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Implement Alley Discussion Forum

Shear pins

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HobbyFarmerInWI

08-01-2005 20:37:40




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Shear pins, cotter keys, whatever you call them in your area. My question is, are they made in different grades like bolts are?

I am asking because I need to replace one in my post hole digger.

If the answer is yes, what "grade" do you install to have it hold when you need it to, but still break off when needed?




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bvomark

08-02-2005 10:29:29




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 Re: Shear pins in reply to HobbyFarmerInWI, 08-01-2005 20:37:40  
Lets define shear pin. If you are talking about a bolt or pin that is designed to break to protect other more expensive parts then they are of a spcific strength. If you are talking about a cotter key or pin the purpose of the key is to keep a pin or bolt from coming out of a hole. The cotter key strength doesn't matter as it only holds the bolt or pin in place and isn't designed to shear and provide protection.

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ClemBert

08-02-2005 04:57:13




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 Shear Pin Replacement in reply to HobbyFarmerInWI, 08-01-2005 20:37:40  
Yup, there's nothin' like being out in the field happily puttin' in posts when you break a shear pin. Unless you have a spare shear pin around this will completely shut down your posting plans.

I discovered after breaking a pin how difficult it is to get a prompt replacement. I have a BushHog brand post hole digger that requires an odd tapered shear pin that is threaded on the tapper end. You don't walk into your standard hardware store and find that pin. In fact I called all of the tractor dealer and farm supply companies within 50 miles to find out that none of them stock shear pins (what a surprise and disappointment).

In the end I found out that not only did I have to order them through a tractor dealer but the shear pins would cost about $12 (a piece!!!!) not including shipping. Also, it would take a week to get them delivered (what a crock!!!). In the end I did order three pins just in case I ran into this problem again.

Since I didn't want to wait a week I decided that temporarily I would "manufacture" my own shear pin. I went down to HomeDepot and pick up a standard #2 steel bolt (#2 is the correct hardness) and with a grinder tapered the end as appropriate (to get it to go into the hole on the post hole digger). Since I didn't have threads to put a nut on it I just used electrial tape to wrap around it to keep it in place.

One year later my "manufactured" pin is still in the post hole digger and my spare "real" shear pins are sitting in the garage in a little plastic baggie.

Just so you know here are some of the most popular bolt grades (you want #2 so that it can "shear" if needed).

Steel grade 2
----- ----- -
Zinc plated low carbon steel. Best for general hardware use where high strength is not required.

Steel grade 5
----- ----- -
Made from medium carbon steel, tempered and zinc plated. Best for automotive use and other areas where higher strength is desired. Steel grade 8
----- ----- -
Made from medium carbon alloy steel, tempered and yellow zinc plated. Best suited for applications where high strength and hardness is required.

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BBx

08-02-2005 04:25:39




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 Re: Shear pins in reply to HobbyFarmerInWI, 08-01-2005 20:37:40  
That shear pin is there to protect the implement and your tractor. Don't put in a pin (or bolt) that is too hard. If the pin doesn't shear when it should, the result may be stripped gears in the PHD or in your tractor. If you have a manual for your PHD, see if it tells you what to use. I use 1/2" #2 grade bolts for all my shear pins and only rarely shear one. But the #2 grade is soft enough to shear when it should.

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kyhayman

08-01-2005 21:59:38




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 Re: Shear pins in reply to HobbyFarmerInWI, 08-01-2005 20:37:40  
Yes, shear pins are made of a specific hardness for the specific job. Metals have properties of toughness, hardness, and brittleness. The alloys determine when these will fail under varying degrees of stress and shock. A pin bending can allow torque to exceed component strenght, a pin breaking too soon will keep you working on stuff all the time. Best bet for shear pins is to get these from the dealer, that lesson has been bought and paid for by many of us in the thousands of dollars and hours lost by trying to cut corners.

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Don-Wi

08-01-2005 20:51:28




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 Re: Shear pins in reply to HobbyFarmerInWI, 08-01-2005 20:37:40  
The generic rule of thumb is to use a grade 5 bolt, long enough for the bolt to pass through the shear point before the threads begin. A post hole auger we borrow on occasion has about a 7" bolt through it, that is bent like a Z going through the hole, it aint ever coming out unless it snaps, which I pray it doesn't while we use it.
Donovan from Wisconsin



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