hi everyone! aaron from gough custom here.i'm going to show you today how to heat-treat an o1 tool-steel knife in your own shop, withjust a few simple tools. the very first thing you'll need is quenchoil. the quench oil is what you put the blade into when it's been heated up to red hot tocool it down fast and make the blade harden. in this case we're just using vegetable oil,which is cheap and easily available and works
wood branding iron initials, very well. the next thing you're going to need is a pairof tongs to hold the hot steel. i use these big vise-grips, they were quite cheap. i thinkthey were only about $6 or $7 and they work quite well.
if you can find blacksmith's tongs then that'sgreat but they're not necessary as something like this works well. the offset head keepsyour hand out of the path of any possible flame from when you're quenching the steelin the oil. the next thing you need is a container tohold your quenching oil. this is actually a small wine-bucket that i got from a kitchensupply place. kitchen supply places are great for this kind of thing because they have lotsand lots of different things that would work. anything that you buy needs to be either aluminumor stainless steel... no plastic because you'll melt through it. anything you can find that's tall enough tofit your knife in is perfect.
then you're going to need a torch. i use abernzomatic ts4000, this is a relatively expensive torch, it costs about $40. it works very well,and it works with both mapp gas and propane. so if you need a hotter flame for brazingor whatever then this is a great torch. if you are looking for cheaper torches thereis one thing that you need to be aware of and that is: if you look at this torch youcan see that the inlet holes for the burn tube are right down here which means thatthey're almost 6 inches away from the head of the flame. on this cheaper torch the air inlet holesare only about an inch away from the head of the flame, what happens is that the burntgases will recirculate into the air inlet
hole when the torch is used with a forge becausesomething else is in such close proximity with it. if you're looking to buy a less expensivetorch is to make sure that the air inlet holes are as far away from the head of the torchas possible. if it too close, like this one, then it will work fine as a blowtorch butit won't work with a forge or for heat-treating. the next thing you need is a forge. this oneis a very simple home-made one it's basically just made of 2 fire-bricks that have semi-circularchannels cut into them. and an inlet hole at the front. the flame goes in at an angle,angled toward the rear, then swirls around the burn chamber before it exits at the back.
having the flame right at the front lets youmove the blade in and out while you're heat-treating it to get an even heat from the handle ofthe blade all the way to the tip. if you have the flame entering at the backthen you'll be able to get the tip very hot, but you'll have a hard time getting the rearof the blade, the tang and the ricasso hot. so i recommend having the hole at the front,it works really well. the next thing you're going to need are fire-proofgloves. i use welding gloves, and these work pretty well. they're not the most comfortablebut you need something that's quite flame retardent because if your quenching oil catcheson fire or spits up a big burst of flame when you first put the hot blade in it can burnyour hands quite badly if you don't have gloves
on, so i recommend wearing gloves. and then finally, unless you like burningyour house down, i highly recommend that you have a fire extinguisher on hand. using waterto extinguish an oil fire is extremely dangerous and you shouldn't do it so make sure you havea dry powder fire extinguisher at hand that's suitable for use on oil fires. here you can see how the propane torch issetup in relation to the forge. the flame is angled upward, and toward the rear of theforge. this helps ensure that the heat is distributed as evenly as possible by causingthe flame to form a spiral around the inside of the forge.
after letting the forge heat up for severalminutes, the next step is to pre-heat our quench oil. warm quench oil will actuallycool the steel faster, because it forms less vapour bubbles around the blade during thequench. to pre-heat the quench oil i am simply heatingup a piece of scrap steel and then plunging it into the quench container. now it's time to start heating our knife blade.notice that i'm constantly moving the blade around in the forge. this helps ensure thati don't over-heat any particular part of the blade. what we're looking for is an even dullcherry-red colour. if parts of the blade get hotter than dull cherry then they may endup being brittle.
you can see that the thin parts of the bladeheat up the fastest. keep them away from the direct flame and make sure to continuouslymove the blade in order to get the heat as even as possible. it will take a few minutes. after the blade is an even, dull, cherry redcolour, remove it quickly from the forge and plunge it straight down into the quench oil.you only have a few seconds to get it out of the forge and into the oil. be carefulof where your hands are, as the oil will often catch fire on the surface for a few seconds.after the blade is in the oil, make gentle slicing motions with it to help cool the blade.do not move the blade sideways as this may cause warping.
after the blade has completely cooled fromthe quench, we need to test that it has hardened properly. to do this we run a file over theedge and spine of the knife. if the knife has hardened properly then the file will simplyskate over the surface of the steel. at this point the knife will be extremelyhard, but also quite brittle. if you were to drop it accidentally it would probablyshatter. so the last thing we need to do is to temper the knife. this process gives upsome hardness in the steel in exchange for much more toughness. to temper the knife wesimply heat it to an elevated temperature and keep it there for a while. in this casewe'll be heating it to approximately 400 degrees farenheit and keeping it there for 2 hours.i'm using a toaster oven for this process,
but you could also easily use a regular householdoven. after the tempering process is complete, yourknife blade will be hard and hold a great edge, but it will also be tough and resilient.at this point the blade is ready for final finishing and use.
