How Do Swordmakers Temper Their Blades?

I have drawn a plan to build a sword tempering salt pot that is PID controlled. It is really a simple build and quite safe to operate (compared to a high-temp salt pot). It will allow marquenching, martempering, regular tempering, and bainite creation ( for anyone who feels the need).

It is one of the projects I will be posting this year, but maybe I'll pull out the sketches and diagrams tonight and post a teaser.

A smaller low temperature salt pot can be built for tempering and quenching knives using a dirt cheap used pottery kiln and a PID. Many of these kilns can be sourced for free.
 
Stacy I am very interested, the wife has a rarely used ceramic kiln I have been threatening to salvage for some kind of oven project but I would welcome ideas to use it as a salt pot.
chris
bladsmth said:
I have drawn a plan to build a sword tempering salt pot that is PID controlled. It is really a simple build and quite safe to operate (compared to a high-temp salt pot). It will allow marquenching, martempering, regular tempering, and bainite creation ( for anyone who feels the need).

It is one of the projects I will be posting this year, but maybe I'll pull out the sketches and diagrams tonight and post a teaser.

A smaller low temperature salt pot can be built for tempering and quenching knives using a dirt cheap used pottery kiln and a PID. Many of these kilns can be sourced for free.
Click to expand...
 
Rick Marchand said:
Interesting... No... admittedly I haven't tried it. Now... a flood of questions, buddy.

1. Are you using thickwalled pipe?
2. How long does the oil stay at temp between firings?
3. How do you maintain 10F using a weed burner? Are you running the flame up and down the sides of the tube or heating the bottom?
4. Where is your thermometer placed?
5. How is the heat being distributed? Is it the nature of the oil or are you agitating?
6. Are you using the gun on the blade? How often are you checking.

The gun is the only thing I don't have.
Click to expand...


1-no, 1/8" wall
2-If I am heat treating it is done in batches, hence I don't have any time in between tempering. I quench all the blades I want hardened, then temper them all at once if they can be.
3-most weed burners have a butterfly valve, very finely adjustable. I do run the flame up and down the sides to get things warmed up but then once I am near 100 I just clamp it so the flame is near the bottom of the tank, like a pot on a stove.
4-thermometer is placed in the top, I take infrared readings up and down the tank at bottom, halfway, then the top pointing downward into the oil.
5- the oil kind of circulates itself, I also have a piece of flat stock with a paddle on the end at a 90 degree I stick in the oil, then go up and down in this motion :jerkit:
6-yes, I check about every half hour.

Salem, the cheapest crappiest oil from walmart, it's like veggie.
 
Thanks, Sam. BTW, that's the most appropriate and polite use of that emoticon that I've seen yet!

Rick, I'm right there with you. The time it takes to build your own stuff, as fun as it is, and as accessible as it makes new capabilities, can be a bit overboard.

Nobody around me hates Stacy, they just think I'm an idiot savant who thinks this stuff up himself.
 
Well, now that I know how to temper long blades, I'm going for that 28" blade again! Kind'a excited, actually. I don't know if I thanked you Sam, but thank you.
 
hate is such a strong word :) I think I will follow Salem's lead and let everyone believe I make all this up! And now added to the list to make: weedburner tempering tank and maybe a salt pot from a kiln.
Chris
 
Hey - a simple way to do this. Let the tang stick out the oven door. Dont put the blade at an angle across the oven, it can sag and bend under the stress and you get a crooked sword.

Just put the sword diagnoally across the top oven rack. Put the rack as high as it will go. With the tang sticking out, there will be a small crack around the top of the oven. Take heavy duty aluminum foil, roll it into hollow snakes, and use two rows of these to seal the oven.

I temper 1 time at 425F for w2, with clay heat treatment. This doesn't cause hamon to fade and is good for dif hardened blade. If you have a fully-hardened blade, I would do two or three temper cycles. The oven can hold relatively well with the snakes in the door. I got the idea from Wally Hayes and Walter Sorrells, who both put something sim in their videos.

kc
 
Kevin, that might work with some ovens, but with mine there is a major gap. The door is open a good six inches. This is due to the construction of the door, which has some interior fitting that fit into the oven opening.Hard to descibe, but trust me, I knew about that method, and unfortunately for me, I can't do it.
 
Stacy

I'd love to see you low temp salt opt tempering

I'd also like to see any suggestions you have on alternate salts.

Oil would work, but I hate the fume vapour that heating oil puts on everything & the temp range is limited.


I know in the USA you can, or used to be able to get Grants Stump Remover, or Spectracide Stump remover & it's fairly pure Potassium Nitrate

But post 9-11 they put lots of control in place, including some anti terror / "green" initiative that eliminated availability of useful pesticides and chemicals.

I can go buy gunpowder with cash and a signature in the book, but getting a few pounds of salts to do a nitre blue with is much more difficult.
Only through proper lab chemical suppliers, with an account and huge hazmat charges for shipping an oxidizer.
or from my pharmacy at 10 cents a gram, which sounds good, but is $200 for 5 pounds.
 
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I have been following this thread on how to temper a sword. Now I don't want to talk out of turn because I have not made a sword, but what I have made is a very long oven to to heat treat bamboo fly rod blanks with.

I use a Milwaukee variable heat gun that ranges from 140*-1000*. I use digital thermometers place along the length of oven to measure the temperature and hitting 400* and maintaining it is not that hard to do once you get to know your oven. Wrapping the oven with some Kaowool help a lot to keep temps consistent.

Here is a webpage that shows an example of one. Maybe this will work for some of you guys. The cost is not that much depending on what heat gun you have. Take a look and see if it might work for you.

http://www.fneunemann.com/fpwot/index.php?id=45
 
That is an interesting concept. I see no reason it wouldn't work, especially if you can control the temp as well as you say. Thanks for posting this. What do you other guys think?
 
David the Milwaukee Variable Heat gun is probably the best out there. I use it for all kinds of tasks around the shop from drying dyechem, knife blanks to breaking epoxy bonds and for a hot air oven.

It is worth the money and can be expensive. But here is the good part. You can buy them refurbished for much less. I bought mine years ago refurbished and it has performed for years flawlessly. Here is a place you can buy one refurbished
http://www.amazon.com/Factory-Reconditioned-Milwaukee-8977-80-Variable-Temperature/dp/B000NY4ARW

You might not get a lot of feed back from people here on the hot air gun oven because they probably have no experience with one.

You can customize and tweek the hot airgun oven for tempering a sword. You can add vents, digital meat thermometers and insulation and come up with something that will work and not cost and arm and a leg.

Good Luck
 
Have at it, but unless you have built one that works, I would tend to believe that the heat output from a hot air gun as the heat source for a 40" tempering chamber is the equivalent of a JTH7 torch on a damascus welding forge. Just because someone does a small task with does not mean it will replace a larger and more tightly controlled device. Baking a bamboo rod for 30 minutes is a lot different than tempering a sword at 400-450F with +/- 10 degree accuracy end to end, for two hours.
 
Stacey this is not replacing a "more tightly controlled device" . Stacey you are sticking your swords in a kitchen oven used for baking cookies with the door cracked open.
So building a heat gun oven to generate the heat is worth a try for someone who is looking for an alternative and does not want wait for dinner because they have to wait for the sword to be done.

If this works it could be a valuable asset for sword making. If it does not work out you end up with some metal tubes and a nice heat gun for the effort.
 
I was merely stating that it will not work like a salt pot, which is what it emulated.
By all means, build it - please post pictures of the build, and the results of the tempering.
 
Actually it was not emulating a salt pot.

It was simply a hot air oven that might be an option.

I am not a sword maker. But if someone tries it out and it works that would be nice. But then again he might not want to post here.
 
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