The rehardening of Stanley tools is encouraging. The steel quality is there to do it, but not all older tools have fared as well. I’ve rehardened a few Ohio Tool irons, which exhibit the characteristics of an iron that is not top quality, though I couldn’t say specifically why. It could be low quality steel or lack of carbon (both can show the same thing).
I’ve also had some specialty irons from oddball toolmakers in the 1800s where rehardening didn’t result in a hard iron. With Parks 50 and an iron (Which is a relatively thin cross section) this shouldn’t be the case and the result suggests the iron isn’t hardenable to the extent that a woodworker would want it to be.
I’ve also had excellent experience with defective new tools. About five years ago, I saw a new set of boxwood handle Marples chisels (tang style, but round tang. I would guess something like 70s or 80s make). I do not recall a tool that was suitably hardened in the group, but three fourths or more of the group was unhardened for any practical purpose (softer than a saw would be) and any attempt to strop a chisel would roll an edge. One push through softwood and the edge would roll badly. In that case, a simple quick heat and quench (handle still on the chisels, just sticking out of the forge with a very wet towel around the wood), and then a blacksmith temper (holding the chisel over heat and tempering to straw and then quenching again to stop the tempering process) results in a good working chisel.
New for those chisels may not be a great term – they were unused, and $160 for a set of 10. I doubt the owner of the chisels knew they were bad, they were probably just a flipper (none had any signs of use or sharpening).
So, A current Version
Buck Brothers used to sell a cheaply made iron (stamped out) for a stanley 4/5 sized plane in home depot. Interestingly, over time, the origin of the plane irons changed from USA to china and back. Some of the blades I’d found (and bought) said “USA” on the packet and had a sticker over the packet that said “CHINA”. Who knows what the case was – maybe they were just packaged here. It doesn’t matter, they were $2.99.
Those irons were actually usable, but they hone and slough on an india stone very quickly, and then they need a little help on the final bevel to hold up to hardwoods. A bit of a roundover with the bevel and they’re OK, but they have the feel of a steel with 0.6% carbon (like cheap imported chisels). They give themselves up in how they feel on stones – lower carbon steels feel a little smoother on a stone without any grip, but hone quickly.
I don’t think there’s much of anything else in those irons, so I rehardened one, and then tempered again in the 400F sweet spot.
What happened? Almost no change. Why? When you lower carbon, you can get high initial hardness, almost as high as a 1% steel iron, maybe just short. If you under-temper an iron you can keep it at high hardness, but it will chip. If you continue tempering, then the hardness of the tool being tempered will be lower than something with a higher carbon content.
26c3 sort of illustrates this. It’s about 2 points harder than O1 or A2 at the same temper, it has more carbon. This comparison goes a little awry when you add lots of other alloying elements – like bunches of chromium, but that’s outside of my scope. The only stainless I heat treat is XHP, which has a huge amount of carbon, but comes out of the quench lower than something like O1, and then lands around the same hardness after tempering. It’s got far more carbon than 26c3, so just carbon content alone isn’t a perfect indicator.
Back to the Cheap Iron
I didn’t take any pictures or do testing, but I did buff the edge of the iron and plane some Louro Preto (high hardness dusty wood, about as hard as indian rosewood). It worked fine, but it wouldn’t wear long in that – buffing the edge helps it avoid instant damage.
The thinner you would get in terms of taking shavings with an iron like this, the faster you’d find out that it’s not that hard. Low carbon and low hardness result in inability to hold a fine edge.
Is the iron useless? No, I used a pair of them to plane knotty pine a couple of years ago. When they get damaged, they grind and hone really quickly. To make them usable, use the cap iron on a plane, buff the tip and keep the plane in the cut and just sharpen quickly.
But they do help illustrate in this case, if the quality of the underlying steel isn’t there, just rehardening it isn’t going to improve anything – it’ll go back close to where it was after temper, and if you try to cheat by undertempering, you’ll have worse problems.
Interestingly, these irons were fair exchange at a $3 price, but I have seen them on ebay now for anywhere between $8 and $25. Avoid them at that cost. I’m guessing flippers feel like they can find a buyer for them because they say “Made in USA” on them. The Chevette diesel was made here. too. That doesn’t make it as good as a truck made in Louisville.
If you have some of these because you couldn’t resist the $3 price, they’re not at all bad in a jack plane where you’re doing just as much wedging of wood as you are cutting.
Of Making by Hand with Wood and Steel 