Turning RPM calculated from Turn Diameter or Stock Diameter? - Page 2
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  1. #21
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    IMO, Tip as that is where the heat and chip thinning is.
    But the real question is how to you pick a surface footage.
    What makes say 600 magical. Maybe 572 or 612 would be better.
    Metric people tend to pick their own set of nice round numbers that don't map into clean imperial numbers.
    Since the desired SFM is a guess the question is sort of mute.

    (On really, really strange applications where your DOC may be a few inches or 1/2 a foot the tip may be a problem.)
    Your customers may be seeing DOC notching which makes them think this way but that's a different issue.
    If you setup a tool on centerline do you use tip or down the side at cut depth? Maybe another matching puzzle but I think most go for tip.
    Bob

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    Quote Originally Posted by zero_divide View Post

    But when you do keed to know the RPM, you might aw well like to have it calculated from the stock diameter.

    Regardless. I will just make that optional.

    At first, I was thinking WTF are ya'll talking about.

    But then thought better and sat on it for a while.

    So, in my case the tip ( as in turned diameter ) is boss for setting SFM.
    BUT!
    If there is excessive wear on the flank ( or whatever you want to call the edge away from the tip ) of the insert, I just slow it down a bit, but nonetheless, the tip is
    what does the "business" so it is the one that is calling the shots.
    That is to say 300 SFM is calculated at the X-tip of the tool regardless of DOC.

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  4. #23
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    Quote Originally Posted by SeymourDumore View Post
    .....
    BUT!
    If there is excessive wear on the flank ( or whatever you want to call the edge away from the tip ) of the insert, I just slow it down a bit, but nonetheless, the tip is
    what does the "business" so it is the one that is calling the shots.
    .....
    Is the excessive wear up the side and away from the tip a sign of too much SFM or a toolholder/insert geometry problem?
    Not that a normal user has much choice in this as they will be limited to catalog standards.... BUT...
    In the world of HSS many like to grind their own tips. Maybe because it is more flexible and the carbide insert/holder world is sort of fixed.
    Bob

  5. #24
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    Quote Originally Posted by Gobo View Post
    A depth of cut of .1 at a diameter of .2 is unrealistic. Your scenario is invalid. Question- how much actual time have you spent operating lathes?
    I've turned .25 material to .05 in a single pass to make a punch, but I was using a manual machine.

  6. #25
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    If you are taking large cuts like 1.25" per side on a 5" bar it seems to me you better be thinking about the bar size. Otherwise the "flank" or the side of the tool will be burning up. Used to see big cuts like that done all the time on screw machines and turret lathes.

  7. #26
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    Just split the difference. Calculate for .250 dia. If your material is so soft that you can take a 50% cut over the finish dia size I don't think it will matter where you calculate the RPM. If you can get more out of it then increase your RPM. If your insert breaks or your .250 dia bends or melts then decrease your RPM. You aren't even considering your feedrate. If you need a calculator for figuring out your RPM then you should go back to the deli counter.


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