Reply To: Plow plane irons won't sharpen, edge fractures
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Hi Berlios,
Your cutters need to be tempered back a little in an oven. You have not got decarburisation – that would have made the surface of the cutter softer and your file would have grabbed that.
Paul has shown a method of tempering in the kitchen oven in one of his videos. This is a little (i.e. a lot!) more controllable than other methods since the electric oven temperature is relatively controlled – the only variable is the “time at temperature”. If you have a gas oven at home then you might need to rethink this.
I will try to find a reasonable tempering temperature and time for an O1 steel for you. I know that Record use what they called Tungsten Steel on their cutters – modern O1 steels have about 0.50% Tungsten so this is probably the closest to what you have from Record. Remember that your iron has already partially been tempered. Thus, I would try your preheated oven set at approx 150 Degrees Celsius with the cutter in for about an hour. Wrap the cutter tightly in a layer of Aluminium foil (kitchen foil) to keep any oxygen out during the heat treatment. Then cool the cutter and try to sharpen again. If you can get a burr easily the cutter is ready – if not, you might have to put the iron back in the oven for another hour OR try 170 degrees for an hour. A process of iteration – if you leave it for far too long then the cutter will lose some of its hardness – but this happens gradually. If you want to look up this process on the internet try searching O1 tool steel – tempering. I am recommending the lowest tempering temperature because I don’t know the current hardness of your cutter and this offers much more control of time (and least potential for disaster!).
The cutter was probably like that from the factory. Cutters were hardened in batches of hundreds. The first cutters out of the austenitising furnace and into the quench got the best quench and were likely much harder than the last cutters out of the furnace. Likewise there would have been some cutters in the tempering furnace for much longer than others. Cutters in the tempering furnace for longest would have been relatively softer than those which were in there for the shortest time. You will get a spectrum of hardness readings – your cutter is likely to be from the harder end.
Tempering a bit more will get you back to a more reasonable hardness.
I hope that this helps
Cheers
Mark H