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  1. #1
    Community Moderator phild01's Avatar
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    Default Core drills

    I am thinking of buying a core drill. My minimum sized hole is 150mm, 10 of them into sandstone. As usual, not interested in hiring.
    I prefer to go cheap with this and looked at some stuff on ebay. Some seller's say 110mm max for their drills, others say 150mm.
    Anyone with any experience with this size hole?

    https://www.ebay.com.au/itm/150x400m...19.m1438.l2649

    https://www.ebay.com.au/itm/Vevor-RT...0AAOSwuHJbAh23

    https://www.ebay.com.au/itm/AU-1600W...r=521792334364

  2. #2
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    I've done heaps in reinforced concrete and limestone blocks over the years. I would never recommend a handheld unit myself at those sizes. Just trying to get the hole started alone it would want to run off.
    There is also the kickback situation to consider as well. Especially if you are going any depth they can jam suddenly. There is a lot of power needed to turn a bit that diameter.

    For deep holes the unit below gets dynabolted in the center for concrete. For limestone being softer I have a u shaped bracket that fits over the blocks by about 50mm.
    Shallow, ie 100mm only I have relied on stand to provide leverage.
    I have used a newer, expensive unit that used a vacuum pump to hold it to the cement. Still had to be bolted for rough surfaces.

    I've never tried ebay bits so can't say if they will last.

    Attached Thumbnails Attached Thumbnails drill.jpg  

  3. #3
    Community Moderator phild01's Avatar
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    First I am digging the holes in soft unstabilised soil soil about 300-400 deep, then continue into the sandstone with the hole saw. So getting a stand in there will be a pain. I thought the diamond blade would rotate easily as I find no issues with any of the cheap diamond blades I have used before including all my angle grinders. Bit it is a big diameter and it makes me feel hesitant. I find starting hole saws at a bit of an angle gets them started without jumping about.

  4. #4
    Community Moderator phild01's Avatar
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    Doova, would it be feasible to drill 4 smaller diameter holes and then hit with a rotary hammer/jackhammer to finish. If so what is a reasonable core size freehand with the drill. I have done ~70mm before with tungsten hole saws but very inefficient. I'd expect it to be far easier with the diamond type hole saws.

  5. #5
    4K Club Member Marc's Avatar
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    Phil. The biggest I have drilled free hand is 100 through concrete with no issues. Having said that, I called a core drilling dude a couple of times for 150mm and he used a steel brace to prevent it from turning. If you have soil on top of the rock, you can improvise a way to anchoring the drill. Ask Bedford, he knows a bit about older drills.
    Also don't discard calling someone to do the holes for you. They can be very reasonably priced if you have 10 to do. I am like you, buy tools whenever possible, but some tools you use once every ten years and in hindsight all they do is take room in the shed. Feels good looking at them though
    “It is not necessary to accept everything as true, one must only accept it as necessary”
    Franz Kafka

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