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  • #61
    Originally posted by nickel-city-fab View Post

    X2 try turning the revs down to a prime number that won't be divided by two... say 737 RPM for example.
    would be interesting to hear an explanation on that.

    kuk, i believe you mentioned always climb milling somewhere. i wonder if up-milling would help stabilize the cutter by pulling it into the work.
    Last edited by dian; 03-21-2021, 06:09 AM.

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    • #62
      Originally posted by dian View Post

      would be interesting to hear an explanation on that.

      kuk, i believe you mentioned always climb milling somewhere. i wonder if up-milling would help stabilize the cutter by pulling it into the work.
      The goal is to find a frequency that the cutter will not resonate at. Since it has an even number of flutes (usually) find an odd prime number for the RPM. The resonance has a lot to do with the chattering, and eventual breakage.

      Of course, the mill still needs to be sharp etc.
      25 miles north of Buffalo NY, USA

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      • #63
        Originally posted by nickel-city-fab View Post

        The goal is to find a frequency that the cutter will not resonate at. Since it has an even number of flutes (usually) find an odd prime number for the RPM. The resonance has a lot to do with the chattering, and eventual breakage.

        Of course, the mill still needs to be sharp etc.
        Reason you get questioned over the "prime number" RPM is that it doesn't make any sense.

        RPM or minute are just man-made units and they could be anything so odd prime number RPM doesn't really affect anything. Would be different if second is defined as your mill frame's natural frequency but since it is not..
        Location: Helsinki, Finland, Europe

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        • #64
          Originally posted by kuksul08 View Post
          I recently got a shiny new carbide end mill - 1/4" diameter, 1" flute length and 1" stickout, 2 flutes, standard helix, ER20 collet, and the darn thing chatters like crazy. I have never experienced this before with any of my tools to this degree. Usually a small tweak in feed/speed will cure it, but this is so bad I'm getting a rough nail-file like diagonal finish on my 6061 aluminum parts.

          I'm running it anywhere from full slot to .010" WOC, 1/8" DOC, 4000RPM, 16IPM.

          I've read some threads about how I need to load up the tool (0.020" chip load 😨) to get it to quiet down and smooth out, or slow it down to the 1000RPM range and keep my .005" chipload to get out of any harmonics that are occurring.

          I'm thinking of staying with 3-flutes forever after this experience.
          I machine a LOT of aluminum and I only use something other than 3 flute if I need it done now and don't have a 3 flute or the size I need (sub 1/32) is not readily available. I have a lot of 3 flute bright carbide end and ball mills on hand. That being said bright roughers can be pretty handy when pushing the HP limits of the machine. If nothing else it reduces the chance of pullout.

          *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

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          • #65
            its not the cutter resonnating but the whole system. there are strategies implemented on cncs that for example identify the resonant frequency and vary rpm in a band around it in real time.

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            • #66
              Originally posted by A.K. Boomer View Post
              3 flutes on aluminum is pretty good practice from what iv experienced but still you should not be getting this bad of results with two... do you have a geared head mill? could be setting up some nasty harmonics,,, I hate geared head mills - my step pulley belt drive has nothing but smooth elastics between the motor and the quill...
              I have a gear head Mill and would not want to go back to Step Pulleys that I used to have,my Max rpm is 2400. Click image for larger version

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              • #67
                Originally posted by Tundra Twin Track View Post

                I have a gear head Mill and would not want to go back to Step Pulleys that I used to have,my Max rpm is 2400.
                You could probably put my mill on that sideways and slice right through it in a minute or two lol

                my guess is also that your gears are so heavy they resist chatter,,, the pitch of the helical is also important as you want more than one gear tooth connected at the same time, straight cut gears definitely set up a pattern no matter how well the grind/finish is...


                I bring up the gear head on the mill rather than lathe for one very important reason --- lathes are generally "single point" cutting where as mills use multi-point or flutes ---- this is where things can take off and set patterns up say with the side flutes of an endmill engaging into material that's not all that thick and then add the complexities of driving that with gears that even with mild helical can then add to complexities in the cut, and yeah only say this because i used a better quality geared head mill for years then went to my step pulley machine and found out just how silky the dang thing cut in comparison...
                Last edited by A.K. Boomer; 03-21-2021, 03:38 PM.

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                • #68
                  Originally posted by MattiJ View Post

                  Reason you get questioned over the "prime number" RPM is that it doesn't make any sense.

                  RPM or minute are just man-made units and they could be anything so odd prime number RPM doesn't really affect anything. Would be different if second is defined as your mill frame's natural frequency but since it is not..
                  Its called "harmonics". Ad even harmonics can very well be self-reinforcing AKA oscillators. How many times *per second* does the cutting edge impact the part? It will resonate at a given frequency. See Dian's post #65 about how CNC's deal with it.

                  You know, the same principles of waves that apply to electronics, also apply to mechanics. Sometimes the same equations even.
                  25 miles north of Buffalo NY, USA

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                  • #69
                    I just had similar problems with my Series II BP, and the spindle is out getting new bearings and a regrind. The spindle had axial play in it. The thing was squealing like a pig in heat.

                    As for carbide vs HSS, carbide has the huge advantage of being a LOT stiffer than HSS. I also can get carbide with ZrN coatings that resist build up of aluminum which is good for us guys not running flood coolant. I make sure I keep my chipload up and really don't pay any mind to SFM. A rubbing tool is far worse for it than a lower SFM, and I am not convinced that a lower SFM is bad at all for a cutter.

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                    • #70
                      Originally posted by dian View Post
                      its not the cutter resonnating but the whole system. there are strategies implemented on cncs that for example identify the resonant frequency and vary rpm in a band around it in real time.
                      Good video of chatter taken with a high speed camera.

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                      • #71
                        I’m a manual or cnc guy and never heard of looking for a prime number to get rid of chatter, there may be something to it, idk... My manual mills rpm readers are just guidelines, but not that accurate and on the cnc’s we just adjust the programmed rpm and feed by percentages on the control and record what works for updating the program itself.

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                        • #72
                          Problems with gear head mills? I have a gear head Grizzly, six speeds and I have not experienced any such problems with aluminum or steel. Perhaps I just have not pushed it hard enough yet.

                          I do use WD-40 when cutting aluminum. It works well.



                          Originally posted by A.K. Boomer View Post
                          3 flutes on aluminum is pretty good practice from what iv experienced but still you should not be getting this bad of results with two... do you have a geared head mill? could be setting up some nasty harmonics,,, I hate geared head mills - my step pulley belt drive has nothing but smooth elastics between the motor and the quill...
                          Paul A.
                          SE Texas

                          And if you look REAL close at an analog signal,
                          You will find that it has discrete steps.

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                          • #73
                            Now that is a milling machine!



                            Originally posted by Tundra Twin Track View Post

                            I have a gear head Mill and would not want to go back to Step Pulleys that I used to have,my Max rpm is 2400. Click image for larger version

Name:	AC53F0BD-F187-49C3-B9F8-181655148947.png
Views:	132
Size:	2.26 MB
ID:	1935096
                            Paul A.
                            SE Texas

                            And if you look REAL close at an analog signal,
                            You will find that it has discrete steps.

                            Comment


                            • #74
                              Prime numbers for the RPM? I can see where resonance can be a problem. It can and has brought down things like bridges and other structures. But since the actual RPM of a machine tool is going to be an in-exact number anyways and is even going to change/drift while working, I can not see where picking any exactly calculated number for your RPM is going to be the ticket.

                              If you are near a resonate frequency for the machine and/or work then YES, do change the spindle speed. But do so for a fairly large percentage of the present speed, like 10 or 20 percent or more. Resonance will start to happen as the resonate frequency is approached and will become larger as you get closer to that peak, resonate frequency. Then it will decrease again as you go past it. So, changing the spindle speed by one or a few RPM just to get to a prime number is not likely to do anything much. And you probably will not even have that prime number anyway unless you have a really precise tack. You need to get completely away from that resonate point. And you need to avoid harmonics and sub-harmonics of any resonate frequencies so 2X (200%) or 0.5X (50%) are other points to avoid. Most gear boxes or pulley drives do not jump in exact number multiples (note below) so just moving to the next higher or lower speed is usually a good bet. Or randomly crank a bit on the VFD's speed control.

                              Note: many gear boxes are designed with an extra tooth on one of each pair of meshing gears. This extra tooth prevents the same pairs of teeth from always meshing with each other and evens out the wear on the teeth of the pair of gears. This extra tooth design feature is often responsible for some of the seemingly odd numbers in the gear ratios. So instead of a 2/1 ratio you get a 2.0312.../1 ratio with an extra tooth.



                              Originally posted by nickel-city-fab View Post

                              The goal is to find a frequency that the cutter will not resonate at. Since it has an even number of flutes (usually) find an odd prime number for the RPM. The resonance has a lot to do with the chattering, and eventual breakage.

                              Of course, the mill still needs to be sharp etc.
                              Paul A.
                              SE Texas

                              And if you look REAL close at an analog signal,
                              You will find that it has discrete steps.

                              Comment


                              • #75
                                Originally posted by nickel-city-fab View Post

                                Its called "harmonics". Ad even harmonics can very well be self-reinforcing AKA oscillators. How many times *per second* does the cutting edge impact the part? It will resonate at a given frequency. See Dian's post #65 about how CNC's deal with it.

                                You know, the same principles of waves that apply to electronics, also apply to mechanics. Sometimes the same equations even.
                                Yes, harmonics are a well known problem. It is just that the milling machine harmonics have nothing to do with prime number of RPM.
                                Location: Helsinki, Finland, Europe

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