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how hard of a steel can you machine

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  • how hard of a steel can you machine

    I was wondering if you can machine hardened steels with carbide. Even though the carbide is harder, is machineability a problem? I am thinking of maybe trying to make a gouge out of something hard, and just wondering if I can do it already hardened. thanks. kevin

  • #2
    depends what it is, heat treated 4140 for example is machined regularly....however hardened tool steel is generally machined by grinding. I know one guy who machines dead hard casehardened parts but he uses ceramics on some heavy duty cnc equipment

    for a home shop, I'd be thinking it would be a lot easier to anneal, machine, then harden
    .

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    • #3
      Evan had some posts on here a while ago about hard turning. It might help to search for it.

      I think it would also depend on your tools, like my mill/drill would never go through anything hard even with carbide tooling.

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      • #4
        I use aluminum oxide inserts on my engine lathe and turn anything. 60Rc+ is not a problem. Been doing it for 30 years.

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        • #5
          You can mill or turn hardened steel with carbide with a rigid, sturdy machine. A Bridgeport is about the lightest one that works good. A mill drill - forget it.

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          • #6
            I have turned hardened bicycle freewheels using carbide. They are about the hardest material I know that can be machined with tungsten carbide. There aren't many steels harder than that but for those that are ceramic/metallic (cermet) inserts will machine them. If they won't do then there are Cubic Boron Nitride (CBN, Borazon) inserts. Even diamond can be machined using diamond loaded abrasive laps. That is how facets are put on gems diamonds.

            Abrasive machining is widely used in industry but is often ignored by the home shop machinist. It is an area that is expensive to tool up for but it greatly expands machining possibilities. Tool post grinding is a prime example and with super abrasives like CBN migration of grit is only a minor issue. I use both my lathe and my mill to do grinding and it requires adequate draping and thorough cleanup afterword. The results are worthwhile.
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              I tried turning a cobalt HHS bar once. Picked a handful of them up on Ebay and thought I would make some boring bars out of them. Nope! Fractured or burned every cutter I tried on it. High speed, low speed, didn't matter. The bar remained virtually blemish free too! Hard stuff. Since they are ground and polished, I use those tool blanks for reference bars now.

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              • #8
                Originally posted by kjbllc
                I am thinking of maybe trying to make a gouge out of something hard, and just wondering if I can do it already hardened. thanks. kevin
                If heat treating seems intimidating to you - don't let it! Rather than suffering the really difficult technique and tooling issues of working hardened steel without losing its desirable properties, give the project a quick try using regular carbon steel - W-1 or O-1.

                If you want do do it REALLY easily, you can make a serviceable wood cutting tool like a chisel or gouge from W-1 steel by milling, turning, filing, grinding, etc. Then, even though the proper quenching medium is water, get yourself a bucket of oil - vegetable, motor, ATF - whatever.

                Heat the business end of the tool with a propane torch until it's red, test it with a magnet hanging on a string from the ceiling to make sure you get it hot enough so it won't attract, and then dunk it in the oil.

                You're done - no need to draw temper, just hone and use.

                That's the quick and dirty method I'm currently using to make wood working tools, and it serves me really well.

                Otherwise, pick up or look up some specific literature on hardening carbon steel. There's great stuff out there, but I've largely abandoned it because most of the time I don't really care if the tool holds an edge forever. I use the tools myself, and I don't mind sharpening a bit more often for these special items.

                Here's a little spoon gouge I made just that way by heating and hammering the end of a piece of W-1 drill rod, filing, and heat treating:



                After I harden stuff, it's all black and scaly, so I just use some abrasive paper to sand it off, then buff for a nice shine. Well, sometimes I do. Mostly they just stay black except for the sharp edges. . .
                Cheers,

                Frank Ford
                HomeShopTech

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                • #9
                  There are some interesting cubic boron nitride inserts over at j&m industrial diamond http://www.diamondtool.com/ that claim to be able to machine full hard tool steel. I got a couple for a good paying job that didn't materialize and they are about 40 bucks each IIRC. I haven't tried them yet.

                  --Cameron

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                  • #10
                    Pretty damn hard I guess 'cause I just got through taking .030" off each side of a roller on a car lift .010" at a pass. It was so hard a file danced across it with no effect at all and hitting on a belt sander barely took metal off the side.

                    I used C6 carbide inserts because that's all I have right now. Ceramic may be better and I am working on getting some Ceramic inserts right now. One place I worked had what I think was a boron insert we used for hard stuff and I may try to get one. It was the only thing that would cut Belzonia? metal filler.
                    Last edited by Carld; 03-02-2010, 11:29 AM.
                    It's only ink and paper

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                    • #11
                      thanks for the info, I will check them out. keivn

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                      • #12
                        I machined this 1/4" dowel pin with regular carbide. Not sure how hard dowel pins are. The back end I turned a shoulder on with no problems. The taper end work hardened on me as I got near the end. Then I used a worn out insert and "forced the issue." Now it's reaaaaly hard.

                        I also had to "take some height off" a case hardened QC tool holder. I used a 4 insert 2" face mill on a bridgeport and it cut quite well. The sparks were very exciting. The inserts didn't even notice.

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                        • #13
                          Hardest I've drilled is adding blow-off pin holes to a mold core. About 2" of mid 50s Rc H13, IIRC. The last bit had to be reamed without chipping out. We used die drills (basically a masonary drill) and carbide reamers. Not too bad but it made me nervous. You had to keep your hand on the feed hold. Once the drill dulled and started squealing, you didn't have long until it shattered.

                          We also used to bore hollow dowel holes with PCBN inserts after heat treat. That was taking out only a little bit though.

                          I've milled taps out with carbide ball endmills. Either one thousanth at a time with the pulse handle on CNCs or a couple at a time by moving the depth stop on a Bridgie. It's real easy to build up too much tool pressure and shatter a little endmill otherwise.
                          Jon Bohlander
                          My PM Blog

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