Making a Wooden Plane: Hardening

Posted 3 February 2014

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Paul walks us through the process of hardening and tempering an iron for a small plane. He then heads to the workshop to clean up and sharpen the blade and finishes off by showing how to adjust the plane.

Previous: Making a Wooden Plane – Episode 3

59 Comments

  1. Thank you so much for taking the time to film and post the hardening, tempering and first sharpening process. It goes a long way demystify the process. I think I built it up I’m my mind to be something much more difficult than it actually is. Fear of the unknown I guess.
    Again, thank you Paul and crew.

  6. Great job of showing a process that anyone can do in the back yard without specialist tools. It’s one of the things I like best about your teaching. For those who don’t have access to an kitchen oven for tempering, due to domestic circumstances or whatever, I would offer an alternative. Polish the scale off with emery paper, etc,, just til the whole blade shows bright metal. Then, holding the blade with the visegrips, play the flame of a small propane torch along the back of the blade and watch the colors move down toward the cutting edge. Just as the straw gold color reaches the edge, quench again in the oil. Take your time and don’t get the colors running too fast. Best to do this process twice for good measure.

    1. Hi Robin,
      For the short term, Paul shows how to do the figure of 8 sharpening slower in the third of the ‘Making Wooden Planes’ videos. We will probably be putting up a shorter video showing just the sharpening of rounded blades at some point, so I will see if I can put a slow motion clip in that.
      Cheers, Phil

  10. Hi Paul. Many thanks for making this process so simple. I have an old Sargent small smoothing plane (1-5/8″ blade, 8″ sole) who’s iron will never hold an edge. I suspect some previous owner has used a fast grinding wheel on it, and ruined the temper. Do you think this hardening/tempering would be a good idea for that?
    Cheers.

  11. Nice Video Paul, I think I will be trying the hardening and tempering with a propane blow torch as Randy identifies above, that was the process I have used ( a very long time ago) as an apprentice engineer when making centre punches and chisels, I have started making a couple of planes but as yet have not got the tool steel.

  14. Great video as usual, and very informative; thank you guys!

    I have a little question: I’m making a scrub plane out of an old #4 but creating the curve on the iron is taking me forever with a file. Is it possible to “soften the steel” using the oven? Will it work? And then, how can I hardener it again?

    Cheers!

    1. The downside will be rehardening and keeping the plate flat and without buckle. Most plates are hardened and then ground or rolled flat. It will be easier to grind on a grinding wheel and plunging regularly in water to prevent overheating the steel.

  16. I noticed three interesting aspects :

    1.The highest temperature is estimated not by colour , but by reaching the Curie point
    2.The figure of eight – finally revealed
    3.The ethernal joy of working wood.

    Thanks for the wonderfull lesson.

  17. Thank you for a very nice video. I have always wanted to do this rather than buying blades for my planes pre-made. This makes so much sense and better than watching for colors moving to the edge. I would love for you to provide a video on building your particular bow saw. Also, do you make one with rotating handles so to cut curves? It would be great to see. Thank you for providing such wonderful skill building lessons while showing us how to achieve the end product without having to spend large amounts of money to purchase high end tools. Rob

  21. Paul,
    Thanks for making the “flashpoint” point about peanut oil vs. automobile oil. I’ve always had a question why people say to use dirty motor oil. Is there some mojo there? Or maybe dirty oil has a different flash point?
    Thanks,
    Jason

    1. Cost, almost certainly Jason. I’d have to experience a massive inflation in my disposable income for me to use virgin peanut oil to douse a billet. If the oil sets alight just chuck an old wet cloth over it (and don’t do blacksmithing in your back kitchen).

    2. I think that it’s because it’s already used and a good use for old oil more than anything. It’s also more readily available. But then again peanut oil will last a long time and can be used over and over.

  22. Paul, I can’t say thank you enough for posting this video. I was always under the impression that I had to build some type of traditional forge in order to heat treat steel. Your method blows that myth out of the water for me. I really appreciate your down to earth methods.

  23. How much I like these videos:

    they are bringing us a step closer to a self-sufficient live!
    Isn’t that freedom!
    (that thing which every human gets for free on his birth)

    Thank you Paul and team for this video!

  24. A quick tip for telling the right temp at which to quench for hardening is to use a magnet. Offer the piece up to the magnet, if it sticks it still needs some heat, once it gets to the correct temp for hardening it will lose its magnetism.

        1. Late to the party but just in case anyone else is having the same issue.

          Reversing audio channels during the outdoor segment will make the audio audible (which is what i did in VLC media player). Alternatively forcing it to mono or just the left channel also works.

  27. I’m 51 and I just discovered the scrub plane. It’s a little more aggressive than the plane you show here. I’m really surprised that I don’t need that planer or jointer that I’ve always wanted. My hand tools will do most anything.

  32. Just a quick comment about tempering in general and O1 in particular:

    My background is a bit different than most people: I am an inorganic chemist (read: metals chemistry) who does a lot of metal work and machining and it was my machining background that got me into restoring old hand tools and, subsequently, into woodworking. My machine shop has this great book called “The Heat Treater’s Guide: Practices and Procedures for Irons and Steels” which contains phase diagrams and Hardness/Tempering temperature graphs for many common steels including O1.

    In this video, Paul recommends tempering the blades at 325 F. According to the graphs, tempering at this temperature is going to knock the hardness down from about 65 HRC to around 63-64. This is a workable hardness, but its still quite hard and a bit brittle in my experience. When I temper, I try to shoot for about 60-62 HRC, which, for O1, corresponds to a tempering temperature of about 450 F. That’s still accessible in a normal household oven, so I think you might achieve better results tempering at this higher temperature.

    Just my two cents as someone who came to woodworking from a different background.

    1. Mike Lipschutz, Thanks for the tip. I just looked up the book and it is $299.00 on Amazon. So that information would be unreachable for most of us if not for your contribution. Again, thanks.

  33. I have purchased several old planes on ebay. The blades can be tricky to deal with because you don’t know what someone has done to them. I bought a stanley 4 1/2 that had a blade edge so hard that I couldn’t file it, so it might not be surprising that it was chipped. That’s why I think this a great video for anyone using planes (new or old).

  34. After reading Mike Lipschutz comments it dawned on me that if a difference of 75 degrees in oven temperature can make a significant difference in hardness and if ovens are off by as much as 25 degrees in each direction (a wild guess) then my oven temperature could be quite a lot different then Paul’s. So maybe use a thermometer to check your oven temperature and experiment with different settings. And don’t forget to have fun.

  35. Apologies for the many grammar and punctuation errors within. lol.
    Cut irons out of: old circular saw blades with a jigsaw, on lowest speed setting, with no orbital motion, if applicable. Most circular saw blades have plenty of steel to work with and are very workable, due to the fact that most blade manufacturers (I use Freud) mount pieces of super high tungsten, cobalt and titanium carbide steel to the teeth for the cutting edge. Leaving the rest of the blade’s steel usable for knife, iron, caltrop, throwing stars, or just about anything. Automotive spring steel: ie. leaf springs and coil springs are also high carbon steel perfect for making tools out of, but without the drawbacks that many “tool steels” exhibit, like being to hard and therefore brittle. I made my own set of: single beveled, right handed and left handed wall cutting knives, plane irons, chisels, and even handsaw blades. As long as you don’t heat up the steel when you cut it, and you are patient with the jigsaw, you shouldn’t ever have to worry about heat treating at all. You can also use electric current, with the amperage sapped out of it in various ways, to heat the steel very quickly and perfectly evenly, but most importantly to a precise temperature if you must. Which is a method that some very expensive, Japanese dovetail and tenon saws use to harden their blades. Of course, those saws are disposable when dulled.

  36. A few tips on hardening and tempering from an amateur knife-maker…

    1) When quenching in oil, try to avoid heat differential across the smallest dimension of the iron. Plunge it in point first and straight down (90° to the surface of the oil). If you emerse at an angle, the temperature differential between faces causes lop-sided contraction of the steel and your piece can bend. I’ve had a knife come out of the oil like a banana and, being hardened, it took a lot of grinding to get it straight again (percussive correction runs the risk lf shattering the hardened steel). It’s always worth checking for square after a quench as steel can sometimes bend at this stage even if you’ve done everything right. Fully annealing the steel before you work it can help reduce inner stresses and make it less likely to bend in the quench (heat it right up and let it cool slowly in the coals), but I never bother.

    2) Remove the black crud from the quench, before tempering in the oven. It doesn’t need to be a perfect finish but having naked steel will help you with tempering, because steel colour-codes itself in the tempering process and tells you when it’s the right temperature. O1 tool steel turns a straw-yellow colour when it reaches the right temperature for tempering. If it starts turning a blue or purple colour, it’s been over heated and might be too soft. Without colouration, it hasn’t heated enough. You can’t see this discolouration under the black crud and it comes off easily-enough with a quick polish.

    3) Wrap your irons in some scrumpled tin foil when tempering. Aluminium is a great heat conductor and evens-out the heat distribution into your iron. This helps to reduce hot spots and gets a more even temper.

    Hope this helps. It would be awesome to think that I might have given a little something back after absorbing your videos and blog posts like a sponge for the last month.

    Chris.

    1. Also…

      4) invest a few pounds in an oven thermometer. Most domestic ovens are terrible at heating to the temperature that is marked on the knob and 20°c difference can make a significant difference to your temper. It also helps your cooking no-end.

  41. So much enjoyed this series of wooden planes making. Thank you Paul for making these videos! Would love to see videos on building that bench stool. I love that large seat bottom! Thanks again!

  42. Mr. Paul Seller and the rest of the production team
    I enjoyed the style of the wood plane. Paul’s efforts have given me very good ideas. My father says ,”great work”.
    Thank you, take care of yourselves.
    Your friend from Canada Dennis

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