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Machining with Small End Mills

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  • 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

    Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

    Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

  • #2
    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.............

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    • #3
      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
      __________________________
      Just one project too many--that's what finally got him...

      Comment


      • #4
        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.

        Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

        Southwestern Ontario. Canada

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        • #5
          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.

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          • #6
            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.

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            • #7
              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

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

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                • #9
                  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.
                  Chilliwack BC, Canada

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                  • #10
                    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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                    • #11
                      Cutter diameter divided by 200 usually lands in the good zone.


                      Sent from my iPhone using Tapatalk

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                      • #12
                        For work that needs 1/16" milling cutters I prefer to use my Unimat. It has spindle speeds up to 7500 RPM and the right speed can help a lot. I would hesitate to push a 1/16" cutter beyond 0.005" depth of cut or feed per flute. There just isn't much space in the flutes for big chips. But at high spindle speeds the work can still go fast.

                        But sometimes you need to cut a full width slot (1/16"). Go heavy on the cutting fluid and easy on the feed rate. Breaks can happen, but I usually wear the small cutters out instead of breaking them.
                        Paul A.
                        SE Texas

                        Make it fit.
                        You can't win and there is a penalty for trying!

                        Comment


                        • #13
                          Originally posted by Mcgyver View Post
                          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
                          Using that GWizard tool for a 1/8"diameter 2 flute mill running at a chip load of .0015" per tooth and the 2800RPM max value I can get from my mill the answer seems to be a feed rate if 8"/minute.

                          But at my 2800 RPM max the SFM is only 92 feet/minute. So it likely would not take a whole heck of a lot to cause an issue if you feed at all too fast.

                          My mill's lead screws are 10TPI. So at 8 inches per minute that's 80 turns of the handle per minute. Or 80/60 =1.33 turns per second. Dang, that's a lot faster than I was expecting!

                          In looking up "chip load for small end mill" I also found THIS PAPER on micro end mills and how to reduce their breakage. I didn't read it all the way but it looks like it's worth the time.
                          Chilliwack BC, Canada

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                          • #14
                            I'm rather suspect of that bit of software.
                            .

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                            • #15
                              I did a fair amount of contours in 1/8 think O1 tool steel with a 1/16 endmill. Originally I was breaking them far too often but then I searched around more for speed/feed charts and the one I had been using was WAY too aggressive. I now run the 1/16 endmills at between .0003 and .0005 chipload per tooth and they last very well, very rare for one to break. Also, the holder used and its runout is of utmost importance ! Runout is a real killer of tiny endmills, effectively you end up cutting with one flute and WAY higher chipload on that tooth, extreme deflection also happens which is instant breakage with carbide.

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