Why temper a knife

This should yield a Rockwell Hardness of about 59 or so depending on your steel. Source: Sandvik. At this stage, most knife makers will complete the final sanding before attaching the handle. You may want to do it now, or you might be okay with sanding later on with your knife in a vice or clamp. If you choose to go ahead with the last flat sanding, grab your wooden block and a piece of high grit sandpaper—the same grit as the one you stopped at before the hardening grit or so.

Whether wet or dry sanding, begin using the same technique on your blade as before, only moving to higher grits once the previous grit marks are sanded away. On the final sanding grit , change your direction to straight along the blade lengthwise, for a nice finish. Source: 1 , 2. The edge is the thinnest part of the blade, and therefore more prone to cracking during the quench.

Use a strip of grit sand paper to dull the edge and reduce the chance of cracks or warping in the edge. Normalizing involves bringing the unhardened blade to critical temperature a few times to stabilize the structure of the steel. A normalized blade is more resistant to warping during the quench, although some degree of warping is unavoidable.

Heat the blade evenly and touch it to a magnet to test its temperature. Steel becomes non-magnetic at critical temperatures, so torch it, test it against the magnet, and let it cool to room temperature three times to normalize it.

I used this aluminum tube for the regulator block. You won't be able to see past the surface of the oil, so I used nails to indicate the position and direction of the block below the oil.

Do not use plastic Tupperware! It is also a good idea to have an airtight lid for the container to smother flames. I filled the container with water and marked the water level with a red marker see photo where the the blade rested one third to one half its depth under the water's surface on the regulator block.

In order for the oil to provide the right qualities for quenching, it needs to be warmed. Heat the quench container filled with water first to get an idea of what heat to use for the oil.

Before you even start up the forge for the quench, prepare your work area by laying out all the tools and equipment you will need for the process. Make sure you have your container lid and a few sets of pliers. Mentally rehearse all of the steps you need to make.

The most important detail is that the knife enters the oil at or above critical temperature. When the blade comes out of the forge, you should move it into the oil slowly enough not to splash oil, and quickly enough not to lose significant heat. Be prompt about it. Dunk the hot blade into the oil, onto the regulator block for approximately 15 seconds. After the 15 seconds, submerge the entire blade into the oil beside the block. Laying the blade on its side without a regulator block to fully submerge it risks warping due to one side of the blade being cooled faster than the other.

When the bubbling and hissing of the oil subsides around 45 seconds, time is not critical here pull the blade out and allow it to cool in open air. Put the lid back on your quenching container to smother any flames.

Take the quenched blade to your bench when it is cooled. Rest a file on the bevel of the blade and move it back and forth, up and down the length.

If all went well, the file should feel glassy as it slides across the bevel. There should be a noticeable difference in the file's exchange with the steel. A Note on Tempering: Every article I have read on tempering gives a notice to knife makers who choose to use their kitchen's conventional oven for tempering.

Every piece of literature related to backyard knife making I could find gives a foreboding note about angry women coming after you for smoking up their kitchens by leaving motor oil covered steel scraps in the oven.

Some suggest buying a toaster oven for the sole purpose of knife tempering. I just scrub the hardened blade in water with dish soap and then hit it with a wire brush attachment in a power drill and then another soapy water scrub.

This seems to get off the majority of the oil, and I have never noticed a smokey smell. Be sure to dry the blade before it goes in the oven. Recommendations for tempering temperatures vary, If you know precisely what type of steel you are using, search online for the correct temperature.

The knives I have made are what I assume to be mild steel, coming from sources like hedge clippers and lawnmower blades. With my lack of metallurgy expertise admitted, I temper at F. Cook your blade for one hour, allow it to cool to room temp, and return it to the oven for another hour. After 3 one hour cycles, the tempering is complete. During the heat treating process, the surface of the steel was likely marred by scale buildup and oil residue, so it will be necessary to re-finish the blade to the desired level of quality.

I used the roughest stone I have — grit stone from the hardware store to put the edge back on the blade. From here, work your way up through your stones to achieve the desired edge. Question 1 year ago. So my Son is 19 and has been watching forged in fire since it began. In fact he's obsessed with it and wants to start giving knife forging a go. Plus any extras that I don't know about. After minutes the blade and part of the tang aim for the whole knife ideally will be glowing a bright red.

While you waiting for the blade to reach the correct temperature, prepare the oil for quenching the blade. Find a small metal container, such as a large bean tin or metal bucket and fill it with enough oil to cover the knife.

Do not worry too much about what oil you use. There is a lot on the internet about motor oil and its benefits but from my reading vegetable cookin To carry out this stage we are going to need to use the forge again. The key point is that oil will cool the metal slower than water giving the desired hardening.

Once your knife is glowing a bright red carefully remove the knife with you pliers and once the colour of the metal is a cherry red, quench the knife in the oil. Allow the knife to cool completely in the oil before removing. This should take around minutes, but make sure it is cool before you try to handle the blade.

If in doubt continue to use the pliers. This will leave the metal of the knife hard but too inflexible for field use.