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

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  • loose nut
    replied
    Originally posted by Boucher
    Post # 112 Loose Nut said "I use TMNG inserts with good results " Did you mean TNMG? I am having a hard time keeping this straight.
    Sorry, my bad, typo.

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  • lazlo
    replied
    Originally posted by Peter.
    Yup that's a negative negative negative insert
    Well said!

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  • Peter.
    replied
    Yup that's a negative negative negative insert

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  • dp
    replied
    Since I'm now quite puzzled over all of this, is there any dispute that the above tnmp insert with 10؛ positive rake shown is now negative 5؛ rake in the image below? The difference is the tool holder has rotated the insert 15؛ and increased the clearance angle by 15؛.

    Last edited by dp; 07-19-2009, 03:23 PM.

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  • lazlo
    replied
    Originally posted by BobWarfield
    Just as an example, not long ago the CCGT inserts were the ticket for smaller lathes. Peeps thought the "G" meant "Sharp", but it was only the tolerance. It wasn't long before manufacturers were selling "G"'s that weren't sharp because there was demand to pay the higher price. Then I started seeing CCMT's that were Sharp.
    I think the confusion here stems from the up-sharp aluminum inserts: the up-sharp and/or honed inserts use proprietary (i.e., non-ISO) suffixes: -F, -U, -AS, -HP, -1L. Upsharp inserts are ground inserts that have gone through a further edge honing process, so upsharp inserts are only available on ground inserts (i.e., not molded CCMT's).

    The upsharp high-positive inserts have very fragile edges, and are described by the manufacturer as being relegated to fine finishing cuts on aluminum. They were never made, or intended, for hobbyists, so it would be hard to fathom the insert vendors changing designations for a small handful of people

    Originally posted by lazlo
    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:

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  • Evan
    replied
    Can you post an example that is shown in the catalog of a negative/positive tool in accordance with your definition?

    According to your definition, it would have negative inclination with positive side rake.
    No, it would have negative side rake and positive top rake at the cutting edge. It's the orientation of the cutting edge relative to the work that determines top rake actual value (aka back rake), not inclination. The amount of inclination (clearance angle) is specified by the second letter in the ANSI code. Of course the inclination plays a part in the total value of top rake but it isn't specified by the ANSI code in conjunction with a value for the insert that allows one to calculate the top rake. Inserts are only identified as to whether they are negative, neutral or positive at the cutting edge with the inclination included. That's the 4th letter of the code.


    If you use a more modern negative rake insert with a positive chipbreaker, you wouldn't have to baby it:
    I didn't try heavier cuts because I didn't want to remove much material. I have since used heavier cuts and it does alright. It doesn't seem to require noticably more power than the other cutters I use. I run carbide most of the time and I sharpen it to slightly positive for most things. I make most of my own tooling including carbide tools and even carbide milling cutters. I will show an example of a carbide mill cutter soon.

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  • BobWarfield
    replied
    The ANSI standard differs with a lot of what the catalog charts have to say:

    http://www.ccpa.org/pdf/B212_4.pdf

    The catalogs and the posters here attribute a lot more to those 4 letters in an insert designation than I can read into that spec which seems a lot more related to making sure inserts are interchangeable with their holders than anything else.

    For all the pages here, there are really very few points being made that matter for making chips:

    1. Positive rake requires less cutting force and is generally better for lighter machines. In fact, positive rakes are taking over from negative even for heavier machines in many cases because the geometry cuts better. You can see that reading through the PM board to see what those guys use/recommend. Negative rake is principally useful for durability, but as the positives get better at interrupted and other "difficult" conditions, why bother with negative?

    2. The meaning of the various letters in an insert designation is pretty prosaic. Some things we can determine from it but most we can't. We don't know the rake unless we factor in the toolholder and the top surface of the insert. Those two are actually not called out very well by ANSI. Therefore, we have to understand our toolholders and the meaning of positive rake and visualize what will happen with a particular insert. Those "sharp" inserts are clearly very much going to have positive rake. Many other inserts it isn't so clear.

    3. Since you can't really tell from just the 4 ANSI letters what's going on, you'd better have one or more of the following in hand before buying the insert (unless you just want to experiment):

    - Full ID on the insert so you can go consult the manufacturer's catalogs. This is often hard on eBay.

    - A big picture of the insert and enough practical knowledge (more than enough in this thread) to guess how it will cut.

    - A solid recommendation for the insert from someone doing similar work on a similar machine.

    - Help from a rep picking out your inserts. Clearly YMMV depending on how good the rep is. This is why peeps like the "Exkenna" guy over on PM so much, or Frank Mari. Their advice has prooved out.

    Everything else is a crapshoot and can be extremely frustrating.

    Just as an example, not long ago the CCGT inserts were the ticket for smaller lathes. Peeps thought the "G" meant "Sharp", but it was only the tolerance. It wasn't long before manufacturers were selling "G"'s that weren't sharp because there was demand to pay the higher price. Then I started seeing CCMT's that were Sharp. The whole ANSI business ceased being a useful determiner of anything other than whether the insert would fit my toolholders. Hence the 4 criteria above.

    4. The idea of a lathe "too lightweight" for carbide is an interesting one. A small Southbend will clearly handle carbide. My Lathemaster 9x30 does too. The ubiquitous 9x20 is noticeably less rigid than these, but with the common mods, seems like it would work. What then is "too lightweight"? Unimats? 7x14's?

    For the hobbyist, carbide is a matter of personal taste more than anything. Do you want to spend your time trying to understand the minutiae of insert selection (feels like stamp collecting sometimes), or grinding HSS tools? Either takes away from making chips, but I like my carbides though I also do some HSS.

    Last point:

    Be careful if you have an indexable tooling fetish as I do not to accumulate tools that use too many different insert types, or inserts of exotic design. It's just too hard to keep up with it all. Hence all my mill tooling uses APKT (or equivalent) and all my lathe tooling except the boring bars and parting tool uses CCMT.

    Apparently cheap toolholders look like such a deal until you're paying $10 and up per insert on a facemill with 7 inserts. Ouch!

    Cheers,

    BW

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  • J Tiers
    replied
    I think some of the point (maybe ALL of the point?) has become obscured in details many of which are of course useful......


    Evan used a Cermet insert, and if I read/understand correctly, he used it at the specified negative rake orientation, and at a speed correct for the material, about 3 x the HSS speed.

    He is doing that on an SB 9" machine, certainly NOT the most powerful and figid machine available, even in that size range.

    And it works.

    IIRC, it was with 1018, which is notorious for bad torn finishes.

    Evan: have you run any 4140/4140 PH or similar? I found that to require even more power, and I am wondering if you can still get that sort of finish with it.

    Leave a comment:


  • lazlo
    replied
    Originally posted by Boucher
    Post # 112 Loose Nut said "I use TMNG inserts with good results " Did you mean TNMG? I am having a hard time keeping this straight.

    Earlier Lazlo said:
    "I like TNMP and CNMP negative rake with positive rake chip breaker."
    The difference between the TNMP/CNMP and the TNMG/CNMG inserts is that the latter has the flat land in front of the chipbreaker. That greatly improves the edge strength, but then you have to make sure you take a big enough DOC to get past the flat land to the positive rake provided by the chipbreaker. If you don't take a big enough cut, the TNMG/CNMG effectively has a flat top, with a negative shear angle (because the whole insert it tilted down with a negative rake orientation w.r.t. the workpiece).

    That's why I prefer the TNMP/CNMP -- unless I'm taking an interrupted cut, I don't need the edge strength of the flat land, and I'd rather not worry about DOC:




    This thread also inspired me to enroll in Sandvik's Online training course.
    The Sandvik course is great. If you sign-up online, they'll also send you their "Metalcutting Technical Guide": a great hardcover textbook which covers all this material, and much, much more, with gorgeous illustrations...
    Last edited by lazlo; 07-19-2009, 11:46 AM.

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  • Boucher
    replied
    Post # 112 Loose Nut said "I use TMNG inserts with good results " Did you mean TNMG? I am having a hard time keeping this straight.

    Earlier Lazlo said:
    "I like TNMP and CNMP negative rake with positive rake chip breaker."
    Glen Wegman said:
    "If you like those you will really like TNGP and CNGP."

    He is right I ordered some and they are in and they look great.

    Now if I can produce something that has the surface finish anywhere near what Evan's original post demonstrated I will be very pleased.

    This thread has also inspired me to make some of my own tool holders.

    This thread also inspired me to enroll in Sandvik's Online training course.

    Leave a comment:


  • lakeside53
    replied
    Hmmm... I guess it depends on the overall rigidity/power of the lathe... which often follows size, but not always.

    When I first set up my Emco, every expert told me that carbide was a bad choice. Well.. you're wrong It's a 10x24 (?) V10P with a 1hp motor, I use quality positive rake carbide almost all the time, and although it took a while to figure out what really did work, I now get good results. I try it on my neighbors 9x20 Jet (it was mine...), and it's not very happy. At the other end of "my scale", I have a massively rigid (for that size of lathe) 4hp 14x40 Polamco that runs CXA sized tool post and carbide - in a few days I'll power it up again and get to compare The only test I did was pre-purchase, and it pealed off a dark blue spring of 4140 like butter.

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  • loose nut
    replied
    Got to interrupt the snipping here with a basic question.

    The original post was the effect of tooling on SMALL lathes. What determines what a small lathe is as far as carbide type tooling goes.

    Mine is a common type Chinese 13 x 40 Light industrial (which means that it is to light for real industrial work) that is available from all the suppliers.
    To me it is a big lathe at least compared to the 9 x 20 and other smaller types that many are using but to the machinists at work it is a "little" lathe.

    I use TMNG inserts with good results but at what point should a person consider not using carbide etc. When does a lathe become to small for them or what type or inserts don't work well with the smaller less rigid type of lathe some of use.

    I guess more to the point what style of tool should we avoid.

    OK, resume combat operations.

    Leave a comment:


  • Glenn Wegman
    replied
    Originally posted by Evan
    Look at Kyocera tool holders. They don't call the tilt of the tool holder "rake". It's the inclination angle. They list side rake seperately which is the negative in negative/positive. Your diagram above in post 104 is incorrect.

    http://global.kyocera.com/prdct/tool...alog_cp231.pdf
    Evan,

    Can you post an example that is shown in the catalog of a negative/positive tool in accordance with your definition?

    According to your definition, it would have negative inclination with positive side rake.
    Last edited by Glenn Wegman; 07-19-2009, 09:57 AM.

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  • lazlo
    replied
    Originally posted by Evan
    The entire point of this post is to show that isn't true. The results prove it.
    If you use a more modern negative rake insert with a positive chipbreaker, you wouldn't have to baby it:

    Originally posted by Evan
    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.

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  • Evan
    replied
    flat-topped negative rake inserts with purely negative shear angles are not well-suited to a Home Shop Machinist -- they require maximal power and rigidity.
    The entire point of this post is to show that isn't true. The results prove it.

    Last edited by Evan; 07-19-2009, 09:26 AM.

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