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

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  • Peter.
    replied
    Originally posted by lazlo
    They're both negative rake inserts with flat sides. The only difference is that the TNMP insert that Ted uses has a postive rake chipbreaker, which gives you the clearance to tip the negative insert enough to get a positive rake angle. So Evan's SNGA negative insert has the profile (flat sides) of the top insert (sans the chipbreaker groove), and Ted Edward's negative insert has the middle profile, and he tilts the insert down 5° to get a positive rake.

    You could use a more severe chipbreaker like the TNMS insert at the bottom, tip the insert even more (10°) and get even more positive:

    Note that these are all negative rake inserts:

    I've just bought some cheap Iscar TNMP inserts from eBay to try this out. No idea if the grade is suitable for my needs (they were the only TNMP's offered) but for £8 delivered for 10 inserts I get 60 cutting edges to experiment with and the worst it'll be is the worlds cheapest failed experiment. The ad said the chipbreaker was designed for cast iron.

    I'm going to make a couple of turning tools and a boring bar to hold them I guess.

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  • Evan
    replied
    It works the same as a butter knife scraping some butter from a cold lump. Funny thing is that it is really still cutting. It will make tiny fine ribbons of swarf so thin you can barely see them if you have it set to barely touch.

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  • Circlip
    replied
    Wonder what my long deceased mentors would have made of this one as a "Polished" finish would have been met with "Tha rubint' metal off and not cuttin it" an even matt grey being the order of the day.

    Regards Ian.

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  • wierdscience
    replied
    Originally posted by Evan
    There is nothing stopping you from resharpening an insert. All you need is a small diamond wheel. It works with both carbide and cermets. While you cannot restore the exact same edge shape it originally had you can certainly gain a lot more useful life from an expensive insert.
    If it's a double sided insert there very much is.Sharpening one decreases the support for the opposite side when the insert is flipped over.Un-supported carbide as we know snaps off nearly instantly and on inserts it usually snaps back close enough to the hole to ruin the insert.It's false economy to touch up and insert unless it's the last cutting edge on the last insert you have on Saturday afternoon 30 miles from town

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  • Mcgyver
    replied
    Originally posted by lakeside53
    I just bought a bunch of tooling, and found a few pounds of worn indexable carbide. The guy never threw anything away - soldered the worn inserts to a steel shank and ground then to his liking... nice
    I've seen that in a lot of machinists tool kits. all manner of lathe, fly cutters and boring bar cutters homemade from worn inserts

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  • lakeside53
    replied
    I just bought a bunch of tooling, and found a few pounds of worn indexable carbide. The guy never threw anything away - soldered the worn inserts to a steel shank and ground then to his liking... nice

    Leave a comment:


  • Evan
    replied
    Other than removal of too much material off the edge of the insert will allow the holder to drag on the work trashing a holder worth as much or more than the insert
    So don't do that.

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  • Glenn Wegman
    replied
    Here's a sharp edge negative rake Cermet showing a coil (about 3' long) it peeled off of 304ss at .100" doc at 375 fpm. Cuts it effortlessly like it was leaded steel. It's evident by the limited chip breaker area that it is definitely a finishing insert and not an insert for large doc. I use this one for aluminum, some hardened steels, and stainless. It was also done on a very ridgid 6 hp 14" lathe so YMMV.

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  • Quetico Bob
    replied
    QUOTE
    my half brain says I got a bad recommendation andI'm stuck with 8 new inserts that don't f%^$#g work.
    QUOTE

    Next time call Kennametal or who ever supplies you direct. That way the other half can focus on what’s important….making chips.

    Cheers, Bob

    Leave a comment:


  • camdigger
    replied
    Originally posted by Quetico Bob
    QUOTE
    Other than removal of too much material off the edge of the insert will allow the holder to drag on the work trashing a holder worth as much or more than the insert
    QUOTE

    Oh come on, get real! Do you actually realize how much touching up that would take? And by that time, anyone with half a brain would rotate or flip the insert….Gawd.

    Cheers, Bob
    Not a whole lot.... the holder base is already proud of the lower edge of the insert. These were a selection to fit holders included with the lathe. my half brain says I got a bad recommendation and I'm stuck with 8 new inserts that don't f%^$#g work.

    Leave a comment:


  • Quetico Bob
    replied
    QUOTE
    Other than removal of too much material off the edge of the insert will allow the holder to drag on the work trashing a holder worth as much or more than the insert
    QUOTE

    Oh come on, get real! Do you actually realize how much touching up that would take? And by that time, anyone with half a brain would rotate or flip the insert….Gawd.

    Cheers, Bob

    Leave a comment:


  • camdigger
    replied
    Originally posted by Glenn Wegman
    It is truely a "when in doubt, speed it up" type of insert as the higher the surface speed, the better the finish, as long as your machine can stand it without chattering. it's nearly impossible to run one too fast. That's the hardest part to get used to after using HSS.
    It's hard to believe speeding up the process will improve the excessive infeed pressure, squealing, and crappy finish from one insert when another does the job as setup without complaint.

    The lathe should be big enough for carbide - it's a 2 hp 1440 with an 8" chuck.

    P.S. àsk an expert`` I did. Every rep at the counter at ACT in Cowtown had input into the selection....
    Last edited by camdigger; 07-06-2009, 05:54 PM.

    Leave a comment:


  • camdigger
    replied
    Originally posted by Evan
    There is nothing stopping you from resharpening an insert. All you need is a small diamond wheel. It works with both carbide and cermets. While you cannot restore the exact same edge shape it originally had you can certainly gain a lot more useful life from an expensive insert.
    Other than removal of too much material off the edge of the insert will allow the holder to drag on the work trashing a holder worth as much or more than the insert

    Leave a comment:


  • lazlo
    replied
    Originally posted by Glenn Wegman
    I see the confusion. Looking accross the top of the page, as you discovered, you will see three different columns of insert types, Cermet, Coated, and Carbide.
    If anyone's interested, this is one of the better articles I've read about Cermets. Apparently the technological advance that's made cermets much less fragile than they used to be is micrograin ceramics (same basic technology as micrograin carbide):

    Cermets Get Assertive

    The toughness of this material has improved. Today, the applications for cermet inserts go well beyond finishing.

    Leave a comment:


  • Glenn Wegman
    replied
    Originally posted by camdigger
    My point is this, I have neither the time nor resources to go through all the 100s of combinations of carbide to come up with something that works. For the price of an insert, I can buy a HSS blank and change it as I need to to get acceptable results...
    Exactly.

    That was the point I was trying to make a post or two ago in regards to Evan's hitting the right combination. There is really no easy way to figure it all out, and I have had the same experience with carbide as you did with asking a manufacturer for advice on the proper insert for the job. The finish was terrible! I do think that if you find a Cermet grade with a sharp edge that falls under the "finishing" or "fine finishing" column, you will experience some pretty satisfactory results as Evan did. It is truely a "when in doubt, speed it up" type of insert as the higher the surface speed, the better the finish, as long as your machine can stand it without chattering. it's nearly impossible to run one too fast. That's the hardest part to get used to after using HSS.

    Evan,

    I see the confusion. Looking accross the top of the page, as you discovered, you will see three different columns of insert types, Cermet, Coated, and Carbide.

    Thanks,

    Glenn

    Leave a comment:

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