Turning Chisels

After completing my previous Mini-Lathe project it's time to start making some turning chisels. Continuing the theme of doing this on the cheap I'm going to show how to make them from files, more importantly, I'm going to show how to make the chisels safe!

A key thing to remember about files is that the metal is extremely hard, so hard that it may break or even shatter. Considering that using a file as a chisel is subjecting it to different forces than it was designed for there is a risk of catastrophic failure - unless we address the issue.

• Old files
• Wood for handle
• A piece of small pipe or metal tubing.
• Hacksaw or pipe cutters
• Hatchet or axe
• Lathe (you can learn how to make one here)
• Fire! Gas torch or something similar

The process of removing the hardness from steel is called annealing, it's the opposite of hardening. For this, we need to bring the steel up to temperature and then let it cool slowly.

I decided to anneal the entire length of the file, this means I'll have to harden the cutting edge again later. To do this I built an enclosure out of some fire bricks and made sure I got the file red hot over the entire length. Then I just closed the bricks up and waited for everything to cool. Of course you can always just chuck the files into the fireplace overnight.

I wanted left & right-handed skew chisels, so I cut about 40-degree angle with the two files being opposite each other. I used the sanding belt to flatten the sides and top of the files. The bottom doesn't need to be perfectly flat so I just gave it a quick sand and rounded over the bottom corners to make it comfortable in the hand. I then used the grinder to bevel the cutting edge away from the top edge.

Heat treating is split into two phases; hardening and tempering. We want the metal to be hard but as discussed earlier we don't want it too hard, so when we temper it we bring the hardness back a little bit.

To harden it we need to heat the metal to critical temperature and rapidly cool it. Also rather than hardening the entire chisel we want the cutting edge to be hard but the shaft to be a little softer. This allows the chisel to cut and still maintain some flexibility so it won't shatter.

Hardening

To do this we bring the chisel back to the gas torch or fire and get it glowing red hot, or what blacksmiths would call 'Cheery Red'. However, the easiest way to tell if it's hot enough is that a magnet won't stick to it anymore, so keep testing it with a magnet. When it stops sticking heat a little bit more and then plunge it into the oil and move it around a bit.

You will notice I'm only heating the last couple of inches of the chisel as this is the only part you need to harden.

To test the chisel is hard run a file across it, the file should skid over the hardened surface rather than bite in. If it's not hard you probably didn't get it hot enough.

I like to clean the chisel up at this stage, so you can just sand it until it's clean of any burnt oil.

Tempering

This step is super easy, just set your oven to about 180 to 200 Degrees Celsius and bake the chisel for just over an hour. Allow it to cool down naturally and it will be tempered. The metal will likely take on a 'straw yellow' or slightly golden colour.

Cut the timber to a bit longer than you want the handle to be and then split the wood with an axe. You want to get a piece of wood that's good so split off undesired pieces. Make sure to remove the centre of any log or branch as it has that weird hollow straw part growing there.

Turn the handle to the shape and size you want. A cool thing about my mini-lathe is the fact I can crank up the speed when it's nearly finished and using a piece of wire burn the rings into the handle. I just like the look of this, so it's optional.

Make sure you measure the internal diameter of the pipe and turn a flat spot on the handle where the chisel inserts into it. I like to finish the handles with some linseed oil on a rag while it's still on the lathe.

In the photo, you can see a previous chisel I made with this process.

Now cut a small length of the pipe (I'm using a piece of aluminium) and install it over the end of the handle. This should be a reasonably tight fit.

This will prevent the wood from splitting when you bed in the chisel.

Mark the centre of the handle and carefully drill a pilot hole for the chisel handle. You can also use a different file or piece of metal heated up to burn the hole into the correct shape, but I normally just tap it into place with a wooden mallet. You shouldn't need to hit it hard, just hold the handle in one hand and tap the handle with a mallet.

Now return to the grinder and set the angle of the rest to allow you to grind a consistent angle. Keep a bowl of water nearby and keep cooling off the chisel. Be extra careful not to overheat the cutting edge or you will ruin the hardening.

You can give the chisel a strop to really hone the edge.

The chisels are now complete, you just need to give them a light oil to prevent rusting.