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  • grinding hss

    I have seen many guides and opinions about grinding hss bits. Does it damage the bit if you grind it hard, till it is red hot? Does hss "lose it's temper"?

  • #2
    My vote is no, but if the red hot tool bit is subsequently plunged
    into water, this will lead to issues that tend to shorten the tool
    life.

    An aluminum oxide wheel intended for use with HSS will contribute
    to lower temperatures while grinding.

    What wheel type are you presently working with ?

    .

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    • #3
      Although I have not seen it I have read that quenching in water from extreme temperatures will cause "micro cracks" along the cutting edge resulting in early breakdown of the edge. I have also read that HSS can be run red hot, however when it is it never is subjected to the sudden temperature changes that quenching imparts. As a HSM I have never had the need to run anything to the point of red while machining. If production were an issue I would probably be using carbide.

      For insurance, why not just grind it until you can no longer hold it, quench and grind again. It doesn't add that much time to tool grinding and also gives you and opportunity to look closely at the shape and adjust as necessary during the next grinding cycle.

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      • #4
        No red hot does not hurt it . That is why it is called High speed tool steel.
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        • #5
          Originally posted by EddyCurr View Post
          My vote is no, but if the red hot tool bit is subsequently plunged
          into water, this will lead to issues that tend to shorten the tool
          life.

          An aluminum oxide wheel intended for use with HSS will contribute
          to lower temperatures while grinding.

          What wheel type are you presently working with ?

          .
          I am using aluminum oxide wheels. I ask because I needed a bit to cut a groove for a small snapring and the grind and quench method took a painfully long time.

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          • #6
            Originally posted by rray View Post
            I am using aluminum oxide wheels. I ask because I needed
            a bit to cut a groove for a small snapring and the grind and quench
            method took a painfully long time.
            White aluminum oxide?

            How coarse?

            Do you periodically dress the wheel with a diamond dressing tool?

            .

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            • #7
              Red hot??? I think you are thinking of carbide. Iv read to never let HSS get hotter then you can hold while grinding as if you do the tip is nodoubt way past annealing temp. ie never let it even blue from grinding if you can avoid it. when cutting steel you don't want the chips to go any hotter then straw yellow (very light yellow, tint of gold)

              HSS blanks come in pre-hard for a reason, annealed HSS is not very hard, you just never see it because its exceptionally difficult to heat treat so you either buy it pre-hard or buy easier to heat treat tool steels.
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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              • #8
                Originally posted by Black_Moons View Post
                Red hot??? I think you are thinking of carbide. Iv read to never let HSS get hotter then you can hold while grinding as if you do the tip is nodoubt way past annealing temp. ie never let it even blue from grinding if you can avoid it. when cutting steel you don't want the chips to go any hotter then straw yellow (very light yellow, tint of gold)

                HSS blanks come in pre-hard for a reason, annealed HSS is not very hard, you just never see it because its exceptionally difficult to heat treat so you either buy it pre-hard or buy easier to heat treat tool steels.
                Your second paragraph is correct, but as far as your first, you're thinking of regular carbon tool steel. As has been stated, HSS retains its hardness up into red hot temps.
                Last edited by mars-red; 01-28-2015, 07:22 PM.
                Max
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                • #9
                  Maybe everything everyone should know about HSS grinding or maybe just a bunch of opinion.

                  http://yarchive.net/metal/hss_grinding.html

                  The guy doing the writing is pretty sure everyone who agrees with him is right and everyone else is wrong which is probably not a convincing way to make a point. Regardless, the point is pretty well beat home.

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                  • #10
                    Originally posted by mars-red View Post
                    Your second paragraph is correct, but as far as your first, you're thinking of regular carbon tool steel. As has been stated, HSS retains its hardness up into red hot temps.
                    *does some checking*
                    Interesting, it seems HSS does not loose much hardness to annealing till 1200f (Dull red)
                    http://buffaloprecision.com/data_sheets/dsm2hs.htm
                    I will have to remember that next time I grind HSS to not care about it blueing, just try not to make the cutting edges glow much
                    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                    • #11
                      I dip the non-cutting end of the blank into a small jar of water to cool it down. After doing a lot of grinding, that water is going to be fairly warm and so I can't see it being much of an issue although I doubt I use my cutters hard enough to show up any problems anyway!

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                      • #12
                        Unless you are using a bit with cobalt I would expect that the color change will also indicate removal of temper. Cobalt bits will maintain their hardness at higher temperatures.

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                        • #13
                          Originally posted by dp View Post
                          Maybe everything everyone should know about HSS grinding or maybe just a bunch of opinion.

                          http://yarchive.net/metal/hss_grinding.html.
                          Boy does that bring back memories. I remember Ed from RCM which I read religiously for years. It became WAY to much OT and particularly political so haven't been there for years .
                          ...lew...

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                          • #14
                            As I understand it, you have to work pretty hard to anneal HSS. You need a programmable oven and a very specific heating/cooling curve to accomplish it.

                            As far as grinding... I use silicon carbide "green wheels." I know they're allegedly the wrong kind for grinding HSS, and they wear relatively fast, but I find they run a lot cooler and cut well. And given the amount of grinding I do sharpening toolbits, the wear rate isn't an important issue.
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                            • #15
                              Originally posted by rray View Post
                              I am using aluminum oxide wheels. I ask because I needed a bit to cut a groove for a small snapring and the grind and quench method took a painfully long time.
                              If you have a dremel tool or die grinder, cut out "squares" with the cut wheel instead of grinding away all that material. Much faster

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