Friday, September 25, 2009

Crooked Knife Making - Part 2: Tempering Blade

When last posted, the rusty file destined to be my crooked knife blade had been softened and ground down by hand over many laborious days. The edge of the manufactured blade had also been shaped with a file to a more shallow cutting angle. After working on the blades, creating the angled edge, and polishing off as many toolmarks as possible (still left a few), it was time to finally temper them.

Filing off the teeth; Blade shaped and polished

This involved heating the file back up to a cherry red colour (in an outdoor firepit), quickly bending the tip to the desired angle with pliers, reheating to cherry red and then dumping it into cooking oil to quickly quench and harden the steel (the manufactured blade was already bent, so it was simply heated and quenched). I planned to do this at dusk so that I could see the colour of the heated file more accurately. Since the steps had to be done rather quickly in near darkness, all the required stuff was layed out in an organized fashion. I used a small metal vice/anvil place the blade flat while bending the tip with pliers; a tall & narrow tea can seemed perfect to hold the 450 ml of Sunflower oil to do the quenching. Taking pics of the each step was not an option while working alone, but I did manage to take one blurry shot of the bent blade right before it was dunked in the oil

Ready to go; Quenched in cooking oil

All went well. I was expecting the oil in the can to burst into flames when the superheated steel was immersed but all that ended up was sizzling and the smell of french fries. Once it cooled down a bit, the metal was quickly tested with a hacksaw (not in the pics) to see if it was still soft but the blade simply bounced off the steel without any bite. The quenching had worked. Next morning, the blades were examined and of course were covered in disgusting residue that would need to be polished off. Here are the before and after shots.

Grime after quenching; Quick polishing

These were going to be working knives so I didn't bother polishing them to a mirror finish, just sufficient enough to be clean. The other reason for polishing at this stage is because some of the temper needs to be drawn out otherwise the blades may snap under pressure. This involved baking in the home oven at 450F for about an hour until a straw colour appears on the blade. Baking without polishing first means lots of unnecessary smoke in the kitchen.

This stage went well and next up will be a post documenting the making of the handles.

Update Oct. 2/09: Part 3 on making the handle has been posted.


Unknown said...

This is a truly wonderful site and this series on the crooked knife compliments everything nicely. I came across this Instructables post not too long ago and thought I'd pass it along in case you haven't seen it:

I've never made one myself so I can't vouch for the quality of instruction. In any event, I'm looking forward to Part 3.

Murat said...

Thanks John! I hadn't come across the instructables link before. But I've read elsewhere that converting old ferrier hoof blades is another method of making a crooked knife. Should have the next post on making the handle and installing the blade up in a few days.

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