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Chip clearing vs lubrication

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  • Chip clearing vs lubrication

    So recently I have been doing a lot of milling on this Bridgeport knockoff mill that I have access to. One of the issues is that of chip clearing. We all know that chip recutting is bad, both for tool life and also surface finish. In an ideal world, there would be flood cooling, or an air blast to clear away the chips. However, here I don't have those options, so the best I can do is shoot some coolant thru a spray bottle or let it run dry. (It's not my mill, so I can't add these features.)

    I've noticed (at least for carbide tooling) that there seem to be two optimal speed ranges. One of them is to go at full speed (close to the actual recommended speed) and run dry. For particular kinds of cuts, like side milling, this works great because the chips simply get thrown out. In fact, I have read that with TiAlN coated end mills, you shouldn't use coolant anyways due to thermal shock, and that it works well with a layer of heat right over the milling surface.

    The other speed range is "much slower than you are supposed to" and use coolant. Because I don't have a flood, this actually causes the chips to stick around. However, the lubricity of the coolant does tend to give a nicer surface finish and smoother cut, especially in aluminum. I tend to use this technique in more closed cuts like pocket milling and slotting. I tend to limit the speed to the point where it doesn't boil off the coolant and steam up.

    So one question is, given that I don't really have access to flood coolant nor air, is there some other good way to get the chips out? This unfortunately rules out the mist coolant systems also.

    I was recently thinking of making a contraption using a portable bug/plant sprayer (those 1/2 to 2 gallon jugs that you pump up) and connecting the output to a tiny nozzle to shoot a very small jet of coolant at the end mill. Probably just enough to keep the surface lubricated, but unlikely to clear away chips. This might work better than the hand held spray bottle mainly because it would be a more consistent flow.
    Last edited by beanbag; 08-14-2009, 04:10 AM.

  • #2
    With all carbide you want to avoid intermittent coolant use due to thermal shock. Well, in theory. In a HSM enviroment I doubt you would see a difference. With steel I run carbide dry. With aluminum you need something to keep the aluminum from building up as you can rarely keep the feeds up high enough to prevent it that way.

    Shop vac works good to keep chips out. Or invest in a small compressor. You dont need massive amounts of air. My bijur spraymist unit runs about 15 to 20 psi. It works great. I am installing one on my CNC lathe as well.

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    • #3
      Thanks, Macona. You always seem to reply to my posts quickly.

      I was thinking of using a vacuum, but shops vac's are really loud. I would need a really quiet vacuum, since I like to hear the sound of the end mill cutting.

      I think the issue of thermal shock is more on coated endmills, than uncoated. These last few weeks, I have been able to cut a lot of aluminum on an uncoated end mill, using hand-sprayed coolant, with nice surface finish and no wear on the end mill. On the other hand, I tried running dry with a different end mill in a slotting application, and it seems to dull the cutter a little.

      Do you know how much cfm your spray mist unit needs, and whether it is powerful enough to blow away chips?

      PS: whatever contraption I use will have to be very portable, as this mill isn't at my home, so I always end up bringing all my tools in a box.
      Last edited by beanbag; 08-14-2009, 05:14 AM.

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      • #4
        As Macona wrote, you don't need much air to keep the chips clear of the cutter. I use a small airbrush compressor with the jet of air directed right at the cutter. For small work it keeps most of the chips out of the way. One tip if using a low volume compressor; to get the best result the tip needs to be restricted enough to allow the compressor to build pressure so that the air jet has enough velocity.
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