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Re: tool bit angles for aluminum

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  • Clive Foster
    ... Paul Still got Granddad Norton and Babe Bristol. Are you still rota-biking? Drop me a line off list. Mark That s an effective honing jig but you still have
    Message 1 of 29 , Oct 31, 2004
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      >
      >> Now that you've given up fast bikes and fast girls (or have you?) I'm
      >> sure there's hope for you!...
      >>
      >> OK, I jest!.... :P
      >>
      >> Mark
      >> ---------
      >
      > Clive,
      > I hope you still have a Norton Commander or a GTS. :-)
      > P2
      > (Paul Pennycook).

      Paul
      Still got Granddad Norton and Babe Bristol.
      Are you still rota-biking?
      Drop me a line off list.

      Mark
      That's an effective honing jig but you still have to grind the tools
      fairly frequently 'cos the honing angle is slightly different to the
      grinding one.
      By far the best way if you are honing a ground tool 'cos its far faster
      but if you just hone to re-sharpen the honed face gets longer and
      longer and the job slower and slower. Prolly regrind every 3 or 4
      hones with this system but the tool positioning does not have to be
      super accurate.
      Its pretty much the normal way of doing things.

      My mentors approach was to have a block that presented the tool to the
      wheel so repeatably that full face honing could be used and simply
      flipping the block got the different angles.

      Your turned surface finish is basically a replica of the tool edge
      surface finish so you only really need a super finish where the tool
      contacts metal and where the chip flows across the tool. Hence only a
      small part of the edge actually needs honing.
      With full face honing you have to re-sharpen more often so you need a
      really effective and accurate jig lest it become a complete PIA,
      however you always have a really sharp tool.

      I suspect half the reason for his set -up may have been to avoid
      needing both a grinding wheel and a honing wheel, thinking about it I'm
      pretty sure I caught him rough grinding a tool at work once. Good
      grinders and wheels used to be very expensive and I guess he finalised
      his set-up in the late '50s / early '60s period.

      Clive
    • markzemanek
      ... So let me get this right....I should be honing the top of the tool (side rake) AND the front tip of the tool? Also, how big of a radius on the tool tip are
      Message 2 of 29 , Nov 2, 2004
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        --- In taigtools@yahoogroups.com, Clive Foster <clive_foster@t...>
        wrote:

        >Your turned surface finish is basically a replica of the tool edge
        >surface finish so you only really need a super finish where the tool
        >contacts metal and where the chip flows across the tool. Hence only a
        >small part of the edge actually needs honing.
        ----------

        So let me get this right....I should be honing the top of the tool
        (side rake) AND the front tip of the tool?

        Also, how big of a radius on the tool tip are we talking about?...Is
        1/32" enough?

        Mark
      • Clive Foster
        Mark Theoretically the tip radius should be greater than the feed per rev and the cut depth greater than the tip radius. Seems to be generally accepted that
        Message 3 of 29 , Nov 3, 2004
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          Mark

          Theoretically the tip radius should be greater than the feed per rev
          and the cut depth greater than the tip radius.
          Seems to be generally accepted that taking greater = about twice is
          good enuf for government work.

          However this seems to be biased towards knife tools on hard materials
          and bigger lathes. I tend not to worry about the cutting depth one and
          just wind in 'till it all looks about right!

          I've not got a Taig lathe but my Heavy 10 South-Bend is quite happy at
          0.2" tip radius, well honed, on 50 thou roughing and 10 thou finishing
          cuts on pretty much anything for feeds and speeds worked out using the
          standard formulae.

          The big thing, especially on a sticky material like aluminium, is to
          get the chips flowing off smoothly and continuously whether as a
          succession of short curls or long ribbon. Honing all the faces ensures
          that you are cutting with a smooth continuous edge. A little
          discontinuity in the cutting edge is an open invitation for the
          material to build up on it especially as the bottom of the
          discontinuity cannot be as sharp as the rest of the cutting edge.
          Honing the top also provides a smooth surface for the chip to flow
          across as it comes off the work considerably reducing friction which
          has got to help matters. That chip presses down Hard onto the tool as
          it comes off.

          Within reason the larger the radius the better the finish but the
          greater the forces on the lathe. 1/32" sounds a good starting point for
          a Taig but I wouldn't be adverse to trying something larger with a
          small depth of cut, 5 thou or less and slow feed but relatively high
          speed. With a larger radius its easier to get a smooth continuous
          cutting edge but you will be using the tool more scraping or burnishing
          than truly cutting.

          Bottom line is that the books give a starting point but you have to
          learn to watch the chips to judge how well the cutting is going.
          Biggest problem is that too fast or too slow, too shallow or too deep,
          too small or too large radius all give problems and frequently there is
          more than one wrong combination which will give the same effect. Its a
          great help having "one who knows" to show you the effects of the
          various wrong combinations on your size of lathe. Amateurs tend to be
          too ready to drop down to a tiny cut, tortoise feed and low speed at
          the first hint of trouble. Sometimes you just have to lean on things
          to get a result but the little Taig hasn't the physique to lean very
          hard.

          Clive

          > So let me get this right....I should be honing the top of the tool
          > (side rake) AND the front tip of the tool?
          >
          > Also, how big of a radius on the tool tip are we talking about?...Is
          > 1/32" enough?
          >
          > Mark
          >
          >
          >
          >
          >
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          > Let the chips fly!
          >
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        • markzemanek
          ... Amen to that! Let me reiterate that I have a Craftsman 6 x 18 lathe, and not a Taig, if it makes any difference. In theory I should be able to lean on it
          Message 4 of 29 , Nov 3, 2004
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            --- In taigtools@yahoogroups.com, Clive Foster <clive_foster@t...>
            --- wrote:

            >Bottom line is that the books give a starting point but you have to
            >learn to watch the chips to judge how well the cutting is going.
            >Biggest problem is that too fast or too slow, too shallow or too
            >deep, too small or too large radius all give problems and frequently
            >there is more than one wrong combination which will give the same
            >effect. Its a great help having "one who knows" to show you the
            >effects of the various wrong combinations on your size of lathe.
            >Amateurs tend to be too ready to drop down to a tiny cut, tortoise
            >feed and low speed at the first hint of trouble. Sometimes you just
            >have to lean on things to get a result but the little Taig hasn't
            >the physique to lean very hard.

            Amen to that! Let me reiterate that I have a Craftsman 6" x 18"
            lathe, and not a Taig, if it makes any difference. In theory I should
            be able to lean on it a little more than one would on a Taig.
            According to my Atlas Manual of Lathe Operation, I should be able to
            take a 20 thou depth of cut while facing, though I'm still having
            trouble with taking even a 10 thou depth of cut.

            Specifically, I'm still having difficulty getting the chips to flow
            off the tool bit smoothly, and have been trying to tune in to why
            this is happening. While I can normally visualize mechanically what
            takes place in a given situation, there are so many variables taking
            place here that I can't keep track of them all. As you mention, there
            are combinations of several factors that need to be compiled.
            Currently, I keep having to stop the lathe to remove work hardened
            aluminum from the tool tip. From what you're saying, I think it must
            be because I haven't been honing the top of the tool bit, so I'll be
            trying this next.

            I successfully turned one 3-1/2" diameter piece then began another
            (of the same dimension.) At that time the tool began performing
            poorly, and I honed the face again, but it didn't improve
            performance. I didn't know that I only had to hone the tip of the
            radius and not the whole face, as well as the top of the tool, so
            this is another error that will need correcting.

            Thanks again for your mentoring....I'll be regrinding and honing my
            tool bits this afternoon, then will give it another try.

            Mark
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