saw plates old VS new

[Rob Streeper]

So, it seems that the steel is actually increasing in hardness as a function of hammering. Is that the message? That the testing supports the commonplace knowledge, that is a good thing. If there is more here than that you need to esplain it, there's just too much data and not enough information.

The steel is hardened, or appears to be hardened, in the areas adjacent to the hammering.

I made an interesting observation during the testing. When running tests on the hammered zones the needle on the tester stopped at a certain point under load (150kg). When the load was relieved the needle swung back up to indicate the hardness. In the non-hammered zones however the needle stopped at a somewhat lower reading than it did in hammered zones indicating that it penetrated the metal further than it did in the hammered zones and then when the load was released it came back to read harder than the hammered areas.

That's why I think the Bauschinger effect is in play here, there's a plastic compression zone (hammered) surrounded by an elastic zone (adjacent) under tension. So maybe, just maybe, Disston did start out with steel at ~52 C scale hardness and the hammering makes it appear that they are harder when in fact they are under Bauschinger / autofrettage tension. Bauschinger discovered this effect in 1881 (http://esaform2008.insa-lyon.fr/proc...4/p_Le_226.pdf). I wonder if one of Disston's sons read about it?

Nonetheless, I was able to produce hardness measurements approximating those I found on the Disston saws I tested under the handle, including apparent hardening in areas that were not hammered. Further those hardness values suggest the saws can't be file sharpened, but we all know that they can.

Too much data? https://www.youtube.com/watch?v=Q_UsmvtyxEI