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Thread: C2 and C6 carbide

  1. #1
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    Default C2 and C6 carbide

    I've poked around for the last 45 minutes and havent found any information on this... (i must be doing *something* wrong )

    What's the difference between C2 and C6 carbide? I've noticed that they sell carbide tipped cutters with C2 carbide and C6 carbide...what are the different types used for? Is C2 for cast iron and certain non-ferrous materials...i seem to remember that from somewhere...?
    Last edited by Fasttrack; 09-05-2006 at 09:47 PM.

  2. #2
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    Yep. C2 for cast iron, brass, aluminum, etc. Also, use C2 on steels if you have an interupted cut. C5/C6 for pretty much everything else. C2 is on the soft end of the carbide scale. It's needed for cast iron and brass because of the way the material "breaks" instead of shears. The harder carbides will chip or crack on cast iron.

  3. #3
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    Default How to tell

    I have many lathe tools, but the most I do is to ID them as either hss or carbide. Is there a way to distinguish between grades of carbide? I have had some that say right on the tool, and of course thats not a problem...but if there is no indication is it a crapshoot?

  4. #4
    Millman Guest

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    {{is it a crapshoot?}} A lot of times machining is a crapshoot. Actually there are very,FEW hard and fast rules to this trade. One thing I trained guys was show them what NOT to do.

  5. #5
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    Most brazed carbide tooling will have the carbide grade marked on the shank of the tool.

    Carbide inserts can be a totally different matter. Many manufacturers have their own identification system, and there are many grades and sub grades. Added to that the inserts are often found loose and are unmarked and it becomes even more confusing.

    The good news is that the carbide police are overworked, and will seldom raid your shop if you misapply an insert. If you have an unknown carbide, give it a try. The worst that will happen is poor finish or reduced tool life.
    Jim H.

  6. #6
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    You can get some idea by holding the carbide to an ordinary grey grinding stone such as is supplied with the $1.99 chinese grinders. The harder and more brittle the grade the easier it is to grind, generally. The "softer" carbides such as C2 or C1 are usually the toughest and most abrasion resistant and are much harder to grind. I have a handfull of C1 carbide pieces and an ordinary stone merely polishes off the dirt. C6 will take a slight grind although too slowly to be useful.

  7. #7
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    Default Carbide Grades

    The shop I started in 40 yrs. ago used to use nothing but Kennametal carbide tooling. The Kennametal salesman, at that time, with many yrs., experience was quite knowledgebly in his field. Every couple yrs. or so he would come in and teach us a 4 hr. course in the proper grade of carbide to use on any particular material we might encounter. I think I probably had 7 or 8 little certificates from these courses. The following is what I remember.

    Kennametal has it's own proprietary grading or numbering system, as does most other carbide manufacturers. Somebody( this is my opinion) attempted to standardize the system with the C 1-C 7 system.

    Kennametal's K6, which evolved in to a K68 was the hardest and thus used for the harder materials such as hardened steels and alloys, irons(because of it's abrasiveness) and also for nonferrous metals. This compares to a standard C2 grade. The reason this grade is not used for steel is because steel shavings have structrual strength and when a steady stream of steel flows over and into it, it craters. This crater causes steel to weld in place and you have buildup, which leaves you trying to cut steel with steel. This blob of steel will be pushed out and the process starts over again. This is why you get those ugly rings when turning a shaft. This is of course a generality,you can get buildup from turning two slow or when using a large formtool. Coolant also does wonders for preventing buildup.

    Kennametal's grade K21, which compares to the standard grade C5 is softer than K68 but it is alloyed to diminish cratering. Steel shavings will slide off this carbide much better than off grade K68 and give a much better finish on most steels.

    Then they came out with coatings and that's another ball game.

    Jim W.

  8. #8
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    ...and just because this hasn't been mentioned yet. When determining the SFPM (surface feet per minute) calculation into rpm's for turning the workpiece for a lathe, or the cutting tool speed for a mill, you generally refer to some sort of chart. I use the Machinery handbook for cutting speeds/ feeds I don't already have memorized. The book offers suggestions for rpm based on the workpiece material and the cutting tool material. It will list HSS, uncoated carbide, coated carbide, and ceramic. Under the carbides it lists hard & tough. The C5, C6 carbides are the harder carbides while the softer, tougher carbides are the C1, C2 carbide grades.
    The harder C5 carbides don't like shock and will chip in an instant if moved into the workpiece too fast, but they will cut SS and keep an edge longer. The tougher C2 carbides can withstand some shock without chipping, but they are not hard enough to hold an edge when cutting most un annealed SS.
    Hard carbides like higher cutting speeds in ferrous materials, while tough carbides are a bit lower. Both classifications of carbides can handle friction and high speeds much better than HSS.
    Tough carbides, C2, are generally used for non-ferrous and most cast iron because of the shock those materials transfer to the cutting tools.
    Of course I have learned a happy medium is Cobalt 8% or M42 HSCo. It can withstand shock better than carbide, cuts almost as good as C2 carbide in ferrous, better than C2 in SS, it is TOUGH and cheaper than carbide.
    I hope that made sense and helped answer your question.

  9. #9
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    Thanks for the info...i've got another question regarding carbide tooling...

    Do you guys feel like it is a better deal to buy carbide tipped cutters or to buy indexable ones? What are the pros and cons for both? I see grizzly (i know crumby quality) has a set of 20 carbide tipped cutters for 32 bucks (10 are C6 and 10 are C2 hence the original question) and a set of 5 indexable cutters is $33.75. It comes with one set of inserts.

    I am also looking at some HSS stock - I guess an advantage to the 20 piece kit is that it is HSS with carbide brazed on so if i were to severely damage one i'd still have a chunk of HSS i could use...? I bought some el'cheapo cutters that were on clearence from Harbor Freight and one piece of carbide actually just popped right off. There was a little bit of harmonic vibration while i was cutting and just as i was backing the tool off it plopped off. I ground the steel shaft and used it as a cutter and seemed to work ok.

    Also can carbide really be sharpened? I've cleaned up one cutter before with a file but it takes a long time and thats only to remove a very small amount of metal - i've got some that are pretty dull (the ones that came with my lathe) and i was wondering whether i should scrap them for HSS (if i can...?) or if i can sharpen them.
    Last edited by Fasttrack; 09-06-2006 at 07:56 PM.

  10. #10
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    You can sharpen carbide just fine with a diamond or CBN wheel. You must wear a respirator as the cobalt binder is very toxic.

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