Shear bolt question

denglish

Member
Hello.
I have a post hole auger that requires a grade 2 - 5/16" shear bolt. I haven't any experience with shear bolts.
I have two questions.

1) Can I simply buy a grade 2 bolt from the hardware store of the correct length and diameter? I think this must be the case.

2) Is any stainless bolt at a hardware store without any lines on the head automatically a grade 2?

Thank you.
 
Yes common run of the mill hardware store or TSC store bolt works just fine. As for stainless bolt most are harder then grade 2
 
(quoted from post at 12:56:05 03/20/18) Yes common run of the mill hardware store or TSC store bolt works just fine. As for stainless bolt most are harder then grade 2

Stainless is extremely ductile and I would not use for a shear bolt. I was in a meeting last week with a manufacturer of stainless steel tubing and they said there are some particular challenges with burst testing stainless tubing and if you raise pressure slowly you can get 50% elongation out of it before it pops.
 
Yep stainless steel is a totally different animal when it comes to steel. I still remember back when I was working at a dock shop as a welder I took a fence post driver that some one made to work with me so I could use the band saw to cut it off because it was to long. A couple of the guys asked me why I didn't just use the torch to cut it off and I told them you cannot cut stainless that way. They did not believe me and even got stupid and bet me they could. I won a case of beer that day
 
These guys likely know more than I do about what I'm going to offer. If you replace a shear pin, with a standard bolt, I believe it needs to be shouldered so that the unthreaded portion carries the load. If the bolt has no shoulder, then the threaded portion is about 20% smaller effective diameter than the unshouldered portion as the threads are cut in. Now, 20% may not have a noticeable effect, but then again it won't carry the load of an actual 5/16" cylinder. Buy 2.
 
That is true if it was a shear pin not a shear bolt. 2 different things and a pin will fit a bit loose where as a bolt will be tighten into place. And yes the bolt should be long enough the load rides on unthreaded areas of the bolt
 
Yes go to TSC or hardware store for grade 2
bolts and nuts. I keep a dozen or so handy
for when I'm using auger, they are cheap, I
have slate in soils and gets hung up at
times.
 
I have the shaft bolt as you refer and my bits attach with 3 smaller bolts (5/16 I think) to the auger shaft where the two flanges meet..
Changing the bolts on the mating surface is 10x easier than trying to find the hole in the shaft and lining everything up and all that mess at
the input shaft.

So, I take the easy route. I only use 1 ea 5/16 bolt to hold the auger to the unit and do not tighten it all the way. Seem to last longer if a
little slop. One works fine to get the auger to work properly and when it's time to break something the small bolt shears and I have it
replaced and back in business in a matter of minutes. I run a 12" auger all 3+ feet of it all the way down in Houston Black Clay with that rig.
 
I have the post hole digger almost set up except I still need a roll pin that goes in the yolk next to the shear bolt. The roll pin is supposed to ride in a slot and keep the pto shaft from coming off the gear head in the event the shear bolt breaks.

My main problem here is going to be tree roots (I hope) as I don't have any known big rocks in the ground, but who knows what I will hit in this area. Maybe a mastodon tusk!
 
Got the shear bolt and roll pins all installed, pto lubed up and all works well. Using the posthole auger is going to really speed things up around here. Looking forward to planting many more trees this year!

I have the auger on my 49 Farmall M with Saginaw 3 point. I augered a few test holes last night and the tractor doesn't even seem to notice that it is doing any work.
 
"......and the tractor doesn't even seem to notice that it is doing any work."

Not till you almost have the auger buried and it hits some soft ground and decides to head for China. I know everybody digs holes but my
experience has taught me to run at a low rpm and keep moving the auger in and out of the hole to keep the "finds" volume to a minimum till
you get to the bottom. Once there shut off the PTO, pull the auger up and clear of the hole and pop it to toss the finds and produce a
cleaned out hole.

The Ford 3000 with the Live PTO is my post hole digging tractor. The double clutch allows you do do just that without having to fool with
the engage/disengage lever along with being able to move along the path and easily straighten things up while the auger is rotating. Live
is alive for me.
 

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