Forging a small Ulu

I few years ago I participated in a bladesmith's challenge to make a usable knife from 1 cubic inch of steel. It didn't matter what type of knife you made, or what the starting stock dimensions were, as long as the volume did not exceed 1 cubic inch. I but 1-inch diameter drill rods from McMaster-Carr for blade and tool making. They sell two types, O-1 and W-1. Both are high carbon alloys good for blade & tool making and they come in 36-inch lengths. It takes almost 1-3/8 inch of 1-inch diameter rod to get 1 cubic inch, and that's what I started with.

I welded a stick of mild steel onto the rod as a handle and brought it up to abot 1900-200 degress. This appears to most people as bright yellow in dim lighting. The next step is what blacksmiths call "upsetting", or hammering on the end of a bar to widen it. In this cas I am looking to flatten it out into a larger circle.

Once I got it to roughly a quarter-inch thick, I punched a hole in the approximate center.

I then elongate the hole with a flat chisel to create an oblong slot. Continue widening that slot until I can fit a larger tool called a drift into it. when the slot is almost where you want it, start necking down the edges to create the distinctive Ulu shape.

Using the cross peen on the hammer, widen out and thin down the edge until the blade is a little wider than you want it. This allows for some profile grinding to the desired shape. This leaves a bunch of ripples in the steel that need to be flattened out with light hits at a lower (red) heat. Leave the edge thickness about  the same as a nickel coin. The blade needs to be put through a couple of heating cycles called "normalizing". This resets the matrix and refines the grain size from the rigors of forging. This is basically bringing the steel up to an orange heat and letting it cool in still air until it looks totally black. Putting it into a tube so you can see it in total blackness helps. When you can no longer see any color in the steel, it is ready to heat and cool again. Do this 2-3 times with the third time bringing it up to a bright red and then cooling it.

The blade is covered in forge scale at this point and that needs to be removed before grinding or filing in preparation for hardening & tempering (HT). I usually soak these in either a mild solution of PH Down (dry pool acid) or plain white vinegar overnight. This will loosen the scale so it can be mostly removed with a wire brush or wheel. Grinding can be done with files, or on a disc, or even with an angle grinder using 80 grit flap wheels. Do NOT take the edge down more than half at this point.

More on the handle making tomorrow. Any questions?

Before I get into the handle making, I want to talk about the process of hardening and tempering tool steels.
I will forego the scientific terminology and stick with more pedestrian wordings.
In short, when a given steel is brought up to what we call "critical temperature" the crystaline structure changes and the carbon goes into solution, meaning it is released from any fixed points and disperses throughout the steel uniformly. For most of the common tool steels, this temperature is  around 1475 degrees farenheit. It does vary somewhat from steel to steel, but 1475 is a good all-purpose number for most simple steels and some basic alloys like auto springs, anything in the 10XX steels, the W1 bar I used in this Ulu project, or even a chromium alloy like O1.

Now most people don't have any thermometers that go that high, and it's certainly not going to happen in the kitchen oven. You need a forge, a kiln, or an oxy-acetylene torch with a rosebud tip to get  a tool sized hunk of steel up to these temperatures. Even if you have the forge, how do you know when you are at the correct temperature? You could get one of those hand-held IR pyrometer thingys. They are somewhat accurate, but to get a good reading, you cannot test the piece while it is in the forge. You have to remove the piece, measure a couple of spots, and either heat it up more or let it cool until it's just right.

Regardless of what the type of tool steel you work with, there is a certain way to tell if it is at the correct temperature. It's called "decalescence/recalescence" and it is a visual phenomenon that occurrs when the carbon goes into solution. Some older smiths call it "chasing the shadow" because there is a visible shadow that moves along the steel. Decalescence is when the steel reaches critical temperature. The steel starts to glow and a black line or shadow moves across the heating surface until the steel is a uniform color. As it cools, the shadow reforms and moves again, but this time the steel behind the shadow heats up again as the carbon rebonds with the iron. This is best seen in very low light, so your forge should be in a dark place with very little lighting.
This effect can be seen in these two videos:
Recalescence - https://youtu.be/33neAGXxZ94?si=DnP8b3sB1wwh7OOs
Decalescence - https://youtube.com/shorts/2i2h8xDOBec?si=4CkzQc3RejyIgv1y this was heated above critical and allowed to cool down to critical temp. You can see the carbon cloud form slightly and then disappear.
A lot of blade smiths will use a baffle tube in the forge. This works like a small oven and keeps the blade out of the direct flame. You can see the effect much easier inside the tube. It's literally a short length of either square or round steel tube that is nestled into the coal forge or shoved into the propane forge with the blade inside. It helps to throw some charcoal into the tube to burn up any excess oxegen in the tube so it doesn't rob the carbon and cause scale buildup.

Barring that, here are a couple of hacks to get you on spot or at least close enough to get a good hardening.
Steels become non-magnetic around 1425 degrees farenheit. So A little magnet on a string or a piece of wire next to your heating source will tell you when you are getting close. When it goes non magnetic, put it back in the heat and count to 10. Either go for the quench or try and see the decalescence happen.

Table salt melts at 1474 degrees farenheit. If you are using the tube, place a piece of coarse Kosher salt next to the tool or on the handle area of the tool, and when the salt melts, it's time to quench.

Quenching
Quenching is the act of rapidly cooling the blade from critical temperature down to around 400 degrees F and it needs to happen within about 4-6 seconds to achieve a good hardness. They make engineered oils for this and they come in "fast", "medium" and "slow" speeds. Different steels require a different rate. Some medium speed alloys are O1, D2, and A2. Faster steels are 1095, W1 and W2. Water or brine is considered a very fast quench. You can achieve a fast quench with plain old Canola oil if it is preheated to around 130 degrees F. It doesn't last as long as the engineered stuff, but unless you are making tools every week, a gallon of Canola oil can lest a year or more. If your tools are small enough, an old paint can works well. Just heat a piece of regular steel up to a bright orange and drop it in the can and cover it. After about a minute, remove the lid and test it with a meat thermometer. It will cool off while you heat the tool up, so get it above 130, and start your process.
After quenching, you can test the hardness with a file. They make hardness files, that will tell you approximately the queched hardness is, but any chainsaw file will work. If the file skates across the steel and will not cut, it's pretty hard.
Hardened steel is quite brittle and can crack just sitting on the shelf due to the internal stresses, so it's best to temper the hardness down ASAP.

Tempering
Tempering is the act of reheating a hardened piece of steel to relieve the stress and reduce hardness. Depending on the steel type and desired hardenss, this temperature is anywhere from about 250 degrees F to 1000 degrees F. The desired hardness depends on what the tool is and what it is intended to cut. A general purpose camp knife is going to be much harder than a hatchet, but probably not as hard as a skinning knife or a kitchen knife. Tools like punches and drifts are at the low end of the hardness scale and most blacksmiths don't even bother with hardening and tempering any tools that get used on hot steel. Tempering is best done in an oven where you can accurately determine the temperature and hold it for at least two hours. An electric kitchen oven or a simple toaster oven will work but there are a couple of things you really need to do. In a toaster oven get an oven thermometer and test the oven to see where the temp really is. In a larger kitchen oven get two oven thermometers on either side and average the temps. It also helps to take a baking pan (one of those aluminum disposables works well) fill it with sand and bury your tool in the sand. The sand works as a heat sink and the tool will heat evenly.

Hardness
Hardness is measured on different scales in different industries and parts of the world. In the USA, the most common scale is the Rockwell scale and its usable range is from around 25 to 65 points of hardness. As hardness increases, what we call toughness decreases. Toughness can best be called the pliability response to bending or resiliance of the steel to impact. A Kitchen knife will be really hard and prone to chipping while a hatchet will be really tough and able to take or make blunt force trauma. Harder blades are more difficult to sharpen, but will retain an edge longer than softer blades. Softer blades will take a beating but will need sharpening more often than harder blades. Some tools need more toughness than hardness. Prybars, screwdrivers, cold chisels, etc. fall into the tougher tools.

If you know the steel type you are working with, you can find tempering information online for what tempering temp you need for the desired hardness level.

After heat treating, you have a lot of sanding, filing and polishing to get it where you want it to look. You can take the easy way out and just get it clean enough and thin enough at the edge that you can sharpen it. I usually sand/grind the until the blade tapers evenly down to about .01 to .02 inches thick. The weirdness you see in the blade is a result of the steel I am using, which is a shallow hardening steel, and an acid etch after final polish. The steel only hardens to a depth of about 3 mm. So, any part of the steel that was thicker than 6 mm, didn't harden all the way through. After grinding through the hardened part, the softer parts become exposed and the acid makes them a different color than the hard parts.

The handle making portion of this project used a piece of moose antler. The first step is to cut a groove in the antler to capture the top end of the blade (called a tang). I did this using a flat, round cutter in a rotary tool (like a Dremel) and fit the handle onto it. It's a cut/check/repeat process until you have the fit you like.
Once I got the fit where I liked it, I drilled a small hole all the way through for a retaining pin. Blacken one side of the tang with a Sharpie pen and insert the blade. Take the drill and push it into the hole until it just touches the tang. Do not try and drill through the tang while it is in the handle. Remove the blade and you will see exactly where the hole needs to be. Drill that out either to match the pin, or just a tiny bit oversized.
Then I sanded the handle pretty smooth because I am trying to learn how to carve antler.
I am not any good at it, but you have to start somewhere. Dye the carved antler with some leather dye, shoe polish, or whatever you have on hand. Coat anything you don't want epoxy sticking to with a thin smear of petoleum jelly. Just a light coat will keep the epoxy from sticking, so be careful to keep it out of the groove and off the tang end that fits in the handle.
Mix up some epoxy and put a small line in the handle groove. Insert the blade and push the pin through. Put it in a vice or clamp with the blade pointed up and clean off any excess glue with a Q-tip and some petroleum jelly or a paper towel sprayed with acetone. Let it dry overnight. Sharpen as desired.

This is now my leather working version of a head knife, but it is a very useful tool for cutting all sorts of food, chopping herbs, meat processing, etc.