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Discussion Starter #1
Hi everyone,

I'm trying to secure a 4x4 fence post via a 4x4 metal post anchor (with 4 bolt holes on its base) to a concrete post as part of a gate structure. The gate (only ~36" wide) is in the middle of a driveway, and I wanted to be able to remove the structure if I need to resume using the driveway for a vehicle (unlikely I will need to, it is a narrow drive, but just in case i need to get a vehicle to the garage for storage, etc.).

Since I want to be able to remove the fasteners, it seems my best option is lag bolt (aka lag screw) and lag shield (at least, I was told all the other options like toggle bolt and concrete screws could easily come out).

I drilled out the concrete about 3" deep with a 5/8" bit (per instruction), used a 3/8" lag shield and 3/8 lag bolt, both of which were 2.5" long. The bolt sheared off in the shield just above the threads, about 3/4" from flush. :mad: I drilled out the hole...

I repeated using 2" long lag bolt and shields thinking the shorter length may not expand as much and thus not shear off while i was installing. Again, the bolt sheared off in the shield just above the threads. I drilled out the hole again. :furious:

What am I doing wrong besides apparently over tightening the bolt (well before the bolt is flush, however)? Is a lag bolt not supposed to be driven fully into the shield? FYI, the bolt isn't threaded all the way to the head, maybe 3/4" is not threaded. I suspected this might be the problem, but there doesn't seem to be fully-threaded galvanized lag bolts available at my big-box-store in any length... If i thread a lag bolt into the shield in my hand, I can see the shield expands significantly, so it's not surprising there's a lot of resistance when inserting the bolt in the concrete, but i didn't expect the bolt to fail so easily. It seems like the shield can't expand enough to accommodate the lag bolt, and it shears off.

Any help would be appreciated!

Note: if I go to a different anchoring system, i have 4 holes, 5/8" diameter and 3" deep, so many options won't work anymore. I am considering epoxy adhesive and 1/2" threaded rod in those holes but this isn't ideal because i would need to cut the rods off if i have to temporarily remove the gate (the lag bolts would just have unscrewed nicely, if i could get them in in the first place!)

Jamie
 

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What length of bolt is the shield rated for? Sounds like you are using too long of a lag bolt.
 

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Discussion Starter #4
What length of bolt is the shield rated for? Sounds like you are using too long of a lag bolt.
I don't know what the shields are rated for, and the store was no more helpful explaining which lag shield to use. The box has instructions for use but not how long a lag bolt should be. it's what I was told by the store to use, but that doesn't mean anything...

My understanding from reading on the web is the long shields are normally for softer substrates(increased strength), short ones for harder substrates (so you don't have to drill as deep in a hard substrate). There are only 2 sizes available for the 3/8" lag bolt, short (2") and long (2.5").

If i used a short shield (2") with a a long bolt (2.5"), i'm sure it will break again as the bolt will open the shield fully. I have not tried a long shield (2.5") with a short bolt (2") which might not expand the shield as much.

I recommend an alternative approach. There are threaded expansion anchors that are designed to accept a standard nut. You install the anchor per the pattern of the base, then nut down above base. Presto, and it holds really well.
This would work, but it is my understanding you can't remove these type of wedges. (OR CAN THEY BE BACKED OUT?) It's not really any different than epoxy at this point, but that's why i didn't go this route in the first place. Problem is, with a 5/8" hole, i'll need to use a huge wedge anchor (presumably the 5/8 anchor). I'll have to drill out the holes on my metal post anchor, which can only accommodate 3/8" bolts.
 

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This would work, but it is my understanding you can't remove these type of wedges. (OR CAN THEY BE BACKED OUT?) .
We use many of these for installing machinery in factories---no they can not be removed---so we drill the hole right through the slab---the unwanted anchors can then be driven down below the surface and the holes patched--
 

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Discussion Starter #6
...we drill the hole right through the slab---the unwanted anchors can then be driven down below the surface and the holes patched--
Yeah, i've read that as a solution somewhere else, too. Very smart! But not an option for me as my achors would be drilled into the top of a 4ft concrete post below grade...
 

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Discussion Starter #7
Interesting, I just came across this info on a retail site

http://www.confast.com/products/technical-info/lag-shield-anchor.aspx (this is not an endorsement of the company!)

"NOTE: If the lag screw begins to torque-up or tighten before the head of the lag screw mates up against the object being fastened, the shield should be driven deeper into the hole by hand hammering the head of the lag screw until flush to the object being fastened. Re-tighten the lag screw to complete the expansion of the shield and to secure the material being fastened."

Sounds like I could just knock the shield in a bit deeper to get in the last ~0.5" of bolt without breaking it.

Thoughts on this?
 

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Yep--standard practice----you will have this down to a science soon enough----
 

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Discussion Starter #9
Yep--standard practice----you will have this down to a science soon enough----
Perfect, i will try this approach, and if it doesn't work, I will move to the wedge anchor approach.

Too bad everything else I read on using the lag shields said to drive them flush with the concrete (like i would use with light-duty nylon anchors). Even the picture instructions on the box show a flush lag shield with the lag screw fully penetrating the shield. I just assumed they were soft enough to deform more readily in the tight hole!
 

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Discussion Starter #11
We use bolts like this to bolt down all the racking in our warehouse.
Thanks. I saw some similar concrete bolts at the store when I was looking for an alternative to the lag bolts/shields. They didn't carry 5/8" bolts though (the size of my holes). I presume these aren't intended to come in and out though, because the concrete would get damaged. I'm guessing your warehouse racks are pretty much permanent placements...
 
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