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  • Combined drill/counterbore?

    A project I have on the table needs a 3/8" hole drilled, and then, because the surface is slightly curved, a shallow counterbore so the bolt tightens properly. The part is aluminum, so the counterbore needs to be large enough to accept a common washer.

    I've been doing these with a drill-point endmill for the 3/8" hole (even a stub-length drill wanted to wander slightly due to the curvature) and following that up with a standard 11/16" endmill for the counterbore, which is perfect for the thin SS washers the client uses.

    However, there's four to six holes per part, and the next order may be 40 parts. If I could do the drill and counterbore in the same step, that'd save at least third on time per part.

    McMaster has a drill-counterbore that's nearly perfect, except it's just meant to counterbore to clear the head of a socket-head screw. In order to get the counterbore big enough for the washer, the bolt hole would be way oversized. I've also found other drill/countersinks, but again, they're generally just for the screw and head, no washer.

    I was thinking about using a spindexer in my surface grinder to cut down the nose of an 11/16" endmill, but I wouldn't be able to grind clearance or a proper drill tip, etc.

    Anyone know of a source for a commercial drill/counterbore in that size, or barring that, a company that could grind me one, for a reasonable price, and in a fairly short timeframe?

    Doc.
    Doc's Machine. (Probably not what you expect.)

  • #2
    Doc,

    If you can put a 11/16 drill bit in your spindexer and spin it down to the thru hole size, then grind clearance on the counterbore part it should work fine. Especially in aluminum.

    Big B
    OPEN EYES, OPEN EARS, OPEN MIND

    THINK HARDER

    BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

    MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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    • #3
      That's not a counterbore. It's call a spot face. Any tool grinder could make what you are looking for.

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      • #4
        Yeh, seems to be due to standard sizing (re: SHCS counter bores),

        http://www.newmantools.com/cutters/invspotfacers.htm was the first I found with spot facers but problem there seems to be the smallest with a 3/8" hole is 3/4" diameter...so now a bit too large...that may be workable rather than too small though.

        Just throwing this out there, what would happen if you used a counterbore that normally has a pilot and swapped in a drill with a flat ground on the shank for the set screw? From what I can see with that though, the pilot hole diameter is quite small, 3/16" in the range of size you need for the counter bore (sort of the same issue as you found previously). But turning down the shank of a drill maybe relatively easy.

        Aside, funny how you see/hear/read something and it pops up again right away? Glacern site shows spot facing with a center cutting end mill so as to locate a drilled hole precisely on a round or shaft...

        Edit: http://www.cutting-tool-supply.com/M...tters/Home.htm
        guessing this type of cutter will be too large but who knows, they may know of...
        Last edited by RussZHC; 11-25-2012, 11:02 PM. Reason: another possible solution

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        • #5
          If you can spin an end mill down to size , you can put some relief on the relieved part by putting the cutting flute up and then turn your spindex 5 or 10 thousands and use the side of the wheel to grind your relief then just sharpen the end like a drill bit.

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          • #6
            an endmill works if cut from the side, but not so well if plunged - it won't make a flat bottom as endmill bottoms aren't flat, there's relief from the edges toward the centre. Sometimes its good enough, but be aware if a flat bottom really matters. Counter bores in standard sizes won't be a big enough diameter

            I agree spotting tool is what you need; it's simple work to make one. Here's a simple version that works well in small sizes. lots of forms would work, this is just what i made up at the time. drill rod machined, hardened and stoned. This particular one works in either direction. I made it for spot facing the exit side of a casting in a restricted location - its put on after the shaft is through the hole then raised to do its work.





            Last edited by Mcgyver; 11-25-2012, 11:13 PM.
            in Toronto Ontario - where are you?

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            • #7
              McMaster Carr has adjustable depth counterbores, scroll down to the bottom of page;

              http://www.mcmaster.com/#catalog/118/2470/=kbqbuo

              Granted they are carbon steel and not to size, but a clever guy could gin up something similar out of drill rod in an hour or so.
              Jim H.

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              • #8
                http://www.panamericantool.com/reverse-spotfacers.html

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                • #9
                  I don't need to spotface the underside, guys.

                  I need to drill and counterbore/spotface in one motion. The ground-down drill or endmill sounds like my best bet for the moment, but I was hoping somebody made a commercial unit.

                  Doc.
                  Doc's Machine. (Probably not what you expect.)

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                  • #10
                    What you are looking for is a step drill. I've ground many over the years as I've saved money by not buying commercial versions, just take a drill and grind the end to the through hole dimension and sharpen as a usual drill from the end and the spotter lips.
                    Amount of experience is in direct proportion to the value of broken equipment.

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                    • #11
                      Put a spot facer onto a normal drill. Drill untill through, then proceed to feed untill spot faced.
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                      • #12
                        Originally posted by Doc Nickel View Post
                        I don't need to spotface the underside, guys.
                        .
                        understood, in the case of my post I was simply explaining why it is oriented on the shaft as it is in the photo. For regular spot facing, unscrew and reverse.
                        in Toronto Ontario - where are you?

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                        • #13
                          Originally posted by tdmidget View Post
                          That's not a counterbore. It's call a spot face. Any tool grinder could make what you are looking for.
                          TD,

                          Not sure if you were addressing the OP or me. The difference between a spot face and a c'bore is how deep you cut, unless there is something I have been missing for the last 35 years.

                          Below is a picture of a combo drill and c'bore/spot face that I got with a bunch of other stuff I bought. I have also made many of these on a Cincinnati Monoset when I was still working.

                          Brian
                          OPEN EYES, OPEN EARS, OPEN MIND

                          THINK HARDER

                          BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

                          MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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                          • #14
                            Googel Step Drills Unlimited
                            in Downey Ca

                            jimsehr

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                            • #15
                              There are counterbores with removable pilots. Choose a 11/16" counterbore and make a pilot to fit your 3/8" hole.

                              P.S. Check product CBSS-11/16 here: http://www.victornet.com/subdepartme...ilot/2127.html

                              They also sell pilots: http://www.victornet.com/subdepartme...ores/2128.html. You'll need PI-3/16-3/8
                              Last edited by MichaelP; 11-26-2012, 12:16 PM.
                              Mike
                              WI/IL border, USA

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