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How Would You Make This: cutting a disk into a BIG flycutter

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  • How Would You Make This: cutting a disk into a BIG flycutter

    I've tried things like this before and haven't been happy with the results, so I'm wondering how you guys would do this:

    I have a few aluminum disks, 8-11" OD, 1-1.25" thick, and I would like to turn one into a large flycutter for my Bridgeport J-head. I would like to use it for jobs like surfacing cylinder heads (aluminum usually, but occasionally cast iron) and similar parts, till now I've been doing it with a largish Sandvik shell mill on an R8 (just under 7", just barely short of the width of a lot of the cylinder heads I'd like to do, but I get away with it by making a full pass across the chambers and then just clean up the edge near the intake in a second pass, which doesn't cut across anything important that might leak). I'm leaning towards using a 10" disk (I figure the more overhang I can get the better/more consistent the finish will be, also more mass can't hurt, I've seen similar cutters made with everything from an aluminum arm, to assorted aluminum disks to even cast iron flywheels...), and attaching it to an R8 shell mill arbor (I know, someone is going to say that an R8 or the bridgeport isn't rigid enough, but it's done every day, so I'd like to stay away from that discussion).

    More specific questions:
    - How would you bore the center hole to attach the arbor? The big machine tools I have the bridgeport and a 10x22 Grizzly lathe. I've had sort of questionable luck with just boring a hole for something like this on the mill and getting very, very little appreciable run-out, though to be fair I've only tried something close to this size once and it was junk steel that didn't machine well. I'm tempted to just clamp it to the table, find center and try boring. The lathe seems like a better idea but I'm very close to it's capacity and don't have a clue how to hold the blank to it
    - What would you use for a cutting tool? I have a few 1/2 shank insert holders that I'm leaning towards using, I also have a good assortment of 3/8" shank brazed insert lathe tools (and an assortment of 1/4 and 5/16"). I also have a few carbide inserts for assorted sadvik shell mills (they use different sizes of triangular inserts without hold down holes), a few of the standard triangular and a couple diamond with a hold down hole inserts that work in assorted 1/2" tool holders. I also wouldn't be beyond buying something if it would be prefect and not crazy expensive.
    - One or more than one cutter? I've seen a few made with multiple cutters (in some cases one side got a rough cutter, the other a clean up cutter set _slightly_ deeper, but I have a hard time seeing how to set them up perfectly so they'll never move around...
    - How would you mount them? My feeling is that this would work best with the cutter mounted radially at the edge of the disk, but I am a little worried about it flying out... small fly cutters with a 1/4" shank cutter are one thing, but a 1/2" shank cutter spinning in a 5-6" radius makes me a little nervous (maybe I shouldn't be?). Mounting them vertically in a hole through the disk is another, safer option but I'm not sure I like that idea, especially since it greatly decreases the swept radius (probably into the 4" range with the 10" disk)

  • #2
    Just an idea: http://www.youtube.com/watch?v=I-iVLgILSFY

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    • #3
      Well if you wanted to do it on the mill, you could bore your center hole as close to center as possible and then mount your arbor to it. I would then mount it into the spindle of the mill and put a lathe cutting tool into your vise. You could then take light cuts to true the OD of the disc to the spindle of the mill. You could also take a cut on the bottom of the disc as well if wanted.

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      • #4
        Does you lathe chuck have internal jaws to use as external ones to hold the disc for boring?

        Another way would be to bore the hole on your mill. Then attach the R8 arbor and use it to hold the whole assembly in the lathe chuck for final machining of the disc perimeter.

        Even if you limit machining to boring on the mill, slight eccentricity of the disc shouldn't dramatically affect work of your flycutter. The bit itself creates more mass imbalance than a slight disc eccentricity will.

        P.S. Per your request, I'm not going to say that using such a large flycutter on a Bridgeport is not a good idea.
        Last edited by MichaelP; 01-06-2014, 01:43 AM.
        Mike
        WI/IL border, USA

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        • #5
          The first, and major concern, I would have is that a Bridgeport head is no where near heavy enough for this sort of operation. After that it really doesn't matter how you poke a center hole or matter much how you attach the cutter. Running true isn't a concern for a single point fly cutter as long as the cutter is rigidly mounted.

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          • #6
            As others have said use the mill as a lathe , and with the issue of using a big flycutter in a mill do so with care and take light cuts .

            I have not used a Bridgeport , however have done quite a bit of milling on large and small ,machines if the setup or tool isnt rigid its easy to compensate by taking light cuts .I dont like big disc type fly cutters , my large diameter method is a bar with adjustable cutters along its lenght.
            Never had a problem with resurfacing cast iron heads or even blocks if you can set the machine up with the block mounted on a 1'' plate which is also under the mill to provide a common base , swing the arm around and cut away with 1-2 thou passes until the desired flatness is achieved.

            Using machine tools often calls for ingenuity and the ability to not listen to the people who continuously sy "it can be done that way."
            Michael

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            • #7
              I saw a large Cincinnati That had a rotor from a car disc brake set up as a fly cutter.
              I think it had two or four cutters mounted.

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              • #8
                Do you think the material at that diameter will be thick enough? I might be afraid that it might start to "ring" when using and cause a poor surface finish. Look at the one this guy is using for reference. http://www.youtube.com/watch?v=Lbq_oXw7Zgo

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                • #9
                  I have run large flycutters on Bridgeports lots of times. The main thing is to have it well balanced. You can get an R8 arbor for a shell mill and machine the center for a close fit on the arbor. Mill a slot across the hole for the drive keys and a counterbore for the bolt to hold it on. Drill a vertical hole near the edge for a 1/2" brazed carbide tool and drill and tap for a setscrew in the edge of the flycutter so it pushes the tool against the back of the hole. Use a tool with a 45 degree point similar to a threading tool. You may want another hole exactly opposite to put a balancing weight in if needed. As long as everything is balanced and running smoothly it will work fine.
                  Kansas City area

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                  • #10
                    Originally posted by Toolguy View Post
                    I have run large flycutters on Bridgeports lots of times. The main thing is to have it well balanced. You can get an R8 arbor for a shell mill and machine the center for a close fit on the arbor. Mill a slot across the hole for the drive keys and a counterbore for the bolt to hold it on. Drill a vertical hole near the edge for a 1/2" brazed carbide tool and drill and tap for a setscrew in the edge of the flycutter so it pushes the tool against the back of the hole. Use a tool with a 45 degree point similar to a threading tool. You may want another hole exactly opposite to put a balancing weight in if needed. As long as everything is balanced and running smoothly it will work fine.
                    I agree with all of that when surfacing where the cutter is always over the plate. Interrupted cuts, like on a cylinder head, will be a different matter.

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                    • #11
                      Originally posted by oxford View Post
                      Well if you wanted to do it on the mill, you could bore your center hole as close to center as possible and then mount your arbor to it. I would then mount it into the spindle of the mill and put a lathe cutting tool into your vise. You could then take light cuts to true the OD of the disc to the spindle of the mill. You could also take a cut on the bottom of the disc as well if wanted.
                      I'm glad I posted this, you've reminded me of things I used to do when I didn't have the lathe (using the mill spindle as a lathe, I even have 2 lathe cucks, a 3" and 4" that are mounted to an R8, and then I would clamp a lathe tool in my vise suported by a set of parallels and turn away...).

                      Originally posted by MichaelP View Post
                      Does you lathe chuck have external jaws to hold the disc for boring?
                      Yes, but I'm not sure what I'm going to hold, I have a flat 10" disk and a 10x22 lathe, how do I grab it to cut it?

                      Originally posted by 1-800miner View Post
                      I saw a large Cincinnati That had a rotor from a car disc brake set up as a fly cutter.
                      I think it had two or four cutters mounted.
                      I seriously considered this, I have a bunch of 10.5-12" rotors sitting around, as well as 2 massive ones (I haven't measured them but I would guess around 13.5 and heavy off of my cummins ram), Making some sort of hub to hold it shouldn't be too bad, but I couldn't figure out how to hold the cutting tool, since they all have vented centers. If I could make this work I would actually think it would be better because of the mass of the iron rotor... I might even have an axle that I could cut up and use to make the hub out of

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                      • #12
                        I think you could hold a 10 inch disk on a 10 inch lathe by using a faceplate and drilling three or four holes in the disk to match the slots in the faceplate. Or tap some holes in the face plate. You would have to rough cut it fairly accurately, probably with a saw so it will turn over the ways. Then some light cuts to true up the OD.

                        Boring the center should be fairly easy if there are some spacers between the disk and the faceplate. 1/4" to 1/2" should do: just enough to allow the boring bar to go all the way through and stop before it hits the faceplate. You can drill a starter hole in it on the drill press before taking it to the lathe.

                        I have made some fair sized fly cutters for use in my lathe and mill and one thing you have to be careful of is making them too big to allow them to both start and end the facing cut off the edges of the work piece. with a 9 or 10 inch cutting circle you need to subtract 10 to 20 inches from the X travel of the mill. You could easily wind up with a tool that is too big to do practical work. If you stop the cut before the cutter circle clears the edge, you risk leaving a small step on your new face. Of course, I do not know the X travel on your Bridgeport so you may have enough to spare.
                        Paul A.
                        SE Texas

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

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                        • #13
                          Originally posted by Silverback View Post
                          Yes, but I'm not sure what I'm going to hold, I have a flat 10" disk and a 10x22 lathe, how do I grab it to cut it?
                          I meant the 8" discs that you had.

                          I edited the original post a bit to correct errors and make it more clear.
                          Last edited by MichaelP; 01-06-2014, 01:44 AM.
                          Mike
                          WI/IL border, USA

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                          • #14
                            Think id prefer using a brake rotor, less flex than ali, just drill a hole for the toolbit clamp, cheap and cheerful but it works, ive seen ali ones on the tube but they would be 1/3 of the mass of the iron one i think that might be a disadvantage when flycutting, im lucky enough to have a big ol sandvick side and face, its about 35 lbs of steel but it needs a big machine to spin it, nt40 ish, sticking big cutters on a r8 seems a little harsh to me
                            Mark

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                            • #15
                              I actually wouldn't be surprised if the big sandvick that I have wasn't somewhere near that weight, it's heavy enough that I left it sitting on an upside down 5 gal bucket overnight and when I cam back to it the next day I found that it caved the plastic in completely, if I could find one an inch or more bigger I'd be all about that, I have 3 right now that are by far my favorite tools in the mill, one just under 3", one just under 4" and then big one.

                              I still don't have a clue how I'm going to hold a tool to a brake rotor, I love the idea but I just don't see it with the maybe 1/4" top and bottom surfaces and fins in between... am I missing something?

                              Paul, good point, I keep forgetting to measure the travel on the mill, I suspect even with the big knee/table (it has the larger of both sizes available for both), I'm going to end up very tight on travel... I remember the first time I tried something like this, didn't really pay that much attention to the setup (didn't center it at all), and tried to auto feed it I found that the PO didn't center the DRO scale when he mounted it and it shattered the inner scale and broke the mounts when it hit the end if it's travel before the table reached its...

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