[TheForge] Damascus warpage and blade rivets

[Andy Vida]

Mike McKim wrote:
> 
> I was referring to recovering a previously warped blade.

	If the warp is slight and doesn't involve twisting, you can
	try to bring the blade back into alignment with a heated
	metal block.  This is how Japanese smiths correct the curvature
	of blades.  Martensite is a somewhat less dense structure
	than the softer ones.  This is why when you do a clay HT job
	on a blade that is dead straight, it will curve away from
	the edge.

	So if, as you're looking down the blade's length, it curves
	to the left oh so slightly (I'm guessing not more than 1/8
	to 3/16 per foot) you apply very localized heating on the
	large radius side, as the structure transforms the blade
	may pull itself straighter.  Do this along the length of
	the blade until either it is straight, or you've convinced 
	yourself that it's sufficiently buggered up to start over 
	again.

	This technique will work only if you have a good martensitic
	structure, as far as I know.  I may be wrong about this, so
	do more research before proceeding.

	The only other way I can see to fix this is to anneal the blade,
	straighten, either anneal again or at least normalize, and start
	over.  I agree with the opinion that having the blade as
	bilaterally symmetrical as possible is a good idea.  For knives,
	I am a big fan of salt pots.  It's a little bit hazardous, but
	minimal prudence provides good safety.  You finish your blades
	in the annealed state to final polish, then into the HT salt
	and quench in the LT salt.  Blade comes out bright and shiny
	and ready to rock.  

	If warping is VERY slight, like maybe 0.010/ft, you MIGHT be able
	to coax it into shape with a hammer, but that's way risky and
	introduces added stresses that could cause the steel to fail and
	I would not recommend it.