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

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  • #76
    I had thought that the terms rake, clearance, etc., had to do with the angle of the various faces relative to the work. So, for example, I can create a cutter with no rake and no clearance by taking a squared off HSS blank and bringing the sides only to a point like an old steam ship's bow (this old beauty comes to mind: http://lighthouseantiques.net/photos/27295.jpg), and by placing it in the proper holder angled down, achieve both negative rake and clearance. If that is so then the concept of rake and clearance in carbide is one of intent of design, perhaps to warrant tool life, given that we can put any cutter at any angle relative to the work to produce desired rack or clearance, and sometimes both. I guess that's a long way of saying I thought the angle of the tool holder mattered in establishing rake, etc., and that the machinist would consider the vendor's guidelines as to what the range of operation is. I think, in fact, that is exactly what you have done with your cermet cutters, no?

    This of course can be a completely misguided newbie misunderstanding

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    • #77
      Ummmmmmmmmm......

      Well.......... I was talking about the original issue, not the semantics and whatever one.......

      Seems that if you use carbide or other hard material inserts, at speeds which are appropriate, with depths of cut which are appropriate for the insert, you should not be surprised to get good results.

      The argument about carbide seems to be that "you can't DO that with your little hobby lathe, so you are doomed to run them with slow speeds and tiny nibbling cuts for which they are not suited."

      However, once you DO run the inserts at speeds etc that they like, the issue of"you can't do that" is negated, since you DID do that.

      At that point the machine is by definition sufficiently powerful, rigid, or whatever to do the work. Therefore arguments to the contrary are obviously futile and somewhat stupid.

      Since you did use the inserts more or less within their "good zone", it is no surprise that they worked.

      I am somewhat surprised that an old and presumably flatbelt S-B would run that speed with a DOC of 0.020, but if it does, it does. Usually the flatbelt won't transmit more than a fraction of the motor power, generally the belt speed is too low and the belt slips long before the motor bogs down.
      1601

      Keep eye on ball.
      Hashim Khan

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      • #78
        Serpentine belt with belt dressing. It will stall the motor.
        Free software for calculating bolt circles and similar: Click Here

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        • #79
          I guess that's a long way of saying I thought the angle of the tool holder mattered in establishing rake, etc., and that the machinist would consider the vendor's guidelines as to what the range of operation is.
          Then why does the ANSI nomenclature system contain information to identify the rake angle of inserts? Conversely the ANSI specs for tool holders do not contain rake information. How you choose to hold it is up to you but when I am buying inserts frequently the only information I have to go on is the ANSI spec in the type number.
          Free software for calculating bolt circles and similar: Click Here

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          • #80
            Originally posted by dp
            I had thought that the terms rake, clearance, etc., had to do with the angle of the various faces relative to the work.

            by placing it in the proper holder angled down, achieve both negative rake and clearance.
            That's exactly right Dennis. Negative rake inserts don't have negative rake -- they have square sides. They're designed so the toolholder tips the pocket down 5 or 10° to give you the negative rake.

            Positive rake inserts actually have 3 - 30° positive rake, so if you're making your own toolholder, you have much less latitude in changing the rake angles than a negative rake insert.

            If that is so then the concept of rake and clearance in carbide is one of intent of design,

            I thought the angle of the tool holder mattered in establishing rake, etc., and that the machinist would consider the vendor's guidelines as to what the range of operation is. I think, in fact, that is exactly what you have done with your cermet cutters, no?
            Exactly. A flat-topped negative rake insert like the SNGA Evan is using is a worst-case scenario for horsepower and rigidity. But take that same negative rake insert with a positive rake chipbreaker, and you end up with a "Negative/Positive" insert that requires much less power and rigidity:

            Metal cutting theory and practice, David A. Stephenson

            Last edited by lazlo; 07-12-2009, 09:21 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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            • #81
              Originally posted by Evan
              Then why does the ANSI nomenclature system contain information to identify the rake angle of inserts? Conversely the ANSI specs for tool holders do not contain rake information.
              The ANSI/ISO designations do specify the toolholder rake angles. The TNMG negative rake insert, for example, is intended to be used with the "MTGNR-XXX" toolholder:
              "M" is clamp and pin, "T" for triangular insert, "G" for offset pocket with no additional relief, "N" for negative rake insert, "R" for right-handed tool:

              Last edited by lazlo; 07-12-2009, 09:34 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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              • #82
                Originally posted by BadDog
                But a small point, and I'm sure you are aware, but others may not be. That 3rd position is actually "tollerance". "M" is not "Molded", and "G" is not "Ground", though it works out that way often enough that it's a decent mnemonic.

                Reference Chart
                Yeah, I know that's confusing. The tolerance actually indicates whether the insert is ground or molded. With a molded insert, the carbide is sintered in the actual insert mold, so the "M" tolerance is 2 - 5 thou.

                A ground insert is sintered oversize, and ground to final dimension, so the "G" tolerance is 1 thou. In fact, this book is a little dated -- Sandvik spec's a tolerance of 5 tenths for their ground inserts. Also, the text doesn't mention this, but as Glenn was implying, the ground inserts are sharper, and cut nicer, but they're more expensive:

                Last edited by lazlo; 07-12-2009, 09:51 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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                • #83
                  If you can turn the insert up side down and use the bottom side it is a negative rake insert. Period . Lay a square on top and if the edges are 90؛ it is considered a negative rack insert.Period again.
                  Last edited by lane; 07-12-2009, 09:54 PM.
                  Every Mans Work Is A Portrait of Him Self
                  http://sites.google.com/site/machinistsite/TWO-BUDDIES
                  http://s178.photobucket.com/user/lan...?sort=3&page=1

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                  • #84
                    Originally posted by lane
                    If you can turn the insert up side down and use the bottom side it is a negative rake insert. Period .
                    Agreed Negative rake inserts have square sides, period.

                    Originally posted by lazlo
                    Note that these are all negative rake inserts:

                    That's a huge advantage for the HSM'er -- because negative rake inserts have square sides, they can be flipped over, and you get twice the number of cutting edges.

                    You can't do that with positive rake inserts, because they have the positive rake angle molded or ground into the insert itself.
                    Last edited by lazlo; 07-12-2009, 10:15 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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                    • #85
                      The figure you posted is refering to negative/positive tooling as an insert with a negative side rake. Side rake is altogether different than back rake as it describes the plane of the top of the tool and it's relationship to the long axis of the lathe. If the tool is tilted down on the side toward which it moves as it cuts it has negative side rake regardless of the top rake angle or the cutting edge angle.

                      I wrote: "Conversely the ANSI specs for tool holders do not contain rake information. " I said nothing about clearance information which is a different matter. The clearance of an insert does NOT reflect the cutting top rake angle it provides.

                      N does not stand for negative, only insert relief angle provided. The tool holder clearance angle provides no information about tool top rake angle since that is dependent on the tool top surface features. Further, that clearance angle only applies to inserts with no clearance.

                      It would make no sense to specify both a clearance angle for the insert, which is the case, and another separate clearance angle for the tool holder. One or the other provides the required clearance, not both. In the case of inserts with no clearance then the tool holder provides the clearance. In the case of inserts with clearance then the insert provides the clearance and there is no specification for tool holder angle.
                      Free software for calculating bolt circles and similar: Click Here

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                      • #86
                        Originally posted by lazlo
                        Yeah, I know that's confusing. The tolerance actually indicates whether the insert is ground or molded. With a molded insert, the carbide is sintered in the actual insert mold, so the "M" tolerance is 2 - 5 thou.
                        I agree that it works out that way, and I've read it in more than one "reference", but I just don't buy it.

                        If M is Molded and G is Ground, what are A, C, E, F, ... and all the rest? Just arbitrary aberrations with no meaning? I can't prove one way or the other, but I expect it is just a convenient mnemonic that became adopted fact by virtue of common application. It shows up in conversational texts, but never on official standard/spec sheets as far as I've seen. Or maybe it's the reverese. Those were common tollerances for the process, so adopted into the standards, and then expanded with others for better definition. But even if so, it still eliminates the original association as far as I'm concerned. For instance, I would expect an "F" to also be Ground, but that does not imiply it's really a G, and so on...

                        This is much the same as P in the second position. Folks will say that it means "Positive", but it's really just clearance angle, and there are "positive" inserts that use other designations (and that's as close to that discussion as I care to get! )

                        So if a molded insert process (or selection standard) produced inserts that met the spec for "G", I would expect them to label it "G". That's my story and I'm sticking to it... at least for the moment...
                        Last edited by BadDog; 07-12-2009, 10:19 PM.
                        Russ
                        Master Floor Sweeper

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                        • #87
                          Originally posted by BadDog
                          If M is Molded and G is Ground, what are A, C, E, F, ... and all the rest? Just arbitrary aberrations with no meaning?

                          And if a molded insert process (or selection standard) produced inserts that met the spec for "G", I would expect them to label it "G". That's my story and I'm sticking to it... at least for the moment...
                          Hey, I didn't make this stuff up, I'm just reading the spec. Believe me, I've read far worse ANSI/ISO specs. In fact, based on your profession, I bet you have too Russ

                          If you look at the tolerances, "M" and "U" have the worst tolerances -- 2 - 5 thou. All the other letters are "G" (ground ) tolerance or better. If you look at the "A" tolerance -- that's 2 tenths. So I bet there's a Godlike Swiss TNAG-xxx insert out there somewhere that's ground to 2 tenths...
                          "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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                          • #88
                            Originally posted by BadDog
                            This is much the same as P in the second position. Folks will say that it means "Positive", but it's really just clearance angle, and there are "positive" inserts that use other designations (and that's as close to that discussion as I care to get! )
                            It's actually not a coincidence that negative rake inserts have an "N" designation. "P" was chosen for "Positive Rake" because it's the 11° positive insert, and for the first 20 years that carbide inserts were available, most of them were either N or P inserts (TPG's, etc).

                            So if you look at the relief angle table, there's "N", and "P", and the remaining slots are A - G. It's pretty obvious that they reserved N and P for the common Negative and Positive designations:

                            "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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                            • #89
                              Originally posted by lazlo
                              Hey, I didn't make this stuff up, I'm just reading the spec. Believe me, I've read far worse ANSI/ISO specs. In fact, based on your profession, I bet you have too Russ
                              LOL! That's the truth!

                              Ageed in general.

                              As I've said, I've read some of the same references stating things just as you describe. But I maintain it's useless except as a mnemonic because there are ground inserts that are not G, and molded that are not M. Someone probably said something to the effect if "In the beginning there were molded and ground inserts, and their tolerances were typically of this value, so we'll use 'M' and 'G' to denote that value for coherency (folks that write specs like words like that ), and add in all the rest to fill out the field..." But regardless of the origins, I don't think you can really say "G is ground and M is molded". <shrug> Doesn't matter, too many "references" out there use this descriptions, and my pedantics aside, really doesn't matter to me either way. At least now folks who didn't know otherwise may register that there are other options beyond M and G, and so not be too surprised if/when they see them. Likewise for "P", though N is pretty clear cut and final...

                              Man, I wish it would cool down a bit. I got things I want to do in the shop. Suns been down a while, and it's just now dropped to 109...
                              Last edited by BadDog; 07-12-2009, 10:57 PM.
                              Russ
                              Master Floor Sweeper

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                              • #90
                                Originally posted by BadDog
                                But I maintain it's useless except as a mnemonic because there are ground inserts that are not G, and molded that are not M.
                                I agree the forward case is correct -- G's are not the only ground inserts, but every "M" insert I've ever bought was molded, and not as sharp as a ground insert.

                                I've also found that coated inserts are not as sharp as un-coated -- they grind first then PVD/CVD coat, and the coating rounds off the cutting edges. Which is, I think, why the "Upsharp" or "Honed" inserts are almost always uncoated.

                                Man, I wish it would cool down a bit. I got things I want to do in the shop. Suns been down a while, and it's just now dropped to 109...
                                We feel your pain down in Austin. For reasons I don't entirely understand, there's been a high-pressure zone that's been sitting on Central Texas, and we've had 105 - 107° for the last 5 weeks straight. That's 15° over our normal June/July temperatures, which is scary, because the temperature here peaks at the end of August...
                                "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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