capo-hardening?

[jolly roger]

>Based on Roger's post, I'm guessing the key is the skill of the welder, not 
>just the type of welding device used.
>
My metallurgy knowledge is non-existent, but I wonder about the hardness of 
>cast iron at the v-bar from normal surface cooling at the time of 
>manufacture, vs. torch-hardening and/or TIG reflowing. 
>
>Bill Shull

Hi Bill,
            Yes there is a high level of skill happening here, It is done
so there is barely any discoloration of the finish, and the result is just
case hardening of the surface area.

In a sand cast pour, the water in the sand acts to quench the surface, and
case harden  the surface.  If too much shaping and filing takes place at
the piano factory, the hardened surface may be completely removed. Just one
of the reasons that a new piano may exhibit excessive V noise right off the
bat.   The mere act of stringing starts to form a significant groove in the
soft cast iron.

In the foundry, if the sand box is too dry,  hardly any case hardening
takes place, due to the absence of water.

Roger