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Any Tips For Machining A Small Cast Crankshaft?

Discussion in 'A BEGINNER'S FORUM (Learn How To Machine Here!)' started by tomw, Mar 5, 2016.

  1. tq60

    tq60 United States Active Member Active Member

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    Use the bad one for setup testing.

    Carbide and adjust cutter height.

    Sent from my SAMSUNG-SGH-I337Z using Tapatalk
     
  2. TOOLMASTER

    TOOLMASTER you don't want to know Active Member

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    crankshaft grinders are fun to watch..

     
    tomw and Fitter Bill like this.
  3. 4gsr

    4gsr Global Moderator Staff Member H-M Supporter-Premium

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    I would have thought of using steel for a crank shaft or even ductile iron, but cast iron? I remember making one back when I was 12 years old on dad's 9" SBL that was made from a old bolt. Came out ok. Went back later and tried to fix it up a little and messed it up! Never did try to make another one after that.
     
  4. tomw

    tomw United States Active Member Active Member

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    I received the replacement crankshaft today. Here it is after some initial filing and sanding:

    New Crankshaft.jpg

    I noticed immediately that this was a much softer material. I could easily remove the casting flash with my 1" belt sander, and finish up with a file. I had to use a carbide bit in my Dremel on the previous piece.

    So, I mounted one end of the crank in a 3 jaw chuck, faced the opposite end, and center drilled that end.

    Crank in chuck.jpg

    Crank center drilled.jpg

    I secured the tail end with a center. I then used a carbide bit to remove 30 thou, in two 15 thou passes, which got rid of the rough casting surface. The surface was still a bit rough. But the cut did not make me think of banshees, and a spring pass was uneventful. The material cut like CI I have cut before.

    Below is the surface after a few few strokes with a file.

    New Crankshaft rough.jpg

    It is still ugly. But this was a rough cut, without trying to make things smooth. I am really happy with the result.

    Thank you all for your help.

    Cheers,

    Tom
     
    francist likes this.
  5. kvt

    kvt Active User Active Member

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    Glad that the replacement was good. Now you know what to do to the other one, Then you have a spare crank.
     
  6. benmychree

    benmychree United States John York H-M Supporter-Premium

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    I think the amount of clearances you are using on your HSS cutting tool is quite excessive, this leads to a weak cutting edge that is more apt to burn or chip off. using a large radius will create chatter and also the angle of the tool to the work can exacerbate the chatter, it should be a little less than 90 degrees or near perpendicular to the work; the more angle, the wider the width of cut, increasing the tendency to chatter. I have machined both cast cranks (100-70-03 ductile iron) and steel cranks, both two throws @90 deg. for compound steam engines, these had 1-3/8" dia. journals and were about 30" long overall. If there is a secret to success, it is to run at slow speeds. All the turning was done between centers, a steady rest was used for the machining of the main bearings, but for machining the throws, that was not possible. The shafts were roughed out all over, semi finished on the diameters, finished on the lengths, then sent out for final grind finishing.
     

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