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Fly Cutter: Cutting Tool Bit Geometry

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  • Fly Cutter: Cutting Tool Bit Geometry

    Are the following tool bit angles correctly located on the fly cutter
    shown in the images below?
    • Side cutting edge angle
    • End cutting edge angle
    • End relief (clearance) angle
    • Side relief (clearance) angle
    • Side rake angle





  • #2
    A rounded edge is needed for a good finish.
    Have a look here, it is quite a good right up
    http://madmodder.net/index.php?topic...sg6442#msg6442
    Dave
    Edit
    Here is another
    http://www.thewarfields.com/cnccookb...faceFinish.htm
    Last edited by Davo J; 04-17-2010, 04:24 AM.

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    • #3
      Bits for fly cutters

      When you sharpen a tool bit for a fly cutter, think of it as if it was a turning tool for the lathe. Really, there is no difference other than it is going in a circular pattern instead of straight. The result is the same. You have to sharpen the bit with the material you are cutting in mind and adjust the clearance angles and rake accordingly. The angles are not black and white but many shades of grey, if you know what I mean.
      Jim (KB4IVH)

      Only fools abuse their tools.

      Comment


      • #4
        First photo, the angles labeled "cutting angle". I don't usually worry too much about the one you labeled "end cutting" as it really is not a "cutting" angle. Fly cutters are usually used in a sideways motion to produce a flat surface so only the tip will actually cut on the "end". But if you are cutting to a shoulder, the one you labeled "side cutting angle" will produce that shoulder and if you want a square shoulder, you will need to modify that angle on this cutter.

        You have the other three angles correctly labeled. There would also be an "end rake" angle but it is of less importance as a fly cutter would not be used for a plunging cut so 0 degrees would be just fine.

        The side relief angle must be large enough to allow clearance for the radius of the cut. One good way to do this is to use the angle you want for the primary clearance here and add a secondary clearance facet that ends a bit behind the cutting edge at a larger angle.

        As Davo said, do round the tip a bit for a better finish unless you just must have a square corner in a shoulder.
        Paul A.
        SE Texas

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

        Comment


        • #5
          The surface/edge you have labeled "side cutting edge angle" is actually THE cutting edge. That is what you want to worry about getting a nice edge on (stoning), or at least the bottom 0.100 or so (depending on desired DOC). If you want/need "rake", it will be back from this edge. Also remember that the end is sweeping a radius, so you need more clearance "under" (behind) the cutting edge than normal. You need to clear the inscribed circle PLUS a bit to allow for in-feed clearance.

          Also as stated, you may want a small radius at the bottom contact point in order to get a good finish. And your "side cutting edge angle" varies depending on what you are doing. As shown, it will give you a nice cut without as much drama/hammering, but you can't get close to a wall, and you sure can't get under an overhang (I have ground them to cleanup a dovetail).

          Most of the other angles should be established by the fly-cutter body, though clearance is easily if needed.

          So it works somewhat like a cheap boring bar using replaceable HSS bits, but the cutting edge shifted 90*.
          Russ
          Master Floor Sweeper

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          • #6
            Guys, I think that's just an unground, new tool bit he's using for illustration purposes.
            Lynn (Huntsville, AL)

            Comment


            • #7
              I think if you ignore the labels which I doubt many would agree on, the angles are the right ones.

              Here's an image I edited from one on Wikepedia:

              http://metalworkingathome.com/images...ergeometry.jpg

              It is essentially a left-hand lathe cutter, rather common geometry and which should slip right into your flycutter holder. The surface labeled side view becomes the advancing surface in your holder.

              and here's the original from Wikepedia - a right hand version of the same thing:

              http://en.wikipedia.org/wiki/File:Tool_Bit_Geometry.JPG

              Edit: I edited the surface names in the image to make it more appropriate for a flycutter.
              Last edited by dp; 04-17-2010, 03:25 PM.

              Comment


              • #8
                your last photo correctly shows where the rake and clearance are...not many seem to get this for a fly cutter. The right tool to use is NOT a lathe knife tool, a knife tool has the cutting edge on the side of the bit, whereas a fly cutter cuts on the end of the bit

                The links dp put up are imo misleading in the sense that the give the location of the angles for a knife tool. The identity of the angle isn't determined by their orientation to the tool bit, but by where the cutting action is taking place, which i think you've nailed. For a flycutter as you presented the cutting is at the end as you've shown, not on the side as it is for a left hand knife tool.

                The nicest fly cutter tools imo, and the nicest lathe facing tools, are those with the cutting edge on the end with positive rake formed by grinding a chip breaker

                Dennis i know thinks himself pragmatic for not knowing or caring where the cutting edge is and me a nanny for paying attention to it ....but I think you're on the right track; if you can't actually identify where the cutting edge is, how the heck are you going to grind things properly? Fundamental I say.

                .

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                • #9
                  First off, I really dislike fly cutters. IMO they are hard on milling machines. Especially the light duty mills seen in home shops (I am including BP's in this). Think of it this way. While the tool geometry is similar to a lathe tool it is also like taking an interrupted cut on the lathe. Every revolution you are putting a load on the bearings and drive system and then unloading them. Just think of the strain the keys are being subjected to in the pulleys. That said there ways to limit the shock load on the machine. 1)Try to make the tool entry as easy as possible. That means finding a cutting path that upon entry intt the work the amount of material being cut is as thin as possible and the cut gets progressively thicker as the tool rotates. Think of it as conventional vs climb milling. 2) Grind the tool so it has more shear angle on the top rake. Better 10D than 5D. Keep the tool nose radius to a minimum if possible. The longer the radius the more material being sliced off each pass. Side rake has to be enough that the tool does not drag against the back side of the cut if the feed rate per revolution is high. 7D is about right IMO. 5D for the front clearance should work . Go to a web site like Sandvik or Valenite http://www2.coromant.sandvik.com/cor...SA_klick_D.pdf and look at the insert geometry for and how they are mounted in the cutter for the light cut and low HP face mills. Granted they pound when only one insert at a time is in the cut but once one insert is in the cut all the time the load on the machine is much smoother and puts less of a strain on it. another analogy to this is if you ever have to order a Woodruff Keyseat Cutter spend the extra couple of bucks and get the stagger tooth type versus the straight tooth version. The difference in cutting performance is really noticable.
                  Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

                  Comment


                  • #10
                    Originally posted by Mcgyver
                    Dennis i know thinks himself pragmatic for not knowing or caring where the cutting edge is and me a nanny for paying attention to it ....but I think you're on the right track; if you can't actually identify where the cutting edge is, how the heck are you going to grind things properly? Fundamental I say.
                    I actually didn't care for the poor orientation in the original lathe cutter view as applied to a flycutter so I rotated the end view and labeled the surfaces for a flycutter orientation. Never attribute to pragmatism that which can be explained by pure laziness

                    Comment


                    • #11
                      Hope this is not redundant comment, haven't read every word in this thread.

                      To help visualize fly cutter tool angles, grind a left hand lathe facing tool (for turning the left, or headstock, face) and install this in the fly cutter.

                      Mark

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                      • #12
                        Thank you to everyone for the replies - I apologize for the lengthy delay
                        in replying.

                        Originally posted by Mcgyver
                        Your last photo correctly shows where the rake and clearance are...
                        not many seem to get this for a fly cutter. The right tool to use is NOT
                        a lathe knife tool, a knife tool has the cutting edge on the side of the bit,
                        whereas a fly cutter cuts on the end of the bit
                        Thank you.

                        Originally posted by Mcgyver


                        The links dp put up are imo misleading in the sense that they give the
                        location of the angles for a [left hand] knife tool. The identity of the
                        angle isn't determined by their orientation to the tool bit, but by where
                        the cutting action is taking place, which I think you've nailed [in the OP].
                        For a flycutter as you presented the cutting is at the end as you've shown,
                        not on the side as it is for a left hand knife tool.
                        If a Right Hand turning bit was positioned vertically as shown in the revised
                        image below, then I believe that the respective angles and clearances
                        would be correctly located for a fly cutting operation. However, just
                        mounting a Right (or Left) Hand bit in the illustrated fly cutting tool
                        would not position the bit optimally for cutting.



                        Originally posted by Mcgyver
                        The nicest fly cutter tools imo, and the nicest lathe facing
                        tools, are those with the cutting edge on the end with positive rake formed
                        by grinding a chip breaker.

                        Thank you for this picture, it validates the suppositions made in the OP.

                        Would you be able to provide another image showing the type of finish
                        this bit produces and post about feeds/speeds (along with a bit of
                        background about the class & HP of machine: drill/mill, BP or other)?

                        .

                        Edit: Changed 'suitably' to 'optimally'
                        Last edited by EddyCurr; 04-20-2010, 12:53 AM.

                        Comment


                        • #13
                          This is my collection of flycutters and cutters I use in them. I run the flycutters at 1000+ rpm and take up to .050" on most metals. It helps to have a 30 to 45 deg leading angle on the cutter to cut smoothly and I don't use a radius on the cutter except for special cuts. A radius will make the cutter hammer and the larger the radius the more it hammers.

                          It's only ink and paper

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                          • #14
                            I haven't used a fly cutter in years because I don't much care for the hammering on the spindle of the Bridgeport. I suppose I'd use one if I needed to get a single full-width finish on a piece of aluminum, but for everything else I've been satisfied with the results I get with a 2-1/2" 45؛-lead 4-insert Widia face mill I have.

                            As long as the spindle is trammed-in right, the finish has been outstanding and no steps. It runs 4x the feed rate of a fly cutter, and much more if the fly cutter has HSS bits. Smooth as butter, light loads on the 1HP motor and the high shear angle imparts no hammering. I think I've rotated the 4-sided inserts once in 2 years of infrequent use, though if I needed more inserts the SEHN43's available from a wide variety of sources, in milling-specific grades and coatings.

                            Comment


                            • #15
                              This image shows the flycutter as installed in the tool. These cutters do not advance into the work as your arrow shows - they cut a sweeping spiral as seen from above like stretching a Slinky (tm) sideways into a flattened series of spirals.

                              The specific relief angle shown on the work facing surface is not correct for this service (zero degrees is fine, in fact, as shown in McGyver's photo) and further demonstrates that all cutter angles are ground to satisfy a specific need. If you see specific angles shown for a cutter then there should also be a description of how it is expected to be used or at least be obvious.

                              http://metalworkingathome.com/images...teroverlay.jpg
                              Last edited by dp; 04-21-2010, 05:03 PM.

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