# Carbide Vs Steel



## designer (Oct 6, 2014)

There has been some discussion as to whether carbide or High Speed Steels are sharper or better.  Please comment if you agree or not.



 I use M2, M4 and M42 HSS and carbide tools.  Mechanically there are some major differences.

Steel cannot take a lot of abuse on the end.  It will give or dull or chip.  Hey, it is steel.  We have all seen it.

Carbide
 Carbide in the metal industry for high speed lathes and mills can work or fail if not used properly.  The depth of cut Must be greater than the edge radius.  Most are not "razor sharp".  They have a radius built into them.  If the inserts that are being used on wood were designed for the metal industry, they will have a min of about .003 radius on the edge.  Some up to .016 or more.

Again in the metal industry (not wood at this point) carbide has been able to shine over HSS when loaded down.  Carbide does NOT like light cuts.  Carbide does NOT like interrupted cuts.  Now put it under a heavy load that is steady and it will peel off steel like butter.  


 On a mill with 4140 pre-hard steel at Rc 28-32 a 3/8 (side cut on and end mill) X 1 ½" (length) depth of cut will go just fine with carbide at some scary feed rates.  HSS will burn up in a heart beat.  This particular process was taking approximately 15 minutes with HSS with only a few thou depth of cut per pass.  Changing to carbide it only took 32 seconds.

Wood will never stress carbide the same way.  The wood will give long before the carbide will.  Sometimes with catastrophic results.  In other words, Explode.   


 The abrasiveness of wood will just dull the carbide like it will steel.  It just normally takes longer with carbide based on the same cutting edge on each.  The hardness of carbide is significantly higher.  That does not mean it is always better for a given application.

Will HSS or carbide solve all your problems going with one or the other?  You decide based on your experience and abilities.

Can carbide be sharpened as sharp as steel?   
 Carbide comes in a multiple grades from each of the main vendors.  Is it a standard carbide?  Fine grain or is it a Micro grain material?  Is it C2 carbide or an exotic?  Exotics can be sharpened closer to a razor edge (some can).  I have sharpened a basic C2 (very basic and hard carbide) and cut myself on it and did not realize it till the blood got my attention.

Yes, carbide can be razor sharp with the right material and the right sharpening equipment and methods.  Unfortunately, most of us do not have all this available to us.  That does not mean we cannot sharpen it to a good edge for our use.  Look at the CBN wheels for example.


 The positive or negative rake on an insert to me is academic since we control that with the tool rest and angle of the the tool to the wood.  Correct me if I am wrong on this.

What is next in wood turning?  PCN or Diamond tools?  Talk about over kill.  Heaven forbid if one of them were to crack in use due to the cost of them.  And don't ever drop one.  Ouch in more ways than one.

I have asked the three largest carbide insert manufacturers about inserts for wood.  All three looked at me like a deer in the head lights of a car at night.  After getting with their engineering departments the answer was the same.  "We have nothing for turning wood at all and would not know where to start.  In other words, they don't make inserts with razor cutting edges.  Carbide normally does not like that in the metal industry.  Not wood, metal.


 One round insert I bought I took to work.  I put it on an optical comparator with 10X, 20X and 50X magnification with a DRO on it.  I asked each of my three techs to check the edge radius (I needed a gage R&R anyway on this unit) at each magnification.  The average results were .004 radius.  Certainly not razor sharp at all.  And this was a new unused insert.  I spent lunch at my desk with  diamond to hone it.  I used digital micrometers to check the thickness to begin with.  After reducing the thickness .005 I still had a .002 apparent radius on the edge.  Was this due to a hone that was too coarse or the material the insert was made from?  The hone was a cast iron lapping plate and diamond lapping compound.  The surface finish was checked and was down to a 4 micro which is almost a mirror finish.  It was the material in the insert being too coarse to get to a razor edge.  It was a coarse grain material is all.  That particular carbide will never be able to have a razor edge.

I have never done a hardness test on a carbide tipped saw blade.  I assume they are a C2 material.  It will hold an edge well due to the hardness.  If someone has some good info as to what grade carbide they are I would like to know for my own knowledge.  Those are sharpened to a very sharp edge  and no radius of course.

Now which is best?  M2, M4, M42 or carbide?  What about D2 or Stellite?  It might all depend on your own skills at sharpening and techniques in use.


 Was the steel double or triple drawn?  Was there a good controlled cryogenic process added?

I guess I am just suggesting to keep an open mind.  Practice and get comfortable with each and learn how to sharpen to your own liking and use.  


 Well this should start some interesting comments.


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## Rich L (Oct 6, 2014)

designer said:


> There has been some discussion as to whether carbide or High Speed Steels are sharper or better.  Please comment if you agree or not. Sharper or better for what?
> 
> I use M2, M4 and M42 HSS and carbide tools.  Mechanically there are some major differences.
> 
> ...



I think some of your comments are correct, some provocative, and some way too general to be correct and I've added my comments in the quoted text. I have some practical experience with the subject matter, I've heard these arguments before (and they're good arguments), and I've heard categorical statements either way about suitability, sharpness, hardness, wearability, etc. but I've never heard a convincing argument, backed up by a reasonable process and experiment under scrutiny, that confirms carbide can't be as sharp as steel, stellite, etc. 

All the ornamental turning I do on wood is done with carbide tools and those tools need to have extrememly _sharp_ edges and points. The finish they leave is pristine and needs no further sanding or fillers unless one is trying to protect it from liquids.

Cheers,
Rich


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## plantman (Oct 7, 2014)

Only comment I have is, because of the moleculer makeup of Carbide, you will never obtain the edge that can be had with steel.   Jim  S


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## 1080Wayne (Oct 7, 2014)

I have had only patchy success sharpening inserts with 400 followed by 1000 mesh diamond stone . What do you guys recommend ?


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## Curly (Oct 7, 2014)

My Dad was from the very old school of woodworking. He took a rock from the driveway and ground it flat on the cement walk of the house and sharpened his tools with it. In this instance he would say "Quit fooling around and just turn something." :tongue:


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## designer (Oct 7, 2014)

I use a cast iron lapping plate and diamond lapping paste with an oil base and lapping oil.  Depending on the grade of paste, you can remove the carbide fast or lap it down to a mirror finish based on what you want.  Carbide does not have a grain like steel so the direction you move it in does not matter as much.  I tend to use a figure 8 on the lapping plate.  I personally do not use a diamond hone for carbide.  But that is me and there are others that do use them.  Someone else can give you better input on the diamond hones.


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## designer (Oct 7, 2014)

Rich.  You bring up some valid points.  The insert I was working with is a standard wood turners round insert.  I have not seen any with a chip breaker for wood working.  

Yes, for metal working you can order any of a number of chip breakers and rake angles.  The Sumitomo, Iscar, and all the others have very thick catalogs just for inserts for metals.  Different coatings as well.  In wood working the tool rest is adjusted and the angle of the tool changes to accomplish that though.

You are correct.  I did not hone the insert.  I actually lapped the surface on cast iron plates with diamond compounds.  Not a honed edge as the terminology means.

I might be wrong, but most wood turners do not have access to all the ideal equipment for sharpening carbide correctly.  That leaves them with an edge that is not razor sharp.  Sharp yes, not razor sharp though.

I cannot prove it, but I highly doubt that the inserts sold for wood turning are micro grain material that is (IMO) able to get a better edge.  The grain size when lapping seemed to be more of a standard grade carbide.  Hind sight says I should also have checked the hardness of the carbide as an indicator as to the grade to some extent.

Yeppir, the variables in metal industry are vast when it comes to inserts.  I doubt the wood working industry will ever have the same variety or the number of choices.


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## Wildman (Oct 7, 2014)

I totally disagree with majority of what you say about Carbide Vs Steel 

Some of my carbon & HSS tools been using for over twenty years.  Even my crappy Kryo ½” skew more than six or eight years old. Through abuse or use have replaced or added to my steel tools over the years.  Only some of the tools talking about at the end of their useful life, many have years to go before being retired!

Bottom line have no problem re-sharpening any steel tool I own, been doing that for decades!  Cannot say that about carbide tools! 

Important facts you did not mention is all tools need sharpening eventually.  While can re-sharpen steel tools for many years not so with carbide cutters.  Replacement carbide cutter expensive to replace.  While can cut & scrap with steel tools, carbide tools can only scrap!  

Yes, carbide scrappers excel in some areas, but will never replace steel turning tools!


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## rherrell (Oct 7, 2014)

I think debating which material is sharper is pointless, for WOOD turning anyway. They're both PLENTY sharp enough to cut wood.

I think the beauty of carbide is it's simplicity, both in turning and ESPECIALLY in sharpening. I remember how terrified I was when I first started, sticking a sharp pointy tool into a rapidly spinning object seemed like a BAD idea!:biggrin:

The carbide tool eliminates all that, just hold it on center an go, how much simpler can it get?

I also remember how intimidated I was with the whole sharpening process, it seemed like EVERYONE had a different method or some kind of jig to make it "easier". It seemed like the more I read on the subject the more confused I got.

Enter carbide...WHAT A RELIEF, NO SHARPENING! Just pop in a new one and you're good to go! I know they're expensive but think about it, how much have you spent on grinders, wheels, jig, books and how many tools have you ruined, I've trashed a few.:biggrin:

Don't get me wrong, I still use my traditional chisels for almost everything but the carbide tools have made it a lot less intimidating for the beginner, that's a GOOD thing. Once they get comfortable turning with the carbide they can, if they choose, learn the more traditional way, which is also a GOOD thing.


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## KenV (Oct 7, 2014)

plantman said:


> Only comment I have is, because of the moleculer makeup of Carbide, you will never obtain the edge that can be had with steel.   Jim  S




Jim -- depends on the carbide and the steel for sharpness of edge.

And it depends on what "obtain the edge that can be had with steel" means.   Some steels cut well but under high magnification, are pretty irregular."

Any more, with the careful selection of each, carbides and steels can produce comparable edges.

In practicality, there used to be the same "conventional wisdom" about the differences in edges between high speed steel and high carbon steel.   That has pretty well gone away too.   

Work by Brent Beach and others points to the sharpening techniques being more important to determining the precision of the edges -  

Practically -- the steel or carbides can be matched to the job and conditions -  and cost is often the determining factor rather than capability of taking an edge.


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## Wildman (Oct 7, 2014)

Agree with Rherrel, sharpness of different steels pretty much a wash. Where we part ways is scraping vice cutting.  Nothing personal, know several long time bowl turners that use traditional scrapers. Before carbide tools met a champion game caller/ turner that got excellent results scraping his way to success.  Have not seen him in years so only assume he has bought or made his own carbide tools. 

Freely admit carbide tools do make life easier turning many things like antler, bone, domestic & exotic woods, and manmade or natural stone. So do my traditional HSS & exotic steel turning tools.

I turned a lot of Poplar year or so back and had to run to the grinder several times due to torn end grain. Almost went through bottom of my bowls couple of times.  My Sorby carbide shear scrapers no help, they performed even worse. Probably my lack of tool control or experience with the tool maybe.  I simply contend will run into that piece of wood or other material on a lathe that will give you fits. Nothing to do with you, tool, or technique!


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## plantman (Oct 7, 2014)

As for the debate of sharpness, how many carbide scalpels have you seen in the hands of a surgen in an operating room ????    Jim  S


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## designer (Oct 8, 2014)

Carbide indexable inserts cannot be sharpened like you can steel.  Steel tools have longer relief angles under the cutting edge.  When you adjust the tool rest height and the angle of the tool itself, you can cut or shear with it.

Carbide inserts cannot do this.  You can get a pretty good edge on it, but never into a shearing action for wood.  First, if you were to grind the same clearance angle on carbide, it would have to be a huge piece.  The price would go up accordingly.  Second, carbide needs support.  It does not like being left hanging out in the open.  Carbide will fracture and break under the same grinds.  

Since I have never seen a wood insert with a chip breaker due to the attack angles used on wood, I am going to try an experiment with no chip breaker.

I am going to take a C2 and C6 brazed carbide tool for a metal lathe and grind a relief angle more along the lines of a steel tool would have.  I will try them out on some wenge, pine and apple wood.  Just turning from square to round.  No special features, just basic turning.  I will make a handle for them so I can adjust the angle of the tool when using.

The question is, can I get a shearing action with this setup and not have tool breakage?  I have access to surface grinders with diamond wheels and radius dressers as well as other equipment so this will be more of a "lab" test than a home shop test.

Are there other variables that should be included in this test?  I can't include force or load sensors to check the amount of force being exerted on the tool so we will leave that one out.  It would be a nice comparison to steel, just not within my abilities.

I will grind 3 each of the grades of carbide for this trial.

I do not believe I can do a gouge in this configuration.  The carbide is just not thick enough to accomplish this.

Otherwise, please give me suggestions as to what you would like to see.  Experimenting is fun for me.  What kind of information would you like to see as an outcome of this test?


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## steve worcester (Oct 11, 2014)

designer said:


> Since I have never seen a wood insert with a chip breaker due to the attack angles used on wood, I am going to try an experiment with no chip breaker.



We need to clarify something here. If we put carbide inserts into two categories, Easy Wood and Byrd tools flat tops (scrapers) and the Hunter type insert.

Easy wood doesn't have a chip breaker, Hunters do. 

Hunters are the type that are nano grain and highly polished, they have a sharp edge and a gullet going towards the center point. That is what I would call a chip breaker.

True, inserts for metal won't work. Not sharp enough, not polished, but those used in plastic manufacturing might work. They are a sharp edge and highly polished. The problem with woodturning is we can only choose what is already out there, the woodturning market isn't big enough to warrant (in their eyes) the cost of tooling and manufacturing just for the small market.

As far as negative rake vs positive. Anytime you tilt a positive rake down to obtain an angle to engage the cutting edge of a carbide insert, you start to loose control of the tool.

As you may be able to tell, I am not a fan of carbide scrapers. Sure, they are great to get people into turning. Easy to use, low learning curve, but I haven't found a lot of beginning turners willing to take the next step to use a gouge. Then they complain about the tools finish. A gouge has a much longer learning curve but can give a much better finish than a carbide scraper.

One last part to my rant. I see several carbide turning tools like gouges and skews using what I presume are an investment cast tip on a steel base. Since they are nearly impossible to sharpen, as soon as you hit a rock, they're toast. Not to mention that they can't be as sharp as a HSS steel gouge or skew.


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