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    Default Drill Bit?

    Hey Guys,

    Please school me on what type of bit is shown in the photo below.

    No tip, so I figured a spiral reamer, but I am an uneducated dolt. I would prefer what the pros have to say. Also, is there any value in them (1/4-inch to 1-inch)?

    Thanks for the insight,

    Greg

    drill.jpg

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    I've heard them called core drills. Might be other names too.

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    Quote Originally Posted by Booze Daily View Post
    I've heard them called core drills. Might be other names too.
    Used for coring/drilling what material? Last I heard a core but was used to core concrete. These do not appear to be for that>

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    Used to enlarge an existing hole. The extra flute(s) keep the drill from walking.

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    Yes they are core drills. They are for enlarging pre-existing holes. Punching through a cast hole for instance to rough it out. Note, the part of the pattern in a casting that creates negative space is called a "core." They use multiple small flutes that are shallow so that the central part of the drill is as thick and stiff as possible.

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    Could they be used on a lathe to achieve a final drilled diameter, following up a smaller hole, or are they primarily for thinner material?

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    yes. and a drill bit is a woodworking tool. as in "brace and bit " or ship augur. those are core drills.
    for enlarging existing forged or cast holes.

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    Quote Originally Posted by bug_hunter View Post
    Could they be used on a lathe to achieve a final drilled diameter, following up a smaller hole, or are they primarily for thinner material?
    Absolutely not limited to thin material. As previously stated, these are intended to make round holes out of rough cast holes in castings. Castings with cored holes are generally not especially thin. However, they do not serve the same purpose as reamers. If you want a typical drilled finish (not very good), core drills will work fine. If your "final" diameter needs to be precise, drill undersize (with any sort of drill) and ream or bore for finish.

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    Quote Originally Posted by bug_hunter View Post
    Could they be used on a lathe to achieve a final drilled diameter, following up a smaller hole, or are they primarily for thinner material?
    Yes, they could. Expect a butt-ugly hole finish. Usually.

    Core taper varies. Metals have recommended minimums, but the cores aren't made by a book. They are made by craftsman with their own ideas and judgement. Some tapers even steepen, part way along, and not all are even close to perfectly round.

    A core drill is optimized to not grab, get "sucked-in" and bind in a TAPERED core hole. Like a self-tapping screw does. And which a conventionally tipped helical-twist drill CAN do. DAMHIKT!

    So they have characteristics that makes them akin to a three-way cross-breed between an end-mill, (the tip..) a reamer (the sides can cut if need-be).

    And the Devil. Because most of them are s**t-lousy for attempting to drill a "virgin" hole from scratch. Or just "cannot". More than one core drill type has existed.



    They are meant for a cored hole. They NEED a pre-existing hole. They will manage a taper. But that part they do NOT "need".

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    Quote Originally Posted by tnmgcarbide View Post
    yes. and a drill bit is a woodworking tool. as in "brace and bit " or ship augur. those are core drills.
    for enlarging existing forged or cast holes.
    In the UK a drill bit can be used for drilling metal,just buy the right bit.

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    Quote Originally Posted by camscan View Post
    In the UK a drill bit can be used for drilling metal,just buy the right bit.
    And remember which end of the horse to install it on.

    English Horse Bits: Check-out the Different Types of English Horse Bits

    There are SOME things even a very docile horse just won't "put up" with.


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    if you are after a precision hole, a boring bar or endmill . a reamer will just follow the sloppy hole
    and make a pretty, off center hole.


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