Cutting contest...Flat or Convex?

Robert Hankins

Robert Hankins

Joined
May 19, 2003
Messages
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Doing a cutting contest in the near future and need some advice.
Convex or Flat grind?
Blade style?
Legal OAL I believe is 15"
Done in a stock removal blade...Which steel? Normally I use 5160
 
What you see doing most, if not all the winning in a cutting contest involving diverse objects is a flat ground with a convex edge or what I call a shallow full convex grind.
Whether the guys that cut good like these edge geometries, or these geometries make these guys cut good is up for interpretation.
I don't think you would go wrong with either style. mike
 
HMMMM. Mike answered the question but for what it's worth I'd like to go a little deeper. IMHO and only IMHO, I feel that flat grind produces a better edge as far as fine cutting. simply put, I feel it is sharper. It is also more delicate and will not stand abuse. A convex edge is better for harder use. It requires less resharpening and it does not need regrinding as often as flat under the same conditions.

Some people like Laurence use the convex grind almost exclusively and there is no question that his knives cut well and hold up well.

I use both grinds depending on the intended task for the knife. With some of my knives I abuse them and they get a convex edge and I have never had reason to complain.

That said the geometry that Mike described is almost perfect for a contest knife.
 
Great Thread.

Would the cutting contest edge also be the best "Camp Knife" edge necessarily? I am doing flat grinds with convex edge and working on some what I hope will be good camp knives. I always like to do the best I can, so any advice is greatly appreciated.

Thanks, Tom
 
If it's an ABS thing, they won't allow stock removal blades in the cutting competitions, as of this year.

I won't speculate as to why they added this rule, but, IMO, it stinks to high heaven. :eek: :barf:
 
Too many makers...they are just thinning the herd.
Local contest anyway between friends...actually will be a fun thing:D
 
I'm not sure how thin the others do it Robert but I take it to the point where I would put a secondary edge. I would guess about 30/1000's for the contest knife and 50/1000 for a camp knife.
 
Robert
I will have to go with the convexed,I do all hollow grinds but put a convexed edge on all them and it is just wick,
I am with Peter,30/1000 sounds about right,convexed grinds are just made for cutting,just my thoughts.
 
I'm really interested in this subject and never seem to stop trying different edges.

Right now I'm playing with:

THIN starting edge (trying to stay under .010")
Flat initial edge bevel
Convex final bevel

Method:

1. Put the edge on with a hard platen
2. Remove the burr by drawing across wood
3. 'strop' with a leather/green chrome belt on the grinder for the final edge. (http://www.handamerican.com/products.html). This creates a slight convex final bevel.

As I was taught, after the burr comes off, the edge is not the best it can be. The leather will polish the edge back to maximum without re-creating a burr.

My initial tests are beyond scary sharp. I test cutting ability by push cutting leather about 1" wide. The first time I did this method. I was disappointed because I thought I was pushing pretty hard to cut leather. Then I realized it had aready sliced it! I tried again with gentle pressure and found it would glide thru the leather. None of that 'crunching' sound you usually get.

I'm not EVEN a competitor, so I'd like opinions on this.

Steve
 
PS,

How thin do you take your flat grind before putting a final edge on it?
Click to expand...

With COMPLETE respect and deference to the previous posters, I feel .030" is too thick for a slicer.

But there is another issue with flat grinds: how wide the bevel and how thick the steel. You still need some meat behind that edge.

Say your steel is 1/8" thick steel and the grind is 3" wide. If the edge thickness is at .005" that sucker is going to be too thin for most applications. However, if it is 1/8" thick steel and 1/2" wide then there is plenty of strength to support a .005" edge.

So a super thin edge can't be flat ground as wide as a thicker edge.

Still with 1/8" steel, I think you can make your flat grind 1" wide and an .010 edge and be just fine.

Actually I made a vegetable chopper 3" wide with a .015 edge in 1/8" s30v. Holds up very well and slices like mad.

(Nice thing is with a thin edge is if it's too fragile you can shave a little off and put the edge back on. However, if you want a thinner edge you have to re-grind and re-finish the entire blade. Much harder to do on a finished blade.)


Steve
 
Well I sort of agree Steve but we aren't talking about the same knife. You are talking about kitchen slicers and I'm talking about camp knives and rope slicers. To me that translates into a 1/4" thickness and 2" wide blade.
 
What are you cutting? That makes a difference. A full flat grind will perform better on things like rope, tatami mats, bunches of grass, etc. Each fiber or blade of grass is not firmly connected to its neighbors, so it can get out of the way of the blade easily as the cut continues.

For substances that will flow around the blade or are more solid, such as meat or wood, the more "aerodynamic" shape of the convex grind will flow through meat better, and will be better at continually "wedging" its way through wood.

For tests involving several kinds of these substances, a good compromise would of course be a flat grind with a convex edge.
 
Peter,

Oooohhhh I assumed we were talking about hanging rope competitions!

I used the veggie thing as another example of a thin blade and edge. But never the less had hanging rope in mind.

Sorry.

Edge retention stuff I'll bow out. Something I've played with, but not enough to get involved.

Never mind.

Steve
 
Steve, I might be on another astro plane because I assumed you used larger knives in the hanging rope competitions. The only ones I've been in have been the "MY knife is sharper than your Knife" contests.
 
Act one, scene two.

Setting: interior of a blacksmith shop.

Two friends discussing a topic in violent agreement, simultaneously discover they are talking cross purposes. There is a moment of silence while each considers the other. Then, in unison, they turn to a third party and exclaim:

"Hey Blinker! what's the question again?"


Steve
 
Personally, I prefer a flat cutting contest. Not too crazy about them convex cutting contests. :D
 
Originally posted by Mike Hull
If it's an ABS thing, they won't allow stock removal blades in the cutting competitions, as of this year.
Click to expand...




Mike, now it's not like I will make it to such a competition in the near future, but I still like to do them things on my own in my shop to see how I could have done in such a competition,,,

So could you tell me more about this rule change you speak of?

I forge my blades out of John Deere load shafts,,,but once I get them to a point with my hammer, I do all the rest of the work with my belt grinder just as if I were doing a stock removal blade.

so,,,would I be allowed to test one of my blades in such a competition?
 
Originally posted by DaQo'tah Forge
Mike, now it's not like I will make it to such a competition in the near future, but I still like to do them things on my own in my shop to see how I could have done in such a competition,,,

So could you tell me more about this rule change you speak of?

I forge my blades out of John Deere load shafts,,,but once I get them to a point with my hammer, I do all the rest of the work with my belt grinder just as if I were doing a stock removal blade.

so,,,would I be allowed to test one of my blades in such a competition?
Click to expand...


Ask the abs!!
 
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