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Thread: Drilling Into Cast Iron

  1. Any conventional High Speed Steel Twist drill will do fine.
    Cast iron is supremely easy to machine. Use no lube whatsoever. An air hose will be helpful. to clear chips.

    When machining cast you need no oil or coolant because the chips come out so cleanly and do not adhere to the cutter. This means the heat will stay in the chip. Any lube you use will create an adhesive bond ( surface tension) holding the hot chips against the tool and work causing the heat to transfer to the tool and work.

    In a machine shop the only time one will use a lube on cast is when it's possible to literally flood the work flushing the chips away in the stream of coolant fluid.
    Otherwise cut it dry.

    For a half inch hole I'd drill a pilot hole first with a .250 drill or maybe a number 7 drill: no bigger and certainly no smaller.

  2. #17
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    When I drilled and tapped my tables for power feeders, a machinist at work set me up with three tools. First was a prick punch to make a dimple dead center on my paper template holes. Second was a pilot bit that drills an 1/8" center about 1/4" deep then has tapered sides to add a slight chamfer to the beginning of the hole. Two birds with one stone. These are available from EMCO for around $5. This makes it much easier to get a bolt started in a threaded hole (or a thru hole without threads) than one with a square edge, and made it easier to start the drill bit and subsequent tap. The third item was a HSS jobbers bit sized to allow tapping a 1/2" #13 thread. I used a low speed (300RPM) hand held drill, just a drop of 3 in one oil to get things started, literally one small drop, not a pool.

    If you are drilling holes in iron to accept bolts it is far easier IMO to tap the holes with threads than to use a nut and bolt combination, which is a real nuisance. Of course if you were say, drilling holes in an OEM iron table on a powermatic 64 to bolt it to a quality grinding router extension wing (just for instance) I'd only want one side of the connection threaded. The other hole you might want to make fractionally over sized, like say 9/16" or 17/32", to allow some room for setting the two tables flush.
    Last edited by Peter Quinn; 12-11-2008 at 6:32 PM. Reason: Another thought

  3. #18
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    Aug 2008
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    Drills with a high Ferromanurium content seem to work very well.

  4. #19
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    Quote Originally Posted by Gary Click View Post
    Drills with a high Ferromanurium content seem to work very well.
    What about ones with a high dilithium crystal content?
    No matter where you go, there you are. B. Banzai

  5. #20
    Best would be a bit with a high Leveright content alloyed with a small percentage of Unobtainium. But if you can't find those, plain old HHS bits will do fine.
    David DeCristoforo

  6. #21
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    Peter, your "pilot bit" is otherwise known as a center drill.
    Please help support the Creek.


    "It's paradoxical that the idea of living a long life appeals to everyone, but the idea of getting old doesn't appeal to anyone."
    Andy Rooney



  7. #22
    +1 on using a punch first. I prefer cobalt bits, but HSS should do the trick as well.

  8. #23
    None of the advise you've recieved here at this woodworking site is completly correct.

    Depending on the dimention of the piece and/or the size and location of the hole, cast iron can be very delecate to do some of the suggestions made so far.

    http://www.practicalmachinist.com/

  9. #24
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    Quote Originally Posted by Bruce Page View Post
    Peter, your "pilot bit" is otherwise known as a center drill.

    Thanks Bruce, didn't really know what it was called. Works great though.

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