Turning cast iron

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Turning cast iron

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  • #635899
    Hopper
    Participant
      @hopper

      Or you can grind on the bench grinder by hand if careful. Usually (but not always if the iron is badly chilled right through) you only have to remove the crusty black skin off the outside.

      The other thing is low RPM in the lathe, especially for large diameters like wheels. IE well sub-100 rpm. Backgear if you have it.

      The traditional softening method used to be to bury them in the glowing ashes in the fireplace to get them up to red hot then leave them there to cool slowly overnight. But not sure if fireplaces are even allowed in this day and age so it might have to be propane torch.

      Edited By Hopper on 03/03/2023 12:38:06

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      #636626
      John Reese
      Participant
        @johnreese12848

        There is a problem with small lathes having variable speed drives and no back gear. When you dial down the speed, you do not have enough torque to make a deep enough cut to get under the skin of the casting.

        #636636
        JasonB
        Moderator
          @jasonb

          Just use a carbide insert and cut through the skin in a few fine passes, **GT even better. Carbide also lets you run a lot faster than HSS so you can get the motor back towards it's sweet spot the old books would have you running a Myford is slowest back gear to turn say a 7" flywheel so what's that 50rpm or less. I'd happily run at 3-400rpm with carbide.

          #636644
          Simon Collier
          Participant
            @simoncollier74340

            My Springbok castings from Winter (before the new owner) were chilled right through. I ruined two new carbide inserts before I gave up. I took them to a heat treatment place to have them annealed.

            #636647
            Samsaranda
            Participant
              @samsaranda

              I have had problems in machining some of the cast iron components for my Allchin TE, it wasn’t just chilling on the surface, there was extreme hardness extending to quite some depth in the castings which made them unmachineable. These were sizeable castings, I gave them a few days in the base of our woodburner in the lounge, this made very little difference so I bit the bullet and ordered in some billets of cast iron of the necessary diameter and made the parts from scratch. I have previously read of problems encountered by other modellers when dealing with the supplier in respect of exchanging poor quality castings with them, their attitude wasn’t helpful. Castings that have surface chilling are relatively easy to deal with, you just need to remove the surface skin, but poor quality castings that have deep areas of real hardness and with hard inclusions are no good and only fit for the scrap bin. I was lucky with my castings it was possible, with a lot of extra machining, I was able to make them from cast iron bar, albeit some was 100 mm diameter, it was a joy to machine and the tool went through like a knife in butter. Dave W

              #636649
              bernard towers
              Participant
                @bernardtowers37738

                Try heating it up in some barbq charcoal and allow to cool slowly.

                #636668
                Jelly
                Participant
                  @jelly

                  If all else fails, switching to a CBN insert will happily turn the hardened scale and chilled spots all day long, even taking light passes that don't cut through and under the scale in one go.

                  You'd ideally need to run at somewhere around 1200 sfm (so in the 600-900rpm range for a 6" workpiece), with CBN, which does raise a consideration of work-holding and machine rigidity…

                  So in practice it would be "as fast as you think is still safe", and don't worry about sparking or glowing chips, that's very much par for the course with CBN.

                  CCMW inserts suitable for small hobby lathes are available in CBN, but they're about 5 times the price of a carbide insert so it might not be the first port of call if you're cost-conscious…

                  But I wouldn't go back to not having a couple of them stashed in the workshop now I've used them, the flexiblity to machine really hard materials without just mullering inserts is quite a useful one (especially in a workshop with no surface or cylindrical grinding facilities).

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