Advice needed on carbide inserts for lathe use
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  1. #1
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    At this time I have zero cutting tools for my 17" Mori Seiki lathe.

    I'll buy some 3/4" square HSS to have on hand but I sure do like the convenience of carbide.

    I have extremely limited experience with carbide insert toolholders. I had a set of the 1/2" triangular import holders from Enco that I used on my 10x24 bench lathe that went with the lathe when I sold it.

    I suspect the Mori Seiki has the beef and speed (1800rpm max) to run negative rake tooling for roughing, and it sounds like I'd want to run positive rake for finish work.

    I'm not doing production work, and much of what I'll do is smaller parts (motorcycle stuff). Is there any sense to buying some negative rake tools, or can I standardize on all positive rake and have it be a little less effective for roughing? Or just use HSS for roughing and save the carbide for finishing?

    My Multifix toolholders will easily accept 3/4" tools. I'd have to look but I think I can go up to 1".

    I'm not clear on the relative advantages of the standard 60* triangular vs 80* diamond vs the trigonic shapes. It sounds like chip breakers are a good thing to have.

    It would be nice if would only need to stock one shape and size of insert for all the tooling, including boring bars, but I'm not sure if that is possible. I know I'll need different nose radii and grades of carbide for different materials.

    I presume that if there was a universal insert that did everything there wouldn't be so many different types of inserts. But I'd like to come as close to a universal insert as I can. Getting an insert that goes on sale regularly at a good price would be appreciated.

    I want to buy a name brand for the insert holders. Would it be safe to figure that Iscar, Kennemetal, Sandvik, Valenite etc are all likely to do the job for me and I can go with whichever one has the best price?

    I'm trying to change my previous "buy cheap" habits and only get good quality tooling for the lathe and mill. But I still want to maximize my bang/buck ratio.

    cheers,
    Michael

  2. #2
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    Micheal,
    I would look at Iscar, or Kenametal ect...
    Go on ebay where the toolholders can be had for $10 ea. You can buy a couple of different style of tool holders. I would but a Rh, and Lh trigon for ruff turning and facing.
    I wuold also buy a Rh 55*, and a Rh 80*
    Those happen to be my favorites.
    For boring, pick up a 50*, and an 80* 1" diameter boring bar.( they have a lot more chip clearance than a trigon boring bar) That way when the inserts used for turning are dull, you insert them on your boring bars, and get to use the back side of the dull cutting edge that is nice and sharp. You can then get up to 8 full edges b4 the insert is trash.

    Inserts are a dime a dozen on ebay. Everybody steals them from work, and then sells them on ebay.
    Call it "profit sharing"
    You should be able to outfit your lathe for lees than $150 on ebay. Not bad considering if you bought new you would spend $500 or more for the same things.

    My .02.
    Doug.

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    I've become somewhat fond of plain old TPG inserts. They can be had in coated, uncoated, cermet, diamond, etc. I picked some up recently for $1 each and while they were good quality, they had a large radius which would not clear the shim on my toolholder. They were uncoated and ground on all surfaces. I let them hang out a bit to clear the shim and the finish they give on aluminum is spectacular. The TPGs work well for everything from moderate roughing to fine finishing (especially with the uncoated, ground or honed ones). I use an Aloris holder for these but there are plenty of other options.

    Also use DCMT, CCMT and TCMT and generally, the narrower the insert, the more it is intended for profiling or any tight access operation. I've found that Dorian holders, US made, can be had for as little as half the price of Iscar, Valenite and some others. I've bought several from Carbide Depot and the prices were pretty good, they seem to be well made, finished and are laser engraved with info including spare parts (screw, shim, etc.) types.

    The biggest PITA with carbide is edge buildup if you do not run a high enough speed. On larger lathes it is just about impossible to run smaller diameters where they should be run. I knock off the buildup when it occurs by running a sharp edge of mild steel scrap along the top of the edge.

    Den

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    as to what will work best for you...depends on
    your setups and style of machining and habits.
    on my 16", 5hp machine -i run the same tnmg 432
    c7, ticn or tin coated insert for 95% of the
    time, turning ,facing, chamfer.....
    and on all materials...production, one off,
    prototype,maintenance...i've the experience with
    that tool to know what feeds and speeds will
    rough the fastest or give me a mirror finish.

    there are exceptions- pos rake for thin or
    delicate parts ,boring bars , shaky setups....hss for tiny
    diameters that ( 1250 rpm top speed ) i don't
    posess the rpms for carbide to cut properly.

    neg rake tools will cut at least 10x more chips
    per index than pos rake on most materials. there
    are so many variables too...a tnmp is a hi-pos
    insert that works in a neg holder.

    trigon, diamond, triangle will all turn to a
    shoulder and face out - something to consider.
    i've never paid more than 15.00 for a 1x1"
    turning tool(ebay) and tnmg inserts are among the
    least costly(abundant) in tool catalogs($2-5)
    and on ebay (.40cents - 2.00)

    you may find my suggestions don't work well for
    you, and another tooling setup is more appropriate
    for your needs. i'm sure someone in this thread
    will post much different advice . which is an
    excellent way for you to use your best judgement.
    good luck.

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    "I'm not clear on the relative advantages of the standard 60* triangular vs 80* diamond vs the trigonic shapes. It sounds like chip breakers are a good thing to have."

    The 60 degree can't turn and face with the same setting.

    The 80 degree and trigon type can.

    In my CNC lathes for general turning all I use are the 80 degree, CCMT & CCGT type. A good percent of our parts can be done with a single tool (no tool change). A downside of 80 degree single sided, positive rake 80's is only two cutting edges.

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    Michael,
    The trigon shape is definitely the way to go if you're buying new toolholders. The trigon essentially bulges the sides of a triangle such that each corner is 80* instead of the normal 60* of an equilateral triangle. The nearer the corner can approach 90*, the stronger the insert becomes. An 80* neg rake diamond such as a CNMG essentially has 4 useful corners. While you can buy holders that make use of the 110* corners on a C insert, the use is limited, giving rise to the common opinion that the bulk of these corners end up unused. The neg rake trigon, WNMG for example, has 6 80* corners and costs about the same as an equivalent CNMG, so you get 50% additional life for free. If you go with inserts with a 3/8 IC instead of 1/2 IC, then you can also get reasonably sized boring bars that will take the same trigon insert. There are also bars that utilize 1/2 IC trigons, but they're fairly large bars. Ultimately, you'll find in doing a range of work, you'll end up with a lot more invested in various boring bars than in turning tooling. For turning, a MWLNR holder is a good first purchase, as the insert is oriented such that the same tool is used for both facing and turning.

    Someone does actually have a "universal" insert on the market now, supposedly suitable for both ferrous and non ferrous work. From the pricing I've seen, I can buy one ferrous insert, one non-ferrous insert, and a cup of coffe, all for the price of one of these universal jobs. Not a great deal, IMO. Personally, I like Sumitomo's AC2000 or AC3000 grades for general purpose steel work with neg rake tooling. I use their ENG edge geometry, and find it gives a good balance of strength for roughing and ability to make finish cuts. To show you how small a percentage of job cost the carbide really is, I made 3 parts last week, starting from plate burnouts, that required turning and facing a total of over 340# of chips. One edge of one $6 insert did all of this work, including the initial roughing of the burned OD. When the parts were done, the insert was ready for indexing, but not worn to the point of affecting size or finish. That was $600 of turning, with a carbide cost of $1.50 for the one edge of a CNMG insert. I, like most people at one time or another, have bought cheap no-name inserts because of price. Its false economy in the worst way. On this particular job, a $3 insert would have saved me 75 cents, IF one edge would have done the job. In my experience, one edge wouldn't have done the job, nor would 4 edges of one insert. They ultimately have a higher direct cost because they won't hold up, and the indirect costs of multiple indexing and replacing inserts costs even more than the inserts themselves in lost time.

    If you're going to be doing much aluminum work, probably the best deal going today for nice finishes, good durability, and price is the Korloy aluminum specific inserts handled by Travers Tool. They're a micrograin carbide with fully polished surfaces that look as if they're chromed. They hold up well, and for some strange reason they're priced at about half what everyone else gets for similar aluminum specific micrograin inserts. These are TCGT and CCGT inserts typically, and use neutral rake tool holders. The insert itself has a high positive rake built in. I use a Dorian Tool STJCR toolholder for these in turning applications, which I modify for clearance such that it looks like an MTJNR with the insert sitting out at the corner. For boring work, I've bought several Pafana bars for these screw-down inserts from JTS Tool off Ebay, and have been well satisfied with them. A 1" bar to use CCGT inserts costs about $32 versus about $140 for a similar bar from the major manufacturers. They're made in Poland, and the ones I've bought have had good overall quality. IMO, there's no comparison between the tooling being produced in eastern European countries and the stuff coming out of China. Steel cutting inserts are also available in this screw-down geometry, so the same tooling can be used when positive rake work is required on ferrous materials, but I wouldn't recommend running them for general purpose steel roughing, etc. as their geometry precludes them having the strength of negative rake inserts for this type work.

  7. #7
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    "The 60 degree can't turn and face with the same setting"

    i disagree.....do it ALL the time! it depends
    on the approach of the toolholder . i set mine
    with a 10-15 deg lead angle to the x axis ,and
    my inserts have deep, bumpy chipbreakers. maybe
    with a cnc turret, it's not easily positioned
    this way.

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    I like Sumitomo's cermet inserts. I have TNMG 331 ENK, TNMG 331 EFP, & CCMT 332 ESU. They pricey but are really hard to kill and withstand remarkable abuse. I've used them to turn down hardened truck driveshaft splines at 300 FPM. This is an extreme interrupted cut. The inserts are available as WNMG, which might be a better option in some ways. Note that the TNMG and WNMG inserts give you six edges per insert, so the price per edge is competitive. The only problem with the negative rake inserts is that they can push away long skinny work, leading to taper. If it's a critical situation, I will rough with TNMG and finish with a sharp, high-positive insert, like the CCMT or this little Circle machine toolholder I have that takes their sharp triangular boring bar inserts.

    All this happens on a manual Colchester that can go up to 3,000 RPM.

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    In my CNC lathes for general turning all I use are the 80 degree, CCMT & CCGT type. A good percent of our parts can be done with a single tool (no tool change). A downside of 80 degree single sided, positive rake 80's is only two cutting edges.
    Doug, have you looked at switching to WCMT's? They're about the same price, and you get the 3rd 80* corner for free. On another note, Dorian makes a face mill that uses the unused edges of a CNMG. I've looked for, but haven't found, the same sort of face mill that would use the unused corners of a CCGT for face milling aluminum. The high positive rake on a CCGT should work well, and it sure would be nice to get some use out of those unused corners instead of buying aluminum facemill inserts at $9 a pop for 2 edges. Has anyone seen a cutter like this on the market anywhere?

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    Personally I like the DNMG style of inserts. Smooth finished surfaces, and good chip control.

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    Cermets - Yum. Those things are amazing.

    I'm also a fan of TPG stuff. At home I bought
    a set of valenite holders for tpg221 size.

    Where's the best place to get *un*coated carbide
    inserts?

    Jim

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    Go with a couple of holder's from Ebay...get one 80 deg. & one 35 deg. As previous poster's have mentioned, CNMG's (or equiv.) are dirt cheap there. Get neg. toolholder's...don't anguish over it, the chipbreaker molded into the insert usually turn's those neg. insert's into positive. They'll cut fine on a 17" lathe.

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    Your Mori Seiki is gonna love you for it. The bulk of my turning is done with CNMG inserts. 80* gives a stronger, harder wearing insert for heavier cutting than 60*. This depends on the work you have in mind. I work in a heavy jobbing shop. Boring bar chip clearance may be an issue with WNMG. A 35* is great for acessability, ie facing a shaft between centres, but is a luxury HSS equally can do. Definitely go with 25mm shanks, even if the tools need milling to fit the holder. Two insert grades will see off most jobs. A roughing that can handle s/steel, 0.8 nose radius, and a 0.4 cermet finishing insert for the final cut on accurate jobs. Speeds and feeds are important. Depending on work holding, start at 500 fps for softer steels down to 250-350 for 316 s/steel and experiment with in between. Feeds HAVE to be adjusted for correct chip breaking. If you're making razor sharp ribbons, stop the cut and increase the feed until you get manageable chips. Ribbons=feed too low! Don't be afraid of freehand grinding old inserts for brass, aluminium etc. Finish with a diamond lap. Brass and bronze love ground tools. Happy chipmaking. You'll never look back.
    PS 80* inserts allow for much larger facing depths of cut vs 60* at the standard tool orientation (90*). Roughing tips give negative geometry, the cermet finishing closer to positive.

    [ 12-18-2004, 09:02 AM: Message edited by: Solidus ]

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    What I use on a 15"x50" Colchester and get good results:
    Turning-- MTJNR12-3W using TNMG 332 inserts
    Boring-- S-MTFNR 16-3 cool-through using TMNG 332
    Boring-- BBS-12-3 using TPMT 322 inserts
    Parting-- Iscar SGFH 26-3 using GFN3 IC328 insert
    Threading-- kenametal top notch with NT3R inserts

    There others I use for differnt jobs, but thses are my main tools.
    take care
    edie

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    As someone mentioned to me, this gets to be alphabet soup pretty quickly. I was really hoping there would be one insert clearly towering head and shoulders above the rest.

    I guess I've got to get out the catalogs and edumacate myself some more. I think I'll try to come up with a point/$ comparison on the inserts. I'm not sure I can think of any other way to get a handle on things.

    As always, you've given me plenty (maybe even too much [img]smile.gif[/img] ) food for thought.

    cheers,
    Michael

    (edited to add: is there any reason to choose/avoid the clamp style holders over those that just use a screw?)

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    (edited to add: is there any reason to choose/avoid the clamp style holders over those that just use a screw?)

    sorry mike , you've left out the kind that uses
    an eccentric pin . the screw is simplest, but
    i'm a skeptic that assumes the cam/pin or overclamp
    would be stronger.
    good luck.

  17. #17
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    Michael, negative rake toolholders pretty much always use an eccentric pin plus a clamp. The pin pulls the insert back tight into the seat, and the clamp retains everything in place. Negative rake inserts are subjected to much higher forces than neutral or positive rake inserts. The ones that use only a screw are typically neutral rake. The CCMT and CCGT inserts mentioned earlier are typical of neutral rake inserts. The second letter in the designation of an insert specifies the rake geometry. tNmg is negative. tCgt is neutral. tPg is positive. The only inserts which are double-sided are the negative rake ones. Neutrals and positives are single-sided. Negatives will give the cheapest operating cost, but are not suitable for all types of work. All the different letter designations can be confusing, but, once you learn what they mean, they work well in helping you find whether or not some oddball tool is available or not without having to try to give a 3 paragraph explanation to an order-taker who has not the slightest idea of what you're talking about [img]smile.gif[/img] Also, most any large shop that's doing a range of work with much complexity will always be using tools and inserts from a variety of sources. You'll see ads from some of the carbide manufacturers indicating they can be a single answer to any and every metalcutting problem you'll ever encounter, but the reality is that each of them has certain things they do better than anyone else. Even with everything that's out there, you'll still find it necessary to improvise fairly often to do what you need to do. Some of these improvisations will outperform anything thats available in the commercial market, and cost very little to implement.

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    If you are not doing production work and buy your inserts on Ebay cheap, make your own holders. Get the inserts with holes in them and it is pretty simple to make a holder in about any configuration you want or need. I have made them from CRS and also unhardened O1. For hobby use they work fine. If you offset the screw hole a thousandth or so towards the back of the holder it will clamp the insert firmly against the holder when tightened. I even made an endmill with two WNMG inserts that I have been using for months without changing the inserts. I use it for roughing cuts and save the carbide endmills (also off Ebay) for finish work.

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    metalmunchr,
    Regarding indexable milling cutters that use CCMTs:
    The Travers catalog lists a European import milling cutter that uses the 100-degree corner of CCMTs and CCGTs. It is available in two sizes with straight shanks and one size with R-8. It's on p. 376 of their catalog. (Sorry, it wouldn't link a URL here.) It looks like it would be the cat's pajamas for attacking aluminum if you equipped it with the Korloy high-shear polished inserts special for aluminum.
    Rich

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    Thanks a bunch rklopp. That's a new one for Travers I think. I had looked at last year's catalog and found the Dorian for CNMG's, and hadn't even thought to look in this year's new book to see if they had added anything like that. Exactly what I was looking for. I'll let everyone know how this works out, but with the high shear angles on the CCGT's and the results I've with them on aluminum turning, I'd think they'll work great. Korloy actually lists these inserts as suitable for milling use as well, so any interruptions in the cut shouldn't be a problem. Thanks again.


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