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Tooling question

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  • Tooling question

    I did a search, but really didnt find what I am looking for.

    Long time ago, years before I had a lathe, I purchased a box of tooling. $5 bucks.

    In it is a bunch of Mo-Max tooling. Cobalt and HSS.

    I understand that cobalt is harder than HSS.

    Is its use different that HSS? same speed and feeds?

    And what does Carbide look like as tooling?

  • #2
    .......Hopefully I don't embarrass myself answering a couple of these, but the addition of cobalt I believe is basic to allowing the bit to withstand higher heat in use.

    Cobalt should be able to withstand higher feeds-speeds due to it's higher heat handeling properties.

    "And what does Carbide look like as tooling?"

    The bare uncoated carbide tooling I've aquired has all had a slight bluish/grayish cast to it. It is also notably heavier.

    I'm also fairly new to this lathe and machining stuff. Lots of my lathe tools came from Da Bey in 'lots'. I have lots of Rex Crucible, Circle C, and Mo-Max in various types (cobalt, M42, etc).

    I bought some import bits from ENCO to fill out an order and they came etched only, 3/8x3/8, India, HSS. I was using one to cut some steel and it cratered and pocketed so bad by the 3rd workpiece it looked like I was threading or using a fork to cut!

    Now I very much could be to blame, not following sound practice. However that would have been the case also with the Rex, Mo-Max, etc bits. Yet they showed no bad results. They may cost 3-4 times as much, but my future money will be spent ONLY for known US HSS cutting bits.

    Son of the silver stream ..... Bullet caster.


    • #3

      A good explanation of HSS, Cobalt & Carbide.

      Cobalt tooling can generally run 50% faster than HSS, while still retaining a great deal of toughness. Not as hard as carbide, not as brittle as carbide.

      Barry Milton


      • #4
        FWIW I used MoMax in my small pneumatic engraving machine. Evidentally MoMax doesn't mind pounding (might be considered same as interrupted cuts).

        I might add, the next guys post is right on. Ain't nothing magical about grinding your own bits if using HSS or cobalt. Just need to try it a few times. As for the backyard machinist, way to much weight is assigned to getting the perfect angle. Just get a good close look at some cutters in catalogs and see how close you can grind yours to look like theirs.

        (I'm not telepathic, just edited this after reading his post!)

        [This message has been edited by Your Old Dog (edited 07-16-2005).]
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        Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

        It is true, there is nothing free about freedom, don't be so quick to give it away.


        • #5
          If you are a home shop type I would say buy only HSS steel and learn to grind tool bits.
          HSS is very forgiving, regrinds easily and can produce better finishes than carbide. Which by the way often breaks or chips if the cut is interrupted.
          Unless you are machining something very hard and need to go fast don't waste your money on cobalt-- not needed.
          Grinding tool bits takes a good grinder wheel of the right type and lots and lots of experience. After you screw up 1/2 dozen bits you'll have the experience! Two things that need to be brought up to date from all the tool grinding literature. Forget back rake. All it does is reduce the amount of power required for a cut and really complicates grinding the tool. How much power reduction? The experts say 5%. Oh wow!
          The other item is learn to grind in a chip breaker. There are times it really is a life saver or at least a temper saver.Your temper not the metal's.
          Be glad to help with this subject.



          • #6
            Fairly new to posting but have some machining experience and training, also an avid technical book collector and reader. First of all entire books have been written about cutting tool material selection. The previous posts have some very good advice.
            First cobalt bits are not realy made of cobalt! they have usualy 5% to 10% cobalt added to the HSS. This increases the melting point of the metal and improves tool life. I was taught to be consevative on te lathe rpm this is epecialy true with a lathe that only has say, 6 speeds.
            If HSS is cratering try the following
            1 use coolant/cutting oil (This subject fills another book)
            2 reduce cutting speed
            3 reduce feed
            4 widen the chip breaker groove
            As for what carbide lathe tools look like?
            they have a piece of carbide brazed to the end of a mild or carbon steel blank. keep in mind also there are different grades of carbide intended for different materials. Many of the "fancy" cutting tool materials were developed to increase shop productivity and production rates by incresing tool life as well as greater speeds and feeds.
            One of the best way I have found to learn about Tools is to browse catalogs. Vendors will often give info on tool applications.
            HSS steel and cobalt can be sharpended with a 6"bench grinder. Cobalt takes a little longer to grind. Carbide needs a special "green "wheel or a diamond wheel to sharpen.
            I personaly do not usualy grind a chip breaker but learning how is certaily not a bad thing.
            Hope this is helpfull
            Ad maiorem dei gloriam - Ad vitam paramus


            • #7
              I have another question along this same line: I got some "Tantung - G" lathe cutters a while back. They appear to profile cutters that had been sharpened by surface grinding the top. They are .5 x about .45 and 4.0 ins. long. I did check my catloges and the net. All I found was that it is tougher than Cobolt steel. A couple of places would give a quote for custom cutters but no one had any standard blank cutters for sale! What is this stuff?