Climb Milling Question

Hi..     I'm confused.. I have been given advise that one should not do climb milling on lighter, Atlas mills, but after reading some tutorial
information:
        http://www.hanita.com/hanita_protected/tec00006.htm
It seems like you would WANT to climb mill when using a mill attachment with a lathe. I would *think* that you would want to make sure that the rotation of the end mill in regards to the material travel, forces downward pressure on the material in order to insure maximum rigidity. According to the tutorial, this seems backwards. Where has my thinking gone wrong? Please help a confused newbie!!
Jim
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On Fri, 20 Feb 2004 13:30:49 -0500, James Flanagan

Tubal Caine in his little booklet "Milling Operations in the Lathe" states that down cut milling "should NEVER be used in the lathe, as in the absence of backlash eliminators in the feed-nuts the feed is uncontrollable." i.e the mill tends to pull the work inward, away from the feed. Then the feed catches up. Chatter... bigtime.
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wrote:

And that holds true with any milling machine as well that may have a bit of slop in the lead screws. Its VERY noticable with a two or three flute cutter. My Clausing horizontal has a loose nut, and it really digs in and makes a mess when climb milling as it over runs the thread in the screw. slams forwards, takes up the slack, slams forwards , takes up the slack..etc.
With conventional milling, its a nice steady push against the screw threads.
Gunner
"To be civilized is to restrain the ability to commit mayhem. To be incapable of committing mayhem is not the mark of the civilized, merely the domesticated." - Trefor Thomas
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Any idea how a "backlash eliminator" might work? A double nut with an adjustable clamping action on the leadscrew maybe?
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John Ings wrote:

On my old horizontal it is a double nut with hydraulic pressure to take up the slack. This pressure is only applied while feeding and is release for "fast return". Nice bit of "oil, values, and pipe"
logic designed into the machine controls.
Ray Spinhirne
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John Ings wrote...

Depends on lead screw wear. If it's new, or worn very evenly (ha!), it might be ok. Not if the lead screw is worn considerably worse in some areas than others (like mine).
Jim
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wrote:

I think the hydraulic mechanism Ray mentions might take care of that problem. Hmmm... could I make a small hydraulic ram, or maybe something that would work with air pressure...
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Climb milling can give a nicer surface finish, but the machine gots to be extra rigid. In climb milling the tool is trying to pull into the work instead of push away for conventional milling. You'll break stuff, or have severe chatter, on all but the most rigid of setups. On my old bridgy, I used to ruff conventionally to 5 thou. Then turn the speed up and take a climb mill pass for a finish smooth as a babies behind.
I've not used an Atlas mill. Me thinks its less rigid than a bridgy.
Karl
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Try it. Go for a light (three or five thou) cut and you will rapidly see what the trouble is. The workpiece gets sucked under the cutter and this can get out of hand and lead to things like a part rip-out.
Jim
================================================= please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================
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[This followup was posted to rec.crafts.metalworking and a copy was sent to the cited author.]
james_r snipped-for-privacy@raytheon.com says...

Thanks guys.. Seems obvious now.. I WILL give it a try this weekend. Take care all.. Jim
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    [ ... ]

    Just be sure that you're wearing eye protection. There is a risk that the milling cutter may shatter once it grabs, depending on the size, and you don't want to have a "Mark I Eyeball" in the path of a bit of shrapnel.
    The one style of leadscrews most likely to control this would be ball-screws and ball-nuts -- which are made to tune out any slack, and which wear so little so the tuning holds for a long time.
    They are great on a CNC mill (where the leadscrews are controlled by servo motors), but with handwheels, it is possible for the cutting forces to accomplish the same thing unless you keep your hands firmly on *both* handwheels. (Or all three, with a Z-axis feed in the game? :-)
    Good Luck,         DoN.
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I would not want to see a manual machine with ball screws used for climb milling! One reason I can do this to a small degree on my horizontal is that the leadscrews and nuts are in good shape, and acme threads don't 'backdrive.'
But I do take care to snug up the table gibs if I know I'll be climb milling.
Jim
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    I agree, and if you read what I wrote, I think that you will find that I was saying that you really should have the CNC servo motors controlling the leadscrews when you have ballscrews. I just mentioned them for the sake of completeness.

    Yep!
    Of course.
    Enjoy,         DoN.
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On Fri, 20 Feb 2004 13:30:49 -0500, James Flanagan

Climb milling lifts the cutter away from the work, conventional milling forces the cutter Into the work done by the cutter before it..
Look at the first two drawings. The conventional milling cutters are digging into an already rounded face. The Climb milling cutters are hitting a flat face, which not only makes a hell of an interupted cut, but each impact as the chip is loaded slams the machine and cutter away from the work piece.
Gunner
"To be civilized is to restrain the ability to commit mayhem. To be incapable of committing mayhem is not the mark of the civilized, merely the domesticated." - Trefor Thomas
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