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

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  • Evan
    replied
    Serpentine belt with belt dressing. It will stall the motor.

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  • J Tiers
    replied
    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.

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  • dp
    replied
    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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  • Evan
    replied
    The issue is one about insert nomenclature. It seems that the ANSI nomenclature for insert designation is meaningless. It is being argued that the rake of the cutting edge relative to the work does not determine the insert type as per ANSI nomenclature. In actual fact it does although apparently you may need to buy what is being called a negative insert in order to get a positive one. Proper interpretation of the ANSI labeling system does reveal the type of insert which is of course the objective of a standard.

    The argument posed by Robert results in the rather awkward circumstance of specifiying a negative rake insert to obtain one with a positive rake cutting edge. He has also made some statements that are flat out incorrect, such as that the second letter of the insert identification system indicates the rake angle of the cutter when in fact it only specifies the clearance angle below the cutting edge.

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  • J Tiers
    replied
    Originally posted by Evan
    It can make a great deal of difference. Here is an example.

    It is frequently said that negative rake carbide inserts will produce the best finish. In the same breath it is also said that they require a lot more power and rigidity to use. Both statements are more true than false but not entirely accurate. Negative rake is not the cure-all for finish problems and negative rake cutters do not necessarily require a large, rigid and powerful machine.

    I was turning some schedule 40 welded seam pipe of dubious metallic content which was imported from India, that bastion of quality control and unmatched consistency of product.

    Recently I traded an item to Rockrat in exchange for some old stock cermet (CERamic-METallic) coated carbide inserts. They are as plain as they come, simple radiused squares with no chip breaker, no rake and symmetrical top and bottom.

    I applied this to the job running the lathe at 800 rpm and taking light cuts of no more than .020" and less for the finish pass. The insert cut a near mirror finish with none of the usual tearing, skipping and other usual grief seen when turning mild steel. No lubricant or coolant was used.

    As can be seen, even if you have a light import machine there is much you can do to improve the quality of your work by simply spending the money to buy quality tooling. These inserts have 8 usuable corners and the one I used turned at least three passes of nearly a foot by 1.5" diameter. If used for only the finishing pass on 1018 steel that equates to turning at the very least a total of 24 feet of pipe with a realistic expectation of much longer life than that.
    Not sure what the problem is here......

    1) Evan is running "carbide type" speeds, over 300 FPM with material which nominally would be cut at 100 with HSS. (he states 1.5" OD) usual quote is 2x to 3x the HSS speed for carbide, presumably similar for cermets, if not higher.

    2) the cuts of 0.020 are well within the range normally suggested for carbides, which is generally more than 0.005 DOC. I hae taken off 0.001 type cuts with TNMG inserts, but it isn't normally a swift idea.

    The major issue with the use of this type technique is having the power to turn the part against the tool. presumably the 0.020 and lower is OK at those speed, power-wise.

    the secondary issue is whether the machine can take the pressures, but unless your machine is particularly obnoxious, it should be fine with those light cuts.

    REAL carbide cuts are similar to taking off 0.5" DOC at high FPM... that takes power and rigidity.

    The machine in the pics looks like Evan's SouthBend, although I suppose it could be something else. Does not look like a 9 x 20, which is the poster child limber and bouncy import machine.

    I'd never argue carbide is useless on a lightweight SB or whatever. Sometimes you need to use it.

    As to whether you can count on that sort of mirror finish, that's another issue. The sweet spot can be hard to find.

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  • Peter.
    replied
    That's brilliant Glenn - thanks a lot.

    Got me straight here and since I have IC20 K10 it tells me just about everything I need. Nice to see they will be good for stainless as I do a fair bit of machining of that for my bike.

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  • Glenn Wegman
    replied
    Excellent point Peter!!

    As far as your question about a grade chart:

    Each manufacturer has their own grade designation for inserts so you would need to go to a specific manufacturer to research what grade they recomment for your purpose.

    Another method, if you plan on browsing eBay for inserts, is to look it up according to it's listed grade. Find an interresting looking insert and then go here. http://www.carbidedepot.com/. As long as the manufacturer's Icon is shown on this page, just click on the icon and that will take you to a support page for that manufacturer. Then click on the link next to "Online application support" and that page will have lots of links to different sorts of info. I use the "Grade look up" link and type in the grade listed on the insert on eBay and it will tell you what it's primary use is.

    Sounds complicated, but it isn't bad once you do it a few times.

    Glenn

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  • Peter.
    replied
    The fact is though that Lazlo's use of terminology managed to convey his meaning perfectly to at least my novice's mind. Since many HSM'ers are novices like myself this is the kind of post we find easiest to assimilate, not arguments on technical exactness.

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  • Glenn Wegman
    replied
    Originally posted by lazlo

    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.
    And I will further mention that the CNMG (CNGP) or TNMG (TNGP) style are amoung the most common and inexpensive as far as price per insert. The best part is that since they are 0° relief and are used in Negative Rake tooling, you are able to flip them over and use both sides. This gives you a possible six cutting edges on a TNMG style, and four on a CNMG style if you have the more comon style holder, and four more for a total of eight edges if you incorporate a second style holder to utilize the obtuse corners as I do with this combination of tool holders.



    Using positive rake tooling that needs the relief ground on the insert only utilizes the top side of the insert where negative rake tooling with 0° relief on the inserts allows for use of both sides which is much more economical.

    I have no intention of trying to "convert" anyone with a smaller lathe or HSS to Indexable tooling, but this may be of interest to those who want to try carbide or other indexable tooling etc.

    Glenn

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  • Evan
    replied
    What we are left with according to Robert's interpretation is that the ANSI code does NOT specifiy whether the insert is positive or negative. The second letter only refers to the clearance angle and not the top rake. The only information we can use to determine the rake angle of the cutting edge is the 4th letter which strangely enough provides us with the positive vs negative rake angle information of the cutting edge. The 4th letter specifies not just the chipbreaker shape but the tool GEOMETRY according to it's surface features.

    That is why the ANSI standard does not refer to the fourth letter as indicating chipbreaker style but instead surface features. Surface features obviously includes the cutting edge and a negative rake cutting edge is one that is presented to the work with plane of the cutting edge inclined toward the work.

    How the tool holder is positioned means nothing without the information about the included angle of the cutting edge to the relief angle. That is why there is no ANSI standard for tool holder angle. Clearance on a zero relief angle tool can be easily obtained by cutting slightly below the centreline of the work. Cutting at some position other than at centreline if frequently done when boring to provide adequate clearance for the bar.

    Calling an insert a negative insert when the cutting action is via an edge with a positive rake angle to the work in actual use is at the least misleading and inconsistent with the ANSI identification code. If we are to accept that interpretation then we no longer have the ability to identify the type of insert geometry via the ANSI code.

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  • BadDog
    replied
    Originally posted by lazlo
    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.
    I'm not even getting into the other part. 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

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  • Peter.
    replied
    Arguing semantics in the middle of a good thread

    It's a matter of how different people/companies use the terminology - what does a small difference matter so long as the understanding is conveyed.

    Reminds me of my school metalwork teacher who would go nuts if he heard the term 'drill bit'. "This is not a drill bit - it's a DRILL. You put it in a DRILLING MACHINE - there's no such thing as a DRILL BIT!". When someone pointed out the lists of 'drill bits' in his catalogue he went purple and had to go sit in his office.

    Whilst we are on the subject of carbide inserts - is there a standard terminology for 'grades' of inserts that make it easy to determine which grade is best suited to the HSM'er. I had no choice but to buy IC20 K10 grade as it was the only one offered but in the case of many grades being available I'd like to be able to refer to a chart or something.
    Last edited by Peter.; 07-11-2009, 04:11 AM.

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  • toastydeath
    replied
    Lazlo is nailing it.

    If I had read this thread at work today, I'd have taken pictures to show what he's talking about for those still confused.

    Toolholders usually angle the insert downward by 3, 5, or 7 degrees. That, by definition, adds 3-7 degrees of clearance on a neutral insert, and subtracts 3-7 degrees of rake off your insert.

    So say I pick up a toolholder with 3 degrees of rake on it. And say I pick up an insert with 13 degrees of rake. That means my zero-clearance insert now has 3 degrees of clearance, and 10 degrees of rake in that toolholder.

    If I stuck it in the 7 degree toolholder, I'd have 7 degrees of clearance and 6 degrees of rake.

    For those who don't believe Lazlo, just go look in any tool supplier's catalog - Sandvik, Kennametall, Iscar, whoever. The toolholders are all sold by pocket inclination in addition to lead angle, insert type, size, etc.

    For our HLV clone, I use very positive (20-35 degrees of positive rake) stainless steel finishing inserts from Sandvik that have a long (~.4") cutting edge and are capable of deep cuts. They work brilliantly on just about everything.

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  • torker
    replied
    The VERY best finish I've ever obtained was with a square chipbreaker insert that I made a toolholder for...for my ol' SB9 @400rpm (maxed out)
    Turning annealed 4140...the finish was flawless.
    Russ

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  • oldtiffie
    replied
    Good stuff - many thanks

    Thanks Lazlo.

    That's cleared it up nicely.

    The main reason I asked is that many here have "low power(ed)" lathes and this discussion may encourage some to move out of the "HSS comfort zone" and make more or better use of their lathe without flogging or hammering them.

    The same principles apply to milling machines - perhaps even milling in the lathe - as some do - hopefully with collets - but "chucking" it can work.

    Again, many thanks - especially for the very informative diagrams and illustrations of the types and uses of those "tips" and "inserts".

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