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How not to destroy your end mills?

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  • How not to destroy your end mills?

    I was milling a set of truck frames for a 1/8th scale diesel locomotive, and managed to destroy all of my end mills. Snapped a 1/8th and 3/16th's 4 flute, and the rest of them, managed to turn them into corner rounding end mills that cut like crap.
    They all are cheap made in China end mills.
    In a different forum it was mentioned that my speeds and feeds were off, and I agree with that, especially on the two that snapped. My gibs were also loose which is a death sentence, along with lack of rigidity of my Sieg X3 milling machine.
    But I also have another theory that contributed to my end mill carnage, my work holding.
    What is the maximum overhang per thickness of part should there be?
    My frames are made from 3" wide 1/4" thick 1018 Cold Rolled steel. My 4" milling vise has jaws about 1" tall. I placed two 1-2-3 blocks between the jaws and the truck frames to increase the height of the clamping forces to help keep flex away, but that still leaves 1" about above that.
    The two frames are tack welded together, at the opposite end from the one being milled. What this means is that it is possible for the two plates to ever so slightly spread apart from the milling forces. Can this also kill end mills, or knock the corners off? I was cutting slots for the pedestal binders, which are perpendicular to the long axis.

    What I am thinking is that I need to get some thick steel plate, just high enough to allow for milling clearances, to keep the plates together. I suppose I should tack weld with my TIG the same end that I am milling as well, to keep them from flexing apart.
    I just spent 50$ on two quality end mills, one is a 3 flute rougher, the other is a double sided 4 flute end mill. Ordered them from McMaster Carr, so don't know who makes them, but McMaster Carr has never sent me poor quality anything in the past. The taps I get from them are either OSG or Greenfield, so I am thinking the end mills are good quality too. I am really going to be depressed if I kill these end mills as well.

    Now that I recall, about 6 or so years ago, I was making engine frames for a Kozo A3 steam locomotive, same exact setup, and it sheared a tooth right off my 1/2" rougher I was using.. Probably too much overhang...
    I can see why people get these things water jet cut.

  • #2
    Play and slop will kill them. Are you climb milling?


    • #3
      Appropriate speeds, feeds and all flavors of rigidity get it done.

      Some materials are worse than others. Scale on hot rolled can be problematic. Stuff that likes to work harden can get ugly.


      • #4
        I had a little drill mill sieg thing, it used to eat cutters, it's so flimsy I think, I can stick an 1/8 in my old cincinatti and it comes off the same as it went on, though an 1/8 cutter in a 40 taper chuck is overkill


        • #5
          generally, BREAKING stuff comes from feeding faster than the sfm can handle, which is the exact same thing as giving too much cut depth per tooth.

          Conversely, burning the corners off is usually from way too much sfm, too high an rpm for the cutter diameter.

          That often means small end mills get snapped, and large cutters get the corners burned off. It's hard to get the sfm high enough for small diameters (needs high RPM), and it's hard to hold the rpm DOWN on large cutters.

          Whenever you have slop in feeds, flexible material, or a poor setup, that can give you a huge feed all of a sudden, when the work suddenly flops into the cutter, putting a cutting edge against a solid wall of material, instead of letting it attack the material near an edge where it can peel off a chip. It's really not anything different, it's just a way of getting too large a feed unexpectedly.

          Keep eye on ball.
          Hashim Khan


          • #6
            The depth of cut should not exceed the diameter of the cutter. Also I'm sure you have a lock to stop the table from moving in the x and y direction. If cutting aka feeding in the x direction, have the y lock tight and the x lock taught.


            • #7
              Can you post a pic or two of your setup?

              As to feed & speed here is a handy app for your android phone FSWizard.



              • #8
                I'm with the other Paul. I do not understand your use of the 1-2-3 blocks and I wonder if it worked in the reverse of how you intended: allowed more movement instead of less. Please do post a photo of your set-up.

                And have you tried to test the hardness of your milling cutters? Will a file work on them? Perhaps they were not properly hardened.
                Paul A.

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


                • #9
                  How odd, similar thread running over at 'arolds place.


                  Even stranger, in General and not in Milling!


                  • #10
                    You had a good idea with the 1-2-3 blocks, but it could help to add a c-clamp or something onto them to make sure nothing moves.

                    Do you have to end-mill these pieces? If you're taking material off, just for a flat edge, it would be easier to clamp to the table and side-mill. Side-milling produces less heat than end-milling, you also don't have small, sharp points to chip off.

                    1018 CRS shouldn't have much scale or work-hardening and such... odd... as others have said, if you're cutting with .125 or .188-size end mills, you may as well run flat-out.

                    Say 80 SFM:

                    80 x 4 / .125 = 2560 RPM. Ballpark number for soft steel, HSS .125 end mill. But chip evacuation is very important with such a small cutter... as well as not taking deep cuts. I am a fan of deep, thin cuts, as opposed to less-deep, wider cuts.


                    • #11
                      That other thread is also mine, since most of you don't visit both forums, I thought I would expand the pool of brilliant minds to help me.
                      I left this morning for work, will be away from the shop for a few days. The 1-2-3 blocks basically add an additional 1 inch of clamping force for the plates, since the plates are sitting upright, extending 3 inches from the base of the vise. That overhang allows the plates to flex from milling, much like turning something on a lathe, with it extended away from the lathe chuck more than it needs to be. Most of the milling was done in fact, with the plates mounted horizontally, clamped to the table. During these operations, there was no flexing going on, but I was feeding too fast and cutting with a too high of an rpm. I didn't notice the damage to the EM's until I had to cut the slots for the pedestal binders. In fact, the mills are cutting slight keyways. My pedestal binders will slide in just fine from the sides, but not from the top down!
                      Drat... I would post a picture but I didn't renew my web hosting service...


                      • #12
               is free and directions for use are in the forum at the beginning. You ABSOLUTELY are not going to fast on the rpms with a 1/8 endmill. Feed YES but not rpm.