View Full Version : C2 and C6 carbide

09-05-2006, 09:43 PM
I've poked around for the last 45 minutes and havent found any information on this... (i must be doing *something* wrong :D)

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...?

09-05-2006, 10:11 PM
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.

Ed Tipton
09-06-2006, 08:25 AM
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?

09-06-2006, 08:48 AM
{{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.

09-06-2006, 10:29 AM
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.

09-06-2006, 11:22 AM
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.

09-06-2006, 12:38 PM
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.

09-06-2006, 03:26 PM
...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.

09-06-2006, 05:18 PM
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.

09-06-2006, 06:02 PM
You can sharpen carbide just fine with a diamond or CBN wheel. You must wear a respirator as the cobalt binder is very toxic.

09-06-2006, 07:46 PM
The cheaper Silicone Carbide wheel works too. A diamond dresser works wonders as well. You could spend hundreds of dollars just on wheels. Each one would be used for a different purpose. Then there's the demounting and mounting of different wheels so you'll spend more just to have dedicated grinders. I've got six! It can easily get out of hand.

09-06-2006, 08:14 PM
The shanks of most brazed points are nothing but toolsteel,not even HSS.At work we have everything,HSS,brazed points and inserts because we see all sorts of jobs.
I never buy sets of brazed points,you are better off buying 1 or 2 of each style in a quality brand from somebody like MSC or Travers etc.HSS everyone should have some,it is still very verstile and can be readily modified for special jobs.

Inserts,well pic a common shape,like a triangle or diamond and stick with it for all your OD turning tools,that way you don't end up buying a different insert for each tool.

Something like a TPG322 is a good general purpose insert that is easy to find and cheap to obtain even in a quality brand like Kennametal.If you have a small lathe stick to the positive ground inserts,the negative rake styles require more HP and mass than you have availible,also they can be used on non-ferrous materials with better results.

You will find that outfits like JTSmach on Ebay will have Kennametal inserts on sale at closeout prices.You can checkout the various grades they have online and get an assortment fairly cheap.

09-06-2006, 08:14 PM
Heck. I only have four not counting belt sander and a small linisher. Wait, I forgot one. Five. Actually, if you count the one the magic smoke came out of then six. Oh, and I forgot the wire wheel. Seven. Oh yeah, my tool post grinder. Eight. And my dremels. Nine. :D

09-06-2006, 08:17 PM
Thanks! I know the brazed point ones i got from HF advertised that they were brazed to M2 HSS - which was a curiosity to me since i figured HSS wasnt really neccessary since the carbide should do the cutting. I guess i just figured that they all would be like that - guess not!

09-06-2006, 08:19 PM
If you want to read up on carbide,inserts and tooling in general read through these pages-


09-06-2006, 09:16 PM
Heck. I only have four not counting belt sander and a small linisher. Wait, I forgot one. Five. Actually, if you count the one the magic smoke came out of then six. Oh, and I forgot the wire wheel. Seven. Oh yeah, my tool post grinder. Eight. And my dremels. Nine. :D

ROFLMA http://img.photobucket.com/albums/0903/CCWKen/Personal/icon_lol.gif :D

I didn't count the TPG, Dremels, Die Grinders or the antique manual grinders or I'd have fifteen+. ;)

09-06-2006, 09:25 PM
Thanks for the link! That's exactly what i was looking for...

as long as i'm here i'll just shoot one more quick question:
the biggest size bit my tool post will accomodate is 1/2 inch - should i be going for 1/2 or can i use 3/8? What is a good size range for say 1/4, 5/16, 3/8, and 1/2 inch cutters? Do the bigger ones just handle heat better?

09-06-2006, 09:31 PM
Crap. I forgot the manual grinder and the angle grinders or die grinder. Does a sand blaster count?

Dang, I gotta stop thinking about this. What about my 8" hand held cutoff saw?

09-06-2006, 09:52 PM
Hmmmm...maybe I'm having a memory lapse, but I always thought C2 was harder than C6. C2 being used for abrasive materials like plastics and nonferrous while C6 was for steels.

Since most inserts now have whiz-bang proprietary coatings the "C" grading system isn't so relevant anymore.

09-06-2006, 10:41 PM

I have that Grizzly C2 and C6 20 piece set. I don't usually use carbide, but it is nice to have "something" in the shop. They are ok, not great, just ok. If I was going use the tooling to earn my living, they would definately not be the first choice.

As for the grinder count I think I have at least 6 Dremels ...

09-07-2006, 12:47 AM
I just looked up a table of carbide hardness. The softest is C1 at 90.5Ra and the hardest is C8 at 92.6Ra.

There isn't much range and the others fall in between with C2 and C6 both being about 92.2. There isn't a real difference in hardness. The main difference is in brittleness vs toughness and the abrasion resistance. That also determines how good an edge can be developed.

loose nut
09-07-2006, 07:55 PM
Some suppliers color code there brazed carbide bits ie: c2 gold c6 blue etc.
stay away from the the cheap stuff it does't hold up nearly as long so it costs more in the end. I found that out the hard way.

09-08-2006, 10:06 PM
Oh,forgot to mention,the run of the mill brazed points aren't really suitable to use as is,they really need grinding to correct the angles before use.Some of the imports have little or no relief on the leading edge and won't cut hot butter as a result.

09-08-2006, 11:55 PM
I never dreamed the "pre ground" carbide cutters would need additional grinding! I ended up buying a relatively cheap set of indexable cutters - not the cheapest but still cheap. I figured i'd give it a go and see how they work out for me and then maybe i'll consider investing in a better set. I also got some HSS stock to make my own.

09-08-2006, 11:58 PM
You will most likey find that between the HSS and inserts you won't have much need for the brazed points.

So,what insert type did you select?

09-09-2006, 12:12 AM
I ended up going with TCMT 32.51 inserts - they are the equilaterall triangle inserts with 7 degree relief and a chip breaker. They were on sale at grizzly and i figured they'd be a good set to get used to indexable cutters and see what they were like. I won't feel to horrible if i chip one of these. I liked this idea because i plan on making my own tool holder that will do internal threading for that part on my mini-bike project. I tried making my own just out of scrap spring steel but with my old worn out grinding wheels and in-expert filling i've had a hard time getting exactly 60 degrees at the point. I'm thinking i should be able to design an effective tool holder that will use these 60 degree inserts to do my threading. I'm not sure how hard this will be though - any thoughts are welcome!

09-09-2006, 07:40 AM
I use this to hold a small diamond insert for boring and threading non-ferrous materials. It's just a piece of 1/2" crs with a slot in the end and a counterbored hole for a clamp screw. It holds the insert just fine and I can adjust it for threading as shown or to cut to the bottom of a blind hole.


09-09-2006, 10:23 AM
Now out of curiosity...isn't diamond a pretty poor choice for cutting steel? I guess on non-ferrous materials or when threading at slow speeds it work great but for like ordinary turning operations one wouldn't want to use diamond right? I seem to recal that at high temperatures and pressures the covalent bonds are broken and it will begin to form microscopic graphite layers on it. I don't know though - maybe you wouldnt ever encounter enough heat to worry about anyway.

09-09-2006, 10:29 AM
Diamond, CBN, and carbide are overrated. 99.9% of the time, just use HSS. Just think of ALL the things that were created before carbide tooling was invented. You'll gain more valuable experience grinding and using HSS than all the "Plug and Play" inserts. Nowdays, people think those inserts are the cure all to all their problems. Not so!

09-09-2006, 11:05 AM
I don't use diamond on iron, iron dissolves diamond. Diamond is especially useful when cutting through hard anodizing which I do from time to time. Hard anodizing is the same as ruby which is harder than carbide. It also doesn't dull when cutting high silicon aluminums or bronze. It leaves a mirror finish boring aluminum or silicon bronze.