Best (better) insert for 4340 steel; not so rigid lathe.
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  1. #1
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    Default Best (better) insert for 4340 steel; not so rigid lathe.

    Greetings!

    I run a Haas ST10 CNC lathe, and I'm cutting a steel numbered 4340. I am told this steel is pretty hard since it is used for tooling. The problem I am facing is that I can only rough cut somewhere around .005" per pass @ around 400-500 rpm; anything deeper and/or faster, the frickin' machine starts vibrating excessively. The round stock I use usually doesn't exceed 1"-2" in diameter, although sometimes it can.

    My current synopsis is that this machine stinks overall, and it wasn't made for cutting harder metals like 4340.

    -or-

    I may be using the wrong kind of insert.


    If at all possible, I would like to take deeper cuts at faster speeds on this machine. Below is a link to an insert I am considering:

    DNMG432 MF2 TH1 Grade Carbide Turning 372172 - MSC

    Would an insert like that be better? The current insert I'm using is not designated for the hardest metal(s); the one I'm considering (see link) is rated to cut the hardest metal(s), according to Seco.


    Thank you for reading!

  2. #2
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    I have found 4340 steel turns well with the correct insert grade and chipbreaker. A .005" DOC per side is extremely light, a Haas ST10 Lathe isn't the most rigid machine but it does have 15HP so you should be able to take a much heavier DOC than .005". I'm surprised the machine is vibrating at heavier DOCs, are you running a Heat Treated Lot of 4340 or is the material hanging out far from the chuck without a center?

    If the material isn't harder than 45 HRc then you should at least be able to take .050"-.060" DOC per side at around 400-500 SFM and .004"-.008" IPR. Here are 2 options depending on your DOC:

    DNMG431 Insert for Less Than .040" DOC per side

    DNMG432 Insert for .040"-.160" DOC per side

    If the material is harder than 45 HRc then let me know and I'll send you a different option. Hopefully this helps!

    Mike


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