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Thread: How to sharpen a zero flute countersink

  1. #1
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    Default How to sharpen a zero flute countersink

    I was given a zero flute countersinking cutter which is blunt. How is it re sharpened?

  2. #2
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    You need an eccentric relief grinder attachment.
    Usually used on a tool-cutter grinder or surface grinder.
    Also use them for putting back relief of taps.
    Hybco made attachments and whole dedicated machines.

    -Doozer
    DZER

  3. #3
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    The kind with an angled hole through it? When you figure it out let me know. I have a bunch of dull ones around.

    Actually I would think grinding the hole bigger would sharpen it. Even a diamond cylinder stone on a rotary tool might work.
    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

  4. #4
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    Yes, that's what I read. People use diamonds or sandpaper cylinders with die grinders to cut the ID of the opening at the cutting end of the countersink.

    IIRC, I tried the sandpaper points a few years back, and they worked acceptably.
    Last edited by MichaelP; 05-21-2019 at 06:02 PM.

  5. #5
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    At first I saw the "zero flute" bit and checked to see if it was April 1....

    The ones I've got with the hole have been sharpened with a fine white grit cylindrical point I have for the Dremel. For the smallest I had to use a smaller grey point. Each time they spruced up nicely.

  6. #6
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    I do them by hand. Start about half way across the hole and use a wiping action on the stone in the direction of the relief. By wiping I mean I rotate the CS while it travels across the stone by 20 to 30 degrees. After five strokes I rotate the CS in my hand about 10 to 15 degrees, again in the direction of the relief. I continue ALL the way around the cone until I am about 1/4 the way across the hole from the opposite direction. I don't want to hit the cutting edge as I am finishing up a rotation. If it needs more I skip forward to the original positing and go around once more from there. I use the same number of strokes and the same amount of force at each position. With the 20 to 30 degree rotation on each stroke and the 10 to 15 degree rotation for each set of strokes, the sets of strokes will overlap and the amount taken off all sides is about equal. This preserves the the countersink angle, the relief angle, and the original spiral/conical shape.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  7. #7
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    The recommended and best way is to use an MA Ford Unicam fixture. But that requires a tool and cutter grinder or a surface grinder.

    Jeez...the Unicam fixture was around 50 bucks when I bought mine, now they're $245!!!

    Grinding the hole does work, it makes the cutting edge more fragile though.

  8. #8
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    Re: Grinding the hole.

    Anything that you do to one of these cutters will change the geometry some. And there is only so far that you can go before it is no longer useful.

    I think that grinding the hole larger will take you toward that point of use it up faster than carefully grinding on the cone. I think doing it my way will allow it to be resharpened more times and the geometry at the cutting edge will change less each time.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  9. #9
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    Here is what I just found: https://www.youtube.com/watch?v=df8vP8pYquU

    This is exactly what you need: resharpening of zero flute countersinks.

  10. #10
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    I guess I'm missing something here, which wouldn't be a surprise to those who know me, but it looks like the original relief was established by offsetting the through hole. If that's the case, it could be easily sharpened by simply grinding the cone symmetrically. But, that seems too simple.
    Jim

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