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spotting drill v. screw machine drill

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  • spotting drill v. screw machine drill

    I am looking to drill several .500" diameter holes 1" deep in brass and I'd like to do it without having to continuously change tools from spotter to drill. Is it cool to drill a 1" deep hole with a spotting drill assuming the flute length is long enough or should I be looking at a screw machine length drill? Is there a significant difference in rigidity between spotting drills and screw machine drills with the same flute length (there's a significant difference in price)? The hole will be bored afterward to .530, so a little bit of walking would be corrected.

    Thanks,
    Stuart
    Stuart de Haro

  • #2
    I drill literally tens of thousands of holes every week using stub length drills reground to 4 facet with no pilot or spotting operation.

    I am just setting one plate up at the moment that has 3,331 holes in it, I have 8 of these to do so that my weeks 10,000 quota used up already

    .
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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    • #3
      Like John said.
      If you can grind/sharpen your drill into a nice 4 facet split-point, you won't need the spot drill. Brass is pretty soft, the drill shouldn't wander.
      Like this:

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      • #4
        I don't have a lot of experience with spotting drills, however screw machine drills are much more robust from what i have used than jobber etc drills, I'm not sure if it's the shorter length, or they are just built that much better. You will also notice screw machine drills are always on the expensive side. I'm sure cobalt would not be needed in this situation, however I always spend the little extra on cobalt screw machine drills, they are outstanding in my opinion.

        On a side/semi off topic note I have been trying to remember to put a drill mill in the order, I have never really heard or read anything about them though.

        Clint

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        • #5
          A 1/2" split point screw machine drill in a tight drill press will drill the hole 1" deep. If the hole has to be located with close tolerance to location and be an exact size a drill is not going to do that job with one pass.

          How close it the tolerance of the location and hole size?
          It's only ink and paper

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          • #6
            Thanks guys. The hole will be done in the CNC lathe at the local community college. I'm writing a program to make a bunch of braces for the Horns I make and I want to keep tool changes to a minimum (I've already got 5 in the program).

            Stuart
            Stuart de Haro

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            • #7
              Since you are going to bore them afterwards, go with the Screw Machine Bits. Buy good quality drills. Work them hard enough that you dont work harden the material and the heat goes in the chips.

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