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Different guidelines for using roughers?

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  • Different guidelines for using roughers?

    I recently got a 1/2" Tin coated cobalt rougher end mill to use on my Bridgeport knock-off mill. For aluminum, it seems to work fine, full width cut, no problems. Stainless is another issue. I looked at a chart that said 50 sfm, which is a bit slow, but ok fine, whatever. The problem is that for any reasonable cut, the end mill really wants to pull itself forwards. If I do even a relatively slight climb cut (1/2 inch length, .1" width), I can feel it pulling the stage. But if I try a falling cut, it gets really hard to push the mill.

    On the other hand, I can run a 3/8" high helix carbide TiCN mill at a similar cutting depth, and since I can spin it a lot faster, I can remove steel faster with less stage pulling and a better surface finish.

    Anyway, I'm just wondering if there is a "different set of rules" when using a corncob type rougher. How about if I get a smaller diameter carbide rougher? Or should I stick with cobalt?

    I did a search on PM, and even though they are CNC people, the almost never use the corncob type, instead preferring one of them variable flute roughers.

  • #2
    Anyway, I'm just wondering if there is a "different set of rules" when using a corncob type rougher.
    Yes. The general recommendation for a roughing endmill (a "corncob") is to increase the feed per tooth by 50 - 100%.
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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    • #3
      And why would you be climb milling with a rougher???????
      ...lew...

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      • #4
        Originally posted by Lew Hartswick
        And why would you be climb milling with a rougher???????
        Are you implying that the guideline is to NOT climb cut with a rougher?

        If someone's asking what to do differently with a rougher endmill, I think it means they do not know everything, and it makes a lot of sense that they may have experimented to find out what happens.
        So I guess the answer would be "to find out what happens."

        -Matt

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        • #5
          Usually with a rougher you want to bury the whole end mill and cut. Like cutting a slot through a plate. But watch for the end mill to creep out of the collet. (use a end mill holder so that want happen).
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          • #6
            It gets really hard to push the mill in a roughing conventional cut because your pushing against massive cutting force!
            Conventional milling (Not climb milling) is the way to go for everything except the lightest of finishing cuts on a standard mill, because if the climb milling pulls the backlash outta your X or Y, you can easily destory your endmill (moreso with harder metals and mills with more backlash)

            The problem with stainless is it can work harden on you, meaning if you don't feed fast enough, it becomes about 10x harder to cut! thus ruining your endmill, making it about 100x harder to cut.
            You need to learn about 'Flute load' as in, how much each flute of the endmill cuts at your given RPM and feed rate. You basicly have to maintain a min flute load for stainless to cut properly.

            Also note that flute load is reduced from the 'basic' calculated value when your 'width of cut' is less then 1/2 the diamiter of the endmill.

            And never forget the cutting oil! even if you just dribble it all over your workpeice before turning the mill on and only apply more when it starts to smoke (Gets to hot, a squirt of oil on the spot greatly helps cool it)
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            • #7
              Thanks for the advice so far.
              I'd already adjusted the lead screws on the mill such that there is only a few mils of backlash in each direction. I usually don't have problems climb cutting with carbide, but conventional cutting is much more of a problem. It takes a lot of force to make the end mill "go", and even then, it doesn't like it with a lot of squealing.

              This problem is especially bad with the new rougher I have. Conventional cutting takes a LOT of force to push the end mill in, such that my "intuition" is that something is wrong. Climb is easier, but in this case, like I mentioned earlier, it really pulls the stage.


              If roughing mills are designed to do full width cuts, that sort of makes sense because at the the pushing and pulling forces cancel out, and the mill only wants to go sideways? On aluminum, I've done full width cuts with the rougher no problem. Perhaps because aluminum is softer. Only problem is that it shoots hot chunks of metal at me. On stainless, I didn't have a chance to do full width, only about 1/4 D or less.

              I forgot to mention that I was using the spray mist system I built recently. I'm pretty happy with it. When I cut the stainless with the high helix TiCN carbide bit, there was no noticeable wear on the end mill. Lower cutting forces (perhaps due to smaller diameter and higher helix angle.) Shoots out little slivers of steel and aluminum, which don't fly very far, but still clears the end mill. Very pleased. Maybe I will try one of those carbide rougher/finishers some day, with the variable flutes and little chipbreaker notches here and there.
              Last edited by beanbag; 09-29-2009, 06:02 AM.

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              • #8
                It is slightly possable your rougher is incorrectly made.
                Iv heard about really cheap chinese endmills/taps/etc that are made without a relief angle on the teeth, result is they can't cut worth a damn without TONS of force as the teeth are allways rubbing, I kinda suspect such a cutter might still cut in climb cutting however, like you are experianceing.

                I think you can tell if you apply layout dye to the endmill, and see if its all worn off where it should be relieved.
                Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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