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Thread: Hard cast iron

  1. 2nd April 2012, 11:23 PM #1
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    Default Hard cast iron

    Hi,
    I was going to post this in the show us your project thread, but thought it worth a few answers.

    I have wanted to make a graduated collar for the Conriks saddle feed for some time now. The biggest problem is that the saddle feed about 38mm (not sure exactly yet) per turn so a pretty big collar would be needed to be anything but a rough guide.

    Anyway whilst rummaging around today (looking for something else that i didn't find) i found a nice large sprocket, 200mm dia by 20mm thick with nice meaty hubs on both sides. Perfect! Just machine off the teeth, one of the hubs, bush and voila, ready for marking!

    At first i put it on the lathe just to see if it was cast or forged, i cleaned up the hub and took a facing pass off the, um, face! Nice, free machining cast- EASY!

    Then i tried to take a cut off the teeth....red hot bullets of cast everywhere (carbide in use) ouch....So i slowed the machine down (60rpm or so) and tried a healthy cut with HSS...it was like cutting like hardened steel!

    I took the vid below to give you an idea. Cut is .75mm deep, feed is .15mm (fine as i can go with the gears i have). Any more and the machine starts to slow, and the chatter is unbearable.

    [ame="http://www.youtube.com/watch?v=d3215tucKzI"]VIDEO0015.3gp - YouTube[/ame]

    Is it just because its a broken cut, or could the teeth be through hardened somehow?

    Sorry if that got a bit long-winded...

    Ewan
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  3. 2nd April 2012, 11:25 PM #2
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    Default

    Sorry, can't seem to got the vid to imbed in the post. Any tips?
  4. 2nd April 2012, 11:30 PM #3
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    Default

    Hi Ewan,

    Get rid of the https... change to http.[ame="http://www.youtube.com/watch?v=d3215tucKzI"][/ame]

    Gotta love interrupted cuts... but it might be white cast (chill) , try filing it and see how hard it is, if it's too hard, then you can heat it up and hold it hot for a time to normalize it.

    Regards
    Ray
  5. 2nd April 2012, 11:31 PM #4
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    Default

    Thanks Ray
  6. 2nd April 2012, 11:35 PM #5
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    Default

    Hi Ewan,

    To get it into your original post, when you edit click on "go advanced" and it will re-parse the post and should pick up the youtube url.. the simple edit doesn't do the same thing,

    Regards
    Ray

    PS Ok, I see you've got it.. I'll delete my copy...
  7. 3rd April 2012, 10:51 PM #6
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    Default Teeth gone

    Well, it was definitely harder towards the outer edge of the sprocket, i'd say a good 2-3mm lower than the valleys in the teeth. Once i got through this though its just like normal cast. With the dia coming down i was also able to swing the tool round to a dragging cut. Vid is 3mm cut .15 feed 60rpm. Not bad for half a horse.

    [ame=http://www.youtube.com/watch?v=Tt_OFVp3FIA]Conrik lathe cutting old sprocket - YouTube[/ame]

    Ewan
  8. 4th April 2012, 05:34 PM #7
    Retromilling
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    Default

    The teeth are mostlikely case hardened with the body left softer to absorb shock.
    Most sprokets and gears are made from something like EN36A which has very low carbon in it and then after the teeth are machined they case harden , adding the carbon and then sometimes a final grind to specs .
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.
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