Turning a rough finish on purpose
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    Default Turning a rough finish on purpose

    Hey guys,

    I have a Nitronic 60 tube about .500"dia by 2"long. When machining the OD to final size I would like to end up with a Ra around 125. Any suggestions on tooling, feeds, other odd ball ideas? We've currently tried increasing the feed rate while barely touching the OD.

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    Try for a 32 finish, then you will get a 125 .

    I suppose you could calculate scallop height for various tool nose diameters and feeds, and get 125 micrometers per the math, then see what it comes out as. But, surface roughness takes many forms, so if you are actually trying for a specific value, it helps to know what characteristics are desired.

    Regards.

    Mike

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    Use a threading cycle with the calculated desired scallop height. You could also do a pseudo knurl with multi-start threads.

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    https://www1.mscdirect.com/images/so...faceFinish.pdf

    With a 1/16" tip radius you're around 0.016"/rev or with a 1/32" radius around 0.012"/rev or with a 1/64" tip radius 0.008"/rev. I know which one I'd go with on a 0.5" OD tube.

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    Sounds like a phonographic finish. We used a square insert with a 1/32 rad. and feed it around .030 IPR. We used this technique for facing a sealing surface on a flange.

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    Try a carbide cutter whose once-sharp edge has been chipped off irregularly.

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    Quote Originally Posted by edward.santos View Post
    Hey guys,

    I have a Nitronic 60 tube about .500"dia by 2"long. When machining the OD to final size I would like to end up with a Ra around 125. Any suggestions on tooling, feeds, other odd ball ideas? We've currently tried increasing the feed rate while barely touching the OD.
    your going to have to take at least a few thought per side for it to work., all insert rads will give you a 125 finish or a 250 finish or a 63 finish. finish is only adjust by feed rate nothing else.
    if your breaking the tips or wearing them down on harder material like you have, your going to have to use a bigger rad tip. a .015 or .032 should work fine

    how are you checking the finish? visual or meter, if you have a profolometer(sp) just double your feed rate and see what it reads compared to what its currently running.
    if you are checking visual a comparator helps with a sample finish gage and compare it to the part your running.
    remeber with the visual gages a mill finish, lathe finish, grind finish all look different. good eyes help

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    Use a super slow surface speed and a dull insert. Used to do this all the time when prepping for metallizing. Also raise the insert just a tad above centerline height so it rubs real good

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    Could you anneal a set of knurls, turn smooth, grit blast heavy, reharden, and take a single pass across? Might take a few to get the roughness right, but once you hit it it would be repeatable.

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    Quote Originally Posted by JCByrd24 View Post
    https://www1.mscdirect.com/images/so...faceFinish.pdf

    With a 1/16" tip radius you're around 0.016"/rev or with a 1/32" radius around 0.012"/rev or with a 1/64" tip radius 0.008"/rev. I know which one I'd go with on a 0.5" OD tube.
    Thanks JCByrd24, that chart was really useful.


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