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Almost all concrete anchors specify an edge distance not less than 10 times diameter. Because you will be decreasing your design strength, you could probably go to a smaller diameter anchor. This would decrease your edge spacing problem, make drilling easier, and make breakage less likely.
As an aside, nine 7/8 I 4 holes is not alot.
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Howdy, I have to drill 9 holes 7/8" dia. by at least 4" deep. They are spaced far enough apart as to not affect each other. The rub is that they are on a elavated melevatedc porch and I have to drill 3 1/2" in from the edge. I am afraid that a hammer drill will crack and possibly break out a piece off the edge. The idea of drilling that many holes of that diameter in rotory mode onlrotaryn't thrill me. Any advantage to drilling a small dia. hole first and progresively maprogressivelyer? Suggestions ? Thanks LVC
*Hi Link,You should be fine with any good roto-hammer. Of course I could be wrong, especially since I don't have a clue what a i melevatedcis. I'm not really sure what mode i onlrotaryn't is either my drill doesn't have that.Probably drilling a small hole first is a good way to break off a piece of concrete or melevatedc from the edge.joe d
*Is this something like Linda, Linda, bo-Linda, fee-fy fo-Linda? I don't understand some of your words -- computer hiccup?Three and a half inches should be sufficient to prevent chipping off four inch concrete, but there's nothing wrong with increasing the hole diameter incrementally if that would make you feel more confident. I've drilled holes almost that large that close to the edge of concrete and never gave your concern a thought. Either overconfident or dumb..take your pick.
*My guess is he tried to use the new spell checker. I tried it and ended up with a few words I'd never heard of either. I'd say he typed rotary mode only, just a guess. Chuck
*I think 3-1/2" inches is far enough from the edge to be safe. Actually, I suspect that the progressively larger bits might be more dangerous than just one pass. If each bit is a tight fit in the hole made before, It seems that the force trying to expand the hole would be greater and more likely to crack. Just some intuitive reasoning with nothing to back it up so it sure could be wrong.By the way, I tried that spell check thing on my first post on the new site. I ended up with words like maprogressivelyer too. I guess I'll just stick with my bad spelling.
*Thanks guys. I would say to skip the spell check as you have already surmised. miqxzy0934ymlahil!! LVC
*Link, I am not sure what your porch is exactly like , but if it is like most, it is probally be only 4" thick or less and you will be drilling all the way thru it, buy design or accident? I think you would b disturb the concrete much less by using a coring bit and would have a better hole as a result. Although nothing wrong with roto-driling the hole.What are you doing with such a large bolt in concrete, it seems something big is about to be placed on the concrete and the slab is likely not going to be strong enough for your planned activities.b Just Wondering ?
*good insight anderson, Bthe same thing *989(*89 myself ((989080.
*The spell check strikes again?!Rich Beckman
*I've had one or two experiences where going up in steps instead of using what you need the first time has caused the bit to hang up in the smaller hole. Core drilling would be the best but is going to be alot more expensive. Skip
*Almost all concrete anchors specify an edge distance not less than 10 times diameter. Because you will be decreasing your design strength, you could probably go to a smaller diameter anchor. This would decrease your edge spacing problem, make drilling easier, and make breakage less likely.As an aside, nine 7/8 I 4 holes is not alot.
*Thanks Mark,That is the little known kind of specs that we probably all can use in the future.joe d
*What didn't get translated is:good insight Anderson. I was wondering the same thing myself (what is the purpose of the 9 holes so close to the edge), support for columns of some sort I would guess. If this is the case, usually there will be a trench footing or poured wall below the edge of this elevated slab, but then again if the holes are for post dowels the posts would be in compression, and the dowels only function would be to center and keep the posts aligned. What is the intended design for the 7/8" holes?? We probably need more info from link, and possibly could offer some other ideas for what is needed.
*Link,This is no big deal. Use a good quality hammer drill, like a Hilti TE5 (the kind where the bit is splined and chucks in place with a keyless style collar. These bits work very well and will not spall the concrete. The light-weight (do -it- yourselfer style at Lowes) hammer drills (that require a jacob's chuck ) along with "standard issue" concrete bits don't work so well. They just bounce around; and can spall your work. The industrial type will "auger" right in. To drill 9 holes 7/8 dia with a good industrial hammer drill, it should take you less than half a minute per.Do what Ryan suggested, use the 7/8 dia bit only. No need to "step up" in size gradually.I'm assuming the porch is sound, and not all cracked to hell.Davo