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Fly Cutting Mill Damage

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  • Fly Cutting Mill Damage

    Over the years I've heard that fly cutting is hard on a mill. I have not needed or used a fly cutter and have avoided using them because of the extra wear on the mill. I'm now in a position to take advantage of using a fly cutter.

    It looks to me as though the main damage would be to the quill bearings. I can see that replacing the quill bearings is not trivial but it shouldn't be that difficult.

    Are there other areas of potential damage? Am I underestimating changing the quill bearings?

  • #2
    What mill? If a BP knee mill, the main issue is typicially to the spindle splines. No fix there expect for a new spindle. Bearings can handle it.
    Same happens with a face mill if not cutting on several inserts. OK, so they get noisy... but you've cut a lot of metal to make them that way!


    • #3
      Probably not much more, for the wear:material ratio.

      I do know it played hell on my Sieg mini, though. Plastic gears instead of steel or a drive belt did not get along with interrupted cuts.


      • #4
        I suppose theres a grain of truth that a fly cutter is harder on a mill (the splines like lakeside said, not bearings) but geez its nothing like accelerated wear like 50 uses of a fly cutter and you gotta overhaul it. In the home shop after a 2-3 thousand times you might pick up a slight rattle, if then...

        A fly cutter is one of my favorite tools, getting that almost mirror finish on a piece of crap dug out of the scrap yard is a satisfying thing, I use em a lot!
        If everything seems to be going well, you have obviously overlooked something........


        • #5
          Lets put it this way: It will likey cause less wear to your mill then removing the equivilent amount of material with 10+ passes of an endmill and ending up with a multi tool path finish, compared to a (nicer) flycut finish.

          If you are worryed about the wear, then don't use a flycutter for bulk material removal, use a multi insert facemill or a roughing endmill.
          Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


          • #6
            If you don't use it, it won't wear out.

            Go wear it out and have some fun. Once you wear it out, you deserve the next bigger/better mill.

            Any questions?



            • #7
              If it's hammering and rattling more than you feel comfortable with, then make some changes. I've done a fair amount of flycutting without getting any unusual noises, so it's not like it's something to avoid. The usual rules apply- keep the cutter sharp, keep the material solidly clamped, keep the material as low to the table as practical, keep the depth of cut within reason, keep the SFM in the correct range, try to keep the cutting forces off the gibs-

              Also look at how the cutting edge enters the material. You don't really want it slamming straight on to an edge.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


              • #8
                Frank Ford designed a clever fly cutter that has two opposed cutters, one a roughing cutter, the other a finishing cutter. That seems to me a good idea.



                • #9
                  Here is my version of a two cutter, balanced fly cutter:

                  It uses standard 1/4" HSS lathe tools. I cut one in half for two short cutters.

                  Another neat trick is to set the diameter to 4". This makes the linear cutting speed (FPS) approximately equal to the rotary speed in RPS. No tables or calculator needed to set the cutting speed you want.

                  This one has a threaded hole to mount on my SB lathe spindle, but other types of mount can be used.
                  Last edited by Paul Alciatore; 10-30-2012, 04:40 AM.
                  Paul A.
                  SE Texas

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


                  • #10
                    The shock of a single tooth flycutter certainly has an effect on a milling machine and it's exacerbated if the dynamics result in back lash being present when the tool contacts the work. But that's minor.

                    The big concern are those mills whose spindle does not feature a robust keyed drive. I refer to the keyed flange of 30, 40 and 50 milling tapers.

                    The R8 spindle typical of turret mills and many mill-drills is at a particular disadvantage. It has no key other than a tiny collet indexing dog point screw which has no effective torque capacity on the scale of cutter loads. If the dog point of the index setscrew shears the broken end stuck in the tool shank's keyseat will damage the straight portion of the R8. Extraction of the tool may be difficult.

                    Damage from shearing the R8 indexing feature is no doubt one origin of how flycutting is "bad" for a mill. I strongly suggest those of you who use R8 equipped machinery remove the indexing setscrew as a precaution. The occasional slip of an R8 tool in its taper is several orders of magnitude less damaging than shearing the indeing setscrew.

                    I've run flycutters on mills small to very large and encountered no damage to tooling or machine as a result. The disadvantage to flycutting is its slow and uneconomical. OTH some jobs seem to be made for it.

                    Those without positive keyed drive take care you don't spin the tooling in the spindle taper. Those with positive keyed drive procede with due caution.
                    Last edited by Forrest Addy; 10-30-2012, 04:55 AM.


                    • #11
                      Don't hog with them - keep an ear for major rattles - even if not hogging you might hit a hardened spot in your material or something, LOCK your quill lock tight or you will put wear in the quill bore... use the knee to adjust depth.


                      • #12
                        If your cutter cuts a square shoulder then it will hammer like hell. If you use a 45 deg leading angle on the cutter it will cut fairly smooth. Also, use about 1000+ rpm flycutting and use the feed that feels the best. I have seen and used BP mills that have been used with flycutter for years with no issues.
                        It's only ink and paper


                        • #13
                          Originally posted by Forrest Addy View Post
                          The big concern are those mills whose spindle does not feature a robust keyed drive. I refer to the keyed flange of 30, 40 and 50 milling tapers.
                          To be fair, it does take a LOT of torque to slip a properly fitting 40 taper toolholder even when not using the key feature. I have a 4" flycutter I use in my iso40 equipped mill (it mounts into a clarkeson autolock) to surface heads etc and I've never had slippage when using it. I imagine the 50's are even more difficult to get to slip.
                          I bought a iso50 collet chuck once by accident and when it arrived I had to use two hands to lift the box it was such a monster. One day, I plan to try and machine it down into something useable on my current machine sizes, I'm just glad I didn't buy the machine it was out of by accident too and turn up with my usual lifting gear of a pallet jack and a panel van and some steel ramps


                          • #14
                            I've said it before ..depends how you position the work to be cut and the angle of attack.

                            rather scruffy drawing ..but hope you get it

                            just experiment with a piece of metal ..cutting it different ways'll hear the difference .

                            all the best....markj


                            • #15
                              Mark is absolutely right - the difference is very large. To further smooth the cutting action, I favour a heavy fly cutter - a big solid disk, not the wimpy little cutters that are often sold as ready made fly cutter bodies. My mill is a typical German style machine with loads of gears transmitting the power. The amount of banging that can propagate through maybe ten spur gears needs to be heard to be believed if you get the cut setup wrong. Since some of those gears cannot economically be replaced I worry about this type of thing.