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  • #31
    I have to say it's your cutter. I milled these blocks with my 2" shell mill. Three Kennametal TPG 322 KC 730 grade inserts in the mill. I don't remember the RPM's or feed rate, no coolant either. I get a mirror finish with just about any RPM as long as I don't over feed it. You need dead sharp inserts and not too sharp of a radius on the insert.
    Pictures aren't too good but !
    JL...............


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    • #32
      Update

      ... 'Very slow to medium' is NOT A NUMBER.
      Okay so my description of speed is not the greatest!!

      Did a little math today and figured out that I was moving the table at
      somewhere between
      2 and 2 1/2 inches per minute

      with more practice i am sure I will get used to proper hand speeds
      still learning the ins and outs of milling as a whole

      as for a mirror finish I am not trying to see my pretty face, but I was trying to
      get something with hardly any tool marks. At least reflective to light.

      As far as the carbide tips go, I just tried to replace the dull ones in my shell cutter with something equivalent.

      Thanks everybody for all yor input and links to other pages of info

      Tim
      Jet Jmd-18. -Sold it.
      Upgraded to a Harbor Freight 44991!!
      should have waited and bought a knee mill...

      Comment


      • #33
        Originally posted by timcki
        Okay so my description of speed is not the greatest!!

        Did a little math today and figured out that I was moving the table at
        somewhere between
        2 and 2 1/2 inches per minute

        with more practice i am sure I will get used to proper hand speeds
        still learning the ins and outs of milling as a whole

        as for a mirror finish I am not trying to see my pretty face, but I was trying to
        get something with hardly any tool marks. At least reflective to light.

        As far as the carbide tips go, I just tried to replace the dull ones in my shell cutter with something equivalent.

        Thanks everybody for all yor input and links to other pages of info

        Tim
        ah!! some numbers

        Your Feed rate is-
        2.500" / 800rpm = 0.0031" per rev, thats a roughing feed with that cutter !
        You should be looking @ 0.0005" for a fine finish.

        Milling Feed rate is how much a cutter advances into the work (per spindle rev) / number of teeth (that are cutting).

        A cutter such as you are using needs to be properly set [+/-0.0001" ] to ensure ALL teeth are removing an equal amount (best way is to dress it in a tool & cutter grinder).

        From your pic, it looks like 1 tooth is doing all the work, so is acting like a fly-cutter -

        Up your speed to 1500 rpm & reduce your feed to 0.75" /min


        Here's a useful calc-
        http://www.custompartnet.com/calcula...speed-and-feed
        Last edited by jugs; 12-12-2011, 03:46 AM.
        John

        I used to be indecisive. Now I'm not so sure , but I'm not a complete idiot - some bits are still missing

        Comment


        • #34
          Originally posted by jugs
          ah!! some numbers

          Your Feed rate is-
          2.500" / 800rpm = 0.0031" per rev, thats a roughing feed with that cutter !
          You should be looking @ 0.0005" for a fine finish.

          Milling Feed rate is how much a cutter advances into the work (per spindle rev) / number of teeth (that are cutting).

          A cutter such as you are using needs to be properly set [+/-0.0001" ] to ensure ALL teeth are removing an equal amount (best way is to dress it in a tool & cutter grinder).

          From your pic, it looks like 1 tooth is doing all the work, so is acting like a fly-cutter -

          Up your speed to 1500 rpm & reduce your feed to 0.75" /min


          Here's a useful calc-
          http://www.custompartnet.com/calcula...speed-and-feed
          What? he's already at 523 sfm. Without flood coolant that aluminum will be a huge built up edge.

          Comment


          • #35
            Originally posted by tdmidget
            What?
            Sounds like jugs is a little out of his element with strictly manual machines to me I couldn't tell you what specific feed rate I use while manual milling... You'll pick up what happens, timcki, over time. IME it really doesn't take too long. As they say, 'make chips'!

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            • #36
              Jet JMD-18
              Also not the sturdiest machine to begin with....

              Comment


              • #37
                Originally posted by Arthur.Marks
                Sounds like jugs is a little out of his element with strictly manual machines to me I couldn't tell you what specific feed rate I use while manual milling... You'll pick up what happens, timcki, over time. IME it really doesn't take too long. As they say, 'make chips'!
                Sorry, I didn't know it's a drilling machine,
                I wouldn't be happy using a fly cutter in a round column machine unless it's keyed.

                I run an 11" fly cutter (balanced) @ 300 rpm (785 sfm) when skimming heads - Ti coated tips = no build up
                John

                I used to be indecisive. Now I'm not so sure , but I'm not a complete idiot - some bits are still missing

                Comment


                • #38
                  Update New Tool

                  New tool better results...
                  Thanks for recommending glacern 45 degree face mill, when my budget analyst(wife) says okay I get to order it!!!
                  FM45-250
                  I did try some of the suggestion from last week , like only using one bit on the shell mill, but it was still the same results
                  Below is my new fly cutter (import) from RL Stevens al7 c2 bit
                  tried various speeds and feeds all with about the same results

                  I am still trying to learn the math correctly IPM and IPR(asked in a different post)...

                  below the fist 2 pics are, left: last week with the shell mill and right: with the new fly cutter 600 rpm 2 IPM.
                  Jet Jmd-18. -Sold it.
                  Upgraded to a Harbor Freight 44991!!
                  should have waited and bought a knee mill...

                  Comment


                  • #39
                    timcki, look closely at the cutters I use in my fly cutters. If you will grind a 30 to 45 deg leading angle on the cutter as shown in the photo you will get a much better finish and it won't hammer like yours is doing. I know it is hammering because I have been through all that years ago. Also, it you will run the spindle ant 1000 or more the cut will be much better. The only time I use the 90 leading edge is when cutting up to a 90 deg shoulder. Also, if you grind the 45 deg angle with a slight radius at the edge near the surface where it cuts you will get a better finish. You will notice I have several shapes for different jobs.

                    Last edited by Carld; 12-19-2011, 10:11 AM.
                    It's only ink and paper

                    Comment


                    • #40
                      Great, old video from the Tormach guys on flycutter speeds and feeds versus surface finish:

                      http://www.youtube.com/watch?v=koYGLVGkRsI
                      "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                      • #41
                        something is not correct re your mill tramming I would have thought also. Alistair ps good luck it's not a difficult fix.
                        Please excuse my typing as I have a form of parkinsons disease

                        Comment


                        • #42
                          Originally posted by Alistair Hosie
                          something is not correct re your mill tramming I would have thought also. Alistair ps good luck it's not a difficult fix.
                          Unfortunately, correcting the tram on a mill/drill is a major PITA: you have to break the paint seam on the head casting, loosen the head retaining bolts and clean out all the casting sand and crap, and shim it up to tram it.

                          You'll find beer can shims under there -- just take them out and start over. They weren't even close on mine.
                          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                          Comment


                          • #43
                            Also keep in mind that the Tormach in the video, while not a production machine, is more rigid than a mill drill. The depth of cut and feeds possible on that machine are greater than on the mill drill. It also has the benefit of good control over RPM and feed rate.

                            Comment


                            • #44
                              fly cutting surface finish.

                              Tram your mill, feed slowly and evenly, and put a radius on your tip and make sure you aren't chipped.

                              Things that will affect surface finish.
                              • Head out of tram
                              • Feed rate too fast for rpm
                              • not enough tip radius
                              • Angle of tip if not radiused.
                              • inconsistent feed rates
                              • more than one cutting edge at different heights.
                              • chipped cutting edge
                              • lack of rigidity/chatter
                              • cutting edge geometry that doesn't cut cleanly



                              Tram is easy to spot. Flycut far enough (finishing cut) that you have a significant section that has been cut by both the leading and trailing edges. If the swirls from both the leading and trailing edge are equally pronounced (note that light angle may affect results so turn the piece to make sure) then the mill is properly trammed. If they are unequal, then head is not well trammed.
                              Or you are roughing and getting significant tool deflection on the leading edge.

                              If you have multiple cutting teeth that are uneven, you can probably get comparable results to a fly cutter if you feed at fly cutter feed rates instead of a multiple of that feed rate appropriate for a multiple tooth cutter.

                              The more pointy (less radius) the tip or the slower the rpm, the higher the feed rate needs to be. If you have no tip radius, then the smaller the included angle of the tip the deeper the gouges will be at any given feed rate. Also, a cutting edge with no radius will soon chip.

                              Your feed per revolution should be significantly (more than an order of magnitude) smaller than your tip radius.

                              Theoretically speaking, with perfect cuts, at 1000RPM, a feed rate of 1 inch per minute will give a surface finish frequency of 1000 lines per inch (1 mil wavelenth). If you have a perfectly sharp 90 degree point, you will have a roughness of half a mil. Those parameters will both be twice as bad with a feed rate of 2 inch per minute or an RM of 500RPM. If the tip is 45 degrees angle, then the roughness depth will be 141% worse. If the tip is 120 degrees, then the roughness depth will be 43% better. If you have a tip radius of 1/8", then the depth of the surface roughness will be about 500 times better at around 1 microinch. A "mirror finish" is around 4-8 microinches. A tip radius of 15 mils will give you about 8 microinches at 1000 cuts per inch and a tip radius of 30mils will give you about 4 microinches theoretical limit. Poor cutting action or chatter can make the surface finish worse. With no tip radius, you would need to feed at 1 inch every 100 minutes (1000RPM) to get a comparable theoretical roughness and your tool would probably be worn out before you finished the job.
                              roughness = tip_radius-sqrt(tip_radius^2-(feed_per_tooth/2)^2)

                              The maximum acceptable fly cutter to center distance is around 1.9" at 1000RPM in aluminum with carbide, and about a third that using high speed steel.

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                              • #45
                                Okay,
                                I am learning the math speed and feed...
                                From what I have gathered so far, I am waaaay to slow on my rpm's

                                I was somewhere between 300-450 rpm's
                                and the new tool i bought didn't have much of a radius at the tip...

                                right now I am in the middle of repairing the drawbar, the head spins in the shaft
                                when I am up and running again I will redo the math and try again.
                                Jet Jmd-18. -Sold it.
                                Upgraded to a Harbor Freight 44991!!
                                should have waited and bought a knee mill...

                                Comment

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