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  1. #1
    Elite Member
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    EarthForce EF-5 mini-TLB (2001)

    Default Replacement shear pins

    I started to post this under the Danuser digger post I just made, but thought that might limit the potential audience a little, since this idea should be useful for just about anything that takes a shear pin.

    My Danuser F8 digger can really chew up shear pins in a hurry when digging in rocky soil. The F8 is very well made and even has a bolt similar to a setscrew to hold the auger on the digger shaft in the right position, but when a pin shears, you have to line the holes up with the piece of bolt left in the center of the shaft, take a punch and drive out the old one, drive in a new pin, put a nut on it (which 9 times out of 10 has to be a new one because the old one got flung who-knows-where), etc. I finally got tired of all this nonsense and bought some bolts that were way too long (so the shoulder extends out to the outer diameter of the auger collar). My friend Jack and I cut them off to 1/2" sticking out, ground the ends down so they're like a sharply tapered drift punch, drilled a hole 1/8" from where the edge of the auger collar is, and bought a bunch of cotter keys that will go into the hole. Now, all I have to do is get the hole fairly closely aligned, stick a new shear pin in, use it to drive out the old one, and slip a new, much-cheaper-than-a-nut cotter key in it. Much, much faster and a lot less hassle.

    MarkC


  2. #2

    Default Re: Replacement shear pins

    Unfortunately, this is probably not a good idea. The shear pins in most implements need to be under tension (i.e. tightened by a nut) in order to break cleanly under the correct amount of force.



  3. #3
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    EarthForce EF-5 mini-TLB (2001)

    Default Re: Replacement shear pins

    That's an interesting possibility. I'd considered it, but figured the difference would be negligible, especially since these are grade 5 bolts, not the mild steel ones you sometimes see used for shear pins. If there are any tables or formulas on it, I'd sure like to know, though. I can only say that the pins still shear when necessary just like they used to, and they don't "smear" at the shear point as badly as they used to when I tightened them with a nut. So until some concrete evidence to the contrary comes along, these work better than the original ones did, and take about a fourth the time to change.

    MarkC


  4. #4
    Epic Contributor Bird's Avatar
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    Default Re: Replacement shear pins

    Dave, that theory certainly sounds logical, but then the question is: how much tension? How many people ever torque a shear bolt nut with a torque wrench? Of course, I guess I either don't work as hard as a lot of you guys, or maybe it's the lack of rocks around here, but the only shear bolt I've sheared in the last 6 years was one on a neighbor's hay baler.

    Bird

  5. #5
    Gold Member
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    Kubota /L2650/ LA450/B4690 -- John Deere 450 Dozer

    Default Re: Replacement shear pins

    Mark are the new bolts the same grade as the shear pins.. Bolt shear is normally about 40% of the ulitmate tensile strength of the steel. Shear strength is much harder to evualate than other metal properties, and has much highter safety factors in design, or a much lower working stress if you will. Also in this use it is not so much the stress as the impact resitant of the material. The "Pin's" are designed protect the equipment. If the strength of the pin goes up more wear and tear on the equipment. I have seen more than one person put in harder and harder pins till the gears started to come apart. I use the solf bolts in my old bushhog. It is old needs kind care.


  6. #6
    Elite Member
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    EarthForce EF-5 mini-TLB (2001)

    Default Re: Replacement shear pins

    Jag - Yep, same grade. As you say, it's never a good idea to replace a shear pin with one of higher strength than was originally spec'ed. They spec them the way they do for a reason.

    MarkC

  7. #7
    Veteran Member
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    2003 Kubota L3430

    Default Re: Replacement shear pins

    Do augers come with slip clutches?


  8. #8
    Epic Contributor Bird's Avatar
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    Default Re: Replacement shear pins

    Glenn, you can get the augers with either shear pin OR slip clutch.

    Bird

  9. #9

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    Default Re: Replacement shear pins

    A formula that's appropriate for this application (IMO) is:

    max shear stress = sqrt[calculated shear stress^2 + (0.5*calculated tensile stress)^2]

    FWIW, I've got an inexpensive auger and really haven't had any trouble pushing sheared bolts out. I think ductility of the shear bolt and clearance between the shaft and auger are the primary contributors to 'smearing'. I don't put any significant tension on mine.


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