Well, I am a little tardy with the second part of my bowlhook making article. But I’m going to assume that it’s better late than never. I covered the sourcing of the metal (old car springs) and the straightening and preparation of the rod earlier. You can find the article here Forging again – I’m talking more bowl hooks. A very quick disclaimer – I am not a metalworker, nor a metallurgist. My basic understanding is enough for me to make basic tools that I use as a greenwood worker and I am describing the process as I use it – not necessarily correctly!
The business end of the tool, the hook, is formed by tapering out the end of the rod until there is a flattened surface about an inch in length and an eighth of an inch in thickness. Though the dimensions are all a part of the development and sometimes they will vary depending upon how I plan to use the hook.
To work the metal most easily it needs to be at a bright heat, more than red, a very bright orange – but not yellow. The next step from yellow is when the metal starts to burn and turns into a sparkler. Very pretty but you’ve ruined it and will need to start again. Steel will do this very easily – I assume that results from the carbon in the iron, so be careful.
Before making the tapered end it’s a good idea to make the tang on the other end of the tool. This gets me into the habit of beating a taper into the metal before I mess up the first of the hooks and also to learn to gauge how quickly the hearth heats the steel to the right temperature. It doesn’t really matter if the tang turns into a sparkler.
John’s tool has much better definition and evenness in the shape and is less dented – and as you’d expect he used a fraction of the number of hammer blows that I did to achieve the same result. But mine is certainly useable and the point of this comparison is to show that you can achieve a perfectly useable result for a tool without needing to be a professional blacksmith.
At this stage the tapered ends are cooled very slowly by the edge of the fire – perhaps about 30minutes to cool down from cherry red and are not quenched except perhaps just to ensure its cold enough to handle. By cooling it so slowly the iron is annealed which keeps arrangement of the iron and carbon in the material so that the metal is at it’s softest, important for the next stage. While one tool is cooling the next one can be worked. You should just about be able to see one iron in the fire and one just to the side of it cooling down.
With the steel annealed the bevel can be added to the tapered end of the tool. If the metal is soft enough this can be done with a file, though not all steels will soften enough for this, as I discovered and this bevel was added added by a flap wheel disc on a grinder. The bevel angle is somewhere between 20 and 30 degrees.
The most critical stage is to form the hook on the end of the tool. You only get one chance to do this and subsequent attempts tend to result in a less than perfect shape – though the hook might still be quite useable. The tip needs to be at orange heat (it will heat up very fast when its this thin) and then swiftly bent.
Having spent hours preparing the ends you are suddenly faced with a minute of work which is either going to work or ruin it. So don’t rush it at this stage. I originally used a pair of pliers for this – but I can’t find a good pair again and have taken to forming the curve around another piece of iron rod. Notice that the curve is offset which helps the use of the hook on the inside of the bowl, so the first bend is on the shank backwards (which I do with pliers) followed by tapping the end gently around the former.
The final stage is to temper the tool. Correct temper will ensure that the tool keeps a sharp edge, but is not so brittle that it breaks too easily.
It’s a two stage process. First the tool is heated to an orange heat, hot enough that the iron and carbon molecules form a material known as Austenite, and not surprisingly this first stage is called Austenising. The tool is rapidly quenched in water or iron to trap the iron and carbon in this form – at this point the steel is extremely brittle and unusable. If you knock it hard it should shatter -but don’t try it with the tool you are tempering!
The second stage is to reheat the tool to a precise temperature to balance the characteristics of toughness with brittleness and this is tempering the steel.
To do this precisely an oven is a good idea. There is another, less precise method which is to guage the temper by reference to the colour of the steel. This needs plenty of light and a bright polished surface on the tool. A blowtorch is a good way to do this. Using the hearth is probably going to be the least precise method for guaging the temper but it was a bright day and I was keen to try this for once as virtually all blacksmiths would have used this method originally.
There is another madness in my method – and that’s because I don’t actually know the constituents of my material. I know it’s a hard spring steel as it remained too hard to file even when annealed. Also the springs cracked on the vehicle rather than sagged. So for this temper I am going to err on the side of softness to avoid a tool which might break on the lathe – and the downside is that I might have to sharpen more often. But even when annealed it was fairly hard so I think it’s the right way to go with this steel. Since I have enough of the steel for dozens of tools I can afford to take time to learn this by experiment, so it’s of less importance to me to be able to accurately determine the temperature.
Initially the bright polished end of the tool is silver but you soon see a yellow or straw colour creeping along the shank. But this is still too brittle a temper. Somewhat anti-intuitively the steel is tempered softer as you continue to heat it. I am holding the tool so that the shank receives most of the heat in the heart of the fire and the heat is then moving along towards the tip – the tip will reach temperature really quickly as it has very little heat capacity.
The tip reaches a blue temperature – as soon as it starts to turn blue I quench the tip to prevent it overheating and oversoftening. However it is only an approximation as the tool would need to be held at the correct temperature for some time to ensure that as much of the steel as possible is converted from its brittle form (and why an oven would be an improvement) but with an unknown steel I think it’s a good enough way to start out.
So that’s it. One rusty car spring converted into a range of potentially very useful lathe tools. On this occasion I managed to reform a couple of tools I was unhappy with as well as make a prototype curved knife for bottoming the bowls in a very full day.
I am very grateful to the blacksmiths at the old Kiln Forge for allowing me to disrupt their day. We ended in the traditional way by heating some water on the hearth in a giant ladle for a good hand wash.