Objectively measuring sharpness

[SlimTim]

I’m falling down a blade sharpness rabbit hole and have been wondering how to objectively measure blade sharpness at home.

I see people rubbing their finger over an edge and say “yep, that’s sharp” and I’ve seen people cut pieces of paper. Neither of those techniques are objective in anyway. The finger test relies of many physiological parameters and I can both cut and scrunch paper with the same blade.

Has anyone got any other ways that may be a little more objective without special equipment?

Cheers,
Tim.

 

[WoodBow]

If you are wanting to measure and compare, you will probably need some tools to do so. John Lusk does a tremendous amount of testing and I believe you measures sharpness by the measure pressure it requires to cut some kind of wire. Look up Lusk archery on youtube.

If you just want to make sure they are sharp, shaving hair is hard to beat. I try to get mine where they will cut hair mid shaft. So the force required to cut the hair is less than the force needed to push the hair down against the skin.

Sent from my SM-G991U using Tapatalk

 

[gadrahthaar]

I haven't used this product, but it fits your request for objective.

Edge-On-Up Professional Edge Tester

A Standard Test for Sharpness How sharp is the edge? That is both the most important question a sharpener can ask, and possibly the hardest to answer. There are tests like cutting paper or shaving hair that are often used to demonstrate sharpness, and they are helpful to a point, but they lack...

www.sharpeningsupplies.com

If you wanted to get the same setup on a budget, a walmart/amazon kitchen scale and DIY rig of aluminum wire might work. I say aluminum wire because that is suggested test medium in the link. I guess a wide variety of fishing lines might work too, as long as you are consistent.

 

[Mikido]

Finger nail or sharpie, never fails, super easy, immediate

 

[TaperPin]

I see people rubbing their finger over an edge and say “yep, that’s sharp”

When I worked for the Forest Service in my 20’s, when someone from a different crew tested their knife that way, we would offer to sharpen their knife - then chuckle a bit when they cut themselves testing it. Lol

Rubbing a blade softly over a fingernail, in a scraping motion, a dull blade won’t grab and moves smoothly over the nail, but a fairly sharp one will chatter.

Shaving a little hair off your hand doesn’t take a super sharp blade, but to do it with very little effort does. On a fire crew when I’d sharpen other people’s blades out of boredom, my left hand and forearm were often lacking big patches of hair.

 

[TaperPin]

Finger nail or sharpie, never fails, super easy, immediate

Sharpie? I’ve never heard of that one - that’s a great idea. When I show our boys how to test with a fingernail they look at me like it’s crazy. Lol I’ll add a sharpie to their Christmas stockings this year.

 

[Mikido]

yea it’s also super easy to get a feel for it. Dull
Knives also reflect light into your eye. Test with some
Kitchen knives

 

[RandalH]

I check for chatter on the fingernail.

 

[Mikido]

sharp enough for me doesn’t chatter, just gets stuck in the nail

 

[SlimTim]

You can certainly check if a blade is sharp enough by checking for chatter on your nail, reflecting light or rubbing across your thumb. But is there a difference between sharp enough and really sharp? For example, will my arrow penetration be any different if I have a sharp enough blade or a super sharp blade? I suppose there are no surprises for how far into the dirt your arrows sticks after passing through an animal.

 

[WoodlandCritter]

Sorry to necro, but this is an interesting question to me. If you're still looking for a solution, the first thing that pops into my head is building a rig that holds a knife on a double jointed sliding pivot with a space above the knife to rest a weight on the spine. Then you could use the same weight everytime eg; 2lbs and drag the knife across a controlled, consistent medium (clay would be a good option) and measure the depth of cut achieved for the given force. It would require a little built of building, but nothing expensive like buying a microscope to measure edge width. Still leaves a little room for things to control for eg; blade length. But its a start.