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Thread: More boring tooling...

  1. #1
    Join Date
    Dec 2008
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    Default More boring tooling...

    Had another go at making a boring bar again.... 1" shank, 3/4" bar 4" long O1 (8" OAL). DCMT insert Made it specifically to fit the small awkward work envelope of our Nakamura CNC lathe at work, and maximize capability.





    Shaft was offset turned in a 4 jaw from the shank, and the end support under the insert was all blended by hand on a bench grinder.


    Had a chance to try it out quick before leaving today, and......It's works like crap . Chatter's pretty bad, and is un usable as is. Not really sure why, but I'll play around with it a bit more on Monday and hopefully get it to cut better. It's just a bit over 5xd which is pushing it a bit?, but I've gone over that ratio before with better results and other bars? Side/front clearance on the insert is good, (at least I think so...*), and tool height is dead on center. Insert is seated good and snug in the pocket too. I honestly don't have a lot of boring experience so my troubleshooting well is quickly drying up on this one.....

    Had to leave work to pick up the kids so I couldn't play around with it a bit more, but it's going to bug me till Monday.

    *If I had to guess is that maybe it's rubbing on the front? I thought about that on the way home and it's something I never checked before leaving. Am I missing something obvious? It's been a looooong week.

    Any ideas?

  2. #2
    Join Date
    Jul 2017
    Location
    Buffalo NY USA
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    Default

    Looks beautiful. Not an expert, but maybe setup the bar so its just a bit above center?

  3. #3
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    Apr 2008
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    winnipeg/manitoba
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    If you examine how far back from the insert pocket you have relieved, I think you've made a mini-diving board! Notice on commercial boring bars that the relief stops right after the insert pocket. Think maximum rigidity. JMTC.

  4. #4
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    Default

    Quote Originally Posted by nickel-city-fab View Post
    Looks beautiful. Not an expert, but maybe setup the bar so its just a bit above center?
    Thanks. I'll try and play around with tool height. Unfortunately the turret position and tool height is "fixed" and it's not as easy to do as with a manual lathe, but I've got some idea's.

    Examining some commercial bars after posting this that take the same DCMT inserts makes me think now, that I've got the wrong insert pocket geometry for that insert. Damn. . Possibly the wrong insert/corner radius also.

    https://www.iscar.com/eCatalog/Famil...&GFSTYP=M&fr=1

    This shows the insert kicked back a couple degrees on the end (axial), and some radial rake angle too. Might have to just grind the insert into proper cutting angles and flub my way through this job to get by....

    Quote Originally Posted by millwrong View Post
    If you examine how far back from the insert pocket you have relieved, I think you've made a mini-diving board! Notice on commercial boring bars that the relief stops right after the insert pocket. Think maximum rigidity. JMTC.
    Yeah, I did get a little carried away with that..... Didn't think it would have THAT much effect, but you might be on to something too.

  5. #5
    Join Date
    Jan 2010
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    Try it a little above center like NCF said. If a boring bar is on center, when it flexes down, it digs in and chatters worse. If it's above center (maybe .03 on a big hole), when it flexes down, it takes a lighter cut and relieves the pressure some.

  6. #6
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    Like I say, "Shim happens". (I hate shimming but sometimes ya gotta do what ya gotta do...)

  7. #7
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    Success.....Kinda

    Got it cutting good, but still a bit noisy. I can live with it for now as I got my 2 tapered bores done that I needed it for.

    I ended up grinding some more relief on the front edge of the insert, "manipulated" the tool block a bit to push the insert up above center, then I drilled/tapped the back of the bar 5/16-18 so I could screw on a lead hammer face I made a while back to act as a damper.


    first bore done, and some pretty good contact from top to bottom.

    Both bores done.

    The second one is a cat-40 spindle nose for a haas 4th axis.

    Next on the to-do is to make some cat-40 expanding mandrels to fit it, to hold some parts for what I hope is a long running production job.

    I came up with the cat-40 nose idea so that I could quickly swap in some cat-40 er32/er16 holders with smaller one off pin work, and not disrupt the production setup.

  8. #8
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    Looks like quality work. Thanks for sharing.

  9. #9
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    Mar 2008
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    Barrie, Ontario, Canada
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    It looks lovely. Really nice work. I hope you get it sorted out to work well for you.---Brian
    Brian Rupnow

  10. #10
    Join Date
    Jul 2017
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    Default

    Glad it worked out for you! Haas is good stuff...

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