't want to risk my BX25D in that test. So I want to put a homemade grooved shear bolt in its place. What grade of bolt should I use? Grade 5 or grade 8. Again to be safe I am going to groove the bolt. From what I know from the snowblower world, a grade 8 bolt, while stronger will shear quicker, and a grade 5 bolt is weaker but has some stretch in the shearing force.

Sent from my Z850 using Tapatalk

 

[Farmdaddy]

I have plain old bolts in my brush hog. I've been told that grade 8 will hold long enough to actually tear something up before they shear. I've had great luck with grade 5


Sent from my iPhone using Tapatalk

 

[North Idaho Wolfman]

Just bought a BX42S chipper at auction. It is new and it is a Wallenstein Chinese copy. Not bad, just be sure to rebuild it before using it. Anyway it came with a PTO shaft. There is a bolt in the shear bolt place. The cheap Chinese bolts probably would break before anything else, but I don't want to risk my BX25D in that test. So I want to put a homemade grooved shear bolt in its place. What grade of bolt should I use? Grade 5 or grade 8. Again to be safe I am going to groove the bolt. From what I know from the snowblower world, a grade 8 bolt, while stronger will shear quicker, and a grade 5 bolt is weaker but has some stretch in the shearing force.

Sent from my Z850 using Tapatalk

You want to use a grade 2 bolt (blank head) if you want it on the weak side to fail easily if there is an issue, and there is no need to grove the bolt, that just makes them easier to remove.

 

[lordulrich]

You want to use a grade 2 bolt (blank head) if you want it on the weak side to fail easily if there is an issue, and there is no need to grove the bolt, that just makes them easier to remove.

Yep, if you don't get the grove in the exact right spot it won't impact the shear strength (OK a tinny bit but not enough to matter). The grove helps prevent the bolt from getting stuck in the shaft after shearing.

 

[JasonW]

What everyone else said. Use grade 2 bolts for a shear pin. I'd rather break a 1.50 bolt than take out a u-joint, prop shaft, gear box, etc.

 

[sagor]

Most Chinese bolts (un-branded) are about Grade 2, maybe a bit less. Start with Gr2 and if it keeps popping under the lightest load, maybe upgrade to Gr5. Bolts are cheap, repairs are not.

The grove actually helps the shear by allowing space for the metal to "tear" All bolts when they shear, pull metal sideways, deforming the shape. With a grove, the deformed metal stays in the grove area (in theory), allowing easy removal of the remains without hammering it out. Finally, the grove makes a specific diameter of the bolt that is to shear at a specific strength. You can use a 1/2" bolt that is grooved to 1/4", and it will shear at 1/4" bolt strength...