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  • #61
    I sure could have used a fly cutter yesterday- to be more precise a wasp cutter. Trying to change a tire on my van and they're all around me. I used rust cutter instead- penetrating fluid. They don't last long when that's sprayed on them.

    Good for you Bob on making the tool.

    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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    • #62
      If you have a "specialized" cutter, such as a shear cutting tool, well, no, it is not going to work well in a standard traditional angled flycutter. Many of those are set up for a geometry that is not suitable, the tool is not presented to the work the same direction

      But, I have found the same tool to work well for all three uses, if it is a simple tool, either a flat top tool, or one with ordinary side and back rake. The rake is always with respect to the edge, and the edge for a fly cutter can be in a different place.

      I was presuming that one would obviously choose a tool that is generally compatible, having the edge in a place that would actually cut if used as a fly cutter. There are numerous tools that are shaped in such a way that they do not present the edge to the work in one or the other use.

      As for the flat, vs round, that is a matter of clearance angle, and a tool that will work for a large diameter in the lathe is likely to work when used for a fly cutter, given that the edge is presented to the work.

      You appeared to be claiming that rake etc must be approached in a different way for the two (three, including shapers?) types of tool. I have found that the usual principles of rake, chipbreaking, etc apply pretty well to all uses.

      I don't think anyone is claiming that you can take any random tool which was shaped for use on the lathe, and use it in a fly cutter with a guaranteed good result. There are many for which that WOULD be true, but clearly some that are for a lathe, or a fly cutter, and do not cross over. For those, it will generally be a matter of the cutting edge simply not being oriented in a way that crosses over well.

      A threading tool, or any member of the "pointed end" family, or some with "rounded end" is unlikely to work in a traditional angled flycutter. Nor would a cutoff tool.

      But some of those would work well if , for instance, they are mounted at 90 deg to the work as they would be in a lathe.



      CNC machines only go through the motions

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      • #63
        Comes to mind that several criterion enter the picture- motor power, spindle rpm, radial positioning of the cutter, its sharpness, rake angles, resonance points on the machine- that's a start.

        Starting with motor power- typically the smaller the machine, the less powerful, and the higher the range of rpm. If you have lower gears you can preserve torque at lower rpms, but you might find that you have more power at higher rpms. If that's the case, you would want to spin the flycutter faster, which in turn probably means the radius should be shorter. You may not be able to span the full width of a workpiece in one pass to avoid the 'step', but you might get a better result overall if you're not sending the machine into convulsions trying to swing a radius that it can't handle. Even if your machine does preserve power as you lower rpms (gears or belt drive steps) the amplitude of the resonances might be too high to allow a decent surface finish, and to keep the machine from knocking itself to death. Everything suffers if the machine does that. Carbide especially won't like that.

        I've come to really like my 1 inch diameter flycutter. I used a morse taper stub arbor to start with, and milled a pocket for a triangular carbide insert into the stub. The tip of the cutter sticks out past the stub and it sweeps out a circle of about 1-1/4 inch diameter. That breaks all the rules about covering the full width of the workpiece in one sweep, but it's quieter to work with, doesn't break the carbide, and I can run it faster because the balance is closer. In addition, if the tram is out, the step you make will not be as deep- but of course having the machine in tram is much preferred anyway.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

        Comment


        • #64
          Hi Guys,

          I've been a little busy this past couple of days, but I did get chance to take a couple of pictures of a piece that I flycut using the flycutter that I showed the picture of.

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          These are a couple of pictures of a piece of material from the scrap bin, originally 12 mm steel plate. Machined on all edges to be 30 mm X 35 mm. One side has been fly cut at 350 rpm with a 20 thou DOC, the other with the same cutter at 550 rpm and a 5 thou DOC. Both sides at 3" inches/minute. The bottom picture is after a 4 mm hole has been drilled all the way through.

          If you look carefully there is a crack in the steel, bottom picture. Look near the top right hand side, almost level with the top hole.
          Best Regards:
          Baron J

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          • #65
            I tried to find my original pics of one of my first attempts at cutting steel with my flycutter I just built and could not find them --- but I did find the piece of metal with some rust on it so i took a few swipes at it with some fine scotch brite, there's a reason other's have suggested to build the cutter so it accepts inserts - even the cheap one have a very nice radius on them that leaves a great finish...

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            • #66
              You can do actual serious machining with a flycutter. I made the indicator body cutout in a chunk of aluminum for the micrometer stop/indicator holder here by machining the recess using just a flycutter. At that time I had no mill, the shaper was not going to be good for the purpose. Could have clamped it to a faceplate, don't remember why I did not do that. It was LONG ago.

              CNC machines only go through the motions

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              • #67
                BCRider For what little it's worth, I had trouble flycutting a difficult piece. To be fair, mine was mainly mill scale but the HSS was blunt before I'd got a fraction of the way across. I'm pretty sure that was mostly my terrible grinding skill and the fact that I wouldn't know a good rake if it flipped up and got me in the face. I swapped to a left hand lathe tool with a CCMT insert and got mediocre results. I put a cheap import CBM insert in it and got a fabulous finish as it tore off the mill scale. Just don't let the insert come to rest on piece if you stop it on a lathe, it seems to weld itself to the piece and then it's all over.
                For aluminium with an aluminium profile CCGT insert it will happily take out to about a 0.5mm DoC - beyond that the shape/size of the insert is such that it starts ploughing rather than cutting. Light cuts on steel work with the same insert too.
                Holder was just an MT3 off-the-shelf (round and angled down to one side) with the slot widened to take the lathe tool.
                A hand-filed chamfer down the leading edge (where the tool hits) reduces the thumping as it ramps in rather than impacts.

                I'd like to run a face mill but I think my machine is rated for something paltry like 20mm so I'd probably be removing all but one insert....which is a fly cutter by any other name anyway.

                Comment


                • #68
                  Hi Cenedd, Guys,

                  From your description you have probably being running the fly cutter too fast ! Mill scale is very abrasive and will take the edge off a Carbide or HSS tool bit very rapidly. Its a bit like cast iron, you have to take a deep enough cut to get under the mill scale. I admit that in most cases of removing mill scale I prefer to use an angle grinder and coarse flap disc. Do this outside rather than inside then the dust just gets blown away by the breeze, you don't want that abrasive dust on you machines. Once you have got rid of the scale then you can start fly cutting !

                  As you have found a number of tool bits behave in different ways ! For alloys I use a rounded end HSS bit with plenty of back rake and about ten degrees of top rake. For steel I use a more aggressive cutter grind with a more lathe tool shape and more hook to the cutting edge. You have to balance the cutting speed and cutting edge thickness to suit the cutter speed and material hardness, or you just take the sharp edge off your tool bit. Too slow is better than too fast !

                  A lot depends upon the finish that you are trying to achieve. Generally I'm not too bothered trying to get a glass like finish, I'd rather take a couple of bigger cuts to get down to the dimension that I want. A DRO makes this much easier to do.

                  Almost forgot, use lubrication ! I use diesel or white spirit on alloy and any cutting oil I have to hand on steels !

                  HTH.
                  Last edited by BaronJ; 05-01-2021, 03:15 AM.
                  Best Regards:
                  Baron J

                  Comment


                  • #69
                    BaronJ I think you may be unduly crediting me with grinding a viable tool in the first place! It is an art that I've failed to devote the required learning time to, I'm afraid. Inserts - and cheap ones at that - have been working for me so far. I'll play with grinding HSS more when something forces me to need it - like a form tool perhaps. Also, I now try to avoid hot-rolled steel for just that reason!

                    Comment


                    • #70
                      I've been away for a few days so catching up.

                      JT, I suspect you posted reply #62 in response to my earlier post.

                      It's little subtle changes to the usual angles that I was suggesting. If I made it sound like cutters for any of the machines would be radically different then sorry about that. You're perfectly right that the angles and such must still all fit within the basic principles. It was the idea of subtle changes to the angles to suit the cutting path geometry that I was suggesting.

                      For example I'm used to seeing rake angles given for lathe tools at around 5 to 7°. This allows for the fact that we spiral cut into the work so we need to allow for the angle of the spiral into the work as well as keep enough angle to avoid contact with the front or side face and the drag and galling which would occur. But shaper tools step over then make a straight pass. And this is reflected by the angles being specified at 3 to 4°. And it sure did make a huge difference to the life of the tip and edges when I went for this shallower angle.


                      And now a minor side track from thinking about the example given above......

                      If we think about it there is some degree of similarity in the fly cutter tool and an internal boring bar. It is somewhat like we are on the lathe and using the boring bar to take a light facing cut from the bored hole out across the end face of the part. So it needs a suitable angle to avoid dragging the heel of the side relief. But that can make for a more delicate edge when it thumps into the next cut. So perhaps a spiral shape for the side rake that ensures heel clearance while reducing the side rake just behind the edge to a fairly durable 5° angle?

                      And at the same time taking a hint from my shaper cutter experience we can reduce the clearance angle of the "front" or bottom of the cutter facing the surface to more like around 3° to encourage a more durable edge for the interrupted nature of the cut.

                      If this sort of fine tuning were to be used it would certainly make for specific cutter differences between flycutter, lathe and shaper tooling aside from the obvious overall shapes required by how the tool blanks are held. Typical case would be the often seen angled body with slot style fly cutter.
                      Chilliwack BC, Canada

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                      • #71
                        Here's an idea- shoot me down if I deserve it. Ok, start with a round insert. On the side of your square fly cutter body, machine a bit of a recess to nest the cutter into, and drill and tap for a holding screw. Position this behind the rotational axis of the body, and make sure the OD of the insert hangs below the body by some amount. Now as it spins it will shear material away instead of gouging it away. Hammering should be reduced to a bare minimum.

                        Because the insert is round it will tend to rotate. With the usual right hand thread holding screw, it will tend to unscrew, so you'd either use a left hand holding screw, or design the fly cutter to rotate the other direction and use a regular right hand holding screw. This is just a detail though, having nothing to do with the shearing action you're setting up.

                        To help visualize the action, draw a line on a piece of paper, then align your thumbnail with the line and crease the paper. Then go back and misalign your thumbnail and follow the line again. Your thumbnail will want to follow a new line, but you make it track the old line. That's the shearing action

                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                        Comment


                        • #72
                          Hi Guys,

                          I seem to recall that someone made a tool for a fly cutter that was specifically designed for round inserts ! At the time I thought that it was a good idea and bought some round inserts. I've never used them, they’re still in the packet. I think that they would make better lathe toolbits.
                          Best Regards:
                          Baron J

                          Comment


                          • #73
                            Originally posted by Cenedd View Post
                            BCRider For what little it's worth, I had trouble flycutting a difficult piece. To be fair, mine was mainly mill scale but the HSS was blunt before I'd got a fraction of the way across. I'm pretty sure that was mostly my terrible grinding skill and the fact that I wouldn't know a good rake if it flipped up and got me in the face. I swapped to a left hand lathe tool with a CCMT insert and got mediocre results. I put a cheap import CBM insert in it and got a fabulous finish as it tore off the mill scale. Just don't let the insert come to rest on piece if you stop it on a lathe, it seems to weld itself to the piece and then it's all over.
                            For aluminium with an aluminium profile CCGT insert it will happily take out to about a 0.5mm DoC - beyond that the shape/size of the insert is such that it starts ploughing rather than cutting. Light cuts on steel work with the same insert too.
                            Holder was just an MT3 off-the-shelf (round and angled down to one side) with the slot widened to take the lathe tool.
                            A hand-filed chamfer down the leading edge (where the tool hits) reduces the thumping as it ramps in rather than impacts.

                            I'd like to run a face mill but I think my machine is rated for something paltry like 20mm so I'd probably be removing all but one insert....which is a fly cutter by any other name anyway.
                            cbm=cbn?

                            Comment


                            • #74
                              Originally posted by dian View Post
                              cbm=cbn?
                              Yes, sorry. Not sure if it was fat fingers or autocorrect but Cubic Boron Nitride if you're trying to Google it - otherwise all I get is search results for cannabis.

                              Comment


                              • #75
                                Originally posted by darryl View Post
                                ......Ok, start with a round insert. On the side of your square fly cutter body, machine a bit of a recess to nest the cutter into, and drill and tap for a holding screw. Position this behind the rotational axis of the body, and make sure the OD of the insert hangs below the body by some amount. Now as it spins it will shear material away instead of gouging it away. Hammering should be reduced to a bare minimum.......
                                That's an interesting idea. I sketched it up as shown. Is this the idea?

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                                In the straight down top view any but the most extreme insert or used on a VERY big diameter of cut will foul the heel of the clearance angle.

                                But down in the side view there's enough clearance. The clearance will reduce as the area of the cut moves up from the lowest point to some higher amount towards the situation in the top view. The point where the back side heel starts to foul would be determined by the insert diameter, swept diameter of the fly cutter and the feed rate of the cut. But I don't think it would be hard to make it so one could achieve about.04 to .05 DOC cut. And of course most of the time the DOC would be a lot less as is the usual nature of fly cutting.

                                I'm not sure about the spinning part though. With out some manner of thrust bearing behind the insert I think there would be enough friction to stop it moving. I'd also worry about any play at all which allowed it to spin also allowing the insert to bounce around even just a trifle and lead to chipping away of the edge. To do the rotating thing I think we'd need a little shaft and bearing setup that spins which the insert mounted onto firmly to get the proper support.




                                Chilliwack BC, Canada

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