Making the cutting iron.
I bought a piece of O1 flat-stock 3.5mm (1/8”) X 38mm (1 1/2”) X 460mm (18”). these sizes correspond to imperial conversion. 4mm x 40mm x 460mm may be a near alternative in metric availability. This is a common high carbon steel used for tool making and you can use it to make many different tool types including knives, chisels and cutters draw knives or travishers.
It’s an inexpensive way of replacing blades for planes and spokeshaves or for making inshaves and such. Adding some heat for bending and shaping and a few bends on the horn of an anvil will give you curved blades as needed. The steel is not hardened on arrival. You will grind and shape first and then harden and temper the steel after all of the shaping and grinding work is done. Also, let no one convince you differently, O1 steel is perfectly acceptable for making tools from. there is little benefit to using harder alloys. This is not necessary for any hand plane or chisel.
To make my iron I used my wooden bow saw with a metal cutting blade to cut the steel; a hacksaw is just fine for this too. I find that hacksaw blades are lesser quality than they once were. They dull quickly, even on mild steel, so I make my blades from bandsaw hacksaw blades that have harder teeth and last a hundred times longer than conventional hacksaw blades. They also have great teeth. I buy blades when I am in the US where they sell handheld hacksaws with blades that yield several short blades. The length of my blade is 90mm (3 1/2″).
I ground one iron on a grinding wheel, but then I filed a second one which took the machine out of the process. There was only about ten minutes difference between the two and so if you prefer not to use the grinding wheel, it’s not a big deal.
I centered a punch in the width of the iron and 70mm (2 3/4”) from the cutting edge end. This gave me a centre-spot indent to sit the point of my compass in. The radius for the cutting edge is therefor 70mm. As a scribe point, I used a common woodscrew in the compass to describe the arc across the end of the blade. To help visibility, I blackened the cut-area with a black felt tip.
First I shaped the profile by filing to the profile line I scored. You could also use the grinding wheel for this if you prefer an indeed if you have one, but the risks are higher and it is not much faster than hand filing.
I then angled my blade in the vice and filed in the bevel. Again, you could use the grinding wheel. Present the blade at an angle to the face of the wheel and rotate to the profile into the wheel at an angle of about 30-degrees. I watch the edge as I file or grind until the square edge disappears and I have a ground edge up the the very end. If I use the electric grinder, I plunge the iron periodically as the steel heats to prevent burning my fingers. Overheating at this stage will not affect the steel except plunging too soon can harden the steel, which is not what we are trying to do at this stage. Hardening is a process and we will show this as the next stage.
Placing the iron into the throat of the plane and semi-tightening the wedge will help you to refine the profile if you need to. Remove the iron and regrind in increments until it matches close to the curved profile of the sole.
To harden the iron I used charcoal in a charcoal barbecue pit, but you could use a coal fire or a blow torch of some kind. A little extra air from a hair dryer increases the temperature quickly (No, not the heat from the dryer, the forced air) and soon the steel reaches the cherry red I need to quench it. Not all steels are created equal and depending on the steel you are using, it may take a hardness straight away or not. I have never had a problem but it can happen. I heat until the steel reaches cherry red and then plunge into used engine oil. To test for hardness, try a file on the steel. If it glides of it is now fully hardened. Now I temper the steel in the oven by leaving it in there at 300-degrees for an hour. Remove it and cool in warmish water and the steel should be hard but sharpenable.