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Making a large fly cuter

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  • Making a large fly cuter

    Tomorrow, weather and wife permitting, I plan to make a large fly cutter capable of ~10" sweep. My intent is to make it roughly 2" wide and 1" thick, with a 3/4" straight shank. The center will have a shallow recess with chamfered edge to match my BP 2J spindle nose protrusion OD. Plan is to put it in relatively firm up on the spindle nose as I tighten the collet. The pull-in action should further set the chamfer on the nose for greater stability (every bit helps, right?). Both ends will be cut offset for 3/8" bits (because I have numerous suitable Kennametal L-Hand bits in that size.

    I've searched and found a bit, but not easy when searching for something like "fly cutter". So I figured I would post and see if anyone had any nice tricks I might incorporate.

    I have a specific job that needs this, but not needed regularly, so I borrowed a suitable fly cutter. Problem is, it was made for dealing with (apparently) large pipe flanges or something, and was intended to do both top and bottom of the part with one tool. So a bit was put down on one side, up on the other. But to clear for the top cut (I assume?), it has about 4" protrusion from the 3/4" shank, and the cross beam(?) was about 5/8" thick and 2" wide. The protruding part of the shank is about 2.5" diameter, but it still chatters no matter what I did. Speed, feed, DOC, grind geometry, nothing seemed to matter when making a full 9.5" wide uninterrupted cut. I'm not satisfied with the finish, so I'm making one with no overhang and about approximately twice the thickness.

    Finish is the primary goal. Any suggestions?
    Master Floor Sweeper

  • #2
    How about a big HSS big holding boring bar in a boring head?

    Or just a round short shank heavily/securely welded onto the middle (for balance) of a long thick bar, alignment doesnt matter very much since its a single tooth cutter. then drill/mount a hole for a small HSS bit and another taped hole for a set screw to hold it in place
    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


    • #3
      My guess is that you're getting a good deal of flex in your bar resulting in harmonics and uneven pressure. It's got plenty of mass, but it doesn't likely have as much rigidity as you might think.

      For something that long, I'd think some kind of ribbed gussets would help, but you're going to lose some daylight implementing them.

      Since we don't know what you're after for final effect, maybe it's possible for you to burnish or polish the surface after doing multiple passes with a smaller cutter?


      • #4
        One of mine

        Here's one I made for a job.

        Can't remember the size. It has a 20mm (~0.800") spigot for my largest ER-32 collet. It is made from a spare tool-holder for a HSS tool bit.

        It worked quite well.

        I used it in my HF-45 square column mill.


        • #5
          Some previous offerings here

          Post #13 is my version of what I think you are intending.




          • #6
            Here's a grind

            This might help w/the grind

            Note: I saved this from a thread posted previously about flycutter grinds. It was either from this site or PM. Either way, I neglected to reference the original poster of these images when I saved them. I apologize as I feel the op should be credited for the original info.

            They are handy pics as flycutter grinds/design seem to be a reoccurring topic.
            Last edited by recoilless; 02-28-2010, 08:15 AM.
            I bury my work


            • #7
              Cutter shape is important and an angled leading edge gives the best finish as well as fast cutting. If the cutter is cutting a square shoulder as it progresses across the work it hammers like hell and has a poor finish. The two flycutters on the right in the photo and the cutters above them are the best cutting of all my flycutters. A cutter with a 45 deg leading angle cuts much better than anything I have tried. The other cutter shapes were for special jobs and could never be run fast or with heavy cuts like the 45 deg leading edge will do. The insert holder is a negative rake cutter and is great on hard material. Mass in the flycutter is your friend with a large span so make it heavy and stout.

              Last edited by Carld; 02-28-2010, 10:02 AM.
              It's only ink and paper


              • #8
                Here's a wonderful thread on fly cutter design:


                • #9
                  There are several huge flycutters on Youtube, cutting cylinder heads. Here's one of them:
                  It does have considerable mass as he says it's made from 2" alloy.
                  Last edited by nheng; 02-28-2010, 12:49 PM.


                  • #10
                    I know about grinding for the fly cutter. Thanks, but this is not my problem. I've had great success with my existing fly cutters, but they have a swing only up to a max of 5" or so. With the borrowed fly-cutter, I tried various angles of lead angle, rake, HSS and brazed carbide. Some better than others, but all chattered, and I am pretty sure the main problem was the relatively flexy bar with excessive hang-out from the spindle.

                    My main thought is to reduce the stick out to near nothing, and double the thickness (to ~1") to both increase mass (hopefully remove the harmonic) and rigidity. A trussed type arrangement isn't out of the question, but may be reserved for a v2 mods if v1 does not work.

                    And the boring head is an option that would produce a very similar fly cutter to the one that did not work for me. Lots of stick out, flexy arm.

                    I'll check out the links too. Thanks...
                    Master Floor Sweeper


                    • #11
                      Just followed the links.

                      That youtube fly-cutter was a beast!

                      This one is very much like what I have in mind to build.

                      Maybe it should be 2" x 2" square, rather than 2" x 1" (oriented flat). That does give a lot more vertical material to help stop the up/down chatter I was getting. And it still lays on it's side to store flat, unlike the one in the youtube vid.

                      This post by madokie is pretty close to my plan to make it pull up hard on the spindle nose. Maybe that's where I got the idea? The only diff is that instead of just making it pull up on the flat, I want to match the taper on the spindle nose so that it pulls up in a female taper on the cutter. Better? I don't know...

                      I also have a piece of gray cast iron, about 2 x 2, but not quite long enough. I want to make a ballanced cutter, but I could offset it and add a steel ballance weight to the back. That would give better damping still.
                      Master Floor Sweeper


                      • #12
                        It would be interesting to bore out the center of that 2x2 cast iron bar, and fill it with mixed-sized lead shot. Won't chatter
                        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


                        • #13
                          I actually pondered something like that earlier on, but was thinking of the steel bar at the time. But I figured I could always pursue that later if needed. So, what "mixed size" shot would work well? Only needed in a pocket near the ends? How big? And would you want it on both ends, or just the cutting end?

                          Might just finish killing the POS HF 2 lb poly dead blow that split the side a while back, and use it for donor material?

                          Looks like I may not get anything done today anyway. It's raining and cold, not good for my legs, and I won't run the machines when I've taken something for them...
                          Master Floor Sweeper


                          • #14
                            Originally posted by BadDog
                            So, what "mixed size" shot would work well? Only needed in a pocket near the ends? How big? And would you want it on both ends, or just the cutting end?
                            It's a shear damper, like DynaMat, so the particle size determines the damping frequency. Bigger shot will damp lower frequencies, smaller shot (or sand) will damp higher frequencies.

                            I've often seen audiophiles make mass dampers with a mixture of bird shot, sand and mineral oil. The mineral oil would be a mess if there are leaks when it's spinning, but automotive exhaust dampers are often just lead shot loosely packed in a cylinder.

                            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


                            • #15
                              'how to make a large fly cuter'- I don't care what you say, large or small, flies are ugly. I can't see how you could improve their appearance.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-