Page 4 of 4 FirstFirst ... 234
Results 31 to 37 of 37

Thread: "Resting" HSS tool bits after grinding

  1. #31
    Join Date
    Aug 2004
    Posts
    424

    Post

    There may be something to it. Grinding steel is a pretty nasty process. At the microscopic level you are plowing up ductile material with a cutting tool that may have up to a 70 to 80 degree negative rake and never less than about a 20 degree negative rake and it generates a great deal of localized heating at the grind interface. Tru turning with a tool having a 45 degree negative rake to appreciate the plowing of the surface and the amount of heat generated.

    When you grind you end up with two things at the surface. Really high residual stresses and metal that has been raised above the austenite temperature and then very quickly quenched to the tool temperature. The high residual stresses will relieve themselves over time and the rapidly quenched material in high speed steel will have a high likelyhood of having retained austenite which will convert to martensite over several hours. Cryogenic treatment will force retained austenite to convert to martensite almost immediately. I am aware of heat treated high speed steel tools that blew up after several hours when not placed immediately into tempering after the quench due to the conversion of austenite to martensite.

    Something similar happens in iron castings left for several years to "age". The residual stresses relieve themselves over time and the iron casting becomes more stable.

    I would expect little difference between a freshly ground tool and an aged tool if the honing process was done on all ground surfaces with enough material removed to eliminate the heated metal and all of the residually stressed material. I don't know anyone who hones a tool enough to accomplish the materal removal.

  2. #32
    Join Date
    May 2003
    Location
    52N 122W Western Kanuckistan
    Posts
    40,418

    Post

    Umm,, I do. I use a diamond hone. Yeah, I know, steel is soluble in diamond. so what? It works and my wife has an endless supply of such tools....

    [This message has been edited by Evan (edited 09-06-2004).]
    Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

  3. #33
    Join Date
    Mar 2004
    Location
    Sheboygan Falls
    Posts
    205

    Post

    It's true!!!

    If you set it aside for two days it will last two days longer.

    Same footage of chips though.
    Keep it cool when grinding.
    Super Dave
    RapidtoCNC.com

  4. #34

    Post

    I have one tool that gets used all the time I inherited from my grandad that is still razor sharp - his double bit axe. Five new handles and two new heads, but it's still grandad's old axe.

  5. #35
    Join Date
    Nov 2002
    Location
    Kenosha, not the pass the other one
    Posts
    2,416

    Post

    <font face="Verdana, Arial" size="2">Originally posted by vinito:
    I have one tool that gets used all the time I inherited from my grandad that is still razor sharp - his double bit axe. Five new handles and two new heads, but it's still grandad's old axe.
    </font>
    I wondered how long it would be before grandads axe showed up
    The optimist says the glass is half full, the pessimist says it's half empty. The paranoid in me says somebody put a hole in it.

    Remember pessimists are at heart opptomists. They know things can and will get worse.

  6. #36
    Join Date
    Dec 2001
    Location
    Claremont, NH
    Posts
    2,017

    Post

    I am not sure on this one, but I do notice that if I sharpen tool bits and end mills and "cycle through" using the most recent ones ground last (rotating the stock), I do get better results than if I grind the bit then use it immediately.

    I have a few thread bits, form tools, and turning bits that have lasted me for years, and have quite a bit of actual usage.

    Just an observation. I have heard this for many years as well, and do rotate 'stock". However, this may be because of this...If I keep myself "ahead" on endmills and tool bits, I am less in a hurry to get the bit done for when I need it at that exact time, thus probably more careful, and use more craftsmanship and care in all aspects such as honing because I have that luxury of time to do so.

    May try this for fun sometime though....

    As for castings, Bridgeport did the "castings in the yard" thing, as did the company I worked for with the cast iron ones. The temperature extremes in areas such as Colorado and New Hampshire do allow for a bit of stress relief from the first casting process. It also allows for any stress cracks to show up better.
    CCBW, MAH

  7. #37

    Post

    You know.....

    If you climb under your school desk during a thermonuclear attack, your survival rate is sufficiently enhanced.



    [This message has been edited by scooter (edited 09-08-2004).]

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •