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Best Practices for Flycutting / Interrupted Cuts On Bridgeport

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  • Best Practices for Flycutting / Interrupted Cuts On Bridgeport

    I just got a proper mill and I'm interested in being kind to it as it has already lived far longer than I have. One thing I know is a tough job is interrupted cuts. My old mill/drill didn't have gears so I was probably just punishing the spindle spline, but from what I've learned so far the clutch dogs in the bridgeport style heads don't care for the beatings that interrupted cuts give.

    Is there a way to do this best with minimal pummeling? entering the workpiece with the fly cutter set not right down the middle, but to the end of the part, to try to ease it into the work instead of punching the edge like a wall?

    Using an insert face mill, ideally with enough inserts that it's always got contact with the part and then never interrupts?

    Higher RPM, lower depth of cut? Low chip load I presume is good for it, so a higher RPM and a lower DOC with more passes would be nicer to it, albeit taking more time to accomplish the task.

    I suppose I can perform the "see how it sounds" test and stick to the quieter methods.

  • #2
    Milling is all interrupted cuts, but unless you are in a terrific hurry, then smaller cuts put much less strain on the machine. If you use solid carbide, then on a manual mill you can use maximum rpm as the cutters are designed for much higher speeds. A shell mill of up to 100mm diameter will have at least 5 tips, more likely 8, will spread the forces. I use a Ceratizit 50mm 5 round tipped shell mill for all types of steel, as it cuts easier and the tips can be indexed to 8 positions, so there are 16 edges per box. I think the Ceratizit is limited to about 11000 rpm as long as the screws are changed with the tips, so my max of about 2100 is not going to worry it.

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    • #3
      Smaller fly-cutters are ok I think - I cut several traction engine cylinder saddles on my old girl, thats a 12" dia cut using a single tip on an extension arm mounted on a large boring head, each saddle was about 10" deep so i used the quill and knee for the cut, happy days

      Anyway she managed it OK and is still running today as a CNC mill, the splines and the dogs take a beating but seem like they always rattle anyway, certainly didn't get any worse, i always made sure she was well oiled, including the splines, maybe that helps?
      If it does'nt fit, hit it.
      https://ddmetalproducts.co.uk
      http://www.davekearley.co.uk

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      • #4
        I think the only reason for fly cutters to exist today is simply that they are the cheapest cutter available for a mill. In the old days of carbon steel cutters and very slow spindle speeds they were a good match. They can produce a nice looking finish.

        If you want flat to the limits of your machines capability an end mill wins because it won’t deflect like a fly cutter. If you want the highest metal removal rate a solid endmill sized to use the spindle rpms available while maximizing the load on the motor will be fastest by far.

        There is lots of talk about HSM High Speed Machining today. What most people don’t realize is that it is becoming popular is not so much that it faster cutting. It is because non-geared spindles are simple, cheap, and accurate, but don’t produce lots of torque and at 1/4 speed they put out 1/4 the power. So small tools turning at higher speeds match those spindles better, and use more of the available hp

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        • #5
          Originally posted by garyhlucas View Post
          I think the only reason for fly cutters to exist today is simply that they are the cheapest cutter available for a mill. In the old days of carbon steel cutters and very slow spindle speeds they were a good match. They can produce a nice looking finish.
          Another reason being that its much faster to take a one 12" wide cut on a manual machine vs. gazillion 1/2" cuts. Big fly cutter and carbide tooling is good match as you get enough high SFPM even with museum mills.

          I don't know why the fly cutter is always envisioned as a bar sticking out of spindle.. make it solid disk and it won't deflect and the rotating mass helps with hammering.
          https://youtu.be/reQxZOjaNaA

          My "little giant" flycutter:
          Location: Helsinki, Finland, Europe

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          • #6
            Originally posted by garyhlucas View Post
            I think the only reason for fly cutters to exist today is simply that they are the cheapest cutter available for a mill. In the old days of carbon steel cutters and very slow spindle speeds they were a good match. They can produce a nice looking finish.

            If you want flat to the limits of your machines capability an end mill wins because it won’t deflect like a fly cutter. If you want the highest metal removal rate a solid endmill sized to use the spindle rpms available while maximizing the load on the motor will be fastest by far.

            There is lots of talk about HSM High Speed Machining today. What most people don’t realize is that it is becoming popular is not so much that it faster cutting. It is because non-geared spindles are simple, cheap, and accurate, but don’t produce lots of torque and at 1/4 speed they put out 1/4 the power. So small tools turning at higher speeds match those spindles better, and use more of the available hp
            What are working on? And how many 6 to 10 inch face mills do you own?

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            • #7
              Fly cutter or larger size insert face mill for a nice finish looks. Reasonable diameter end mill and multiple passes if you want a flatter and more true surface.

              Now before that idea gets jumped on let me explain.....

              If the mill is perfectly in tram, bearings are good and the mill does not flex then either can do just fine. But if things are out a touch on the tram then a flycutter or large face mill will cause a tilted or scooped cut depending on the tram error. And if out at some angle then both a scooped and tilted cut.

              Now an end mill will do the same thing. But being a smaller span the error for any single pass is going to be very small. If a 4 inch flycutter on an out of tram setup produces a .0015 scoop in the middle of the cut then a 3/4" diameter end mill will only produce .75/4 x .0015=.0003 roughly.

              The surface left from an end mill may not be as pretty to look at but if the need is more for flatness then that's how I tend to go.

              It's also not any slower. In fact Guy Lautard wrote an article in one of the Machinist's bedside readers comparing the two. The flycutter has to cut at a lower RPM. Plus it only has one cutter so the feed rate has to reflect that or the chip load goes up. On the other hand a 4 flute end mill running at the same SFPM and chip load is going to speed through each pass at a far faster rate.

              Also if the mill is in perfect tram the flycutter has an advancing line and a trailing line in the cut. And it needs to feed onto the part and off the other end for a little over half the diameter on each end at the same glacial feed rate to keep that pattern looking good. The end mill needs that same treatment. But with the multiple teeth and matching feed rate it is moving faster and has less distance to travel.

              Bottom line was that a "by the numbers" comparison between something like a 3" flycutter with HSS and a .5" HSS end mill on a 2" wide bar was that the end mill was actually faster. But I can say from personal trials of both that the flycutter when set up just right leaves a really nice looking surface which the end mill can't match by a country mile.

              Back to your question. I would not worry about it. Mills are designed and made knowing that much of the cutting done on them is going to be interrupted cuts. And it's not like you hog off yards of metal with a flycutter. That's what insert shell mill cutters are for. To speed things up though do use a screw insert style tool or a brazed insert tool so you can up the RPM to a value that is a little more reasonable. And since it is a "one tooth wonder" if you find the trailing sweep is cutting deeply instead of just tracing a line then by all means switch corners. And when the corners are all used hone it with a diamond slip if you don't have a new insert. A flycutter is only to be used for lighter cuts anyway. I'd never think of taking off more than probably .005. If I need to cut things down by as much as .010 then I'm switching to an end mill to hog the majority of it away and leave the last .002 to .005 for the flycutter.

              It would also be a mistake to use too light a feed. That's a great way to rub the cutting edge into dullness. You want to see little curlies coming off as actual chips. If you're just getting dust then speed up the traverse a touch. You certainly don't want to see big blue coarse chips either but the edge needs to get into the material and form an actual chip. I find that when things are running neatly that the sound the cutter makes is a light bump with a little short sizzle sound.
              Chilliwack BC, Canada

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              • #8
                Originally posted by BCRider View Post
                flycutter is only to be used for lighter cuts anyway. I'd never think of taking off more than probably .005. If I need to cut things down by as much as .010 then I'm switching to an end mill to hog the majority of it away and leave the last .002 to .005 for the flycutter.
                My Aciera F1 is totally spindle power limited with fly cutter (no real suprise there) but it was easy also to push a 2500lbs russian toolroom mill to max power with disk style carbide flycutter. Chips fly f**** everywhere when you push 8" fly cutter at 900 sfpm and 1/8" DOC.
                Sounds nasty but the russian tools are always designed for hammering&sickle duty
                Location: Helsinki, Finland, Europe

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                • #9
                  Originally posted by MattiJ View Post
                  I don't know why the fly cutter is always envisioned as a bar sticking out of spindle.. make it solid disk and it won't deflect and the rotating mass helps with hammering.
                  A bar is simple. Once you add a solid disc, you may as well add more inserts and make it a face mill.

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                  • #10
                    One thing about flycutting, you can choose the finish you Want or Need.
                    Flatness is relative.. in engine resurfacing the cutter is intentionally out ofmtram, at least 1/2 thou in a foot.so it cuts a not flat surface but adequate for intended use..

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                    • #11
                      What I've found is when ever you have an interrupted cut your setting up a vibration pattern that will show up in your surface finish.
                      I use a Bison 5" shell mill with one carbide insert for my bigger fly cutting jobs. As massive as that head is for my BP and even with .005 DOC and varying the R's I still got a pattern from vibration. It started where the insert met the work and gradually faded away to a perfect finish just before the insert exited the work surface.

                      JL...............

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                      • #12
                        Thanks for the insights. I've been using a small fly cutter with HSS and later a TCMT and round insert holders I made, which work pretty well and hold an edge much better. The glacial pace as mentioned is a pain. I built a power feed for the mill drill just to help that.

                        I just ordered an import 6 insert face mill to try, at least it can be fed at a more reasonable rate and should give a nice finish with purpose-designed inserts instead of the triangle and round types which seem to need just the right feed rate to leave a nice surface.

                        I feel I'll be planning another power feed design pretty soon.

                        Sent from my SM-G930W8 using Tapatalk

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                        • #13
                          It's not the dog clutch that take the heat; if that's adjusted correctly and not in bad shape, it "locks" well. The dog clutch still drives splines. Both the male and female splines wear. The female is part of the lower dog clutch part. The male (spindle) can easily be tested by trying it at full extension verses the middle or close in. You can hear the difference.

                          But.. Just ignore it. Make chips. If it wears out, fix it.

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                          • #14
                            Originally posted by 754 View Post
                            One thing about flycutting, you can choose the finish you Want or Need.
                            Flatness is relative.. in engine resurfacing the cutter is intentionally out ofmtram, at least 1/2 thou in a foot.so it cuts a not flat surface but adequate for intended use..
                            intentionally out of tram? why would that be and how will you hold the tolerance?

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                            • #15
                              You can put a drag on the spindle to keep the quill splines loaded. I did it once with an Aluminium disk and a couple of hard drive head magnets.

                              I've seen it done with a set of vanes driven from the end of the drawbar.
                              Paul Compton
                              www.morini-mania.co.uk
                              http://www.youtube.com/user/EVguru

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