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Thanks and round over bit?

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  • Thanks and round over bit?

    Hi Folks,
    Thanks for the responce on the mill/drill.
    I would like to get a table feed for it soon.

    I have a question,
    What is the proper way to use/set up a round over bit?
    It is 3/8 radius and HSS and working on tool steel.
    There should not be a lip on any of the egdes?
    Say you are doing a .775" key and rounding both egdes what do you do about the lip or flat spot between the two radiused edges?
    Again thanks guy's and have a Good/Safe holiday.

  • #2
    Check the tool for straight edges from the radius to the diameter and tip. Comparator works well for this. Not all are perfect. If a good one with no straights, I tend to touch the radius at th bottom, move out .002, and touch the edge at the top of the rad, move up .002 I tend to lap or polish in when possbble.

    I am interested in other responses, this is also a bit of a mystery to me.


    • #3

      You can leave the edge (lip) if that is what you are looking for - looks good with wood. 3/8" radius on a 3/4" part is a little large - but, again it depends what you are looking for. Just practice on scrap till you get what you need. I would not mill it in one pass.


      • #4
        The only way I know of is trial and error (hopefully not too much error). As Thrud suggests, I don't do it all in one pass. I get it close, then creep up on it until it looks as though I'll start getting a lip if I go any further.

        But it does seem as though there ought to be a more scientific way to go about it. spope14 describes what is probably the most rational way to get it reasonably correct without trial and error.
        Try to make a living, not a killing. -- Utah Phillips
        Don't believe everything you know. -- Bumper sticker
        Everybody is ignorant, only on different subjects. -- Will Rogers
        There are lots of people who mistake their imagination for their memory. - Josh Billings
        Law of Logical Argument - Anything is possible if you don't know what you are talking about.
        Don't own anything you have to feed or paint. - Hood River Blackie


        • #5
          I do it pretty much snopes's way. Most of the time I'd rather leave the radius incomplete than let an edge dig in at all, unless, as Dave mentions, you want a small step along side the radius. The problem with creeping up on it is that it's so easy, (so very very easy) to overshoot. You must have a target to go for and no farther. Check at both ends, because if the workpiece tilts even a couple of thousandths Murphy's law dictates that you will set up at the low end and dig in at the high end. Make one or two rough passes an one finish pass of .002 to .005, preferably climbing with a table feed so you get uniform tool marks. When I'm setting up tool offsets on a CNC job I'll actually stop the feed, stop the spindle, back up a little bit, turn the spindle by hand to get a cutter flute lined up with the workpiece and eyeball the gaps between the workpiece and the cutter edges. You could do the same on your last rough pass to see if you want to modify your target figures a few thou. If you're not too good at eyeball measurements you could use feeler gages, just depends on how anal retentive you are.