Sunday, February 10, 2008

Heat Treating & Tempering a Blade

Before you heat treat and temper your plane iron, cut it to shape, because the untreated steel is much easier to cut and grind beforehand. There are a number of detailed articles online for the heat treating and tempering process, so here is just a brief rundown when working with O-1 tool steel.

I use one propane and one mapp torch (Why? Because that's the way I was taught). Clamp your steel in locking jaw pliers at an angle so that when you dunk it in the oil (I use peanut oil) and the oil flares up, you won't burn yourself. Position the blade in between the two flames, about 1" from both, so the blade is heated from both sides. Keep the blade moving so the heat is distributed equally across its width. Start heating the blade about 2" from the cutting edge. With a blade this thick and wide, it will take a while to get it hot enough (it took maybe 6 or 7 minutes). Once this part of the blade gets orange, start moving the flame toward the cutting edge until the entire 2" end is orange and glowing. Quench it quickly, dropping the blade straight down into the oil so the width of the blade is cooled equally, otherwise it may warp. The oil will flame for a bit. Keep moving the blade back and forth in the oil while it cools. I'd give it several minutes, then take it out, wipe it off, and let it cool enough for you to touch it.

Your blade will now be black. Before you temper it, you need to remove the black coating so that you can see the color of the blade as it's being tempered. You can remove the coating by rubbing the blade on a sheet of fine drywall screen or sandpaper that is resting on a reliably flat surface, like thick glass or granite.

Now you're ready to temper the blade. Bake at 350 degrees for an hour but keep an eye on it, as ovens temperatures vary. Other sources say 20 minutes at 400 degrees. When the blade becomes a straw color, it's done. Let it cool completely and you're ready for final sharpening.

You can get pretty technical with this whole process, and if you're a stickler for perfection or if you must have consistent and accurate results in making blades, you'll want to do more research than this post. But because I'm just a hobbyist, and chemistry and metallurgy make my brain hurt, this works just fine for my needs.

Here is another article on tempering steel, by Ron Hock, of Hock Tools.


Anonymous said...


Or, in the case of this blade, hot :-)

Thanks for the write-up, VC. It will make it a *lot* easier for non-metallurgists to tackle the heat treatment and tempering processes head-on.

Identity Mixed said...

I can't get over the sexy gloves in the last pic.

Nick Brygidyr said...

Hum...the flaming oil worries me, am i going to get flaming oil in my eyes when i try to do this? :(

Kari Hultman said...

Amish, you could try air hardening tool steel. I've never used it, and don't know if it's better or worse or the same result as oil hardening steel, but there is no quenching involved. FWIW, the oil only flares for a second and I always wear a facemask when heat treating. that's just scary!

Kari Hultman said...

Al, there are more in depth articles online if you want to try this or you could take a class (I did), but I'm glad you are encouraged!

Anonymous said...

Thanks, VC!

By the way, Stu, of Stu's Shed fame, posted just last night about steel, and what happens during heat treatment. He even included photos.

If you read it, I can almost guarantee you won't get a headache :-)

Kari Hultman said...

Thanks for posting the link, Al!

Anonymous said...

It's part of the addiction, isn't it? Tool making, a meditation beyond the wood working itself...home plane building, now home blade making, soon your feet will simply float up off the floor, like Yoda, the teacher... great stuff, lucidly explained. thanks.

Kari Hultman said...

Vinny, if I start levitating while I'm woodworking, I believe I'll need a taller workbench!

You're right...tool making is addictive. There's something profoundly satisfying about making a tool from start to finish.

Anonymous said...

Hi All,
I recently did a class on heat tempering blades, and they were using old automotive oil. It boils at a higher temperature so you don't get flames, but OOOOOh does it stink! Going back to my chemistry days, I recalled that parraffin oil has a very high boiling point, so I tried gently melting some canning wax (very pure parraffin) in a double boiler, then dunking the hot iron in the parraffin. It worked a treat - no flames, and no stink - it just smelled like candles.


Kari Hultman said...

Ian, if there's no flame....where's the drama???

Just kidding, thanks for the comment!

Anonymous said...
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Hank Gillette said...


It always impresses me how immersed you get into the projects you do. I want to build a plane one day (Dave Marks had a good program on making one on “Woodworks”, but I think I'll be content to buy the blade.

Anonymous said...
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Yalcin said...

Hi Kari.

Just wanted to let you know that
I have been sharpening my blade very
well the last couple of times. So
again thanks for all the info.

I was having some problems with the
8000 stone. It was not giving a mirror
finish. I found out that the nagura stone I was using, was just too coarse. I used a 6000 waterstone on the 8000 waterstone to create the mud. Worked fine. Now I have that mirror finish on the microbevel.

The blade you are using is very thick?
Looks like 5 mm or so. Where did you
get that blade Kari?

The blade in my no4 stanley is thin(about 2.1 mm or so). I have been
reading about thicker blades/chip breakers reducing chatter. Maybe
I will buy a new blade.

Take care.



Yalcin said...


I see that I should read all the
info and not just look at the pictures
before I ask a question. You have
described the process very well.



Kari Hultman said...

Hi Yalcin, glad to hear that you've managed to get a mirror polish. I thought all nagura stones were the same, but I'm obviously mistaken. The blade is 1/8" thick and I'm pretty sure I bought the steel from MSC Direct. I agree that a thicker blade will reduce chatter. I'm just using a wooden wedge with this blade but other planes I made have a chip breaker. I'm not so sure that a chip breaker is better than a wedge at reducing chatter—I think they work about the same. Also a very sharp blade will help with a chatter problem.

Rob Horton said...

So, how did the blade turn out, now that you've had a chance to give it a test drive? I'm halfway through two wooden plane bodies and, before I place an order for some of Hock's blades, am wondering if I could make my own.

While I've got your attention, what's your favorite blade angle for the planes you've made? I haven't cut up the two I'm building (a jointer and a smoother) yet and can pick whatever angle is best but these are the first two that I've ever made from scratch. The plans prescribe 55 degrees for both; but what I've read leads me to think that the smoother plane should be higher and perhaps the jointer lower than that. What would you do?

Kari Hultman said...

Rob, the blade turned out just fine. Maybe a bit too hard--could have spent a little more time in the oven. This is one that I gave away, though, so I don't know how well it's held up. It was used for a spill plane I made which I then donated to a local museum. I do know it's still in use, so that's a good sign.

The wider blades are trickier than smaller blades only because it can be a challenge to get the entire blade white-orange hot at the same time. Smaller blades are pretty easy.

All of the planes I've made have the same angle--45--since I work mostly with easy-to-plane, unfigured cherry and walnut. But I plan to make a couple high angle planes for use with figured woods just in case.

If you plan to work with a lot of figured woods, then a 50 or 55ยบ angle for the smoother is a good idea. If you're just using the jointer for edge jointing, then I'd probably go with a 45. If you're going to use it on the face of figured boards a lot, then I'd go higher.

Steel is pretty inexpensive and it's fun and gratifying to make your own blades so I'd suggest you give it a try. Just make sure you're in a safe area when you use the torches and quench the blade. I try to do it outside if possible.

Rob Horton said...

Many thanks. Higher angles and quenching outdoors it is.

Keep up the good work.

Michael said...


Thanks for the link from your FB to this post. then from your post to Ron Hock's and the one that Al posed here in the comments. these three blog posts have helped me to understand the heat treatment process much better than some other sources. I have just a simple propane torch for plumbing work so it will probably not do the job. I have been thinking of getting a MAP torch for the first step. Thanks for the verification of the idea.