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Edge Fracture – Is It More or Less Likely With A2 Steels?

These past few days I have been working more with bevel ups and bevel downs and in my R&D mode I have found all the more questions in the different steels people are using as well as the plane types and so on. We sharpened to different angles to see what happened at different angles of presentation and looked at carbon steels used in plane making in the pre 1960’s and then A2 steels and others offered by most modern-day planemakers. Different planes installed with different plane irons gave surprising results. These images presented below, whilst in no way definitively scientific (yet), show contrast I found between harder A2 steels and the commonly used carbon steel.

You see, in using two different planes, one a bevel-up and the other a bevel-down, I found that the bevel-up plane with an A2 (harder steel alloy) began to ‘climb’ the surface of the wood much earlier than the bevel down. In other words, after 50 full length plane strokes along a 1 1/4” (30mm) wide by 48” (1.222mm) length of red oak with each plane type installed with different steel types, the edge fracture was much more apparent in one than the other. So markedly different was the obvious visual difference I became totally absorbed by it. What I saw visibly at the cutting edge with an unaided eye was further substantiated by the physical effort it took to effect subsequent cuts.


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The image on the left shows the edge fracture showing on the flat face of an A2 steel blade in a bevel-up plane. The purple line (fluorescent light) shows light reflection off of the leading edge . The one on the right shows the edge fracture on the bevel face of the same plane iron; the bevel up side. The right of the image shows near the centre of the blade where most of the work took place at that 1 1/4″ section of the iron.










The second pair of images above and right show an iron from an older I Sorby plane I use regularly now. After the same number of strokes the edge fracture is markedly less on the flat face of the cutting iron compared to the harder A2 steel from the bevel-up plane (shown in the first two images above) and also on the bevel side of the same iron. I noticed that I had to push harder sooner on the bevel up plane than the bevel down plane because the plane began to ride the cut because the fractured edge on the flat face created a sort of rounded or convex corner to the flat face of the cutting edge. This means that the cutting edge was no longer pulling itself to task but pushing the plane up and over the surface. This is generally the most principal way we can tell that it’s time to sharpen up. With the bevel down plane this began to show only when I neared the closeout of the 50 strokes.

This work piqued my interest and helped me to understand that the jury is all the evermore out on plane types, bevel types, steel types, iron thicknesses and much more. Time to dig much deeper I think. The proof is at the workbench where I discovered the wood ‘climb’ and not only in the lab, but I want to understand why we found what we did and perhaps if it is a consistent finding. We could just have a poor iron. On many older English irons used in wooden bench planes of course the steel was laminated, as with some  Japanese planes. these planes had toughness and hardness. i will be looking more at these irons too. Did we lose something in our progress?


  1. Ian M. Stewart on 29 April 2014 at 10:30 pm

    Thank you for this valuable insight. I will follow the progress of your further research with great interest, as I today acquired an old No.6 plane with a blade so rusty it may be beyond rescue. Maybe it will be worth the effort though, to avoid a more modern blade.

  2. Dave Prks on 30 April 2014 at 12:58 am

    As an aside to your research, today I hones 2 new A2 steel irons. One a new Stanley for a shoulder plane and one for a #4 Lie Neilsen. Both irons took much longer to hone to a 2000
    grit mirror finish. I’m going to guess that the harder steel should hold and edge longer but we shall see. I do know I was making lovely curls in both pine and oak, full width and quickly.
    It will be interesting to see how your further tests come out. Thanks for doing the work for us all.

  3. Bill on 30 April 2014 at 12:58 am

    Just out of curiosity, what angle did you sharpen the A2 blade to? A2 blades perform better with a higher angle, 30-35 degrees, where an O1 blade can be at 25 degrees. This may change the results that you get when comparing the two blades. I mostly use O1 blades because I like the ease of sharpening and the actual sharpness that I get, but I do have A2 blades. I have never noticed this issue with mine, in fact I see the opposite. Because O1 is softer I notice the edges dull and fracture sooner than the A2, which was developed to hold and edge longer than O1.

    • Paul Sellers on 30 April 2014 at 6:36 am

      We did hone the blades at 30-degrees.

  4. Walter Ambrosch on 30 April 2014 at 3:49 am


    Thanks for al you do. I believe we are losing a great deal in our “progress”. There was nothing wrong with the tools used centuries ago as you referred to in a recent video.

    We all ask ourselves: Is it better to sharpen less but have a brittle edge, or have a more durable steel we nee to hone more often? Much like Plain HSS and Carbide in power tools. The Carbide held its edge longer, but it was never as sharp as the keen edge on the HSS.

    To me, sharpening is a way to end or start the work day, a quiet time to collect one’s thoughts. Today, everything is super high speed so it requires tooling with longer “UP” time. We had Cryo hardened Tantung gouges on my CNC Wood lathe. High RPM and fast feed rates took their toll on regular HSS gouges. But, for Softer woods the HSS actually cut cleaner since the Tantung fractured a bit on the first pass.

    There is allot of science that goes into getting steel alloy correct, but I firmly believe no two blades or chisels will ever be 100% the same. I have some 100 y.o. Stanley chisels, there is one that rarely need sharpening even though it is my favorite chisel. There is just something in that steel that is super hard. Maybe it was at the beginning or end of a batch.

    Then there are the different heating and quenching methods followed by tempering. And now companies do a second hardening by cryogenics followed by an additional tempering.

    I think Narex got it right with a special alloy, a single heating and a special quenching to streamline the whole process. I need to see if they have plane blades.

    Thanks again Paul for all you do.

    Peace, Walter

  5. Walter Ambrosch on 30 April 2014 at 4:05 am

    Here is a bit of the explanation on the Narex Steel.

  6. David Pickett on 30 April 2014 at 2:01 pm

    Paul – you’re entering a minefield, here. If you want to start a war on a woodworking forum, start comparing tool steels. There will be an instant deluge of comments from people with no understanding of metallurgy or heat treatment, but with definite and unshakeable opinions.

    There are a great many grades of ‘tool steel’ (not all of them suitable for edge tools), and slight variations in heat treatment regime can affect some of them quite markedly. Even the old crucible cast steel can vary in chemical composition depending on when it was made and which firm made it, so will vary in performance. A ‘scientific’ comparison of tool edges must take account of exactly what is being tested, so the chemical composition and heat treatment condition of every sample cutting iron must be known for comparison to be meaningful. That’s not really within the scope of the working craftsman. Best to leave metallurgy to the metallurgists.

    There’s no benefit to a maker of edge tools to supply tools that won’t take and hold an edge, so all of them will to an acceptable standard. True that some may be a shade better than others in some circumstances, but all (short of a failure in the manufacturing process) will do the job.

    A better measure for the craftsman at the bench may be to assess whether a particular cutting iron gives good service, by it’s ability to take and hold an edge measured against your own expectations. If it won’t, ask the manufacturer to replace it. If it will, get on with making stuff, and leave the metallurgical experimentation to those with the equipment and expertise, and those on internet forums with nothing better to do with their time.

    • Paul Sellers on 30 April 2014 at 7:16 pm

      This was more a passing surprise that caught my attention and piqued my interest. the subject has interested me but I haven’t really looked into this before. I do know that I was using regular carbon steel in a thin iron and comparing it to a thick A2 iron deemed by all and sundry to be a superior iron. So, having heard all the arguments, I was surprised to see the superior show so much edge fracture. As I said, this could be a just a faulty blade. It’s not scientific and I think I was clear about that. As far as the scientist metallurgists go, we just thought we would share in some of the fun too. We have sharpened up a couple of other planes to see how much degrade we get in the everyday of use. That’s about as scientific we will get with this most likely.

    • Vodkovski on 30 April 2014 at 10:13 pm

      Hear hear!

      • Vodkovski on 30 April 2014 at 10:18 pm

        That is, hear hear to what David Pickett said.

        • Walter on 30 April 2014 at 10:31 pm

          Paul, opening the door to discussion on steel is like opening the discussion to sharpening stones and methods. Oh My it can lead down all sorts of Rabbit Holes.

          Today I tuned up my planes and chisels and it is amazing the differences in the tools and the steel use for the Blades.

          A few hone up nice and clean very quickly and give me a very keen edge and other take forever to hone they are so hard. Many of these tools are 50-100 years old, some laminated steel blades.

          I have thought about upgrading many of the Stanley blades to Hock or other modern steels. But lately I do not see the benefit in spending all that money.

          I’m not even sure I would buy new tools from even the best makers unless, I can feel the performance difference in my hand on the same wood I used my old tools on. LN does allow testing at their Hand tool events and their showroom so Kudos to them for that.


  7. Gordon Clark on 30 April 2014 at 3:46 pm

    I found this explanation at about why the A2 edge gets ragged. It’s small bits of carbide breaking away, apparently. Read below:

    AISI A2 differs from O1 with the addition of 5% chromium and 1.1% molybdenum, allowing it to quench in still air (“A” for Air.) While “stainless” amounts of chromium (12% or more) make tool steel “gummy” and hard to sharpen, the modest amount of chromium in A2 improves its toughness and abrasion resistance, but imparts only a slight measure of corrosion resistance (like high carbon steel, it will rust and appropriate preventative care must be taken.) But there is a trade off. During heat treatment the chromium addition combines with some of the carbon in the alloy to form chromium carbides – tough, hard particles dispersed through the steel. These carbides are the primary contributors to A2’s celebrated edge retention. However, during heat treatment, the chromium carbides can grow quite large – large enough to affect your ability to hone the edge as close to zero-radius as you may want. And these carbides are held in place with less strength than the rest of the steel matrix which can allow them to pop out under the stress of honing or cutting leaving a small gap in the edge. To strengthen the edge we recommend a larger bevel angle for A2 than we would use for O1. For a bench plane iron, try your A2 blade at about 30° or 33°. A chisel or block plane blade can be even steeper; try 35° or so and see if edge retention is improved.

    A2 is one of the steels that respond well to cryogenic treatment. This extreme cold treatment (-320°F) essentially finishes the original quench, increasing the steel’s toughness without any decrease in hardness. You get increased wear resistance without any increase in brittleness so a cryogenically treated blade will hold its edge longer. You can keep working instead of sharpening. A2 is a great steel that offers a real improvement in edge retention. O1, on the other hand, is still preferred by many for its relative ease of sharpening and its ability to get sharper.

    • Walter on 30 April 2014 at 3:51 pm

      A2 might hold “its” edge longer, but can it hold as keen an edge?

      If bits fracture off like Carbide, then it is not as sharp as O1 or even other plain carbon steel.

  8. Joe on 30 April 2014 at 5:58 pm

    That doesn’t look like fracture, to me it looks like flat face wear. Low angle bevel-up planes suffer accelerated flat face wear because of inadequate clearance angle and that’s what I think you’re seeing.

    Would like to see the comparison between a regular bench plane, like a #4, with an A2 blade to see if the same thing happens. Lets compare apples to apples and not apples to oranges.

    • Paul Sellers on 30 April 2014 at 7:04 pm

      Good idea. Send me an A2 blade for a #4 and we’ll do it.

  9. John Crosby on 30 April 2014 at 11:21 pm

    Good one Paul. Why oh Why must some people take such great offense at a simple observation and discussion. Come on, it’s not like we are talking about King Obama!

    Now I will throw my two cents in ( how come a person only gets a penny for their thoughts). I have type 11 Stanley planes, 4, 4 1/2, 6, 7, 8 and a type 12 no.5. I refurbed all of them myself and almost all have their original irons, or at least the right time period. I have not noticed any big differences in any of the irons, they all hone about the same and last about the same. I would like for the iron to retain it’s sharpness longer, but it is an even trade off, in my mind, for the ease of honing. Buying all new, state of the art irons for all my hand planes would definitely set me back quite a bit, maybe $300 or more. That is not something I would like to do at this point, especially since there is no clear cut (haha pun) consensus on whether A2 is worth the price in the long run. Honestly I think if I were to buy a couple new irons for my smoothers, I think I would most likely go for the O1. O1 to me seems to have more in common with our older irons, and I would rather have scary sharp and sharpen more often than scary hard with fracturing and sharpen less.

    It just seems fairly simple to this simple minded individual, that the harder a steel is the more brittle it will be. But then again I am not a metallurgist.

    • Joe on 1 May 2014 at 3:55 am

      Its not necessarily people taking offense. Its Paul’s ability to mislead people with things he likes to call “facts”, sorry Paul but that’s a fact.

      Just think about this for at least 1 sec.

      If A2 sucked, then why would people buy it???

      And no, the answer isn’t because the “companies” tell them to.

      If A2 wasn’t a good metal, and 01 was so much better, the word would spread fast, the facts would be overwhelming, and production would stop.

      It costs more to make an A2 blade, LieNielsen would save money by just making 01 blades for everything. But, the facts are, it is a good metal, it does a good job.

      But Paul has his drum to beat and if you buy something new, watch out, because Paul might just have something negative to tell you.

      I would bet my life that if the planes made today were made back when Paul started, he would be bragging about his awesome LieNielsen and not about an old Stanley.

      I write this however knowing that more than likely Paul will not allow this post to go up. But , someone has to try.

      I do respect you as a craftsman Paul, but you seriously need to stick to teaching the craft and stop trying to cram your personal agenda down peoples throats.

      • Walter on 1 May 2014 at 4:39 am

        Joe, A2 is not necessarily “Superior” it is different because it has different properties.

        LN make O1 Blades as well and double hardens and double tempers all of their Irons.

        Every Manufacturer tries to be “Different” Paul is trying to simply compare the old irons to the new ones which seemed to him to be fracturing which I agree to be true.

        If I would have spoken back to my Master I would not have any teeth left. Paul is a master of his craft, but like many of us are tired of the modern makers cramming what they call better down our throats.

        Fact, Iron is Brittle, Steel is tough and hardened steel is brittle. Finding a balance that does not cost a fortune and is easily refreshed as we work is the key.

        This is not a battle of what is Right or Wrong, or what is “Best” (there is nothing that is the best for everyone)… it is about a highly respected Master of our craft posing alternative thoughts on what we all see each day in our shops.

        I have been at this 43 years, and the old tools are still on my bench and the Modern stuff either proves its worth to me in use or gets sold or trashed.

        • Damien King on 6 May 2014 at 6:16 pm

          Walter, Here, Here!!!

  10. Maurice on 1 May 2014 at 6:22 am

    It’s incredible how people like to suppress opinion and experience with so called accepted norms. That is the sign of a really ignorant person that is incapable of giving a constructive reply that either answers or furthers the question.
    We should be encouraging experienced people to give us feedback on any issues that affect them and their peers. This is how Veritas and Lie Nielsen have developed/perfected their products and why many manufacturers pay expert consultants to improve the function and useability of their products.
    I am an engineer myself (not a metallurgist) and one of the first things you are taught is to ask for feedback not assume that you have all the answers. I recognize and appreciate good engineering, but not a the expense of function.
    In closing I thank Mr Sellers for his fearlessness in expressing his opinion and I encourage him to keep doing so, regardless of the countless free speech deniers.
    Let’s see all these companies flogging their products at an inflated price put their money where their mouth is.

    • Damien King on 6 May 2014 at 6:36 pm


      Well said! I’m constantly amazed by the many people who read Paul’s blog yet seem to think that Paul shouldn’t express his opinion. It’s HIS blog. If you don’t want his opinion, read something else. That’s like going to a Dr. and expecting him not to tell you if you’re sick.

  11. John Crosby on 1 May 2014 at 7:24 am

    WOW! Joe, they put your post up and I for one applaud them for doing so but at the same time wish they hadn’t. I come this site for inspiration, discussion, education and enjoyment. I am a bit sad right now, not about your tirade, I am sad because you push your opinion very forcefully on us just as you say Paul Sellers does to you. Talk about facts, fact is Paul never said A2 sucked. Another fact is I have never read a post or heard in a video, Paul Sellers say that anything new is not as good as something old. I have never read or heard Paul say Lie Nielsen is a bad plane, quite the contrary. I have heard him say that a person can get the same results using tools that were made 100 years ago and cost less than a quarter of what the top of the line cost. Hey man, I’d love to own a set of Lie Nielsen’s, great tools and they look like pieces of art, but I would rather pay my mortgage for a couple months instead.

    Joe please don’t try and protect us from the bad Mr. Sellers trying to mislead us. The way you phrase some of your statements it sounds like you think most of us are not intelligent enough to look after ourselves or that we are susceptible to tactics used by a cult.

    You want A2? Buy it. You want O1? Buy it. You want to slam a guy for having an opinion based on 50 years of experience, please go somewhere else. There are way too many serious problems in peoples lives and in the world to get this dramatic about a discussion of which plane iron needs more sharpening. Please lets keep this in perspective

    • Ian M. Stewart on 1 May 2014 at 8:10 am

      +1 John. You said exactly what I was thinking. 🙂

  12. Dave on 1 May 2014 at 8:26 am


    Maybe one or two here have maybe missed the point you were actually trying to make, and might owe you an apology. I am surprised by some commenters’ words.

    This may be a minefield, as another commenter already pointed out, but, please remember, Paul’s original post was very unassuming, and was very much worded as an ‘unscientific observation’. He even used those two words. He was not telling anyone to throw away their bevel-up planes or your A2 blades, was he? He was simply sharing an interesting observation.

    Please can we remain polite even when we disagree?

  13. Carl Larsson on 25 May 2014 at 10:49 pm

    There is an urban rumor that A2 blades sharpen quickly on the NORTON wet stone system; do Norton stones have a special grit formula? I notice that the stones remain flater, longer than other wet stones.

  14. Ben on 31 March 2015 at 5:44 am

    Have you had a go at any of the PM-V11 of Veritas / Lee Valley? I’m curious how it compares to the O1 and A2 stuff. They push it pretty hardy… obviously because it’s ‘theirs’.

    • Paul Sellers on 31 March 2015 at 7:43 am

      I haven’t. I generally try to work with what’s readily available and affordable for everyone no matter where they are in the world. Knowing Veritas, I am sure it’s good, but generally I am content with the ordinary things of life.

  15. Barry Keepence on 22 January 2017 at 6:54 pm

    Ok here goes – here are my empirical observations.
    1. I have never had problems with sharpening A2 tools.
    2. I do find they hold an edge a bit longer but no enough for me to change any of my o1 places to A2.
    3. I use water stones and they are friendly to steel and here is why. When you sharpen steel you drag bits out of it with the sharpening material. In solid systems the particles do not move and hence the steel is deformed more under the surface. In a waterstones the abrasive material is mobile and hence does less damage to the substructure of the steel. This is why so many people like water stones and why they are particularly good for very hard steels (e.g. A2 and Japanese steels).
    4. Now this one is a biggie – my blades keep an edge for longer when I hone them. This was mentioned earlier in that A2 especially can have brittle edges that break off when you use the tool. Honing these brittle bits off makes a big difference – and especially to A2.
    5. I only hone for a few strokes on each side and I find it really helps.
    6. For those who care I go 1000 grit, 2000 grit then 6000 grit then hone

    If anyone out there is struggling with getting the best out of their A2 blades I hope this helps.

  16. Tone on 24 January 2018 at 2:01 pm

    Paul, could it be that the wood being planed is effectively “honing” a micro-bevel on the bevel of your I. Sorby bevel-down plan but a micro-bevel on the back of the harder A2 bevel-up iron? A micro-bevel on the front would tend to strengthen the softer iron but a micro-bevel on the back of the bevel-up iron would tend to lift the cutting edge up, above the micro-bevel and the surface of the wood, much as you described.

    In his book, Swedish Carving Techniques, Wille Sunqvist describes in some detail why he considers it important to avoid secondary bevels when sharpening woodcarving tools for similar reasons: it causes the cutting edge to ride very slightly above the surface of the wood, albeit when resting the bevel on the wood, following earlier cuts, in the Swedish style.

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