Friday, May 29, 2015

BBQ'd Plane Irons

Tonight was the night for heat treating my plane irons.  I figured it would only take about a half hour, and I wasn't too far off.

I think I was worrying too much about this step, and it put me off.  I needn't have worried, this was relatively easy.  At least, I accomplished what I meant to.  We'll see if it gives me good steel or not once I sharpen them up.

My plan was to use my barbecue on the balcony for a platform for doing the heat treating.  This was a really good idea, as my set up didn't need to be anything crazy.
My heat-treating forge.
I bought three fire bricks at the big box store yesterday.  I also picked up a special teflon-infused fire glove.  This turned out to also be a good idea, because it kept me from burning my hand while still being able to use my fingers, unlike using an oven mitt.
The rest of my heat-treating set up.
I bought an old pot today at the thrift shop.  It was only $2, and almost too nice to use.  I think it is cast iron with an enamel coating.  Plus, there was a lid which I thought was a bonus.  Handy for when the oil catches fire.  Outside of this picture was a fire extinguisher, just in case.

I hadn't done this before, so wasn't quite sure the best way to go about this.  I set the fire bricks up this way in order to best hold the heat in the spot where it counts most.

I think this was a good idea in theory, but the torch used up all of the oxygen in that corner and wouldn't burn properly.
How I started.  Note that I am holding the iron with a big pair of pliers, using my hand in the fire glove.
I asked the Frau to take photos of this whole process, and when I looked for her while I had the torch going, she was no where to be seen.  As a result, you'll have to paint the picture using only my words.

It took a little while to figure out the best configuration, but I finally got the torch working best when it was shooting the flame at a bit of an upward angle.  It was plenty enough to get the iron hot if I held the iron as flat as I could against one of the side fire bricks.

It turns out the fire bricks hold heat for a long time, so next time I will pre-heat the iron while it is laying flat (to get that nice dark color), then lift it up so the business end of the iron is flat against the side brick and I can torch the crap out of it in that position.

Once it got red enough, and the little pools of iron float to the surface, quench.

Next time I bet this only will take five minutes for the two irons, after everything gets warmed up.

I think I wound up with a couple of decent irons.
Now all that is left is tempering.  I haven't told the Frau I am using her oven for this yet.  Wish me luck!
Edit:  Success!!!


  1. I was likewise intimidated by heat treating until I tried my hand at making a hook knife from an old file (so-so results) and when it was over I was surprised I'd made such a big deal of it in my mind.

    1. Exactly. I think it is something that one should try, just because you never know when you might need to try this skill. Good steel is important to woodworkers.

  2. A mighty fine idea to use the barbecue as base for the fire bricks.
    I am looking forward to hear how they sharpen up, and if they can hold and edge.


  3. Looks great, Brian. Those will be some great planes.

  4. I have long wanted to give this a try, maybe you'll inspire me ...
    How long and at what temp did you tempered them in the oven?

    1. Hi Robert,

      There's a lot of conflicting info out there on how to temper. What I did was just put them in the oven on a piece of tinfoil to help protect the oven, I turned it on to around 180-185 degrees Celsius (somewhere between 350-400 Farenheit), let everything warm up well for 30-40 minutes, then I turned it off and let everything cool down with the oven door closed overnight. My thought was to let it cool down as slowly as possible.

      I'll let you know how it turned out.

  5. One thing about oven tempering in an oven is that you can have temperature spikes and you end up tempering it more than you want. It helps to put some other stuff in the oven, like a big heavy cast-iron pan, to absorb heat and keep the average temp more stable. Peter McBride, the New Zealand planemaker, says "put it in the oven with the lamb roast." I thought he was just being quaint, but it turns out there's a really solid reason for doing that.
    I prefer to temper on the stove top, going by color. I feel like I have more control over the results. But don't worry, I bet it will be fine, and if it's not you can just try again. Looking forward to seeing your Roubo planes!

    1. Thanks, Steve, good tip! I'll keep that in mind next time.

  6. Brian, how much do you heat? and for how long?

    1. Hi Aymeric,

      Supposedly 1450-1500 degrees Farenheit. However, I don't have a way to precisely measure a temperature like that, so I do what many others do, use color. What you are looking for is a bright, cherry red, just when little pools of iron start to float to the top. They look like little white raindrops flashing out on the surface of the iron. Then, it is time to quench.