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tell me what I did wrong with fly cutter

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  • tell me what I did wrong with fly cutter

    I got my new Mini-mill from Micromark about 2 weeks ago and, for my first project, am attempting to make a 'setup tool' for a vice (and anything else that needs to be 90 degrees perpendicular to the table. This is a project from "The Home Machinist Handbook". The instructions in the book, in part, are to surface one side of the project with a fly cutter. Remember, I'm in learning-mode here and don't have a clue as to what I'm doing. I had gotten the '3 fly cutter set' from LittleMachineShop. I took the middle road on everything. I took the middle sized cutter, put the tool bit in the middle giving me about a 2" diameter on the circle it would cut, put the mill in high gear and set the speed at about 1500rpm. The project piece, 6061 aluminium was very secure on the table - bolted to it, in fact, according to the project instructions. I turned on the mill and slowly lowered the cutter to the work. It barely touched the work, not more that .001", made one complete revolution, caught the work, stopped the mill and stripped 2 teeth out of the plastic drive gear.

    What did I do wrong and what should I be doing to properly use a fly cutter??
    (As an aside, I find it interesting that the LittleMachineShop will sell fly cutters and, in their generic mill user manual, recommend that fly cutters not be used with mini-mills.)

    Eagon Leather & Knives

  • #2
    I did almost exactly the same thing.
    First, order a couple extra sets of gears, second, my first thought is that your mill is out of TRAM. go very lightly and if all possible start in side the edges so your cutter does not have to bang the edge of the piece you milling. Then after you get used to what it's doing work to the edge.
    Be there done that

    I would rather have tools that I never use, than not have a tool I need.
    Oregon Coast


    • #3
      What you did wrong, eh? You used a flycutter in a mini-mill

      Flycutters are hard on bearings in just about any mill due to the hammering you get. Hammering happens anytime there is an occurance during rotation where there is not at least one tooth engaged at all times. You are just about guaranteed this with a one tooth least when starting.

      I have flycut with mine...only in aluminum and very gently at that. You mentioned only .001" depth of cut. How about feed rate. Often newbies think in terms of routing wood with a router when they think either about cutting depths or feed rates.

      I would use low range. If I can remember the gear arrangement correctly, you will reduce force on the plastic "failure prone" gear that way. Think fewer spindle RPM's. Think about whirling that cutter around lickety split into its first contact with the material and the impact that creates on that plastic gear. I am going to guess that all my flycutting was at a few hundred RPM and very slow feeds to produce a fine finish in spite of the low spindle speed. You don't want to hurl the tool bit out anyway...that tool bit weighs quite a few pounds spinning at 1500 RPM.

      Paul Carpenter
      Mapleton, IL


      • #4
        1500 way to fast

        slow it down to your slowest speed ..under 150 if your mill has it ...

        put the fly cutter over the work ...wind up the table whist moving the fly cutter through its path with hand moving it ...when it touches back off ... (down with the table or up with the head what ever it is on your mill)

        move the table from left to right with the cutting edge of the fly cutter stationery over the piece you're going to mill ..where the fly cutter contacts first the depth of your first pass..

        you see you don't know the geometry of the piece you're cutting ...could be very high at the other end ...high in the middle etc ...
        so find the highest point first ..

        see here in this pic ...the fly cuter has passed over the whole piece and is just cutting the middle ...

        when the fly cutter travels the whole Length with no misses ...that piece has been surfaced .,

        start of with minuscule cuts ...untill you work out how much you can get away with ...with your mill

        All the best.mark


        • #5
          Fly Cutter

          Was the tool bit or insert clamp screw tight??? I have a 2-1/2" diameter cutter with three inserts that I routinely use only one insert, making it a fly cutter without any problems in steel or aluminum.



          • #6
            Thanks to all - let me reply about your comments/questions -
            " - -out of TRAM - -". As close as I could get with this mill was a .002" difference between the left and right ends of the table on the dial indicator. It's a manual "tap it with a mallet" adjustment and that's as close as I could get in 20 minutes of tapping.
            "how about feed rate?" - Zero. I was not moving (feeding) the table - just lowering the cutter to the work. If I attempt this again, I will follow Mark's method (a picture is worth a thousand words, thanks)
            "1500 is way too fast" - It's a variable speed mill - so, I should be able to get a very slow speed. Is there a speed that's too slow??
            "tool bit tight?" Yes - everything was double checked.

            but the best was
            "What you did wrong, eh? You used a flycutter in a mini-mill "
            loved that one.

            Thanks for all your advice - I think I'll have better luck next time ,if there is a next time, with this new knowledge.

            Eagon Leather & Knives


            • #7
              Originally posted by TexasKnifeMaker
              It barely touched the work, not more that .001", made one complete revolution, caught the work, stopped the mill and stripped 2 teeth out of the plastic drive gear.

              "how about feed rate?" - Zero. I was not moving (feeding) the table - just lowering the cutter to the work. If I attempt this again, I will follow Mark's method (a picture is worth a thousand words, thanks)

              I could just be misinterpreting what your saying, but was the fly cutter over top the work when you turned the mill on? If so that won't work, the cutter needs to spin up to full rpm before you try to remove material.
              -Dan S.


              • #8
                On my mini mill I lower the stopped cutter to the contact point then left it a bit. I engage the microfeed for the vert axis and lock the head to the column. I back the work out from the cutter radius and turn on the motor. I advance the work until there is the barest overlap of the cutter and the work. I unlock the head from the column and use the micro to slowly lower the spinning cutter. I want to take the thinnest shave possible. I lock the head to the column again. I move the work under the cutter to the opposite edge to see if there's warpage or off-level condition on the work. At the end of the feed I loosen the lock, lower the head 0.010" with the microfeed, relock the head, and do it all again.

                The flycutter can vibrate loose in the chuck and lower itself (collets help).

                If I don't lock the head to the column during a pass it will surely vibrate down and bust the cutter.


                • #9
                  Originally posted by dan s
                  - - -, but was the fly cutter over top the work when you turned the mill on? - - - .
                  The cutter was rotating at the too fast speed of 1500 rpm as I lowered it to the work.

                  Eagon Leather & Knives


                  • #10
                    Don't lower the cutter to the work ..

                    Do the checks i said ...


                    Start the cutter off the work ...and advance in ...gingerly

                    The wider the the sweep of the fly cutter ...the lower speed that is required ...because the tip will be travelling very fast ...

                    A little end mill of 8mm will need over 800 rpm to cut efficiently ...

                    A large end mill will be travelling very fast at it slower speed ...same applies to fly cutters ...
                    try 80 rpm ...then if your comfortable .... crank it up to no more than 180 rpm

                    The slower you advance it into the work ...the better finish you will get ..

                    Advance too fast ...and it can overload your machine ...and make a bad finish ...

                    Roughing cuts can be sped along ...

                    You will also notice that the fly cutter will cut one way better than the other ..if not set up perfect ..

                    If set up perfect you should see a cross hatch pattern on your work piece ...the trailing edge of the fly cutter gently grazing the work peice

                    If the fly cutter sweep is wider than the work peice...make it so that its "just" wider ... no more than1/8 of an inch ....the fly cutter will then hit the sides of the work at a gentler arc lessoning shock on the machine ...lessoning deflection of the cutter from the shock better finish...and longer lasting cutter.

                    All the best.markj


                    • #11
                      I think you ate too much. you made a big boner or the mill was super delicate.

                      I have a smithy thats ok but nothing great but it does have belt drives that dont die. You horse it it just stalls. thats way better then dead gears.


                      • #12
                        For what its worth and to who'm it may concern ---- Damn, a flycutter is one hell of a tool to learn on!
                        Second, I second what Aboard just stated, do not lower your cutter to your work, your cutter most likely has a "feed angle" to it, if its not a solid machine .001" can easily turn into .010" on the next revolution, If you do not have a table height adjust for the Z then measure where your at and set the Z on the quill, then go in from the side on the X, you want to be sure you clear by a good measure, then keep taking the Z down in little controlled increments, thats the best I can tell you with what you have to work with.


                        • #13
                          Two things,like others have said,set your depth off the workpiece and then advance the cutter to it.Easy method I use is with the spindle stopped,place a piece of paper on the workpiece.Bring the cutter down until it just rests ontop the paper so the paper won't quite pull out from between the cutter and the work.Crank the table over until the cutter clears the workpiece,crank it down the thickness of the paper and your set.

                          Second seriously consider a belt drive conversion for your mill.That's what I did to mine and haven't looked back.No more plastic gears,no more gear noise and it will transmit more power.

                          I just need one more tool,just one!


                          • #14
                            Just for kicks..................

                            The 1500RPM at 2" looks to me like a cutting speed of 785 ft per minute.

                            That's pretty high, even for aluminum. It will require some power to take a significant cut. (hold that thought).

                            Now, LOWERING the cutter means that you may get in too deep, which may be not very deep. Easy to pass the "right" depth.


                            Good chance the cutter simply "caught", no matter what you may think. Due to out-of-tram, or overshoot, etc. Once it 'caught", refer to what AK said, and consider that thought about "significant cut" and power, and whether those gears can stand that.

                            Follow the advice to set the depth and THEN take a pass over the work.

                            Keep eye on ball.
                            Hashim Khan


                            • #15
                              If your mini-mill is like the mill-drill I had, the quill fine down-feed left lots to be desired and could be jumpy. I made a mount for a dial indicator to make sure that the actual movement was what I wanted.

                              No worries, I've learned the most from my crashes.
                              Jon Bohlander
                              My PM Blog