Today I did some more work on the tools I rough forged on the bladesmithing course. I ground them and polished them then put them in my little “furnace” which is a rather grand name for a pile of firebricks and a blowtorch.
Each one was heated then the small hook formed on the end, larger ones I form with hammer and anvil and smaller ones with a pair of needle nose pliers. When the metal is up to temperature it bends quite easily though I have to work quickly the metal is thin so cools fast and when it comes out of the furnace I maybe have 5 seconds before it is too cool, if I cary on working it I risk it cracking. I try to form a hook in two or three heats. If it doesn’t work in a few heats it is rarely succesful trying to fiddle with the shape of a hook, they tend to end with kinks in the curved profile and do not work satisfactorily.
One thing I learned from Owens bladesmithing course was the importance of “normalising” the tool after forging, this gives the finished tool a less course grain structure and more toughness so its less likely to break. This old file shows the results of normalising, the top piece was not normalised the centre and lower ones were.
As I worked my tools today I realised that during the process of shaping the hooks I am also normalising the metal, that is I am heating it just to the point it changes its grain structure and then cooling it so all that needs to be done afterwards is hardening and tempering. I heat it again and quench it quickly, this gibes me a very hard but brittle tool. It would not get blunt but could easily crack so I have to temper it by heating it to around 240 degrees, in fact as I type this they are heating in the oven.
This is the first time I have tried tempering this way, before I used to heat the tools with a gas torch and watch for characteristic tempering colours which relate to the degree of hardness, it was probably a slightly less controllable process and certainly what I am doing today is easily repeatable if the tools work well.
Well here are the results, the top two are perhaps a little darker and therefore a little softer than I would have aimed for and the next 4 may be a little on the hard side, bottom one looks perfect. The only real way to find out though is to put handles on and work with them for a while, too hard and they will break if they hit a knot, too soft and I’ll have to sharpen more often. In the past I have never taken photos at this stage so hopefully this will help me refer back when in a couple of months time I find that one of these tools is a really good one I will be able to see what colour it was tempered to.