Large Blade Edge Question?

[tippit]

I generally do not use larger blades & therefore tend not to forge many up.  But the ones I've done lately seem to be all given away.  The top two blades are 10 inches OAL...which is large for me compared to my caper that I normally carry.

I can't seem to decide if I like the flat grind to come right down to a frog's hair edge or if I leave a little thicker edge for strength.  Top one is basically ground to hair's edge and the 2nd down to thicker edge.  For those of you who make big blades, what is your experience & preference?  Thanks...Jeff

 

[d. ward]

Now thats a knife...Doc what the heck do you do this to us for I can't decide.I used Lloyd's large blade plenty at camp this year and loved it.I also used the smaller blade you left behind and loved that one too.Dang it Doc knock it off.bd

[DANA HOLMAN]

I like them Doc. you can send me the little one, i don't ask for much.
dana

[Wampus]

I was taught to take the flat grind to "about the thickness of a dime" and then put the final edge on that.  I like a convex edge put on with a fine belt but sometimes do a flat edge like the middle knife in your pic too.  Unless you're just gonna cut soft things like veggies or sushi, I'd think you want a little material backing up the edge for strength.  
I've seen people do strange things with knives like hacking through a leg bone when the joint could be sliced apart easily just a couple of inches away.

Short answer:  I vote #2.

edit to add that MS Joe Keeslar's knives I looked at were hollow ground to a very thin edge on some that were about 10" overall.  They were a lot thinner than I was taught to make, but I sure wasn't gonna tell him he was doing it wrong.     I don't know nothin about hollow grinding anyway.

[kbaknife]

My experience would be that larger blades end up getting assigned the tasks that would include chopping and whacking!
I agree that those are NOT cutting operations, but that's just the way things go.
To better stand up to this abuse, (like those used in cutting competitions and "performance" tests), there should be sufficient mass to support that cutting edge.
You are walking a fine line here. It needs to withstand abuse that would compromise a finer edge, but still needs to be sharpenable to point of being able to shave hair, and/or slice through a free-hanging rope!
You need to sort of "set-up" this geometry pre-hardening so as not to over-heat the cutting edge, but yet, also leave it in a dimension that leaves little stock removal when doing final finishing.
You want that edge HARD! after quenching and don't want to lose any of that when finishing.
It's a fun dance.

[tippit]

Wampus & Karl,
That's the kinda help I needed.  In the past I've left my grind edge too thick so now the pendulum is taking me too far the other way on a Big for me Blade.  I really like a thin edge on a small knife but mostly I use a very shallow hollow grind on them from a 10" wheel.

I seem to have the pre-quench edge & blade pretty much finished before quench & temper.  Thanks to ABS school I'm not over heating at quench so no more warping problems...oops I shouldn't have said that as it might come back to bite me  :eek:  Thanks for help...Jeff

[tippit]

Well it looks like Bowdoc will have a thin blade sushi knife come next spring at bear camp   :D   Although maybe he needs the thick edge as I have seen him start hacking if anyone gets out of line  

[kbaknife]

A lot of times warping can be attributed to other causes than over-heating.
#1.) Make sure you minimize your grain size after forging and relieving forging stresses by thermal cycling and normalizing.
#2.) Assymetrical grinding that leaves more or less material on one side of center will result in irregular hardening!
Martensite has a different size/dimension than pearlite. As martensite forms, it creates a new size of structure.
If you have an uneven grind, leaving more steel on one side of the cutting edge than the other, you'll get more martensite formed there and thus pull or push the cutting edge accordingly.
Of course, making sure that your austenizing temp is equal throughout the blade will affect this as well.
If you have a forge that puts irregular heat in the vicinity of the blade, then the different heat will get extracted from the blade during quench and this irregularity will pull and/or push the blade around as well.
This is why it's important to have a forge that swirls the heat around in the forge rather than directing the heat to specific parts of the blade.
Tons of things to remember.

[kbaknife]

That's why so many people are taught to leave their edges thick is so that the extra mass of steel there will resist irregular heating and irregular grinding.
The closer you grind to finished dimension, the more important it is to make sure ALL!! of your bases are covered.

[imskippy]

Why do I feel like such an idiot when Karl speeks? Thank you for your knowledge Karl. it lets the rest of us know how much more there is to learn. Skippy

[tippit]

Karl, Your insight really helps put the pieces together.  What I have found from all the info gathered here and from my blade symposium is if I do my part by forging hot, followed by all subsequent heats are lower temperatures with multiple normalizations, and finally watching my blade temperature at quench...I get very straight blades even on deep hollow grinds.  Those hollow grinds were the killer in the past as the thickness/heat transfer is so critical.  Ya'll have been a big part of my bladesmithing education.  I guess I'm ready to graduate...from 1st grade     tippit

[d. ward]

thin blade sushi knife ?? yikes you must have me mixed up with your other cook.Thats a bear camp were in son and like the other guy's said already.I've seen them boy's in Que'bec doing some strange things with your knives Doc.
My thought is like when they kind of drive them into the joints unarticulating paws would the tip of said sushi knife survive ? bd

[tippit]

Bowdoc, Not to worry, it comes with a life time warranty...mine at least    Doc

[d. ward]

Oh yeah Doc I think things will work out great.bd

[Lin Rhea]

Test the blade in accordance with it's intended use. Test it to failure, then back up just a little. Lin