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SFM tip

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  • SFM tip

    There was another SFM thread about formulas and calculating SFM.
    Here is a tip that all of you probably know.
    I have a two belt driven lathes and a belt driven mill. All require pulley changes to set tool or workpiece speed.
    I know - I'm really old fashioned.
    There are probably some more here who have old tools like mine.
    Anyway, to the tip ----
    I checked the speeds of my tools with a digital tach and found the posted speeds on the metal plates and in the manuals are so far off as to be useless.
    I made up new charts using the measured speeds and my finishes have dramatically improved.
    My tool life is better and I haven't burned up a milling cutter yet with the new charts.
    I can't figure out how those charts were made.
    I cut it off twice and it's still too short!

  • #2
    as a quick guess

    the motor was made 60hz one now a 50hz one for a four pole that would be 1800 RPM or 1500 RPM for each

    new replacement motor fitted different base speed

    new motor pully fitted

    any of the above will make the name plate invalid


    • #3

      All original motors on a 6" Craftsman, 200 Logan and new import 6X26 mill badged for both 60 and 50 Hz.
      The mill is the farthest off.
      I cut it off twice and it's still too short!


      • #4
        Have you noticed any regular error between the posted and actual speeds? Let's say, for example, each actual speed is 1/5 times higher than the posted one.

        Any belt slipping?
        WI/IL border, USA


        • #5
          SFM off

          There is no regular percentage error. I could explain that.
          The errors are all over the place.
          I dont think the belts are slipping.
          I have checked unloaded and loaded and see the small drop that you would expect.
          The motors are very close to nameplate speed unloaded.
          Some combinations on the mill are off by 25%.
          Some on the Logan by 20%.
          Maybe that's not enough to matter?
          Really odd, almost like some of the pullys on the Logan are turned down, (or up - LOL).
          Who knows what was done to the machines before I got them.
          The problem with the mill is probably the translation of the numbers from Chinese was garbled.
          In any case the new measured speeds work for me.
          If you have these kinds of old technology machines you should check them with a digital tach.
          I cut it off twice and it's still too short!