Mild steel machining dilemma
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  1. #1
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    Default Mild steel machining dilemma

    Hi All,

    I've had this problem in machining mild steels when it comes to the surface finish. There will always come these stripes like material get dragged between the tool and part making deeper grooves and rough finish. No matter if I use carbide insert or sharp HSS tool. Harder steels like tool steel, stainless or aluminium this doesn't happen. How to prevent this from happening on mild steels like 11SMn30+C / SAE 1213 free cutting steel and S235JR / AISI 1018 mild steel?

    soft_steel.jpg

    Thank you.

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    IME. Finish passez need to be 2 or 3 times as deep as other materials. Also run as many RPM as you can. 2000 SFM is not unrealistic.

    R

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    As Litlerob1 says, increase your finish pass material. I have found leaving 0.05 (0.025 per side) for finish works well with C1018

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    Looks like buildup on the cutting bit causing welding and tearing. Mild steel likes oily flood cooling.

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    Dead sharp tool bit.

    Coolant, preferably an OIL based one.

    Higher cutting speed - within limits.

    Use a leaded alloy.

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    I had the same problem turning mild steel with my ancient Stark #4. Felt like hard spots or crap in the material was causing the cutter to jitter or something. Leaded steel cuts great, but i felt quilty about using a material that supposedly rusts easily, so i switched to 1144 Stressproof. Great surface finishes and cuts like butter. Definately worth the price.

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    Get the speed cranked right up like Rob said. That right there's your problem. After you do that run just a trickle of coolant right at the tip of the cutting tool to prevent the work getting marred by any stray chips. Soft steel with good carbide you are going to need 1000+ SFM. Up it until you get a good finish or you can't anymore because you ran out of RPM.

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    Quote Originally Posted by MrStretch View Post
    I had the same problem turning mild steel with my ancient Stark #4. Felt like hard spots or crap in the material was causing the cutter to jitter or something. Leaded steel cuts great, but i felt quilty about using a material that supposedly rusts easily, so i switched to 1144 Stressproof. Great surface finishes and cuts like butter. Definately worth the price.
    LOL! It didn't ship that way. The softness conspires to CREATE those as you go.

    Low RPM budget? Sharp HSS, slow and wet. "Neat" oil or old stinky brown Sulfurized. Lousy for "cooling" ability. Basically a lube and barrier to chip adhering.

    And "Oh, By the way..." there was always a long-angle lathe bastard file to-hand "back in the day" when Carbides were scarce, costly, and dreadfully shitty, as well. One part to make, tool wasn't perfect, file-finish wasted less time than f*****g with that for small gain.


    More RPM on-tap? Modern Carbides, fast and usually "dry". Coated? I'm good with HSS, so somebody else's call.

    Book answer, any tooling, is still a more cooperative alloy. Pays yah back in f**k-with TIME saved. Steel is cheap and recyclable. Time is dear and gone forever.

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    Sharp carbide inserts work really well. Average steel specific insets are useless unless you get enough speed and doc. Aluminium specific ones are almost always enough sharp and work with tiny cuts and low speeds as good if not better than hss.

    Some steel specific inserts work well also, ie Sumitomo T1500Z coated cermets.

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    As already said: higher rpm, cutting fluid, sharp tool,and leave more material for your final pass (not to much as depending on the application you could end up out of round. You also may want to lower your feed rate. It sounds like your having issues with build up or rubbing so make sure your tool has lots of clearance on all trailing sides of the cutting edge.


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