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| Harden a locking pin |
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| ieezitin:
Hi guys.. i have a 3 point hitch bush-hog mower and the PTO angle drive is rated for a 25HP, My tractor is 30HP diesel so its a tad heavy on the torque for this mower. I dont have the original pin that connects the splined PTO drive to the knuckle of the PTO shaft as that sheared off yonks ago so i use a 7/16 grade 7 bolt, if i dont wail it or hit large branches it works fine, hitting a stump or block of concrete shears it as it should, the drive output speed for the mower is 540rpm and thats what i run it at I get a season of use out of this set up if i dont smash it into something to large, this arrangement works fine but after a period of time it just shears on its own while im not abusing it, also the 7/16 bolt it about .050 below diameter of the hole, i compensate for the little wiggle but running up two nuts to lock it tight. I believe the bolt gets work hardened and gives up. my question is: if I turn my own pin true to size of the hole whats the correct way to harden it for the task at hand? Thanks Anthony. |
| vtsteam:
It's there to protect the shaft, so a season of use seems okay to me. If you were replacing it every time you went out that would be different. I'd be wary of hardening it too much and enlarging the holes without shearing it. If the holes are enlarged this will tend to shear the pin more quickly because it hammers. Also it could actually be that the bolt is too hard and fatiguing. Can't remember if that grade is case hardened either. Anyway, it doesn't seem like the right pin per mfr., but if it is working and replaced once a season, and isn't enlarging the holes, seems like it's working properly as is. Actually, forgot to ask the most basic question: Can't you just get a proper new shear pin from the manufacturer/dealer? |
| wgw:
I don't know what a bush hog mower is, but I'm guessing it may be what we call a "topper". First try to get the proper pin, if not it may be metric? 12mm is nearer than 7/16". The holes should not be worn but can wear over time. As said a years use is not too bad. Do not be tempted to fit a higher tensile pin. I used to design these things and the biggest problem was high tensile bolts instead of the proper pin. ps- try some thick grease on the pin ,see if that helps . |
| ieezitin:
Hi I know the pin is there to shear. The bolt i use works great for a season then shears, as i said in my original post i think its work hardening, if i had the correct pin it would not shear after one season it would work until i hit something hard then it would do its job, that is what i am trying to achieve. I cannot buy a pin because the holes are different, that's why i want to make one and make the largest hole a sliding fit. My question was: whats the best way to harden the pin i am going to make.... I am going to make it out of steel. To expand a little on whats in my mind i want something around the hardness of a grade 7 bolt and its shear strength.. i am not up on tensile, proof and shear of carbon steel but i know a grade 7 is perfect, because it works now... i suspect if it fitted correctly (hole diameter) it would not fail but due to the slack fit it work hardens. Thanks Anthony. |
| awemawson:
So why don't you take a larger 'grade 7' and turn it down to a snug fit and use that? |
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