Drilling near edge of footing

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  #1  
Old 11-12-15, 05:33 PM
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Drilling near edge of footing

I need to drill for a post anchor for my deck. It's a 1/2" anchor at the edge of an 8" wide by 12" deep footing. Most of the footing is supporting the stair stringers, but I made it long to support the post base as well.

I'll be right at the minimum edge setback (for the anchor) at 2.5" from the edge. Concrete is 5000psi Sakrete and has had 2 months to cure, so it's close to full strength.

I have a hammer drill (Makita) that was barely up to the task of drilling the 1/2" holes for the main deck posts on the big footings. Took a long time, though. Drilling for some tapcon anchors took a long time as well in the stair footing.

Can I step up through drill bit sizes to make the load on the drill easier? Figure 1/4" and then the 1/2" at full depth. I'm trying think of a reason not to like splitting the concrete since it's near the edge (or maybe it's easier on the concrete this way).

Also, any other advice for drilling near the edge of the slab? I've seen advice of "don't go less than 6" from the edge" to "I put Tapcons 1" from the edge all the time".

Thanks,
Anthony
 
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  #2  
Old 11-13-15, 05:54 AM
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Can you post a picture?
Trying to picture how only a 8" wide footing is going to work.
I'd be using my Bosch Bull Dog SDS drill for this one.
And yes starting with a smaller bit will make it easier.
 
  #3  
Old 11-13-15, 06:37 AM
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I don't have an SDS drill. Most of my concrete drilling so far has been Tapcons in my basement block wall, which the Makita is great at. Even did a 7/8" hole through brick and block to run electrical conduit. But this 5000psi concrete has been a bear (it did it though, just very slowly).

Best pic of the stair footing here
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Sketchup of the post and anchor (which is what I need to drill for).
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  #4  
Old 11-16-15, 02:47 AM
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after 2mos, if you mix'd, plac'd, & cur'd right, i'll bet it exceeds 5K,,, jacobs chucks suck for percussive drilling,,, bulldog's the right size - rent it & a bit - just go slow,,, tapcon holes don't place near as much stress on conc as do lead dropin's - personally i'd drop down to a 3/8" or 5/16",,, are you concerned w/pullout strength or just shear ( side-to-side ) ?
 
  #5  
Old 11-16-15, 06:11 AM
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It's only there to assist the lateral load requirement on the post. Very low uplift requirement. Just whatever leverage the post tries to "cam" up when pushed laterally.

I'm glad it sounds like I can step up, because location will be critical with this one.

It will be an insert anchor. I'm already stepping down from 5/8" to 1/2", one because of the setback requirement and two because I already have the anchor and bit

Thanks guys.
 
  #6  
Old 11-19-15, 08:54 AM
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Did the drilling yesterday. Four steps with my Makita (non-SDS), finishing with the 1/2". Had to "deburr" the hole quite a bit since the 1/2" bit pulled itself in before the cutting tip could make a clean circle. Test fit with a 1/2" bolt before dropping in the anchor. Probably made it 1/4" deeper than it needed to be (above the extra that was already supposed to drill), but I won't sweat that.

No cracks when I tightened the anchor. I used every bit of the slop the anchor plate gave me to get the hole away from the edge. Overall, I can't complain. Time will tell how well it holds up.

Thanks for the advice guys.
 
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