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  1. #1
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    Feb 2020
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    Default Sparks when face milling ?

    I noticed a few sporadic sparks flying when face milling a 20mm wide piece of mild steel plate.
    Cutter and setup:
    IMG_6429.jpg

    From a different angle:
    IMG_6431.jpg

    The mill is small, Optimum BF20 (DIY LinuxCNC conversion):
    IMG_6432.jpg

    Surface finish:
    IMG_6433.jpg
    The surface looks worse than it is, feels very smooth using finger nail.

    Using a 50mm insert cutter running at 1600-1700RPM with a feed of 100mm/min and cutting depth of 0.2mm. Using WD40 as cutting compound.
    The mill specification states max cutter size is 63mm, but that's optimistic at best and a blatant lie at worst, the machine really isn't rigid enough for large diameter (>20mm) cutters.

    I see a few sporadic sparks during the cut, not many and mainly near the start/end. The sparks are not the star shaped type you see on a grinder, just a single bright orange glowing small blob.
    The tramming of the mill is not perfect, but very close.

    My questions:
    Is this normal? What makes it spark? How can I prevent these sparks?

    Any help/opinion/views would be much appreciated.

    Thank you for reading my post.

  2. #2
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    Default

    Generally sparks may indicate the tips are becoming blunt.
    Were you able to adjust your speed to see if things changed?
    Your depth of cut may of been a factor, being shallow there may of been the occasional red chip flying off.
    The type of tip profile may also play some part.
    If you have a 45 degree face mill try that at the above, you may find that it enters the job with a much less shock load than your current face mill.

  3. #3
    Join Date
    Apr 2012
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    Default

    If you are seeing sparks you need to slow your cutter speed and turn your inserts as they have now lost their edge.

  4. #4
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    Mar 2011
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    Default

    I use one of those face mills as my go to for facing just about everything. The sparks are the swarf coming off so hot it’s molten, or very close to it.
    On mild steel I find I get a decent surface running the spindle at around 900rpm feeding around what you’re using (assuming you meant 100mm/min not sec). The swarf comes off hot and blue but not red hot like you’re seeing. Like others have said, check the inserts too.

  5. #5
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    Default

    Quote Originally Posted by racingtadpole View Post
    I use one of those face mills as my go to for facing just about everything. The sparks are the swarf coming off so hot it’s molten, or very close to it.
    On mild steel I find I get a decent surface running the spindle at around 900rpm feeding around what you’re using (assuming you meant 100mm/min not sec). The swarf comes off hot and blue but not red hot like you’re seeing. Like others have said, check the inserts too.
    Thanks for your reply racingtadpole. Yes, feed is 100mm/min (sorry, brain fart on my part!).
    The swarf does come off hot and blue, it's just the odd one that's glowing bright orange.
    I will check the inserts tonight - yes, I suspect they might be a bit but, although the cutter really hasn't done much work..

    How long do your inserts last? particularly when using interrupted cuts.

  6. #6
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    I've found particularly with hot rolled or slightly surface rusted steel that I get the occasional spark. Thats running a 63mm facemill @ 1400rpm and recommended feed.
    Have noticed similar on the lathe - my interpretation being that both were related to the non-clean nature of the material.

    If you're getting reasonably regular sparking then as others have said....

    Steve

  7. #7
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    Quote Originally Posted by TheApprentice View Post
    Using a 50mm insert cutter running at 1600-1700RPM with a feed of 100mm/min and cutting depth of 0.2mm.
    Way too fast and the fact that the chips are coming off blue indicates that. Dropping the speed down to 900ish as racingtadpole suggests should stop the sparking and bring things down to a more normal temperature.

  8. #8
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    Quote Originally Posted by TheApprentice View Post
    Thanks for your reply racingtadpole. Yes, feed is 100mm/min (sorry, brain fart on my part!).
    The swarf does come off hot and blue, it's just the odd one that's glowing bright orange.
    I will check the inserts tonight - yes, I suspect they might be a bit but, although the cutter really hasn't done much work..

    How long do your inserts last? particularly when using interrupted cuts.
    I’m still using the first set of cutting edges on all but one position (that one chipped through a random act of stoopid on my part). I’ve had the cutter for about a year, and probably fed it a couple of hundred linear metres of mild steel and a similar amount of 5 and 6 series aluminium. The machine is an RF45, similar size to yours give or take.

  9. #9
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    melbourne
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    I agree with 900RPM but your feed should be 0.07mm to 0.1mm per tooth which puts the feed around 300mm/min.
    I would check to see if all the tips are in line axially and radially.
    Carbide hates to rub.

    Robert

  10. #10
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    Thanks to everyone for your help.
    I changed the inserts and reduced the RPM to 900 .... no more sparks.

    The face cutter came with a pack of 10 "no-brand" inserts.
    The first set hasn't done a lot of work but I suspect they could have suffered when I machined mill-scale surfaces.

  11. #11
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    I use mine for removing the mill scale from large plates and bar, it shouldn’t be problematic to the cutter to do so.

    Edit:
    A couple of pictures of the surface finishes I’m achieving, the mild steel looks atrocious but is actually very smooth, just seems to be how hot rolled plate finishes. The other picture is 5 series Ally.
    Attached Images Attached Images

  12. #12
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    Quote Originally Posted by racingtadpole View Post
    I use mine for removing the mill scale from large plates and bar, it shouldn’t be problematic to the cutter to do so.
    what inserts do you use?

  13. #13
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    I’m still using the packet that came with it, from memory they are APMT 1604 inserts.
    Its just a generic chinesium 50mm cutting head with four flutes.

    I saw Elan post something about tip radius and feed rates a while back, going to experiment a little once I finish my poor mans power feed (adapter for a battery drill). I’ll report back once I have it if finished. I have a bit of liquifiable cash floating around this month, I might get a couple of packets of other inserts and do some testing in a couple of weeks for funsies.

  14. #14
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    Quote Originally Posted by racingtadpole View Post
    I saw Elan post something about tip radius and feed rates a while back, going to experiment a little once I finish my poor mans power feed (adapter for a battery drill).
    That would have been tip radius in relation to depth of cut on lathes.

    I have no idea if or how it affects milling and how it also interacts with the all the other angles involved. There is a LOT more going on with milling than turning and it's above my pay grade. Some of the stuff here might be useful at least as a guide Milling | MITSUBISHI MATERIALS CORPORATION

  15. #15
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    Ha! This is the internet... plausible deniability is no excuse..

    Thanks for the link, I suspect this is about to become something of a rabbit hole. A few minutes of searching over a coffee has already gone some ways to explaining the finish I’m seeing on the mild steel, appears the standard inserts supplied with those face mills are not particularly good at anything, they appear to be a sort of hybrid roughing/finishing type deal (jack of all, master of none). Bit more research to be done before deciding on which type of inserts to buy for experimental purposes.

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