I've recently made a few different chisels and it turns out I also need a parting tool to cut the finished work off the leftover wood on the lathe. While similar to the others this one is made from an old mill saw blade and has a different cutting profile.

Supplies

Old saw blade (I was lucky enough to be given some large mill saws!)
Grinder
Angle grinder with cut-off disc
Blow torch
Oil for quenching

Step 1: Cut Out the Chisel

Cut out the length of the saw blade, the length will depend on the size of the saw blade you have. I made mine about 25mm wide, but in hindsight, that was too wide. I forgot that when using the cut-off tool it sits on the edge and my tool rest doesn't go low enough.

At this stage, you should cut the angle for the cutting edge. Now cut out a tang for the handle, this needs to be tapered so that it self tightens when inserted.

Step 2: Grind the Chisel

Now using a sanding belt give all four sides a quick cleanup, and make sure the sides and nice and flat. The edge that matters is the top as that's the cutting edge.

Step 3: Heat Treating

I normally use a gas torch and some firebricks at this stage, but you can also use some charcoal and your wife's hair dryer as a blower if you want (I did have permission when I did this). I normally anneal the handle section separately but I did it all at once this time. I just started to heat the parting tool from the handle end to the cutting tip making sure to get it red hot. I gripped the handle with some vice grips and then focused the torch on the cutting end. You need to bring this up to about 724°C (1335°F), but the easiest way to tell that is when it's glowing 'Cheery Red' or a magnet no longer sticks. When it's hot enough dip the tip into some oil (I used cooking oil, but you could probably use old motor oil).

Once it's cooled down give it a quick sand to remove the burnt oil and then stick it into an oven for an hour at about 200°C, this will temper the cutting tip so it doesn't shatter.

Step 4: Fit the Handle

For the handle, you can use a piece of an old broom handle or use a lathe to turn one. The important part is to have some sort of pipe at one end to stop the wood from splitting when you insert the parting tool. You need to drill a hole into the handle for the metal to slide into.

You will notice that I sharpened the tang of the parting tool to allow it to bite into the wood. To drive it in just use a wooden mallet to tap the back end of the handle, the force will drive the tool into place.

Step 5: Final Sharpen

This is the final step, carefully use the grinder to take the parting tool to a sharp edge. Make sure you do not overheat the tip, keep dipping it in cold water to cool off!

Lastly, finish off the parting tool on a strop to remove any burrs.