Question- Sword vs knife

opaul

Well-Known Member
I was watching FIF and the challenge weapon was a type of sword between 32-36” long. Both contestants used 80crv steel.
It was amazing to see the bend/flex test. What is the secret to the HT to have a blade perform like that?
I realize the length has something to do with it but I suspect a 8-10 blade would snap rather quickly. I apologize up front for my ignorance.
 

Chris Railey

KNIFE MAKER
When I was making my first fillet knife I remember Boss Dawg (I think) telling me the flex was more a function of the thickness of the blade than heat treat. Now, that was for 15N20 and a fillet knife, I have no idea if it applies to a sword because I have never made more than a machete but I suspect thickness and taper will play a role. I will be following this one for sure.
 

opaul

Well-Known Member
It seems like I read or saw discussion about tempering. Perhaps that plays a role as well
 

Sean Jones

Well-Known Member
I'm curious as well. A very thin kitchen knife I made from O1 for my wife flexes quite well. The heat treat on her knife is hit or miss though. I'm always sharpening it.
 

Gene Kimmi

KNIFE MAKER
Everything I have seen says that flex comes from geometry, the thickness and the grind. The heat treat doesn't play as much of a role in it.

Kevin Cashen had a great answer to this, as he always does, I just can't remember where I read it.
 

Owl

KNIFE MAKER
I recall seeing one of Kevin Cashen's videos where he discusses this and demonstrates by flexing a razor blade 180 degrees, due to the thinness of course.

^^^^^fixed
I stand corrected...the razor blade flexed. ;)
 
Last edited:

Gene Kimmi

KNIFE MAKER
Here's the thread i was thinking of. It discusses the difference between flexing and bending and how flexing is dependent upon the geometry of the blade while bending is the heat treat.

 

BossDog

KnifeDogs.com & USAknifemaker.com Owner
Staff member
I am amazed at how some of those long blades flex and go back to true. Kevin gives some great points about flex and the heat treat relationship in the link above and is spot on - of course.
If you want a flexible fillet knife grind it to flex. Heat treat normally. I would heat treat and then grind it hard.
 
Top