broaching on a CNC mill
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  1. #1
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    I had heard of this but, know nothing about how its done. Anyone ever done this?

  2. #2
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    I would tend to think that it would be really bad news for your ballscrews... broaching involves a lot of force.

  3. #3
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    believe it or not ive done this actual operation.
    while at McDonnell~Douglas we had a job that needed a 1/2"keyway in a 8" length.
    made a bar to hold a 1/2" HSS lathe tool.
    indicated everything in using a m-19 to orient the spindle and then wrote a program to simulate a vertical shaper.
    kept bumping the feed rates up.
    finally had to drive the spindle in rapid for the cut.
    worked out great...jim

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    Wow - I'm supprised. What kind of machine were you running?

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    50 taper Mazak.
    dont remember the size but the table was approx. 48" X 80" pretty large actually.
    didnt seem to harm the machine as the chip load was .005" per pass...jim

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    >> per pass

    Oh, I get 'cha... I was thinking of a multi-cutter broach that did the whole job in one pass (the kind that's pulled with a hydraulic machine)...

  7. #7
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    no this was basically a shaper job didnt have one i dont think anyone there would have known how to run it if they had a shaper.
    i dont think a .005" per pass would do anything to the ball screws...jim

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    Not the ball screws, but what about the spindle bearings? I've been told that they do not like any axial load without turning. Causes brinelling.
    I've seen this subject erupt into a holy war before.
    Any thoughts?
    Pete

  9. #9
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    I asked Haas about broaching and they did not recommend it.

    Too bad I tried it first, before someone said, hey you can't do that on a mill? Then I thought maybe they are right, lets give a call. Non the less it works. You can also lift up heavy piece and locate them into a fixture with ease using the head, again NOT recommended by the machine manufacturer.

  10. #10
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    well not being a machine repairman i cant make a revelent comment about that.
    what i can say is this.
    i performed that job in 1984. the machine was still running perfectly when it was auctioned off in 1994, 10 years later after the plant was closed.
    i believe that a major Z- crash would stress the bearings more than a .005" depth of cut at 150 ipm.
    remember that was '84 and rapids then werent 1180 ipm like now...jim

  11. #11
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    The story I heard was for a an aluminum corner that had to have a 1/8" radius 4" deep and the passes were .002-.0005 deep.

  12. #12
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    this was a steel job.
    you couldnt even get a bite at .002" DOC.
    .005" was the minium that i could get to pull a chip with a new HSS tool.
    mind you this part is about 7" in dia. and about 14" of stroke length to clear the 8" of key length.
    no story just the facts...jim

  13. #13
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    bummer. i wanted a story

  14. #14
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    well thats the way it goes, sometimes you dont get what you want...jim

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    We have mostly swiss machines(not good for broaching) so I do all the broaching on a robodril(30 taper).Never had a problem.

  16. #16
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    I have broached quite a few small parts on CNC's. I made the broaching tool offset so the cutting edge was on centerline, for less rotational torque on the spindle. A couple of jobs it was a y/z circular interpolation to print, it was drawn for 4" dia. gang cutters.

    I got the idea from the manual forman, who used to broach (shape) a part with the quill on a Bridgeport, and just adapted it for cnc. I thought it was novel, until I saw Mazac demonstrate it at IMTS. They did it on a lathe, and shaped an internal keyway to finish.

  17. #17
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    Hi Machinist kid,
    Sloting is done on our machine centre using .
    spindle stop
    M19 orentation
    G98 (MM or inches min)
    G81 (Drill mode )with a X or Y movements.


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