Heat-treating tools with Robin Wood

During the fire in the workshop, the heat of the flames caused the metal in my tools to soften so the first step in repairing them is to heat-treat them to the correct hardness. I’ve done a little bit of toolmaking before but don’t have my own kit so I was very pleased to get an offer from Robin Wood to do the work in his forge.
For those of you that don’t know, Robin is the UK’s leading pole-lathe bowl turner who rediscovered the craft and has since inspired and helped many other people, me included, to turn bowls using a pole-lathe. In addition to this he is chairman of the Heritage Crafts Association, a spoon-carver and generally great guy.  We share similar ideas about craft, design and making ideology so it’s always a pleasure to spend time in his company.
Outside his workshop at the beginning of the Pennine Way stands his small forge. The first stage is to heat each tool to a dull red and then quench it in oil or water to cool the steel as quickly as possible, hardening it. We started out with a couple of cheap kindling axes to check the method and decide on whether to use oil or water for the quench. Water gives a faster quench but with larger tools like axes, this can sometimes lead to stresses being formed in the metal.
Robin was obviously enjoying himself as he took the first axe head, glowing red out of the forge and plunged it into a large jug of cooking oil which promply burst into flames.  After testing with the file we decided a water quench was needed which gave us the proper hardness without any problems.
Every tool, axes, adze, gouges, chisels, knives, planes blades and drill bits all  went through this process of heating, quenching and testing with the file. When the tool is the right hardness, the file ‘skates’ over the surface rather than biting in. After a while I could also hear the difference in sound the file made on properly hardened steel. All the while Rob & I talked over ideas about making, aesthetics, other craftspeople we know, issues around being an independent maker, the Luddites and loads more. It was pouring with rain but I hardly noticed.
At this stage everything is as hard as possible but also brittle, meaning the edge would break in use so the next stage is to draw out some of the hardness by reheating the steel in a more controlled way. This process is know as ‘tempering’.
We quickly shined up the surfaces of all the tools on Rob’s belt grinder and then took them back to his house and popped them in the oven at 250C, a good tempering temperature for woodworking tools. Part way through we added potatoes for a simple supper.
The tools were left in the oven to ‘soak’ at this temperature for an hour or so until we could see a dark straw colour on the shined surfaces which indicates that the tools have been successfully tempered.
In lots of ways this was the hardest stage of the process to restore my tools and I was glad to benefit from Robin’s experience.
Next stage: handles.