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MattiJ
03-26-2019, 05:51 PM
Was reading some academic jaddajadda about hard turning and what catches my eye was turning tungsten carbide.. Of course I had to try that like everything else that seems stupid:

https://i.imgur.com/a3agdamh.jpg

6mm carbide endmill shank reduced to 5mm. Crapped Sandvik CB50 mystery grade CBN insert re-sharpened on bench grinder& diamond wheel seems to work :cool:

danlb
03-26-2019, 06:41 PM
Was the whole shaft hardened, or just the cutting end?

MattiJ
03-26-2019, 06:53 PM
Was the whole shaft hardened, or just the cutting end?

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.

lynnl
03-26-2019, 06:58 PM
Was the whole shaft hardened, or just the cutting end?

I would think a carbide end mill would naturally be hardened from end to end, from the sintering process. Is that not so? Do they undergo a hardening process similar to steels?

MattiJ
03-26-2019, 06:58 PM
Somewhat related crazy tech :https://www.precitech.com/about-us/press/press-releases/press-releases-and-events/2017/june/nanoformxtc

Laser assisted turning where laser beam is guided trough the transparent cutting edge(diamond) to help soften the material under the cutting edge :eek:

MattiJ
03-26-2019, 07:00 PM
I would think a carbide end mill would naturally be hardened from end to end from the sintering process. Is that not so? Do they undergo a hardening process similar to steels?


Yeah, no need for hardening. Coating can be used to further increase surface hardness but even without that the carbide is really hard.

danlb
03-26-2019, 08:09 PM
LOL. I read that as tungsten cobalt. Totally different animal! :)

Dan

markx
03-27-2019, 03:17 AM
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 :)

Yondering
03-27-2019, 11:58 AM
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?

MattiJ
03-27-2019, 12:58 PM
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.

Yondering
03-27-2019, 04:22 PM
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?

MattiJ
03-27-2019, 04:35 PM
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.
https://www.shop-apt.co.uk/user/products/large/DNMA-150608-CBN-300-TURNING-INSERT.jpg

DEVILHUNTER
03-27-2019, 04:42 PM
My company does high precission carbide machining quite frequently. Mostly milling. They use carbide end mills with special coatings.

old mart
03-27-2019, 04:49 PM
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.

MattiJ
03-27-2019, 04:49 PM
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”

DEVILHUNTER
03-27-2019, 05:08 PM
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.

old mart
03-27-2019, 05:35 PM
I can machine tungsten heavy metal, (Densimet) easily with carbide, turning, parting and milling, but that is much softer than carbide.

Mark Rand
03-30-2019, 07:43 PM
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 :rolleyes:.

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.

old mart
03-31-2019, 08:40 AM
When you went beyond centre, did the cbn tip come unstuck from the insert?

Mark Rand
04-01-2019, 08:45 AM
No, it just crumbled!

old mart
04-01-2019, 10:04 AM
I must remember not to make the same mistake, it's one of those things you could not anticipate.

Cenedd
04-03-2019, 10:03 AM
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.