A lot of variables at work there, so without testing there’s no way to be sure, but at first blush, both cracked blades and twisting suggest to me that the metal in those irons was not properly taken through the hardening process.

Hardening increases brittleness, so failed temper can leave the iron susceptible to cracking under stresses such as hammering. Also, a complete soak releases the stresses in the metal, so again, a failure to follow process could mean those stresses were not fully released, and hammering allowed distortion from those stresses.

Or, I suppose it’s also possible you were just going to town on the iron with a sledge hammer over a bed of gravel and the metal simply conformed to the surface beneath it, is that what happened? 😉 (of course I’m sure it was not what happened)

Hello Ed,

In Paul’s blog, someone mentions hitting their iron, as per instructions, and having it shatter. The OP was more upset that it was one of his scarcer irons. Paul helped him out and offered a replacement iron.

Another instance; someone here mentions using a credit-card-thickness Spacer to lift the iron just a thou or two, before administering the initial blow. Iron in pieces!

We’re more-likely to hear the bad-news occurrences here, but I wonder whether this technique requires more skill and judgement than initially thought? Perhaps Paul is underestimating his ability in this regard?

That method is used on Japanese irons, which are typically thick soft steel welded to a thinner piece of tool steel. I wouldn’t hammer on a western style plane iron. I gave up on flattening the entire back of plane irons and now use the ruler trick. Yes, you are putting a small back bevel on the iron but it doesn’t impair performance and involves far less material you have to remove to get to a decent edge. By the way, don’t use the ruler trick on your bench chisels!

@ed — hand-forged? Very cool! It certainly doesn’t rule out an issue during manufacturing. If, as you mentioned, the blade has no true curve, but instead the thickness grows and wanes causing a belly, that would also be consistent with imperfections in the manufacturing process.

Flattening backs can be so much work that it drove me to buy LN / LV products, with their perfectly-lapped backs. It’s odd that a manufacturer with such a great reputation as Clifton would produce so flawed a blade, I wonder if you just got the one bad one that slipped by QC or if it’s been through some accident (previous owner dropped it from a great height?).

My strop will also cause scratches if I don’t take care of it. I use it so much that it never leaves my bench, so it gets sawdust on it, small bits of wood, whatever it picks up from the bench, and of course plenty of metal from the various tools I have stropped. I therefore clean it regularly. At the very least I’ll rub it vigorously with a clean cloth once every handful of uses, but once every several dozen uses or so I’ll scrape it (with the long side of a chisel, for example) to get rid of clumped-up bits of compound and then re-charge it with fresh compound.

Ed, I think that you will find that your iron was at the hard end of the tool steel spectrum (ie tempered at the low temperature end). Paul’s blade may well have come from the softer end of the tool steel hardness spectrum (tempered at slightly higher temperature or for longer) – given Paul’s propensity to harden and temper his own irons, maybe he had tempered this iron. I would stay away from hammering hardened steel like that. Having said this, a guy in Queensland used to manufacture and sell specialty plane irons and he used to use a snecking hammer to flatten his irons but he was one very experienced operator! Your iron possibly suffered residual stresses from hardening, not fully relieved during the tempering process and which resolved itself during your attempt to hammer it. You would still be able to get a replacement Clifton iron from the new owners of Clifton, or from Ray Iles.

Edmund, You wouldn’t be able to hammer grey cast iron, which is the form of cast iron used in most toolmaking. That article that you referred to had one clue about why the material was capable of being hammered – it was nodular iron having spherical graphite “nodules” instead of flake graphite,(as is the case in grey cast iron). The nodules are produced by the addition of innoculants to the melt immediately prior to casting – much more expensive to produce that common grey iron. Grey cast iron with flake graphite is a brittle material. The machinist had forgotten that his foundry was dealing with a very different alloy! A much higher quality cast iron. Note that the LN iron hand planes are all produced with ductile cast iron – not grey iron. A much more expensive process.

MarkH

@ed I’ve dug out my plane blade manufactured by Paul Williams, who used to make them in NSW and Queensland under the trading name of Academy Saws, and photographed the pattern of indents made by his fine hammer used to flatten the blades. The hammer was almost used to redistribute the residual tension inside the blade by a series of very small blows. The hole which can be seen below the millimetre rule in the picture is the bottom of the adjustment slot on the blade – so this is close to the hardened part of the blade. Note the size and the direction of the hammer marks – each a minute adjustment of the blade’s flatness. The line across the blade bottom left in the photo is residue from some sticky tape – my blade has been in storage for a few years now. As you said above, a series of deliberate small blows – Maguire probably uses the same sort of technique. I’ll have to contact Paul about this and ask him how he did it and how he selected where to hit next during the whole process.