Need Help trying to attain an 8 RA surface finish on a VMC. - Page 2
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  1. #21
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    Do you have a rotary axis on the mill that you can set in the Z orientation? Spin the part on that to get roundness, and put a fine abrasive stone in a toolholder to get finish. You can set up a dressing bort and a macro to dress and adjust offsets. It won't be fast or cheap, but you can do it.

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  3. #22
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    Quote Originally Posted by jrk190 View Post
    They claim they couldn't find the right mil spec. material or something in anything other than plate which I find awful hard to believe.
    You would be surprised how often that happens on government stuff.. Some obscure spec called out on the drawing that nobody is certifying to anymore, so you hunt high and low to find a piece of material that has a piece of paper attached to it that has the correct spec on it.. Though usually its a square part that ends up coming out of round bar, there are a few I do that are like that, and they are quoted appropriately.

    You could also do some googling on the material spec, occasionally, you will find some document somewhere that says its been superseded by a spec that you can actually get easily, and in the correct shape.

    If its a government contract, sometimes its buried somewhere in the contract that you can use an alternate material, but a lot of purchasing agents don't read past the quantity and the due date (and honestly, they shouldn't have to). That one bit me in the ass a while ago.

    Ground support equipment is the worst for this type of thing.. A lot of it is older prints, and I think the ground support equipment division is where they put all the troubled neices and nephews of the big wigs so that whatever they design can't actually crash.


    Our one chance for this part would've been on the lathe but can't do it out of plate on the lathe.

    Another case of making chicken soup from chicken scat.
    Get thicker plate so that you have something to hold onto.

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  5. #23
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    Since the tolerance is not so tight is a nsk planet head an option?
    They are so slow in cycle time but useful to have. You sort of turn your VMC into a lower accuracy jig grinder.
    Trying to finish this at 5/10ths before heat treat would I think be frustrating as it normally a oil quench and that makes things move even if the dump is fast.
    Bob

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    Quote Originally Posted by CarbideBob View Post
    Since the tolerance is not so tight is a nsk planet head an option?
    They are so slow in cycle time but useful to have. You sort of turn your VMC into a lower accuracy jig grinder.
    Trying to finish this at 5/10ths before heat treat would I think be frustrating as it normally a oil quench and that makes things move even if the dump is fast.
    Bob
    planet-uses2-01-1-.jpg

    ^^^ Something like that ? (That's not my shot / me).


    I'm thinking 3 micron runout on spindle * length of gubbins + other minor runout ≈ 8 micron roundness of bore, but with a artful loading and jiggery pokery 5 micron round ness / 0.0002" ish ? and near 12(finish) Ra ?



    I have to re-read the thread as I don't fully understand why having part fixtured to a face plate on lathe would not work ? Better roundness (closer to 2 micron roundness (or better)) and better surface finish (potentially)?

    I agree with "Peeps" that have said harden first (near-ish size) then semi finish to finish in hardened state. There's a lot of distortion that can happen and then there's the coating ?

    I wonder if this thing has been spec'd right, seems kinda similar to commercial / amateur (smaller) lens flanges (spec's and dimensions).

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    I think Op said he didn't have any boring heads but given that he has an M-560V and weird things thrown at him by engineers, (top down) not bottom up...



    ..
    ^^^ I thought this looked like fun.
    ..



    ^^^ This looked kinda fun (also) + ESPRIT , but still not as good as an actual lathe/ turning center.

    U- axis turning on a mill for variable profiles. With the U axis "Thingy" + CAD/CAM (But kinda the opposite of what Op is asking here, but theoretically he could make the whole flange that way ? Not sure what the maximum achievable and safe 'Turning" diameter is on this thing ? ).

    __________________________________________________ _______________________________________________


    * No affiliation.

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  9. #26
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    Quote Originally Posted by Bobw View Post
    You would be surprised how often that happens on government stuff.. Some obscure spec called out on the drawing that nobody is certifying to anymore, so you hunt high and low to find a piece of material that has a piece of paper attached to it that has the correct spec on it.. Though usually its a square part that ends up coming out of round bar, there are a few I do that are like that, and they are quoted appropriately.

    You could also do some googling on the material spec, occasionally, you will find some document somewhere that says its been superseded by a spec that you can actually get easily, and in the correct shape.

    If its a government contract, sometimes its buried somewhere in the contract that you can use an alternate material, but a lot of purchasing agents don't read past the quantity and the due date (and honestly, they shouldn't have to). That one bit me in the ass a while ago.

    Ground support equipment is the worst for this type of thing.. A lot of it is older prints, and I think the ground support equipment division is where they put all the troubled neices and nephews of the big wigs so that whatever they design can't actually crash.




    Get thicker plate so that you have something to hold onto.
    Gov't and aerospace mat'l specs are the worst. Like you said, sometimes you can dig around and either find an approved alt mat'l, or find specs that have been updated (but not on that print from the 70's).

    One reason I (mostly) love my new job, no BS specs (for the most part) to deal with. We design and manufacture our own product.

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