Edge finishes and durability

[Starfish]

Here's another question from a guy who is still learning...

I've seen and experienced for myself the fact that an edge which is finished at a lower grit "feels" sharper and seems to slice very well due to the rougher finish being "grabbier" compared to an edge which has been finished to a mirror shine.

However, I've also heard that the edge which has been mirror finished is more durable.

Is that generally true? And if so, why?

Matthew

 

[Crayola]

A rough finish edge (RFE) will outslice a fine finish edge (FFE) because of what the edge looks like. A RFE has micro-serrations, so they will really grab what you are cutting and saw into it. A FFE will push cut better than a RFE though. Ahaving arm hair is push cutting. The edge is so fien that it will cleave material in half. This works especially well on non-fibroud material. A rope, for example, will best be cut with a slicing motion. So, a RFE with it's micro serrations can bite into the fibrous material, hang oneo it, and cut it. A tomato that yopu want to push cut in half, though, will best be cut with a FFE. This will separate the tomato, as opposed to microscopically sawing it.

The FFE is a longer lasting one as the edge is more refined. If you take a piece of paper and rip it, you'll notice a jagged look to the ripped edge. Look a little closer and you see fibers jutting out like fine hair. This is like a RFE. The micro-serrations ore out there, but they can be broken off much more easily than a FFE can be broken off.

I hope this helps! I hope I am right too!

 

[Cliff Stamp]

Crayola :

A RFE has micro-serrations

Both types of edges have micro serrations if you look fine enough. It is not a black and white issue, just a simple matter of degree. About the coarest edge is done with a bastard file and leaves teeth that large you can see them with the naked eye, however even an 8000 grit waterstone leaves teeth easily visible under magnification.

The larger the teeth on the edge the more material will be cut with a slice, as you are basically going to cut to the tooth depth. However the greater the depth the more force required to drive the blade through the material as you are actually busting what is between the teeth apart. Basically the same issues that govern saw teeth in general. As well as you mention, the larger the teeth the more resistance to a push cutting motion.

The FFE is a longer lasting one as the edge is more refined.

It is more durable in regards to impacts and wear, and thus holds up much better for push cutting. However because its performance is so poor in slicing in regards to a rougher finish, it can suffer faster degredation because it has to do so much more work to accomplish a given task.

There is also an issue when sharpening, a rougher edge can be put on faster and requires less skill, however it eats much more metal off of the knife as you have to take the tooth depth off with each sharpening, which can be up to about one tenth of a mm for say an x-coarse hone.

-Cliff

 

[Starfish]

Wow. I feel so honored! A novice question answered by two guys with a combined posting total of over 6100!!!

Seriously, though, thanks for the informative replies! I feel just a little bit more enlightened (with still a long way to go )

Matthew