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  • sparks from a face mill?

    I was facing some cold rolled steel this morning with a 6" 10 insert carbide face mill. All was going well and then I started to get sparks. Lots of sparks.

    I was feeding slowly and rpm's at 1400. What was wrong? I have done it the same way many times and no problems and great finish. I was just using compressed air for cooling and chip removal.
    Location: The Black Forest in Germany

    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

  • #2
    Might not have had enough cooling because it sounds as if you hit a spot that was work hardened and you dulled some edges

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    • #3
      Assuming it was the equivalent of regular 1018 carbon steel even work hardening won't be enough to explain that. The most likely explanation was some sort of inclusion of much harder material which instantly took the edge off the inserts.

      More important though is that you were running it much too fast. At 1400 rpm you are driving the inserts at over 2000 sfm. That is only a comfortable territory for Cermets and much too high for carbide. You should be running them no more than about 300 to 500 sfm at most which means 200 to 300 rpm.
      Free software for calculating bolt circles and similar: Click Here

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      • #4
        Originally posted by Evan
        More important though is that you were running it much too fast. At 1400 rpm you are driving the inserts at over 2000 sfm. That is only a comfortable territory for Cermets and much too high for carbide. You should be running them no more than about 300 to 500 sfm at most which means 200 to 300 rpm.
        Not to mention what size machine are using a 6" face mill on, this must be a decent sized mill to run that efficently.

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        • #5
          Originally posted by Evan
          More important though is that you were running it much too fast. At 1400 rpm you are driving the inserts at over 2000 sfm. That is only a comfortable territory for Cermets and much too high for carbide. You should be running them no more than about 300 to 500 sfm at most which means 200 to 300 rpm.
          +100

          probably it was squeaking also.

          I was feeding slowly and rpm's at 1400. What was wrong?
          BOTH OF THESE are wrong.......

          Evan has explained the 1400 end of things..... but the "feeding slowly"..... THAT is really bad also.

          You have a 10 insert face mill.... at 1400 rpm, you had 14000 cutters passing the work per minute. Divide your feed per minute by 14000 and see what you get for a depth of cut per insert.

          Carbide would want at least a thou or two per insert, maybe more....

          if you were feeding at 2" per minute, 2/14000 - 1.4 TENTHS per tooth..... Carbide is not that sharp.

          All you were doing was rubbing most of the time, with a cut maybe once every 10 or 15 teeth, when enough thickness of uncut built up due to feed.

          Slow WAY down, and take a more aggressive feed per tooth, like 10 x more PER TOOTH, not 10x faster absolute. at 200 rpm, you have 2000 teeth per minute, so if you want to feed 0.002 per tooth, you must feed at 4" per minute.
          1601

          Keep eye on ball.
          Hashim Khan

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          • #6
            RPM = (CS x4 ) /Dia. Write it on the wall.

            Originally posted by Mcruff
            Not to mention what size machine are using a 6" face mill on, this must be a decent sized mill to run that efficently.
            +1

            Then you get guys that calculate speed and feed properly, and set DOC to a removal rate the machine can handle.....100 passes .005 thou sort of thing.

            To maximize tool life there has to be the right balance between feed speed DOC and machine/set up rigidity and horsepower. This is where the so called calculators fail; they can't judge rigidity and most don't have horsepower function.

            Not to say you shouldn't doing what you're doing BF - great finishing cut might all you're after, it's just a general common on guys newer to it trying to figure out the cut
            in Toronto Ontario - where are you?

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            • #7
              At that speed and feed if you where taking a light DOC those wern't sparks,but the swarf glowing yellow.Like others have already said 1400 rpm on that face mill is way to fast by a factor of at least three.

              400-600sfpm is the happy spot for most inserted carbide tooling I use.That means a 6" face mill should see 250-380 RPM.

              DOC would be whatever you have the HP and rgidity for and feedrate would be 7.5-11.5 ipm at a .003" per insert chipload.

              Coolant,either none(dry machining) or flood.Intermitant coolant is the second worse thing you can do to insert carbide right behind re-cutting chips.
              I just need one more tool,just one!

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              • #8
                OH Oh OH, I guess I had that all figured wrong! Expensive lesson. I ruined 300 dollars worth of inserts. Unless you think the heat didn't ruin the other corners? Meaning somehow diminished the carbide for cutting.

                I was doing this on a big horizontal mill. Plenty of power and very rigid. It weighs two metric tons. About 4500 lbs.
                Location: The Black Forest in Germany

                How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                • #9
                  Flip them over and see if they work. Nothing ventured nothing gained. Odds are they'll be fine.
                  This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
                  Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
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                  • #10
                    Some sparks is normal, lots of sparks isn't.

                    This was busting through a weld, I had already written off the inserts. Besides, it looks cool.

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                    • #11
                      Last time I had sparks and 'dull thuding sounds' while turning a square thing round.. It was because my brazed carbide tool had developed a 1/32 or so radius on the cutting edge... The bad way. (Rake to front relief radius! ie 0 sharpness).. Yea... Dull thuding sounds.. Thud thud thud. Caused by a dull thuding tool.. who would'a thunk it?

                      Tool edge was of course very badly damaged, And I even managed to strip a bolt that holds my compound to my lathe due to the forces (likey was overtight and chinese swiss cheese steel to start with)

                      Sparks are generaly bad if you don't know why they are happening... as is using a dull tool.
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                      • #12
                        Kennametal has some useful calculators
                        http://www.kennametal.com/calculator...tor_main.jhtml
                        They do consider horsepower. They don't consider rigidity but they do give the tangential cutting force.

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                        • #13
                          The other corners will be fine. Heat doesn't hurt carbide tooling. Otherwise brazing carbide tools would destroy them and it doesn't.

                          If you like sparks then try cermet or CBN inserts.

                          Machining a bearing race:

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                          • #14
                            love the clear pic Evan.

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                            • #15
                              I consider that to be one of the best machining pictures I have taken. It just turned out perfectly.
                              Free software for calculating bolt circles and similar: Click Here

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