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Thread: Machining with Small End Mills

  1. #1
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    Default Machining with Small End Mills

    Does any one have "Rules of Thumb" when using small, 1/8" diameter or less end mills? Feeds & Speeds to use? Aluminium would be the most used material but occasionally steel would be the material. Being small, they are very likely to break but would like to "knows the rules" to prevent that. Thanks.
    Bill

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  2. #2
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    Quote Originally Posted by BigBoy1 View Post
    Does any one have "Rules of Thumb" when using small, 1/8" diameter or less end mills? Feeds & Speeds to use? Aluminium would be the most used material but occasionally steel would be the material. Being small, they are very likely to break but would like to "knows the rules" to prevent that. Thanks.
    My rule of thumb is high speed and very shallow cuts up to maybe .020 depending on material. Slow on the feed rate also.
    After you break a few you'll get the hang of it.

    JL.............

  3. #3
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    Quote Originally Posted by JoeLee View Post
    My rule of thumb is high speed and very shallow cuts up to maybe .020 depending on material. Slow on the feed rate also.
    After you break a few you'll get the hang of it...
    I agree---there's no substitute for experience and practice when it comes to running endmills,
    especially smaller ones. Most of the charts and tables will suggest speeds and feeds that are way
    too fast for the smaller, less rigid machines that most people have. I think a lot of the charts
    establish their values based on the assumption that the endmills will be run in a heavy and (relatively)
    rigid CNC machine of some sort. Using those settings on a less rigid machine does not always turn
    out well.

    I have a plastic slide calculator made by Kennametal that probably dates from the 80s and--in the
    cases where I've made comparisons--the values it suggests are more conservative than what most
    of the current online stuff will tell you. I've always felt that the best approach is to start out slow and,
    as you become more comfortable with the combination, increase speeds and feeds till the machine
    tells you it's starting to feel unhappy.

    I very seldom break endmills and I think one of the reasons for that is that I don't try to wring every
    bit of performance out them. The speeds, feeds and DOC numbers that most charts suggest today
    are designed around maximum material removal and in a home shop--or even a small jobbing shop as
    in my case--you can achieve good results without killing a lot of tools...
    Keith
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  4. #4
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    If you get down to 1/16 or 1/32 size then expect them to break. Most mills don't go fast enough to run them properly so light cuts, 0.005" maybe and oil. Even AL can be a problem for the under 1/8th crowd, chips jammed in the cut etc.
    The shortest distance between two points is a circle of infinite diameter.

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  5. #5
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    Deflection and the effects of runout will be exaggerated, so you likely need to be conservative compared to say a 3/8" EM, but the science is the same. Likely running max RPM of your mill. I'd start with, where D is tool diameter:

    Axial DOC = .5D up to maybe D
    Radial DOC = 0.1D
    Feedrate = 0.0005 to 0.001 IPT

    More conservative on axial for slotting.

  6. #6
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    Hi,

    My rule of thumb is all the rpms the mill can muster, light DOC - .02" or less, (not necessarily slower feeds though do the math!), and all the chip evacuation I can get, (I prefer high pressure flood but high pressure air will work also). Carbide endmills are stiffer and generally to be preferred, but some days that ain't going to happen.

    You will break them eventually, no matter what. So keep extras on hand and ready to go.
    If you think you understand what is going on, you haven't been paying attention.

  7. #7
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    Higher speeds, shallower cuts, and really slow feed works. And if you hold your mouth wrong, they will still break. Experience will be your teacher.
    Brian Rupnow

  8. #8
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    I use GWizard . Other online feed and speed calculators are available.

  9. #9
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    I like the idea of a calculator to put in some numbers and get an initial "feel" for what is needed. And yeah, for the small stuff it's hard to spin fast enough and that really slows down the feed rates you can use. After that keeping the cuts clear of chips if making a slot becomes more important as well.

    More than once I've thought about making a plug in high speed spindle for my drill press and lathe. It would be a small "model" electric motor with an O ring drive to a spindle that plugs into the MT socket in the machine's spindle. And a small collet chuck to take small parts or pieces of raw stock for making very small items. This could be extended to a mill as well. Lots of room in an R8 shape to hold the bearings for such a spindle. And we're only talking about sizes for about 5/32 and smaller.

  10. #10
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    so far say a DOC of 10 thou what chip load per tooth do you guys think is about right? I've always watched it and backed off when I saw any flex of the cutter....hardly scientific and it won't do you any good with a carbide cutter or cnc. curious what the smart kids think
    .

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