How do you temper blades too long for your equipment?

kuraki

kuraki

Fimbulvetr Knifeworks
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Jun 17, 2016
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Meaning, I understand how to temper, ideal tempering environments, etc.

I'm wondering how you get around it with a sword, or shortsword, or tool that doesn't fit inside your normal tempering oven. Do you torch temper to color? Do you use IR guns? Do you use your forge somehow?

How do/did primitive or period bladesmiths do it?

Something I've always wondered.
 
I've got a sword in the works, and have a box of fire bricks, elements, and pid to make a tempering oven for long pieces.
 
I saw an episode of the Olde Yankee workshop where a blacksmith tempered a chisel by heating a separate piece of steel to red hot and running it along the steel that needed tempering. He held it on one side and watched the other side for color change.
Easy right?
 
The old way was "color" tempering. You heated the blade over a charcoal forge, or by applying hot iro pieces to it until the surface oxides turned straw color .... indicating approx. 400-450F. Then you cooled it in water, sanded it shiny, and repeated the tempering several timers to assure a consistent temper.

On long swords, I just stick them diagonally in the kitchen oven at 400F and leave the tang out the top corner of the door. I reverse it after an hour for a second hour. I cool off with water and repeat.
 
E.C , not a good way ! Stacy's method is much better.
Lower carbon steels are easier to play with. Color is just an oxide on the surface .You should have some time to heat through the thickness .
 
I saw a guy on YouTube do it on a campfire so uh yeah that's all you need.
Apparently all this temperature controlled equipment is just hogwash.
;)
 
I see this all the time, and I have to admit it irritates me. No, temperature controlled equipment isn't hogwash, but don't discount the low tech way either. It does work, and worked for a long time before your fancy tempering oven came along...
 
I have an older 24 inch Paragon with the standard width door and on occasion wish I had the bigger one with the 10 inch wide chamber.
 
Stacy E. Apelt - Bladesmith said:
On long swords, I just stick them diagonally in the kitchen oven at 400F and leave the tang out the top corner of the door. I reverse it after an hour for a second hour. I cool off with water and repeat.
Click to expand...

Considering kitchen ovens will never hold a temperature consistently with the door open this is not a reliable way to temper a blade. The thermocouple in the oven will cycle the heat on and off and with the door open you never know what the temperature actually is considering it needs to be a closed door to have a controlled temperature.

I hear of makers doing this, it is not because it is the proper way, it just is a compromise because they cannot do it properly.

You could not cook a cake reliably with the door open, much less a sword
 
I've often thought a restaurant surplus convention oven would be a nice option for tempering. Could set it up with a more accurate controller if necessary. A convection oven would help eliminate hot spots though. And if you found a larger one it'd handle anything you'd be making
 
I think for not too much money if one were inclined you could make an oven fairly easy. Granted you'd need to make swords at least some of the time to justify the expenditure. Buy a couple oven heating elements, some sheet metal, insulation and make an oven long enough. A convection fan is easy enough to come by. If you have a plug and play PID system you could switch it between this and your small oven. It could easily be made for 2-3 hundred and you'd have one hell of a sword tempering oven and more than likely be accurate as hell.
 
Metalhead0483 said:
I see this all the time, and I have to admit it irritates me. No, temperature controlled equipment isn't hogwash, but don't discount the low tech way either. It does work, and worked for a long time before your fancy tempering oven came along...
Click to expand...

The trick is gaining the years and years of experance needed to do it right. The problem is people without that experance thinking oh just heat it with a torch till it changes colors. I mean I guess it's not a problem, it's there blade that can do what thy want with it. But our customers are owed the best blade we can make and thy come to us becaus thy want somthing better then store bought. So with that said I'm not for or against the old way, If you do it do it right.
 
AVigil said:
Considering kitchen ovens will never hold a temperature consistently with the door open this is not a reliable way to temper a blade. The thermocouple in the oven will cycle the heat on and off and with the door open you never know what the temperature actually is considering it needs to be a closed door to have a controlled temperature.

I hear of makers doing this, it is not because it is the proper way, it just is a compromise because they cannot do it properly.

You could not cook a cake reliably with the door open, much less a sword
Click to expand...

A steel sword has a lot more thermal mass than a cake. The temp of the oven may cycle a bit but the the temp of the steel should remain fairly stable.
 
DanH45 said:
A steel sword has a lot more thermal mass than a cake. The temp of the oven may cycle a bit but the the temp of the steel should remain fairly stable.
Click to expand...

I would not leave the door ajar when tempering a knife much less a sword.

Not the step you want to hope comes out ok.
 
mete said:
E.C , not a good way ! Stacy's method is much better.
Lower carbon steels are easier to play with. Color is just an oxide on the surface .You should have some time to heat through the thickness .
Click to expand...
Hey now, I'm not saying I would do it, just saying I saw it on TV as the old way.
Kuraki, looks like the only solution is to start making more swords so you can justify building a super cool sword oven.
 
What about the high temp oils?
I'll admit the only time I saw this was on forged in fire.

Either that or farm it out.
 
Oil tempering is (or at least was) common in industry. But like some other industrial heat treating processes (lead pots, cyanide case hardening, ect) it's not the safest or best suited to a home shop.
Nitre bluing salts would be a safer option, but at that point you're looking at building a salt pot in addition to just a heated box
 
I have done it many times with good results. Usually all that sticks out is the tang. IIRC, I have done up to a 38" katana this way. YMMV

I checked the steel temp directly with a non-contact pyrometer, and adjusted the oven temp as needed ( not much, IIRC). I originally stuck some inswool in the door crack, but now just leave it cracked. It isn't that much of an opening.

As far as the temper quality, I never found an issue. A sword isn't like a Rc63 sujihiki. Rc 55-57 is more than high enough. The extra time in the oven using the flip method also helps assure full and even tempering.


If you are really worried about it and have a standard 16", 18", or 24" Kiln, just cut a small slot in the door metal and firebrick ( at floor level). Put in the blade and plug the hole with a wad of kaowool. Turn the blade after an hour and give it a second hour. Two temper cycles like this should do a sword nicely. Make a firebrick plug for the hole when not needed. You could even make a similar slot at the back and have a pass through set of slots :)
I have thought about trying this on my 24" when I get the current batch of swords done. I'll post a thread on it when I do it.
 
That's a good idea because I was thinking how it sucks that I did not make my oven just a tad longer. My inside is 31.5" and it's good for short swords but if I had a slot I could do longer swords and let the tang stick out a tad.
 
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