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  1. #1
    Join Date
    Nov 2019
    Location
    Brisbane
    Age
    69
    Posts
    452

    Default Big drill grinder error.

    SAM_0604.jpgSAM_0603.jpgThis old goat made a mistake.
    The first shot shows where the grinder finished up. Second shot is where it was first.
    While reading thru a cutting tool handbook I realised that as built, the grinding wheel was working parallel to the cutting edge. The edge being ground was vertical and the grain descending on the wheel. This causes the striations to be parallel to the cutting edge and gives stress raisers just behind the edge. You guessed it the drill failed in use. No pic due to temper tantrum. A section 1.5mm X 10mm long peeled off. I would guess 15 thou deep.
    With the drill holder re-positioned and now at the bottom of the wheel the striations are at 90 degrees to the edge. I hope it's fixed.
    BC

  2. #2
    Join Date
    Jun 2007
    Location
    sydney ( st marys )
    Age
    64
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    4,887

    Default

    Never had the problem, but then I sharpen offhand.

  3. #3
    Join Date
    Oct 2010
    Location
    melbourne, laverton
    Posts
    1,910

    Default

    um ok . so what does all that mean??
    Did you relocate to the bottem left hand corner of the wheel?

  4. #4
    Join Date
    Nov 2019
    Location
    Brisbane
    Age
    69
    Posts
    452

    Default Big drill grinder

    Hello Azzrock.
    This attachment holds the drill with the cutting edge vertical and grinds the lower edge. With the drill at grinding wheel centre height and to the left of centre the abrasive grain is moving vertically down and parallel to the edge being ground. After repositioning the grinder and attachment mounting bracket the drill edge is below wheel centre point and the grain is travelling horizontally, perpendicular to the edge being ground. Now the better way to grind a tool.
    Regards
    BC

  5. #5
    Join Date
    Oct 2010
    Location
    melbourne, laverton
    Posts
    1,910

    Default

    hi bc. very interesting sounds pretty technical. befor you moved it . how did you know it was wrong ? was a ground drill looking ordinary.

    its not one of the safety rules that i believe or worry about. I think its a bullship thing that people who dont know about grinds say.You know the side of the wheel busyness
    nice job aaron
    .

  6. #6
    Join Date
    Nov 2019
    Location
    Brisbane
    Age
    69
    Posts
    452

    Default Big drill grinder.

    Hello Azzrock.
    After grinding a large drill the test hole was OK but on later holes the edge chipped out a large chunk. It was parallel to the cutting edge. I came across some info on grinding on to the edge and at 90 deg to it. Made sense and it is easy to hone the edge for a better finish.
    When grinding wheels are made they can be balanced by grit blasting the side of the wheel. It looks like a reverse pimple. If you dress the side of the wheel or grind on it you can destroy the balance. Recessed one side wheels are made to be used on the side. Also toolroom wheels over 180mm may have a black stripe on the side. This indicates the heavy portion and should be at the top when the flange nut is tightened.
    Regards
    BC

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