How sharp is sharp?

[hiddengeek]

Ok people, new to knife making here and reading a lot of the posts and how-to's, I come across a mention of a test of free hanging rope being cleanly sliced.
Personally, I don't think I have ever seen a knife that sharp, so my question is, how sharp is sharp?
I can't see a fresh razor slicing a free-hanging rope, or a gently falling piece of silk onto a blade.
Actaully, I don't think I would want something laying around my house that was that sharp, being somewhat of a clutz occasionally, but still would be neat to see.
What is used for this sharpness?
Diamond, water stones, buffing, stropping...?

Thanks!
Eric

[Bob Sigmon]

Eric,

I'm pretty new here but .............how sharp is sharp? To get what Jerry Hossom calls wicked sharp starts well back from the edge of the blade. The types of steel that are used will be the basis of how sharp you can get the edge and how long it will retain that edge.

Forgers will use 52100 to great effect. The secret to this steel is the forging where the grain of the steel is refined while the blade is shaped under the hammer. Once the blade has been forged they heat treat the blade normalizing, multiple quenching , multiple tempering with cryo treatment thrown in. This all leads to refinement of the grain, which leads to being able to sharpen the blade to "wicked sharp".

The top steel for stock removal guy is Crucible's S-3V. Again, this fine grained steel is the basis for a great edge. The egde geometry will also help determine how long your edge will last. Typically, a convex edge on the blade will last longer than a very flat thin edge.

This is just the ramblings of a newbie, but with the knowledge derived from some great makers. If I am of base, someone let me know!

Final sharpening is done by various methods and each maker will use the "system" that they have developed and works for them.

A final thought on a sharp blade. A sharp blade will cut with much less force than a dulll blade. Dull blades cause you to use extra force and once you break through what is being cut the follow through my lead the blade to your leg, arm or some thing else that you don't want cut. A sharp blade just cut what you want cut. You know that it is sharp and you treat it that way.

I hope that this helps.

Bob Sigmon

[BrianT]

Hi Eric

The cutting through the 1" free hanging rope is part of the test for a knifemaker to become a Journeyman and Master within the American Bladesmithing Society. One must also be able to chop through a 2X4 twice and still be able to shave hair with the blade. The knife must then be bent to 90 degrees without breaking. There is a how to article by Ed Caffrey that outlines how to make a knife to pass the ABS Journeyman test on this site and his site. This will give you an idea of what is involved in forging a knife that is sharp yet tough. Further info on www.americanbladesmith.com. This is ABS's site.

Brian

[Jason G Howell]

Notwithstanding heat treat, the rope cut relies on edge geometry as much, if not more, as sharp to get through the rope. That same edge geometry that does rope like crazy will not do the 2x4's as well, maybe folding on you. The trick is getting it right to do both tasks. Just steep enough of an edge for rope, but enough meat left so it won't fold on the 2x4's. This can't be taught, but you must try it and see for yourself. Playing is fun and teaches you so much about your knives. I can make mild steel cut rope... once!

[hiddengeek]

The top steel for stock removal guy is Crucible's S-3V.

Being someone who has only made one complete knife, screwed up the second, and both from old circular saw blades, is S-3V the same as S30V?

Thanks,
Eric

[Don Cowles]

In a word, no. They are both made by the same company (Crucible), and are both fine steels, but they are different. S3V is not stainless, for example, where S30V is.

[Chris_Crawford]

The most impressive cut that I've seen was at this past Batson's Bladesmithing Symposium. Part of the cutting contest was to cut through a 1" rope hanging from two pieces of upholstery thread without breaking the thread. Two people did it. I wouldn't believe it if I had not seen it.

-chris