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Thread: 3/16 keyway in grade 8 bolt

  1. #1
    Join Date
    Feb 2007
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    148

    Default 3/16 keyway in grade 8 bolt

    I tried to cut a 3/16 inch keyway in a grade 8 bolt today 1900 rpm plenty of oil about 20 th deep no luck . I ordered some carbide end mills will they work? Am I running to fast? Did I shoot myself in the foot trying to use grade 8 bolts?
    Richard

  2. #2
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    I would use a carbide 2-flute endmill, but lower the speed to about 1000.
    On a manual mill slower is usually better because you can 'feel' the tool working.
    Patience.

  3. #3
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    Speed seems a bit fast for HSS but not that much, carbide will be a major improvement. Probably can double your RPM over HSS.

    Was the HSS cutter a quality cutter or one from those nice gold colored sets in a wooden box from Harbor Freight

  4. #4
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    Quote Originally Posted by KiddZimaHater
    but lower the speed to about 1000.
    Me "Probably can double your RPM over HSS."

    That should get him started

  5. #5
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    Here is the suggestion (and not my guess) from MEPro using a DOC of .020 which is pretty mild.


  6. #6
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    Feb 2007
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    It was high speed steel from msc I hope the carbide will cure the problem.
    Thanks for all the fast replys .
    Richard

  7. #7
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    Taylorsville Ky
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    Using a HSS endmill I would use about 300 to 500 rpm .100" DOC for the first pass. Grade 8 is a hard bolt. I think the higher rpm's would work with flood coolant or on a CNC.
    It's only ink and paper

  8. #8
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    Try a different bolt. Bolts don't have a strict spec on alloy or hardness. They only need to meet a strength specification. I have no trouble machining grade 8 with HSS although I usually use carbide. But, every once in a while I run into a hard one that must have been from a different melt. Even grade 11 cap screws are perfectly machinable. Strength and hardness are not directly tied together.
    Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

  9. #9

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    Strength and hardness are not directly tied together.
    I think they are. You can get a good idea of the tensile strength just by knowing the hardness.

    http://www.onlinemetals.com/hardness.cfm

  10. #10
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    Don't try applying that "rule of thumb" to cast iron for example. The stress/strain curve for metals is generally non-linear. Only in the elastic deformation part of the curve is it linear. Beyond that the hardness may increase due to strain hardening while the ultimate tensile strength goes down.

    If the item in question has undergone any sort of cold work then the relation between hardness and tensile strength has been altered. That applies to cold drawn products as well as any product that has been cold formed such as a rolled and headed bolt.
    Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

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