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Boring head / bar lead angle

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  • Boring head / bar lead angle

    Here it is; I have a Criterion .750" boring head with NMTB 30 taper set up in my mill. I am wanting to enlarge a 2.50" hole to a 2.625" hole in a 3" thick peice of colled rolled steel. I am using C6 boring bars. OK here is the problem. I have never used a boring head. When I started, I first touched up the boring bar on my T&C grinder and honed on a stone, at 7 degree rake. I set the tool up in the boring head to be parallel with the advance of the head when adjusted. Does this sound like a proper setting or should it be twisted ahead or behind the lead of the boring head?
    "Just build it and be done"

  • #2
    I would set it for 0 rake myself.

    A 3/4" boring head? you must mean a 3" boring head that takes a 3/4" bar.

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    • #3
      I would echo what Tattoomike said. That's what you should have with it set parallel to the slide. In theory a little positive rake might be nice, but you quickly eliminate the clearance just behind the cutting edge and then it won't cut at all, causing great frustration and uncharitable language.
      .
      "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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      • #4
        Thanks tattoomike68 and TGTool. Yes I did mean a 3" boring head and a 3/4" boring bar. I guess it was past my bedtime when I posted last night. That's kind of how it made sense to me, because rotating the bar to a precise place other than 0 would be hard to set up comparativly speaking. Thanks again. Jay
        "Just build it and be done"

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        • #5
          Remember that the boring bar is cutting on the front edge of the tool and not at all on the sides (unless you screw up like I do sometimes). So you can have the top parallel to the boring head travel and the face of the tool with some rake.

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          • #6
            The plane of the top rake face needs to pass through the axis of rotation for zero rake. It has nothing to do with the advance of the head. What really matters is the relationship of the cutting angles to the workpiece not to the boring head. So forget about the slide and set the angle when viewed against the workpiece not the the head. You can most easily see this when boring relatively small diameter holes. Once you have seen your mistake in practice it becomes obvious.

            Phil

            Originally posted by tiptop
            Here it is; I have a Criterion .750" boring head with NMTB 30 taper set up in my mill. I am wanting to enlarge a 2.50" hole to a 2.625" hole in a 3" thick peice of colled rolled steel. I am using C6 boring bars. OK here is the problem. I have never used a boring head. When I started, I first touched up the boring bar on my T&C grinder and honed on a stone, at 7 degree rake. I set the tool up in the boring head to be parallel with the advance of the head when adjusted. Does this sound like a proper setting or should it be twisted ahead or behind the lead of the boring head?

            Comment

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