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

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  • lazlo
    replied
    Originally posted by oldtiffie
    The title of the thread is:
    How much difference can tooling make on a small, low power lathe?

    Are we still "on topic" - ie for lathes similar to Evan's belt-driven SB - and similarly powered lathes, or have we moved "off" - or "on" - again?
    The point I've been trying to make is that Evan is showing that negative rake tooling can be used on a low-power, Home-shop grade lathe. But he's using an Old School flat-topped SNGA insert. A modern negative rake insert with a positive chipbreaker can greatly reduce the horsepower and rigidity requirements for a HSM'er.

    The ground inserts like Glenn was suggesting have an even sharper edge than the molded (xNMG) inserts, which further reduces the horsepower and rigidity necessary to drive these inserts.
    Last edited by lazlo; 07-10-2009, 11:10 PM.

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  • oldtiffie
    replied
    Where are we??

    The title of the thread is:
    How much difference can tooling make on a small, low power lathe?

    Are we still "on topic" - ie for lathes similar to Evan's belt-driven SB - and similarly powered lathes, or have we moved "off" - or "on" - again?

    Leave a comment:


  • lazlo
    replied
    Originally posted by Evan
    The 4th letter is the chipbreaker designation. CNMP negative rake inserts normally come with a 5° positive chipbreaker. That particular insert has a 10° positive A.K.A "double-positive" chipbreaker:





    You linked to the Valenite CNMP insert. Here is an explanation of negative rake inserts with positive chipbreakers from the Valenite Tech Engineer, from

    http://www.thegallos.com/response.htm
    Valenite

    From: FirstName LastName, on 3/12/98 4:10 PM:
    To: INTERNET[[email protected]]

    Hi, I'm with Valenite Cutting Tools, FirstName LastName from Cincinnati Milacron asked me to respond to your request for information.

    I understand the challenges the home shop faces with regard to using carbide tooling. The advantages of carbide vs. hss are well documented for large shops and hi production and the same can be said for home shops but cost is a big concern for the hobbiest.

    I agree with you in your selection of TPG or ISO positive rake type tooling with respect to rigidity and horsepower limitations however both are single sided inserts which are not the most economical choice. Fortunately a lot of progress has been made in the last few years in the chip groove geometries found on negative inserts (cnmg, tnmg , etc.). These "chipbreakers" can produce positive shear angles in negative rake tooling which reduces tooling pressures and horsepower requirements in a double sided insert. This combination of geometry and economy may be advantageous for the home shop.

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  • lazlo
    replied
    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...

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  • Evan
    replied
    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.

    Leave a comment:


  • Glenn Wegman
    replied
    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

    Leave a comment:


  • lazlo
    replied
    Last edited by lazlo; 07-10-2009, 05:52 PM.

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  • lazlo
    replied
    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:

    Leave a comment:


  • Evan
    replied
    The negative rake angle is generated by the toolholder
    There in NO ANSI spec for tool holder rake.

    Leave a comment:


  • Evan
    replied
    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

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  • lazlo
    replied
    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.

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  • lazlo
    replied
    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.

    Leave a comment:


  • Evan
    replied
    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:

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  • lazlo
    replied
    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.

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  • Evan
    replied
    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:

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