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Lathe- cutoff help (Mini-bit)

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  • Lathe- cutoff help (Mini-bit)

    I have some 1" Thompson steel shafts that I am trying to cut. I ground thru the hardened surface and started to make progess with my mini-bit parting tool, but no matter how I set it up or what speed I go at, the thing will cut for a few revolutions then start to back out of the holder.

    I believe the mini-bit is a carbide tool.


  • #2

    Make sure the cut-off blade is on center height. Carbide should be used at higher speeds. The Thompson shafts are hardened to 60C - this is not a problem for a standard insert type cut-off blade.

    Are you sure your tool is carbide or could it be TiN coated HSS? If you have HSS tools it would need to be M-42 or preferably T-15 to cut this linear bearing shafting.

    Most shops just use an abrasive chop saw for cutting this stuff.


    • #3
      The insert is carbide for sure. I just went to and they recommend deadnuts center to .005 below centerline.

      I was able to cut into the material about .10 before running into a wall.

      Time to look at my setup a little closer. I did use a chop saw to rough cut the shafts, but I made them a tad bit too long.

      Would I be better of "facing" them down to the proper size?

      Also, would the lack of a flooding coolant be a major issue with this? The only stuff I have handy is some tapping fluid that I was brushing on.

      [This message has been edited by Mueller (edited 04-21-2003).]


      • #4
        Facing them would be easier. The reason colant can cause problems is stress fracturing form hot and cold spots due to uneven cooling. Therefore, it is considered safer to machine dry with carbide now.


        • #5
          We cut Thompson rod with carbide cutoff blades quite frequently. If we cut the shaft with a chopsaw we always leave about an inch on each end. This stuff will harden up on you if are not using coolant. Run one inch about 900rpm and goes through like butter. Need a good solid set-up though. The thinbit isn't running into the part is it. The one I've got won't cut that deep

          [This message has been edited by Spin Doctor (edited 04-24-2003).]
          Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.