Apprenticeship Session 12

So after a break of a few months due to the death of my mother and the outbreak of the COVID-19 pandemic, we returned to making progress on our projects. Part of today’s session was simply regrouping after the recent events, but some of it was planning for the remainder of the projects. We’ve got several things yet to accomplish and a short time to get them done, but we’ve made a plan to make it happen.

So to get back into the groove, we decided to work on a cold-cut chisel project today. It was a great choice to get back into the swing of things (see what I did there? 😄 ). The hammering skills were simple enough – just tapering one end of a piece of octagonal steel stock. But tool steel hammers differently than milder (aka softer) steel, so that was a good refresher. On top of that there was a bit of grinder work to do and we hadn’t been at a grinder in months. That too seemed simple enough, except you have to have a pretty steady hand to get a straight grind and we struggled with that just a bit. But after a few pointers and tips, we got the grinds looking pretty good.

So the steps to making a chisel (or pretty much any hardened tool) are essentially:

  1. Forge
  2. Thermocycle
  3. Grind
  4. Heat treat (quench)
  5. Grind (polish)
  6. Temper

Chisels have a tip that has two angles on it, one that is forged in (about 15º) and one that is ground in (about 60º). So we started with forging in the taper. Then we thermocycled the pieces before we started grinding. (Thermocycled means that we heated them up to critical temperature where they become non-magnetic and then set them aside to air cool, repeated three times.) After that it was time for a heat treat. So we heated the pieces once again to critical temp and then quenched them in oil and then water. They had the nice gray color we were looking for and a file just skated off of them. So the last step was tempering the steel and we did that by heating a 4-inch length of 2-inch pipe to red hot and then holding the chisel inside the pipe for short periods of time (maybe 10 second or less) and then looking to watch for the blue almost purple color we were looking for. That means the chisel is done!

The chisel was a nice quick project that called on a variety of skills we have learned. They turned out pretty well!

P.S. We also learned about the various types of chisels. These are really broad distinctions and there’s much more to them all than this.

  • Hot-cut chisels: have a longer, narrower taper so that they slice through hot metal rather than push it aside.
  • Cold-cut chisels: have a more blunt edge to put some weight behind the cut.
  • Stone chisels: have a flared out edge to prevent the chisel from getting stuck in the stone.
  • Wood chisels: have one sided taper (they’re flat on the back).