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Hole for concrete screw

Discussion in 'Tools and Materials' started by roythegrass, 21 Jul 2020.

  1. roythegrass

    roythegrass

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    I need to fix a plate to concrete paving slabs using M6x50mm concrete bolts/screws.
    I've read differing views some saying a 5mm pilot hole others saying 6mm.
    What size bit should I use?
    Thanks
     
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  3. sircerebus666

    sircerebus666

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  4. rsgaz

    rsgaz

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    Too many variables, you need to start with a smaller drill bit and work up until it fits properly. I keep a 4mm, 4.5mm and 5mm SDS bit in my drill kit for DeWalt 6mm wall dogs and 6.3mm TapCon screws.

    A very powerful SDS drill will always drill oversize holes, especially downwards, as the dust has nowhere to escape.
    Crumbly-ness of the concrete is another variable which means you need to start smaller (then possibly run the drill through with the next size up drill bit, but not on hammer, for a cleaner hole)
    On the other side of the coin, a beefy impact driver will be able to cram a bolt into an undersize hole, but you risk it getting stuck or shearing the head off.

    Got a spare slab you can do some test holes?
     
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  5. johnny2007

    johnny2007

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    Nylon plugs are a safer bet.
    Slabs crack very easily and not necessarily when you drill.
    You could go back a couple of months later and find it cracked.
    Nylon gives that little expansion room for metal and stone to move without interfering with each other.
     
  6. ^woody^

    ^woody^

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    The size specified by whoever made the screws, not other people's views.
     
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  7. catlad

    catlad

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    Yes and they recommend sizes based on substrate and doing test holes.
     
  8. Captain Nemesis

    Captain Nemesis

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    This might be a hijack, but I'll risk it as it's closely related. I might possibly need to fix some bolt-down fence-post holders to some concrete (not paving slabs), and can't decide between tapcon, sleeve anchors and chemical fixing.

    Thoughts?
     
  9. johnny2007

    johnny2007

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    I bolted my alleyway canopy posts down 15 years ago with standard 10mm Fischer plugs and haven't moved.
     
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  11. sircerebus666

    sircerebus666

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    I would tapcon , smaller drill hole and are easily power driven in
     
  12. Munroist

    Munroist

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    what thickness paving slabs ? and how close to the edge

    you need to do some test holes on spare bits to make sure your drills/method is getting the correct size hole - too tight and it will just crack the slabs.
     
  13. JohnD

    JohnD

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    Fences are particularly troublesome. Unlike fences and canopies, which may have four legs or more and some dead weight, a fence stands in a single plane, and when the wind blows, it exerts tremendous sideways leverage.

    you may have seen, in or after storms, fence panels sailing through the air and sturdy trees blown over.

    If you had something screwed down, and you wanted to wrench it out, a six-foot lever would be a useful tool to do it.

    A fence post is such a lever.
     
  14. johnny2007

    johnny2007

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    He said "concrete (not paving slabs)"
     
  15. catlad

    catlad

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    Specsavers comes too mind Johnny! :sneaky:
     
  16. JohnD

    JohnD

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    that's the trouble with hijacking a thread into a different, but similar-looking, question.
     
  17. Captain Nemesis

    Captain Nemesis

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