Quick question on blade geometry and flex.

[CUTS LIKE A KRIS]

How much does blade geometry affect pressure needed to flex a blade? I would assume that, starting from the same thickness, say 1/8", that it would be more difficult to flex or bend to break/snap point a convex over a flat grind over a hollow grind, but am unsure how much is due to grind geometry versus actual amount of material remaining to bend (as there is really no way to have same thickness hollow:convex). Not that I break/ bend my knives, but was curious as to this aspect, and have not been able to phrase it in such a way to find searches useful. Thanks for any input.

 

[69_knives]

I can imagine it affecting it somewhat, albeit negligibly, maybe detectable only by CERN unless a totally radical blade design geometry is used like an "I" beam knife. Personally, I would have to think that a nicely polished full convex would probably be the strongest.

 

[james terrio]

...how much is due to grind geometry versus actual amount of material remaining...

Wait... what? That's like asking which is heavier, a ton of bricks or a ton of lead. Geometry determines the amount of material, and that's really all that matters.

More steel is more stronger.

Some folks will claim that a tapered blade is somehow stronger than a blade that's the same thickness all the way to the tip, but they are wrong.

Unless you get into non-knife-related geometries (like the I-beam 69 mentioned), it really is as simple as that. Want it to flex (filet knife), grind it thin. Don't want it to flex (tactical sharpened pry bar), leave it thick.

 

[elementfe]

Respectfully, Terrio, that's like saying, "A calorie is a calorie."
I TOTALLY agree with you that for knife blades the effect of different geometries is slight enough to be negligible, but...it's difficult to determine the exact point at which a given geometry makes a practical difference. Personally, I lean toward calling it irrelevant.

But a pound of steel tube of a given length is going resist bending much more than an equal length one pound round bar.

 

[Rick Marchand]

You can mess with geometry to keep some rigidity or control flex while shedding some weight. Fullers are great for that but it will always be a compromise. Look up "modulus of elasticity".

 

[69_knives]

Respectfully, Terrio, that's like saying, "A calorie is a calorie."
I TOTALLY agree with you that for knife blades the effect of different geometries is slight enough to be negligible, but...it's difficult to determine the exact point at which a given geometry makes a practical difference. Personally, I lean toward calling it irrelevant.

But a pound of steel tube of a given length is going resist bending much more than an equal length one pound round bar.

Respectfully, as cutting tools, um, pipe; round bar... Which one will cut better?

 

[BloodrootBlades]

I suggest you DO break/bend your knives every once in a while! Very useful information can be gleaned from breaking knives. I would say cross section does matter, very much so, but mostly to do with the thickest part of the blade. A hollowgrind is effectively a form of T-beam so if the blades had equal volume of steel, the distribution of the metal would mean a thicker spine. What I mean is that the hollowgrind gives greatest rigidity per weight of any of the grinds, much like fullered sword blades or T-section foils or rapiers.