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Oil Tempering


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I don't know of anyone using oil to temper, but look at low-temp salt pots, they do the same thing.  You just need a steel tube and an adjustable heat source that can hold the temperature at the desired range.  

 

Just to be absolutely clear, you're talking about putting a cooled, hardened, quenched blade into a tube of hot oil to draw the temper, not ausquenching or martempering? Those need special oils with a higher flash point than common oils.

 

Years ago we did have a guy who made swords who tempered with oil. Canola at 450 degrees F, heated by a gas burner.  One day a drip ran down the side of the tank while it was hot.  He never used oil to temper again, and the scars aren't too bad. If he'd been doing it indoors his shop would have burned, as it was it was just a large part of his yard.

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What is wrong with just an oven?  The only thing that matters, unless you have some specific process you're trying to replicate, is temperature control.  I have heard of folks using a large tub of sand in an oven to help even out the hot and cold spots.  Unless you're having a problem, there isn't really a need to complicate the process.  Molten lead used to be used for tempering, but there are dangers (like large vats of molten lead and lead poisoning and the cost of heating large vats of lead to molten) and I don't recommend it either.

 

g

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"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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I've got a counter top roaster that I've thought about using.  It would still involve bringing oil up closer to the flash point that I might feel comfortable with though.  For now, not having a wifey to argue with, I see no real advantage of it over the oven.

 

Doug

HELP...I'm a twenty year old trapped in the body of an old man!!!

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All the sand does is provide thermal mass, which keeps the temperatures more even. It's also nice in that isn't flammable. ;)  The built-in thermometer in ovens is notoriously inaccurate, and the cycle range on most ovens is really wide. My kitchen oven runs 25 degrees hot on average, and will heat 50 degrees hotter than that before it cuts the element. It then cools to 50 degrees lower than the initial temperature before it turns the element back on.  My toaster oven is similar, but worse.  

 

Thermal mass in the form of a pan of sand, a few bricks, or whatever is slow to heat and slow to cool, evens out those temperature swings by staying hot once preheated, thus eliminating the wide swings.  If you're good with electronics, a cheap PID controller will make an ordinary toaster oven into a precision oven.  

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When you think about cost versus effort, a couple of heavy foil baking pans from the local grocery store and a.5 cubic foot of sand from the Home Depot costs you less than $10 total. That will even out the heat in the oven in your kitchen and work for most of the steels we use.

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Ah, now I get it.  You can torch temper, but that's tricky and requires multiple cycles, or you can make a trench forge. Just a trench in the ground full of lit charcoal. Temperature is difficult to control with those, though. 

 

Got an old water heater shell or 55 gallon drum?  One of those on its side and a set of burners off a gas grill, and you have a sword tempering oven.

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How about a piece of pipe in a gas grill?   Two gas grills next to one another with a piece of pipe that goes between them.   How long a sword are we talking about?

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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We used oil tempering in a sword class at Peter's Valley.  This was just canola oil in an old vertical ammo storage box.  With a 1" NA propane burner pointed at it the temperature was adjusted by distance from the outside of the can.  Carefully monitored during heat up process to ensure it didn't pass flashpoint and not overfilling, it worked quite well.

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I've found this discussion very interesting.  Getting my forge set back up after being cleared out, probably by the man who did my yard work,  I've decided to get a 36" horizontal quench tank from Boss Dog to quench but was confounded as to how I was going to temper the blade.  A tall vertical tank that I could heat with a hand held torch might be the was to go.  At least I could use a thermometer to monitor the temperature.

 

Doug

HELP...I'm a twenty year old trapped in the body of an old man!!!

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At one point I was pondering the same thing.  I have a tall 8 inch tank that I cut one end off of.  My thought was a turkey roaster burner at the bottom.  Place the pipe on the roaster and see if you can get a fairly even temp over the column.  A more sophisticated version might be an inner and outer pipe with the inner capped off to prevent air flow.  Heat the space between and let the inner pipe come up to temp.

Don Fogg did a similar thing with a 55 gallon drum (no insulation) and a 3 inch pipe down the center.  A single blown burner heated it and baffle pipe.  As I remember it was pretty easy to get 350-450 F temps.

 

g

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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  • 3 weeks later...

I've been using a very cheap bachelor's oven with baking pans of various shapes & sizes full of swimming pool filter sand, monitored by an equally cheap multi meter with a thermal couple.

I stick this in the sand with the blades, takes a bit of fiddling while it heats up, but it's relatively easy to get it settled on a stable temperature.

 

I find the idea of a large amount Canola oil (which I use to quench) at close to 200C very scary :ph34r:

 

At this stage me equipment allows max OAL of 40cm, I could forge something longer but heat treat and tempering not....bothersome because I do feel there have to be swords in my future.

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