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How much difference can tooling make on a small, low power lathe?

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  • #46
    Wonder what my long deceased mentors would have made of this one as a "Polished" finish would have been met with "Tha rubint' metal off and not cuttin it" an even matt grey being the order of the day.

    Regards Ian.
    You might not like what I say,but that doesn't mean I'm wrong.

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    • #47
      It works the same as a butter knife scraping some butter from a cold lump. Funny thing is that it is really still cutting. It will make tiny fine ribbons of swarf so thin you can barely see them if you have it set to barely touch.
      Free software for calculating bolt circles and similar: Click Here

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      • #48
        Originally posted by lazlo
        They're both negative rake inserts with flat sides. The only difference is that the TNMP insert that Ted uses has a postive rake chipbreaker, which gives you the clearance to tip the negative insert enough to get a positive rake angle. So Evan's SNGA negative insert has the profile (flat sides) of the top insert (sans the chipbreaker groove), and Ted Edward's negative insert has the middle profile, and he tilts the insert down 5° to get a positive rake.

        You could use a more severe chipbreaker like the TNMS insert at the bottom, tip the insert even more (10°) and get even more positive:

        Note that these are all negative rake inserts:

        I've just bought some cheap Iscar TNMP inserts from eBay to try this out. No idea if the grade is suitable for my needs (they were the only TNMP's offered) but for £8 delivered for 10 inserts I get 60 cutting edges to experiment with and the worst it'll be is the worlds cheapest failed experiment. The ad said the chipbreaker was designed for cast iron.

        I'm going to make a couple of turning tools and a boring bar to hold them I guess.
        Peter - novice home machinist, modern motorcycle enthusiast.

        Denford Viceroy 280 Synchro (11 x 24)
        Herbert 0V adapted to R8 by 'Sir John'.
        Monarch 10EE 1942

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        • #49
          Note that these are all negative rake inserts:
          Not according to ANSI nomenclature. For the 4th letter the "G" is zero rake with chipbreaker and the "P" and "S" are positive rake inserts. Strangely enough they are exactly what they look like.

          From the link I posted above:
          Free software for calculating bolt circles and similar: Click Here

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          • #50
            Originally posted by Evan
            Not according to ANSI nomenclature. For the 4th letter the "G" is zero rake with chipbreaker and the "P" and "S" are positive rake inserts.
            The second letter in the ANSI/ISO designations specifies the rake/clearance angle. Negative rake inserts, like the TNMP, TNMG, TNMS inserts I posted, and the SNGA cermet you have, have 0° rake angle. They have square sides, and get the negative rake angle by virtue of the toolholder.

            The 4th letter in the ANSI/ISO designation specifies the hole and the chipbreaker. So a TNMP is a negative rake insert with a 10° positive chipbreaker. A TNMK is a negative rake inserts with a 5° positive chipbreaker, etc.
            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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            • #51
              The second letter specifies the relief angle only, not the rake. Rake refers to the angle the top of the cutting edge makes to tool centerline (normal). That is specified by the 4th character.

              The second letter codes:

              Free software for calculating bolt circles and similar: Click Here

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              • #52
                Originally posted by Peter.
                I've just bought some cheap Iscar TNMP inserts from eBay to try this out. No idea if the grade is suitable for my needs (they were the only TNMP's offered) but for £8 delivered for 10 inserts I get 60 cutting edges to experiment with and the worst it'll be is the worlds cheapest failed experiment.
                I really like the TNMP and CNMP inserts (negative rake insert with a positive chipbreaker) -- they're really the best of both worlds: they have the strong edge of a negative rake insert, with enough back rake from the chipbreaker that you don't need immense power and rigidity.

                Plus, with a negative rake insert you get twice the number of cutting edges: they have square sides, you can just flip them.

                I bought a CNMP boring bar from Hemly Tool (a member here), and it's one of my favorites.
                "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                • #53
                  Originally posted by Evan
                  The second letter specifies the relief angle only, not the rake. Rake refers to the angle the top of the cutting edge makes to tool centerline (normal). That is specified by the 4th character.
                  Yeah, I didn't think you were getting my point earlier in the thread. All negative rake inserts have square sides, which is designated by a 0° clearance/rake -- the "N" in the second letter of the ANSI designation. The negative rake angle is generated by the toolholder.



                  The 4th letter in the ANSI designation specifies the hole and chipbreaker pattern:

                  Last edited by lazlo; 07-10-2009, 05:28 PM.
                  "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                  • #54
                    I really like the TNMP and CNMP inserts (negative rake insert with a positive chipbreaker)
                    They are not negative rake inserts and continuing to say they are will not make it so.

                    Insert designation used by the standards organization. Examples of this attribute are provided below. From ANSI B212.4-1986, the 10 symbol designation is as follows:
                    1) letter identifying insert shape,
                    2) letter identifying cutting edge clearance (relief) angle(s),
                    3) letter identifying tolerance class,
                    4) letter identifying surface type features,
                    5) one or two digit number identifying size of inscribed circle or width and length of insert,
                    6) one or two digit number identifying insert thickness,
                    7) letter or number identifying cutting point configuration,
                    8) number identifying edge length of facet,
                    9) letter identifying feed direction,
                    10) letter identifying edge treatment and surface finish. Example (inch dimensions): S H C N - 6 3 D 8 R T

                    From ISO 1832-1991, the 10 symbol designation is as follows:
                    1) letter identifying insert shape,
                    2) letter identifying normal clearance,
                    3) letter identifying tolerance class,
                    4) letter identifying fixing and/or chip breakers,
                    5) number identifying insert size,
                    6) number identifying insert thickness,
                    7) letter or number identifying insert corner configuration,
                    8) letter identifying cutting edge condition,
                    9) letter identifying cutting direction, and
                    10) manufacturer's symbol, optional. Example (metric dimensions): T P G N 16 03 08 E N - X


                    Insert Rake Angle The manufacturer's specification of the rake angle for the insert. The rake angle is the inclination of the tool face against which chips are severed (i.e., the rake face).

                    The rake face is that surface over which the chips bear as they are being severed. If the inclination of the face makes the cutting edge keener or more acute, the rake condition is defined as positive. If the inclination of the face makes the cutting edge less keen or more blunt, the rake is defined as negative.

                    Also called Top Rake Angle or Axial Rake Angle. The angle of inclination of the rake face toward or away from the end or end cutting edge of the tool, measured in a plane that passes through the side cutting edge and is perpendicular to the base of the to ol body shank. If the angle of incline is away from the end cutting edge, the Back Rake Angle (i.e., axial rake) is positive. If the angle of incline is downward toward the end cutting edge, the Back Rake Angle (i.e., axial rake) is negative.
                    http://www.mel.nist.gov/msidlibrary/...a/resourcc.htm
                    Free software for calculating bolt circles and similar: Click Here

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                    • #55
                      The negative rake angle is generated by the toolholder
                      There in NO ANSI spec for tool holder rake.
                      Free software for calculating bolt circles and similar: Click Here

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                      • #56
                        Originally posted by Evan
                        Originally posted by Lazlo
                        I really like the TNMP and CNMP inserts (negative rake insert with a positive chipbreaker)
                        They are not negative rake inserts and continuing to say they are will not make it so.
                        God, you're hard-headed Evan. Open up a basic machine shop book once in awhile:

                        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                        • #57
                          Last edited by lazlo; 07-10-2009, 05:52 PM.
                          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                          • #58
                            Originally posted by lazlo
                            I really like the TNMP and CNMP inserts (negative rake insert with a positive chipbreaker) -- they're really the best of both worlds: they have the strong edge of a negative rake insert, with enough back rake from the chipbreaker that you don't need immense power and rigidity.
                            .
                            Lazlo,

                            If you like those you will really like the TNGP, CNGP inserts.

                            Give one a try!

                            Glenn

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                            • #59
                              Your last example is a postive rake insert, by definition. It says so in the specifications.



                              God, you're hard-headed Evan.
                              Why yes I am when faced with incorrect information being dispensed as truth.
                              Free software for calculating bolt circles and similar: Click Here

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                              • #60
                                Originally posted by Glenn Wegman
                                If you like those you will really like the TNGP, CNGP inserts.

                                Give one a try!
                                I'd love to try those ground inserts. Like many here, I love the CCGT's (ground positive rake insert) for aluminum, but for some reason, most of the ground negative rake inserts on Ebay are in the 4xx series size, and the biggest holder I have is a 3xx series.

                                I know you can order the CNGP-332 on MSC et al, but those are $6 and up per insert...
                                "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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