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(hard) turning tungsten carbide

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  • Cenedd
    replied
    Another thing to watch out for - and I ought to preface it by saying this was a cheap import CBN insert - is not to stop the spindle with the insert in contact with the workpiece. To measure diameter, for example. With the extra heat involved the tip of mine welded to the workpiece (think it was HSS if I remember correctly) and then it fractured when I moved the tool box or started the spindle again - forget which.

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  • old mart
    replied
    I must remember not to make the same mistake, it's one of those things you could not anticipate.

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  • Mark Rand
    replied
    No, it just crumbled!

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  • old mart
    replied
    When you went beyond centre, did the cbn tip come unstuck from the insert?

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  • Mark Rand
    replied
    I've got four CBN inserts. It was five, but one of them went beyond centre when facing. They don't have a lot of tensile strength .

    Apart from stuff like tungsten carbide and hardened steel, they are great for cast iron where some of it has hard spots. Stuff like sash weights or weight lifting weights, where the cast iron was cheap for the weight but needs to be prettied up for a clock pendulum or base for a stand etc.

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  • old mart
    replied
    I can machine tungsten heavy metal, (Densimet) easily with carbide, turning, parting and milling, but that is much softer than carbide.

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  • DEVILHUNTER
    replied
    Could ask for the brand or catalog examples. All I remember is they where Japanese made, as they where the only ones that had that technology. They were even able to do thread milling.

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  • MattiJ
    replied
    Originally posted by DEVILHUNTER View Post
    My company does high precission carbide machining quite frequently. Mostly milling. They use carbide end mills with special coatings.
    Intresting. I have heard about PCD and CBN endmills but didn’t think that coated carbide would do it.
    Any examples/links of the endmils used?
    (Google is pretty damn useless if you search for ”tungsten carbide milling”

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  • old mart
    replied
    Not only is the dust very abrasive, as already mentioned, but the cobalt binder is somewhat toxic.
    I was lucky to get an Iscar cbn insert with a cheap job lot of inserts, unusually, it has four cutting tips, and came in it's own bespoke case. I haven't yet found a use for it.
    I would think that CBN is not the preferred material for carbide, diamond grinding wheels are the correct solution.
    Last edited by old mart; 03-27-2019, 04:52 PM.

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  • DEVILHUNTER
    replied
    My company does high precission carbide machining quite frequently. Mostly milling. They use carbide end mills with special coatings.

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  • MattiJ
    replied
    Originally posted by Yondering View Post
    Interesting, I guess that makes sense for cutting carbide. Correct me if I'm wrong - are these the same type of inserts used for "high speed machining" in softer (than carbide) materials? Or am I thinking of something else? I'm thinking of ceramic inserts that are intended to remove material from normal steels by high speed/heat shear rather than actual cutting, and I think they're usually white in color. Same thing or different?
    Sort of, except CBN (cubic boron nitride) is black in color and so expensive that its usually used only a tiny nugget on the tip of the insert much like diamond. Normal application is turning hardened steels, turning tungsten carbide appears to be quite rare and somewhat novel/academic interest still at the moment.

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  • Yondering
    replied
    Interesting, I guess that makes sense for cutting carbide. Correct me if I'm wrong - are these the same type of inserts used for "high speed machining" in softer (than carbide) materials? Or am I thinking of something else? I'm thinking of ceramic inserts that are intended to remove material from normal steels by high speed/heat shear rather than actual cutting, and I think they're usually white in color. Same thing or different?

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  • MattiJ
    replied
    Originally posted by Yondering View Post
    That's pretty neat, thanks for sharing. I still haven't tried any CBN inserts. Out of curiosity, have you considered trying the same at higher speeds?
    "maybe" if I get enough big scrap carbide piece without better use. Besides recommended speed range for cutting tungsten carbide was considerably slower than HSS for example. 20 to 30m/min IRRC some numbers from insert brochure.

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  • Yondering
    replied
    Originally posted by MattiJ View Post
    Its tungsten carbide, hard as hell. Cutting edge glows red at 60sfpm and ”cuttings” are heavy powdery stuff. Turning hardened HSS feels like butter compared to this.
    That's pretty neat, thanks for sharing. I still haven't tried any CBN inserts. Out of curiosity, have you considered trying the same at higher speeds?

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  • markx
    replied
    Just be sure to contain the cutting dust and debris from the carbide. If that stuff gets inbetween the ways or other contact surfaces and embeds itself there.....well, you can guess

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