How do you temper blades too long for your equipment?

I'm currently uploading video to youtube, or I'd upload a vid I took recently of my temper oven. Perhaps I'll come back and do that later today. Wish I had a good pic of it to hand.
Anyway, it's a simple concept and easy/cheap with very common items.
Find two old rotten travel trailers, the kind that you demolish and turn into flatbed trailers. Rip the propane oven out of each one. Or, find someone who does these kind of shenanigans, or who sells or trades or stockpiles old RV appliances.
I was lucky enough to salvage two ovens of the same make, the common Magic Chef brand, so they are the same height although one is a couple inches longer.
I kept the controls intact, including thermocouple and gas adjustment knob. I cut a rectangular hole in the right wall of one, and into the left wall of the other, matching in size and position. I used flat steel bar to make a mating flange between the ovens along the top outside and back and bottom flat surfaces, then drilled and pop-riveted the ovens together using the bar as a scab plate. Screws would also work. I stuffed some kaowool scrap around the edges of the pass-through hole between ovens, and bent up a sheetmetal flange to trim the very short resulting tunnel, 1 inch or so between the walls of the two ovens.
So I end up with a double length heat chamber with a controlled burner and thermocouple under each side.
I put an oven thermometer in each side so I can monitor the actual temp, and just set both ovens to run at 400 or whatever I want, using their respective gas dials. I pre-heat and adjust the oven to a stable condition, and temper.
It actually works quite well, I just did a 39.5" damascus khopesh in there, and the one I won FiF with was tempered in that oven too.
Anything seems unclear, I'd be happy to explain further. Here's a pic of the last sword I tempered in it, anyway.
20106297_1426237204119018_8972421869813884927_n.jpg
 
Kuraki I didn't read the entire thread so forgive me if this has been mentioned.

The best method I've heard of for tempering a long knife or sword that will not fit an your oven came from a friend of mine. He took a sword making class with Sam Salvati and I asked how they tempered them. They used a long vertical quench tank filled with canola and put a burner under it. They heated it up to 400 or 500 degrees and put the sword in that for an hour. That is the most simple and safest way that I am aware of and it is cheap compared to the other options out there.

-Clint
 
I don't know how safe that is with canola. My experience frying turkeys tells me getting canola that hot may invite undesired fireworks. That's right around the flash point iirc.

Maybe a different oil with a higher flash point?
 
Come on guys . . . . If I make knives for sale I will make that long temper oven asap !Even if there is only one knife in question !
 
I honestly don't remember what oil they used, but I do remember him saying they used it because the flash point was higher. I'd also guess that the burner was electric. I don't think a gas burner would be safe. I'll shoot him a text tomorrow and ask him what oil and burner they used.

-Clint
 
Peanut oil flash point is 450 F
Avocado 510°F
Almond 495°F
Apricot Kernel 495°F
Extra Light Olive Oil 468°F
Canola 460°F
Palm Fruit 450°F
Safflower 445°F
Sesame (Refined) 445°F


This is far superior then in a kitchen oven with the door left open.
 
The way I do it is one half at a time in my Evenheat. I leave the door open, but plug it with a piece of kaowool which has a slit cut in it for the blade to fit through. The oven holds temp just fine this way.
 
The way I do it is one half at a time in my Evenheat. I leave the door open, but plug it with a piece of kaowool which has a slit cut in it for the blade to fit through. The oven holds temp just fine this way.

A Kaowool door is a great idea for the Evenheat.

Actually if a MFG. made a small door in the main door of a kiln would be a nice option just for this.
 
Last edited:
How about a big flat pizza oven from a restaurant closure clearance sale? I see them on craigslist every once and a while. A thermocouple laid right on the part to check it or build a wire rack to suspend it in the oven for a more consistent heat
 
it's the perfect excuse to make or buy more equipment

If you've made a HT oven, all you do is make another one longer
 
Peanut oil flash point is 450 F
Avocado 510°F
Almond 495°F
Apricot Kernel 495°F
Extra Light Olive Oil 468°F
Canola 460°F
Palm Fruit 450°F
Safflower 445°F
Sesame (Refined) 445°F

You have made a good point, but I'd like to point out that these are the smoke points of these oils. The flash points are at least 100 degrees higher and the burning points higher still:
http://www.centrafoods.com/blog/edible-oil-smoke-flash-points-temperature-chart

The issue with the smoke point is that you are starting to see chemical changes in the oils and your physical properties will change over time and reduce the number of re-uses you can get from the oil in the long run. Motor oil has flash points that range from about 400-450 - probably a little low for tempering.
 
Back
Top